-- --
Xlib - C Language X Interface
X Consortium Standard
X Version 11, Release 6.4
James Gettys
Cambridge Research Laboratory
Digital Equipment Corporation
Robert W. Scheifler
Laboratory for Computer Science
Massachusetts Institute of Technology
with contributions from
Chuck Adams, Tektronix, Inc.
Vania Joloboff, Open Software Foundation
Hideki Hiura, SunSoft, Inc.
Bill McMahon, Hewlett-Packard Company
Ron Newman, Massachusetts Institute of Technology
Al Tabayoyon, Tektronix, Inc.
Glenn Widener, Tektronix, Inc.
Shigeru Yamada, Fujitsu OSSI

-- --
The X Window System is a trademark of X Consortium, Inc.
TekHVC is a trademark of Tektronix, Inc.
Copyright 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1994,1996 X Consortium
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documenta-
tion files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom
the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Soft-
ware.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTIC-
ULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR
ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTH-
ERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to pro-
mote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.
Copyright 1985, 1986, 1987, 1988, 1989, 1990, 1991 by Digital Equipment Corporation
Portions Copyright 1990, 1991 by Tektronix, Inc.
Permission to use, copy, modify and distribute this documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appears in all copies and that both that copyright notice and this permission
notice appear in all copies, and that the names of Digital and Tektronix not be used in in advertising or publicity per-
taining to this documentation without specific, written prior permission. Digital and Tektronix makes no representa-
tions about the suitability of this documentation for any purpose. It is provided ``as is'' without express or implied war-
ranty.

-- --
Acknowledgments
The design and implementation of the first 10 versions of X were primarily the work of three
individuals: Robert Scheifler of the MIT Laboratory for Computer Science and Jim Gettys of Dig-
ital Equipment Corporation and Ron Newman of MIT, both at MIT Project Athena. X version 11,
however, is the result of the efforts of dozens of individuals at almost as many locations and
organizations. At the risk of offending some of the players by exclusion, we would like to
acknowledge some of the people who deserve special credit and recognition for their work on
Xlib. Our apologies to anyone inadvertently overlooked.
Release 1
Our thanks does to Ron Newman (MIT Project Athena), who contributed substantially to the
design and implementation of the Version 11 Xlib interface.
Our thanks also goes to Ralph Swick (Project Athena and Digital) who kept it all together for us
during the early releases. He handled literally thousands of requests from people everywhere and
saved the sanity of at least one of us. His calm good cheer was a foundation on which we could
build.
Our thanks also goes to Todd Brunhoff (Tektronix) who was ``loaned'' to Project Athena at
exactly the right moment to provide very capable and much-needed assistance during the alpha
and beta releases. He was responsible for the successful integration of sources from multiple
sites; we would not have had a release without him.
Our thanks also goes to Al Mento and Al Wojtas of Digital's ULTRIX Documentation Group.
With good humor and cheer, they took a rough draft and made it an infinitely better and more use-
ful document. The work they hav e done will help many everywhere. We also would like to thank
Hal Murray (Digital SRC) and Peter George (Digital VMS) who contributed much by proofread-
ing the early drafts of this document.
Our thanks also goes to Jeff Dike (Digital UEG), Tom Benson, Jackie Granfield, and Vince Orgo-
van (Digital VMS) who helped with the library utilities implementation; to Hania Gajewska (Dig-
ital UEG-WSL) who, along with Ellis Cohen (CMU and Siemens), was instrumental in the
semantic design of the window manager properties; and to Dave Rosenthal (Sun Microsystems)
who also contributed to the protocol and provided the sample generic color frame buffer device-
dependent code.
The alpha and beta test participants deserve special recognition and thanks as well. It is signifi-
cant that the bug reports (and many fixes) during alpha and beta test came almost exclusively
from just a few of the alpha testers, mostly hardware vendors working on product implementa-
tions of X. The continued public contribution of vendors and universities is certainly to the bene-
fit of the entire X community.
Our special thanks must go to Sam Fuller, Vice-President of Corporate Research at Digital, who
has remained committed to the widest public availability of X and who made it possible to greatly
supplement MIT's resources with the Digital staff in order to make version 11 a reality. Many of
the people mentioned here are part of the Western Software Laboratory (Digital UEG-WSL) of
the ULTRIX Engineering group and work for Smokey Wallace, who has been vital to the pro-
ject's success. Others not mentioned here worked on the toolkit and are acknowledged in the X
Toolkit documentation.
Of course, we must particularly thank Paul Asente, formerly of Stanford University and now of
Digital UEG-WSL, who wrote W, the predecessor to X, and Brian Reid, formerly of Stanford
University and now of Digital WRL, who had much to do with W's design.

-- --
Finally, our thanks goes to MIT, Digital Equipment Corporation, and IBM for providing the envi-
ronment where it could happen.
Release 4
Our thanks go to Jim Fulton (MIT X Consortium) for designing and specifying the new Xlib
functions for Inter-Client Communication Conventions (ICCCM) support.
We also thank Al Mento of Digital for his continued effort in maintaining this document and Jim
Fulton and Donna Converse (MIT X Consortium) for their much-appreciated efforts in reviewing
the changes.
Release 5
The principal authors of the Input Method facilities are Vania Joloboff (Open Software Founda-
tion) and Bill McMahon (Hewlett-Packard). The principal author of the rest of the international-
ization facilities is Glenn Widener (Tektronix). Our thanks to them for keeping their sense of
humor through a long and sometimes difficult design process. Although the words and much of
the design are due to them, many others have contributed substantially to the design and imple-
mentation. Tom McFarland (HP) and Frank Rojas (IBM) deserve particular recognition for their
contributions. Other contributors were: Tim Anderson (Motorola), Alka Badshah (OSF), Gabe
Beged-Dov (HP), Chih-Chung Ko (III), Vera Cheng (III), Michael Collins (Digital), Walt Daniels
(IBM), Noritoshi Demizu (OMRON), Keisuke Fukui (Fujitsu), Hitoshoi Fukumoto (Nihon Sun),
Tim Greenwood (Digital), John Harvey (IBM), Hideki Hiura (Sun), Fred Horman (AT&T),
Norikazu Kaiya (Fujitsu), Yuji Kamata (IBM), Yutaka Kataoka (Waseda University), Ranee
Khubchandani (Sun), Akira Kon (NEC), Hiroshi Kuribayashi (OMRON), Teruhiko Kurosaka
(Sun), Seiji Kuwari (OMRON), Sandra Martin (OSF), Narita Masahiko (Fujitsu), Masato
Morisaki (NTT), Nelson Ng (Sun), Takashi Nishimura (NTT America), Makato Nishino (IBM),
Akira Ohsone (Nihon Sun), Chris Peterson (MIT), Sam Shteingart (AT&T), Manish Sheth
(AT&T), Muneiyoshi Suzuki (NTT), Cori Mehring (Digital), Shoji Sugiyama (IBM), and Eiji
Tosa (IBM).
We are deeply indebted to Tatsuya Kato (NTT), Hiroshi Kuribayashi (OMRON), Seiji Kuwari
(OMRON), Muneiyoshi Suzuki (NTT), and Li Yuhong (OMRON) for producing one of the first
complete sample implementation of the internationalization facilities, and Hiromu Inukai (Nihon
Sun), Takashi Fujiwara (Fujitsu), Hideki Hiura (Sun), Yasuhiro Kawai (Oki Technosystems Labo-
ratory), Kazunori Nishihara (Fuji Xerox), Masaki Takeuchi (Sony), Katsuhisa Yano (Toshiba),
Makoto Wakamatsu (Sony Corporation) for producing the another complete sample implementa-
tion of the internationalization facilities.
The principal authors (design and implementation) of the Xcms color management facilities are
Al Tabayoyon (Tektronix) and Chuck Adams (Tektronix). Joann Taylor (Tektronix), Bob Toole
(Tektronix), and Keith Packard (MIT X Consortium) also contributed significantly to the design.
Others who contributed are: Harold Boll (Kodak), Ken Bronstein (HP), Nancy Cam (SGI), Donna
Converse (MIT X Consortium), Elias Israel (ISC), Deron Johnson (Sun), Jim King (Adobe),
Ricardo Motta (HP), Chuck Peek (IBM), Wil Plouffe (IBM), Dave Sternlicht (MIT X Consor-
tium), Kumar Talluri (AT&T), and Richard Verberg (IBM).
We also once again thank Al Mento of Digital for his work in formatting and reformatting text for
this manual, and for producing man pages. Thanks also to Clive Feather (IXI) for proof-reading
and finding a number of small errors.
Release 6
Stephen Gildea (X Consortium) authored the threads support. Ovais Ashraf (Sun) and Greg
Olsen (Sun) contributed substantially by testing the facilities and reporting bugs in a timely fash-
ion.
The principal authors of the internationalization facilities, including Input and Output Methods,
are Hideki Hiura (SunSoft) and Shigeru Yamada (Fujitsu OSSI). Although the words and much

-- --
of the design are due to them, many others have contributed substantially to the design and imple-
mentation. They are: Takashi Fujiwara (Fujitsu), Yoshio Horiuchi (IBM), Makoto Inada (Digital),
Hiromu Inukai (Nihon SunSoft), Song JaeKyung (KAIST), Franky Ling (Digital), Tom McFar-
land (HP), Hiroyuki Miyamoto (Digital), Masahiko Narita (Fujitsu), Frank Rojas (IBM),
Hidetoshi Tajima (HP), Masaki Takeuchi (Sony), Makoto Wakamatsu (Sony), Masaki Wakao
(IBM), Katsuhisa Yano(Toshiba) and Jinsoo Yoon (KAIST).
The principal producers of the sample implementation of the internationalization facilities are:
Jeffrey Bloomfield (Fujitsu OSSI), Takashi Fujiwara (Fujitsu), Hideki Hiura (SunSoft), Yoshio
Horiuchi (IBM), Makoto Inada (Digital), Hiromu Inukai (Nihon SunSoft), Song JaeKyung
(KAIST), Riki Kawaguchi (Fujitsu), Franky Ling (Digital), Hiroyuki Miyamoto (Digital),
Hidetoshi Tajima (HP), Toshimitsu Terazono (Fujitsu), Makoto Wakamatsu (Sony), Masaki
Wakao (IBM), Shigeru Yamada (Fujitsu OSSI) and Katsuhisa Yano (Toshiba).
The coordinators of the integration, testing, and release of this implementation of the internation-
alization facilities are Nobuyuki Tanaka (Sony) and Makoto Wakamatsu (Sony).
Others who have contributed to the architectural design or testing of the sample implementation
of the internationalization facilities are: Hector Chan (Digital), Michael Kung (IBM), Joseph
Kwok (Digital), Hiroyuki Machida (Sony), Nelson Ng (SunSoft), Frank Rojas (IBM), Yoshiyuki
Segawa (Fujitsu OSSI), Makiko Shimamura (Fujitsu), Shoji Sugiyama (IBM), Lining Sun (SGI),
Masaki Takeuchi (Sony), Jinsoo Yoon (KAIST) and Akiyasu Zen (HP).
Jim Gettys
Cambridge Research Laboratory
Digital Equipment Corporation
Robert W. Scheifler
Laboratory for Computer Science
Massachusetts Institute of Technology

-- --
Chapter 1
Introduction to Xlib
The X Window System is a network-transparent window system that was designed at MIT. X
display servers run on computers with either monochrome or color bitmap display hardware. The
server distributes user input to and accepts output requests from various client programs located
either on the same machine or elsewhere in the network. Xlib is a C subroutine library that appli-
cation programs (clients) use to interface with the window system by means of a stream connec-
tion. Although a client usually runs on the same machine as the X server it is talking to, this need
not be the case.
Xlib - C Language X Interface is a reference guide to the low-level C language interface to the X
Window System protocol. It is neither a tutorial nor a user's guide to programming the X Win-
dow System. Rather, it provides a detailed description of each function in the library as well as a
discussion of the related background information. Xlib - C Language X Interface assumes a
basic understanding of a graphics window system and of the C programming language. Other
higher-level abstractions (for example, those provided by the toolkits for X) are built on top of the
Xlib library. For further information about these higher-level libraries, see the appropriate toolkit
documentation. The X Window System Protocol provides the definitive word on the behavior of
X. Although additional information appears here, the protocol document is the ruling document.
To provide an introduction to X programming, this chapter discusses:

Overview of the X Window System

Errors

Standard header files

Generic values and types

Naming and argument conventions within Xlib

Programming considerations

Character sets and encodings

Formatting conventions
1.1. Overview of the X Window System
Some of the terms used in this book are unique to X, and other terms that are common to other
window systems have different meanings in X. You may find it helpful to refer to the glossary,
which is located at the end of the book.
The X Window System supports one or more screens containing overlapping windows or subwin-
dows. A screen is a physical monitor and hardware that can be color, grayscale, or monochrome.
There can be multiple screens for each display or workstation. A single X server can provide dis-
play services for any number of screens. A set of screens for a single user with one keyboard and
one pointer (usually a mouse) is called a display.
All the windows in an X server are arranged in strict hierarchies. At the top of each hierarchy is a
root window, which covers each of the display screens. Each root window is partially or com-
pletely covered by child windows. All windows, except for root windows, have parents. There is
usually at least one window for each application program. Child windows may in turn have their
own children. In this way, an application program can create an arbitrarily deep tree on each
screen. X provides graphics, text, and raster operations for windows.
A child window can be larger than its parent. That is, part or all of the child window can extend
beyond the boundaries of the parent, but all output to a window is clipped by its parent. If several
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X11, Release 6.4
children of a window hav e overlapping locations, one of the children is considered to be on top of
or raised over the others, thus obscuring them. Output to areas covered by other windows is sup-
pressed by the window system unless the window has backing store. If a window is obscured by
a second window, the second window obscures only those ancestors of the second window that
are also ancestors of the first window.
A window has a border zero or more pixels in width, which can be any pattern (pixmap) or solid
color you like. A window usually but not always has a background pattern, which will be
repainted by the window system when uncovered. Child windows obscure their parents, and
graphic operations in the parent window usually are clipped by the children.
Each window and pixmap has its own coordinate system. The coordinate system has the X axis
horizontal and the Y axis vertical with the origin [0, 0] at the upper-left corner. Coordinates are
integral, in terms of pixels, and coincide with pixel centers. For a window, the origin is inside the
border at the inside, upper-left corner.
X does not guarantee to preserve the contents of windows. When part or all of a window is hid-
den and then brought back onto the screen, its contents may be lost. The server then sends the
client program an Expose ev ent to notify it that part or all of the window needs to be repainted.
Programs must be prepared to regenerate the contents of windows on demand.
X also provides off-screen storage of graphics objects, called pixmaps. Single plane (depth 1)
pixmaps are sometimes referred to as bitmaps. Pixmaps can be used in most graphics functions
interchangeably with windows and are used in various graphics operations to define patterns or
tiles. Windows and pixmaps together are referred to as drawables.
Most of the functions in Xlib just add requests to an output buffer. These requests later execute
asynchronously on the X server. Functions that return values of information stored in the server
do not return (that is, they block) until an explicit reply is received or an error occurs. You can
provide an error handler, which will be called when the error is reported.
If a client does not want a request to execute asynchronously, it can follow the request with a call
to XSync, which blocks until all previously buffered asynchronous events have been sent and
acted on. As an important side effect, the output buffer in Xlib is always flushed by a call to any
function that returns a value from the server or waits for input.
Many Xlib functions will return an integer resource ID, which allows you to refer to objects
stored on the X server. These can be of type Window, Font, Pixmap, Colormap, Cursor, and
GContext, as defined in the file <X11/X.h>. These resources are created by requests and are
destroyed (or freed) by requests or when connections are closed. Most of these resources are
potentially sharable between applications, and in fact, windows are manipulated explicitly by
window manager programs. Fonts and cursors are shared automatically across multiple screens.
Fonts are loaded and unloaded as needed and are shared by multiple clients. Fonts are often
cached in the server. Xlib provides no support for sharing graphics contexts between applica-
tions.
Client programs are informed of events. Events may either be side effects of a request (for exam-
ple, restacking windows generates Expose ev ents) or completely asynchronous (for example,
from the keyboard). A client program asks to be informed of events. Because other applications
can send events to your application, programs must be prepared to handle (or ignore) events of all
types.
Input events (for example, a key pressed or the pointer moved) arrive asynchronously from the
server and are queued until they are requested by an explicit call (for example, XNextEvent or
XWindowEvent). In addition, some library functions (for example, XRaiseWindow) generate
Expose and ConfigureRequest ev ents. These ev ents also arrive asynchronously, but the client
may wish to explicitly wait for them by calling XSync after calling a function that can cause the
server to generate events.
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X11, Release 6.4
1.2. Errors
Some functions return Status, an integer error indication. If the function fails, it returns a zero.
If the function returns a status of zero, it has not updated the return arguments. Because C does
not provide multiple return values, many functions must return their results by writing into client-
passed storage. By default, errors are handled either by a standard library function or by one that
you provide. Functions that return pointers to strings return NULL pointers if the string does not
exist.
The X server reports protocol errors at the time that it detects them. If more than one error could
be generated for a given request, the server can report any of them.
Because Xlib usually does not transmit requests to the server immediately (that is, it buffers
them), errors can be reported much later than they actually occur. For debugging purposes, how-
ev er, Xlib provides a mechanism for forcing synchronous behavior (see section 11.8.1). When
synchronization is enabled, errors are reported as they are generated.
When Xlib detects an error, it calls an error handler, which your program can provide. If you do
not provide an error handler, the error is printed, and your program terminates.
1.3. Standard Header Files
The following include files are part of the Xlib standard:

<X11/Xlib.h>
This is the main header file for Xlib. The majority of all Xlib symbols are declared by
including this file. This file also contains the preprocessor symbol
XlibSpecificationRelease. This symbol is defined to have the 6 in this release of the stan-
dard. (Release 5 of Xlib was the first release to have this symbol.)

<X11/X.h>
This file declares types and constants for the X protocol that are to be used by applications.
It is included automatically from <X11/Xlib.h>, so application code should never need to
reference this file directly.

<X11/Xcms.h>
This file contains symbols for much of the color management facilities described in chapter
6. All functions, types, and symbols with the prefix ``Xcms'', plus the Color Conversion
Contexts macros, are declared in this file. <X11/Xlib.h> must be included before including
this file.

<X11/Xutil.h>
This file declares various functions, types, and symbols used for inter-client communication
and application utility functions, which are described in chapters 14 and 16. <X11/Xlib.h>
must be included before including this file.

<X11/Xresource.h>
This file declares all functions, types, and symbols for the resource manager facilities,
which are described in chapter 15. <X11/Xlib.h> must be included before including this
file.

<X11/Xatom.h>
This file declares all predefined atoms, which are symbols with the prefix ``XA_''.

<X11/cursorfont.h>
This file declares the cursor symbols for the standard cursor font, which are listed in
appendix B. All cursor symbols have the prefix ``XC_''.

<X11/keysymdef.h>
This file declares all standard KeySym values, which are symbols with the prefix ``XK_''.
The KeySyms are arranged in groups, and a preprocessor symbol controls inclusion of each
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X11, Release 6.4
group. The preprocessor symbol must be defined prior to inclusion of the file to obtain the
associated values. The preprocessor symbols are XK_MISCELLANY, XK_XKB_KEYS,
XK_3270, XK_LATIN1, XK_LATIN2, XK_LATIN3, XK_LATIN4, XK_KATAKANA,
XK_ARABIC, XK_CYRILLIC, XK_GREEK, XK_TECHNICAL, XK_SPECIAL,
XK_PUBLISHING, XK_APL, XK_HEBREW, XK_THAI, and XK_KOREAN.

<X11/keysym.h>
This file defines the preprocessor symbols XK_MISCELLANY, XK_XKB_KEYS,
XK_LATIN1, XK_LATIN2, XK_LATIN3, XK_LATIN4, and XK_GREEK and then
includes <X11/keysymdef.h>.

<X11/Xlibint.h>
This file declares all the functions, types, and symbols used for extensions, which are
described in appendix C. This file automatically includes <X11/Xlib.h>.

<X11/Xproto.h>
This file declares types and symbols for the basic X protocol, for use in implementing
extensions. It is included automatically from <X11/Xlibint.h>, so application and exten-
sion code should never need to reference this file directly.

<X11/Xprotostr.h>
This file declares types and symbols for the basic X protocol, for use in implementing
extensions. It is included automatically from <X11/Xproto.h>, so application and exten-
sion code should never need to reference this file directly.

<X11/X10.h>
This file declares all the functions, types, and symbols used for the X10 compatibility func-
tions, which are described in appendix D.
1.4. Generic Values and Types
The following symbols are defined by Xlib and used throughout the manual:

Xlib defines the type Bool and the Boolean values True and False.

None is the universal null resource ID or atom.

The type XID is used for generic resource IDs.

The type XPointer is defined to be char* and is used as a generic opaque pointer to data.
1.5. Naming and Argument Conventions within Xlib
Xlib follows a number of conventions for the naming and syntax of the functions. Given that you
remember what information the function requires, these conventions are intended to make the
syntax of the functions more predictable.
The major naming conventions are:

To differentiate the X symbols from the other symbols, the library uses mixed case for
external symbols. It leaves lowercase for variables and all uppercase for user macros, as
per existing convention.

All Xlib functions begin with a capital X.

The beginnings of all function names and symbols are capitalized.

All user-visible data structures begin with a capital X. More generally, anything that a user
might dereference begins with a capital X.

Macros and other symbols do not begin with a capital X. To distinguish them from all user
symbols, each word in the macro is capitalized.

All elements of or variables in a data structure are in lowercase. Compound words, where
needed, are constructed with underscores (_).
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The display argument, where used, is always first in the argument list.

All resource objects, where used, occur at the beginning of the argument list immediately
after the display argument.

When a graphics context is present together with another type of resource (most com-
monly, a drawable), the graphics context occurs in the argument list after the other
resource. Drawables outrank all other resources.

Source arguments always precede the destination arguments in the argument list.

The x argument always precedes the y argument in the argument list.

The width argument always precedes the height argument in the argument list.

Where the x, y, width, and height arguments are used together, the x and y arguments
always precede the width and height arguments.

Where a mask is accompanied with a structure, the mask always precedes the pointer to the
structure in the argument list.
1.6. Programming Considerations
The major programming considerations are:

Coordinates and sizes in X are actually 16-bit quantities. This decision was made to mini-
mize the bandwidth required for a given lev el of performance. Coordinates usually are
declared as an int in the interface. Values larger than 16 bits are truncated silently. Sizes
(width and height) are declared as unsigned quantities.

Keyboards are the greatest variable between different manufacturers' workstations. If you
want your program to be portable, you should be particularly conservative here.

Many display systems have limited amounts of off-screen memory. If you can, you should
minimize use of pixmaps and backing store.

The user should have control of his screen real estate. Therefore, you should write your
applications to react to window management rather than presume control of the entire
screen. What you do inside of your top-level window, howev er, is up to your application.
For further information, see chapter 14 and the Inter-Client Communication Conventions
Manual
.
1.7. Character Sets and Encodings
Some of the Xlib functions make reference to specific character sets and character encodings.
The following are the most common:

X Portable Character Set
A basic set of 97 characters, which are assumed to exist in all locales supported by Xlib.
This set contains the following characters:
a..z A..Z 0..9
!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
<space>, <tab>, and <newline>
This set is the left/lower half of the graphic character set of ISO8859-1 plus space, tab, and
newline. It is also the set of graphic characters in 7-bit ASCII plus the same three control
characters. The actual encoding of these characters on the host is system dependent.

Host Portable Character Encoding
The encoding of the X Portable Character Set on the host. The encoding itself is not
defined by this standard, but the encoding must be the same in all locales supported by Xlib
on the host. If a string is said to be in the Host Portable Character Encoding, then it only
contains characters from the X Portable Character Set, in the host encoding.
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X11, Release 6.4

Latin-1
The coded character set defined by the ISO8859-1 standard.

Latin Portable Character Encoding
The encoding of the X Portable Character Set using the Latin-1 codepoints plus ASCII con-
trol characters. If a string is said to be in the Latin Portable Character Encoding, then it
only contains characters from the X Portable Character Set, not all of Latin-1.

STRING Encoding
Latin-1, plus tab and newline.

POSIX Portable Filename Character Set
The set of 65 characters, which can be used in naming files on a POSIX-compliant host,
that are correctly processed in all locales. The set is:
a..z A..Z 0..9 ._-
1.8. Formatting Conventions
Xlib - C Language X Interface uses the following conventions:

Global symbols are printed in this special font. These can be either function names, sym-
bols defined in include files, or structure names. When declared and defined, function argu-
ments are printed in italics. In the explanatory text that follows, they usually are printed in
regular type.

Each function is introduced by a general discussion that distinguishes it from other func-
tions. The function declaration itself follows, and each argument is specifically explained.
Although ANSI C function prototype syntax is not used, Xlib header files normally declare
functions using function prototypes in ANSI C environments. General discussion of the
function, if any is required, follows the arguments. Where applicable, the last paragraph of
the explanation lists the possible Xlib error codes that the function can generate. For a
complete discussion of the Xlib error codes, see section 11.8.2.

To eliminate any ambiguity between those arguments that you pass and those that a func-
tion returns to you, the explanations for all arguments that you pass start with the word
specifies or, in the case of multiple arguments, the word specify. The explanations for all
arguments that are returned to you start with the word returns or, in the case of multiple
arguments, the word return. The explanations for all arguments that you can pass and are
returned start with the words specifies and returns.

Any pointer to a structure that is used to return a value is designated as such by the _return
suffix as part of its name. All other pointers passed to these functions are used for reading
only. A few arguments use pointers to structures that are used for both input and output
and are indicated by using the _in_out suffix.
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X11, Release 6.4
Chapter 2
Display Functions
Before your program can use a display, you must establish a connection to the X server. Once
you have established a connection, you then can use the Xlib macros and functions discussed in
this chapter to return information about the display. This chapter discusses how to:

Open (connect to) the display

Obtain information about the display, image formats, or screens

Generate a NoOperation protocol request

Free client-created data

Close (disconnect from) a display

Use X Server connection close operations

Use Xlib with threads

Use internal connections
2.1. Opening the Display
To open a connection to the X server that controls a display, use XOpenDisplay.
Display *XOpenDisplay(display_name)
char *display_name;
display_name
Specifies the hardware display name, which determines the display and commu-
nications domain to be used. On a POSIX-conformant system, if the dis-
play_name is NULL, it defaults to the value of the DISPLAY environment vari-
able.
The encoding and interpretation of the display name are implementation-dependent. Strings in
the Host Portable Character Encoding are supported; support for other characters is implementa-
tion-dependent. On POSIX-conformant systems, the display name or DISPLAY environment
variable can be a string in the format:
hostname:number.screen_number
hostname
Specifies the name of the host machine on which the display is physically
attached. You follow the hostname with either a single colon (:) or a double
colon (::).
number
Specifies the number of the display server on that host machine. You may
optionally follow this display number with a period (.). A single CPU can have
more than one display. Multiple displays are usually numbered starting with
zero.
screen_number Specifies the screen to be used on that server. Multiple screens can be controlled
by a single X server. The screen_number sets an internal variable that can be
accessed by using the DefaultScreen macro or the XDefaultScreen function if
you are using languages other than C (see section 2.2.1).
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For example, the following would specify screen 1 of display 0 on the machine named ``dual-
headed'':
dual-headed:0.1
The XOpenDisplay function returns a Display structure that serves as the connection to the X
server and that contains all the information about that X server. XOpenDisplay connects your
application to the X server through TCP or DECnet communications protocols, or through some
local inter-process communication protocol. If the hostname is a host machine name and a single
colon (:) separates the hostname and display number, XOpenDisplay connects using TCP
streams. If the hostname is not specified, Xlib uses whatever it believes is the fastest transport. If
the hostname is a host machine name and a double colon (::) separates the hostname and display
number, XOpenDisplay connects using DECnet. A single X server can support any or all of
these transport mechanisms simultaneously. A particular Xlib implementation can support many
more of these transport mechanisms.
If successful, XOpenDisplay returns a pointer to a Display structure, which is defined in
<X11/Xlib.h>. If XOpenDisplay does not succeed, it returns NULL. After a successful call to
XOpenDisplay, all of the screens in the display can be used by the client. The screen number
specified in the display_name argument is returned by the DefaultScreen macro (or the XDe-
faultScreen
function). You can access elements of the Display and Screen structures only by
using the information macros or functions. For information about using macros and functions to
obtain information from the Display structure, see section 2.2.1.
X servers may implement various types of access control mechanisms (see section 9.8).
2.2. Obtaining Information about the Display, Image Formats, or Screens
The Xlib library provides a number of useful macros and corresponding functions that return data
from the Display structure. The macros are used for C programming, and their corresponding
function equivalents are for other language bindings. This section discusses the:

Display macros

Image format functions and macros

Screen information macros
All other members of the Display structure (that is, those for which no macros are defined) are
private to Xlib and must not be used. Applications must never directly modify or inspect these
private members of the Display structure.
Note
The XDisplayWidth, XDisplayHeight, XDisplayCells, XDisplayPlanes,
XDisplayWidthMM, and XDisplayHeightMM functions in the next sections are
misnamed. These functions really should be named Screenwhatever and XScreen-
whatever, not Displaywhatever or XDisplaywhatever. Our apologies for the result-
ing confusion.
2.2.1. Display Macros
Applications should not directly modify any part of the Display and Screen structures. The
members should be considered read-only, although they may change as the result of other opera-
tions on the display.
The following lists the C language macros, their corresponding function equivalents that are for
other language bindings, and what data both can return.
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AllPlanes
unsigned long XAllPlanes()
Both return a value with all bits set to 1 suitable for use in a plane argument to a procedure.
Both BlackPixel and WhitePixel can be used in implementing a monochrome application.
These pixel values are for permanently allocated entries in the default colormap. The actual RGB
(red, green, and blue) values are settable on some screens and, in any case, may not actually be
black or white. The names are intended to convey the expected relative intensity of the colors.
BlackPixel (display, screen_number)
unsigned long XBlackPixel (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the black pixel value for the specified screen.
WhitePixel (display, screen_number)
unsigned long XWhitePixel (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the white pixel value for the specified screen.
ConnectionNumber (display)
int XConnectionNumber(display)
Display *display;
display
Specifies the connection to the X server.
Both return a connection number for the specified display. On a POSIX-conformant system, this
is the file descriptor of the connection.
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DefaultColormap (display, screen_number)
Colormap XDefaultColormap (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the default colormap ID for allocation on the specified screen. Most routine alloca-
tions of color should be made out of this colormap.
DefaultDepth (display, screen_number)
int XDefaultDepth (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the depth (number of planes) of the default root window for the specified screen.
Other depths may also be supported on this screen (see XMatchVisualInfo).
To determine the number of depths that are available on a given screen, use XListDepths.
int *XListDepths(display, screen_number, count_return)
Display *display;
int screen_number;
int *count_return;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
count_return
Returns the number of depths.
The XListDepths function returns the array of depths that are available on the specified screen.
If the specified screen_number is valid and sufficient memory for the array can be allocated,
XListDepths sets count_return to the number of available depths. Otherwise, it does not set
count_return and returns NULL. To release the memory allocated for the array of depths, use
XFree.
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DefaultGC (display, screen_number)
GC XDefaultGC (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the default graphics context for the root window of the specified screen. This GC is
created for the convenience of simple applications and contains the default GC components with
the foreground and background pixel values initialized to the black and white pixels for the
screen, respectively. You can modify its contents freely because it is not used in any Xlib func-
tion. This GC should never be freed.
DefaultRootWindow(display)
Window XDefaultRootWindow(display)
Display *display;
display
Specifies the connection to the X server.
Both return the root window for the default screen.
DefaultScreenOfDisplay (display)
Screen *XDefaultScreenOfDisplay (display)
Display *display;
display
Specifies the connection to the X server.
Both return a pointer to the default screen.
ScreenOfDisplay (display, screen_number)
Screen *XScreenOfDisplay(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return a pointer to the indicated screen.
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DefaultScreen (display)
int XDefaultScreen (display)
Display *display;
display
Specifies the connection to the X server.
Both return the default screen number referenced by the XOpenDisplay function. This macro or
function should be used to retrieve the screen number in applications that will use only a single
screen.
DefaultVisual (display, screen_number)
Visual *XDefaultVisual (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the default visual type for the specified screen. For further information about visual
types, see section 3.1.
DisplayCells (display, screen_number)
int XDisplayCells(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the number of entries in the default colormap.
DisplayPlanes (display, screen_number)
int XDisplayPlanes(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the depth of the root window of the specified screen. For an explanation of depth, see
the glossary.
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DisplayString (display)
char *XDisplayString(display)
Display *display;
display
Specifies the connection to the X server.
Both return the string that was passed to XOpenDisplay when the current display was opened.
On POSIX-conformant systems, if the passed string was NULL, these return the value of the DIS-
PLAY environment variable when the current display was opened. These are useful to applica-
tions that invoke the fork system call and want to open a new connection to the same display
from the child process as well as for printing error messages.
long XExtendedMaxRequestSize(display)
Display *display;
display
Specifies the connection to the X server.
The XExtendedMaxRequestSize function returns zero if the specified display does not support
an extended-length protocol encoding; otherwise, it returns the maximum request size (in 4-byte
units) supported by the server using the extended-length encoding. The Xlib functions
XDrawLines, XDrawArcs, XFillPolygon, XChangeProperty, XSetClipRectangles, and
XSetRegion will use the extended-length encoding as necessary, if supported by the server. Use
of the extended-length encoding in other Xlib functions (for example, XDrawPoints,
XDrawRectangles, XDrawSegments, XFillArcs, XFillRectangles, XPutImage) is permitted
but not required; an Xlib implementation may choose to split the data across multiple smaller
requests instead.
long XMaxRequestSize(display)
Display *display;
display
Specifies the connection to the X server.
The XMaxRequestSize function returns the maximum request size (in 4-byte units) supported by
the server without using an extended-length protocol encoding. Single protocol requests to the
server can be no larger than this size unless an extended-length protocol encoding is supported by
the server. The protocol guarantees the size to be no smaller than 4096 units (16384 bytes). Xlib
automatically breaks data up into multiple protocol requests as necessary for the following func-
tions: XDrawPoints, XDrawRectangles, XDrawSegments, XFillArcs, XFillRectangles, and
XPutImage.
LastKnownRequestProcessed (display)
unsigned long XLastKnownRequestProcessed (display)
Display *display;
display
Specifies the connection to the X server.
Both extract the full serial number of the last request known by Xlib to have been processed by
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the X server. Xlib automatically sets this number when replies, events, and errors are received.
NextRequest (display)
unsigned long XNextRequest (display)
Display *display;
display
Specifies the connection to the X server.
Both extract the full serial number that is to be used for the next request. Serial numbers are
maintained separately for each display connection.
ProtocolVersion (display)
int XProtocolVersion (display)
Display *display;
display
Specifies the connection to the X server.
Both return the major version number (11) of the X protocol associated with the connected dis-
play.
ProtocolRevision (display)
int XProtocolRevision (display)
Display *display;
display
Specifies the connection to the X server.
Both return the minor protocol revision number of the X server.
QLength (display)
int XQLength(display)
Display *display;
display
Specifies the connection to the X server.
Both return the length of the event queue for the connected display. Note that there may be more
ev ents that have not been read into the queue yet (see XEventsQueued).
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RootWindow(display, screen_number)
Window XRootWindow(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the root window. These are useful with functions that need a drawable of a particular
screen and for creating top-level windows.
ScreenCount (display)
int XScreenCount(display)
Display *display;
display
Specifies the connection to the X server.
Both return the number of available screens.
ServerVendor (display)
char *XServerVendor (display)
Display *display;
display
Specifies the connection to the X server.
Both return a pointer to a null-terminated string that provides some identification of the owner of
the X server implementation. If the data returned by the server is in the Latin Portable Character
Encoding, then the string is in the Host Portable Character Encoding. Otherwise, the contents of
the string are implementation-dependent.
VendorRelease (display)
int XVendorRelease (display)
Display *display;
display
Specifies the connection to the X server.
Both return a number related to a vendor's release of the X server.
2.2.2. Image Format Functions and Macros
Applications are required to present data to the X server in a format that the server demands. To
help simplify applications, most of the work required to convert the data is provided by Xlib (see
sections 8.7 and 16.8).
The XPixmapFormatValues structure provides an interface to the pixmap format information
that is returned at the time of a connection setup. It contains:
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typedef struct {
int depth;
int bits_per_pixel;
int scanline_pad;
} XPixmapFormatValues;
To obtain the pixmap format information for a given display, use XListPixmapFormats.
XPixmapFormatValues *XListPixmapFormats (display, count_return)
Display *display;
int *count_return;
display
Specifies the connection to the X server.
count_return
Returns the number of pixmap formats that are supported by the display.
The XListPixmapFormats function returns an array of XPixmapFormatValues structures that
describe the types of Z format images supported by the specified display. If insufficient memory
is available, XListPixmapFormats returns NULL. To free the allocated storage for the
XPixmapFormatValues structures, use XFree.
The following lists the C language macros, their corresponding function equivalents that are for
other language bindings, and what data they both return for the specified server and screen.
These are often used by toolkits as well as by simple applications.
ImageByteOrder (display)
int XImageByteOrder(display)
Display *display;
display
Specifies the connection to the X server.
Both specify the required byte order for images for each scanline unit in XY format (bitmap) or
for each pixel value in Z format. The macro or function can return either LSBFirst or
MSBFirst.
BitmapUnit (display)
int XBitmapUnit(display)
Display *display;
display
Specifies the connection to the X server.
Both return the size of a bitmap's scanline unit in bits. The scanline is calculated in multiples of
this value.
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BitmapBitOrder (display)
int XBitmapBitOrder(display)
Display *display;
display
Specifies the connection to the X server.
Within each bitmap unit, the left-most bit in the bitmap as displayed on the screen is either the
least significant or most significant bit in the unit. This macro or function can return LSBFirst or
MSBFirst.
BitmapPad (display)
int XBitmapPad (display)
Display *display;
display
Specifies the connection to the X server.
Each scanline must be padded to a multiple of bits returned by this macro or function.
DisplayHeight (display, screen_number)
int XDisplayHeight(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return an integer that describes the height of the screen in pixels.
DisplayHeightMM (display, screen_number)
int XDisplayHeightMM(display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the height of the specified screen in millimeters.
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DisplayWidth (display, screen_number)
int XDisplayWidth (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the width of the screen in pixels.
DisplayWidthMM (display, screen_number)
int XDisplayWidthMM (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
Both return the width of the specified screen in millimeters.
2.2.3. Screen Information Macros
The following lists the C language macros, their corresponding function equivalents that are for
other language bindings, and what data they both can return. These macros or functions all take a
pointer to the appropriate screen structure.
BlackPixelOfScreen (screen)
unsigned long XBlackPixelOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the black pixel value of the specified screen.
WhitePixelOfScreen (screen)
unsigned long XWhitePixelOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the white pixel value of the specified screen.
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CellsOfScreen (screen)
int XCellsOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the number of colormap cells in the default colormap of the specified screen.
DefaultColormapOfScreen (screen)
Colormap XDefaultColormapOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the default colormap of the specified screen.
DefaultDepthOfScreen (screen)
int XDefaultDepthOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the depth of the root window.
DefaultGCOfScreen (screen)
GC XDefaultGCOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return a default graphics context (GC) of the specified screen, which has the same depth as
the root window of the screen. The GC must never be freed.
DefaultVisualOfScreen (screen)
Visual *XDefaultVisualOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the default visual of the specified screen. For information on visual types, see section
3.1.
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DoesBackingStore (screen)
int XDoesBackingStore(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return a value indicating whether the screen supports backing stores. The value returned can
be one of WhenMapped, NotUseful, or Always (see section 3.2.4).
DoesSaveUnders (screen)
Bool XDoesSaveUnders (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return a Boolean value indicating whether the screen supports save unders. If True, the
screen supports save unders. If False, the screen does not support save unders (see section 3.2.5).
DisplayOfScreen (screen)
Display *XDisplayOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the display of the specified screen.
int XScreenNumberOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
The XScreenNumberOfScreen function returns the screen index number of the specified screen.
EventMaskOfScreen (screen)
long XEventMaskOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the event mask of the root window for the specified screen at connection setup time.
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WidthOfScreen (screen)
int XWidthOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the width of the specified screen in pixels.
HeightOfScreen (screen)
int XHeightOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the height of the specified screen in pixels.
WidthMMOfScreen (screen)
int XWidthMMOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the width of the specified screen in millimeters.
HeightMMOfScreen (screen)
int XHeightMMOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the height of the specified screen in millimeters.
MaxCmapsOfScreen (screen)
int XMaxCmapsOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the maximum number of installed colormaps supported by the specified screen (see
section 9.3).
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MinCmapsOfScreen (screen)
int XMinCmapsOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the minimum number of installed colormaps supported by the specified screen (see
section 9.3).
PlanesOfScreen (screen)
int XPlanesOfScreen(screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the depth of the root window.
RootWindowOfScreen (screen)
Window XRootWindowOfScreen (screen)
Screen *screen;
screen
Specifies the appropriate Screen structure.
Both return the root window of the specified screen.
2.3. Generating a NoOperation Protocol Request
To execute a NoOperation protocol request, use XNoOp.
XNoOp (display)
Display *display;
display
Specifies the connection to the X server.
The XNoOp function sends a NoOperation protocol request to the X server, thereby exercising
the connection.
2.4. Freeing Client-Created Data
To free in-memory data that was created by an Xlib function, use XFree.
XFree (data)
void *data;
data
Specifies the data that is to be freed.
The XFree function is a general-purpose Xlib routine that frees the specified data. You must use
it to free any objects that were allocated by Xlib, unless an alternate function is explicitly
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specified for the object. A NULL pointer cannot be passed to this function.
2.5. Closing the Display
To close a display or disconnect from the X server, use XCloseDisplay.
XCloseDisplay (display)
Display *display;
display
Specifies the connection to the X server.
The XCloseDisplay function closes the connection to the X server for the display specified in the
Display structure and destroys all windows, resource IDs (Window, Font, Pixmap, Colormap,
Cursor, and GContext), or other resources that the client has created on this display, unless the
close-down mode of the resource has been changed (see XSetCloseDownMode). Therefore,
these windows, resource IDs, and other resources should never be referenced again or an error
will be generated. Before exiting, you should call XCloseDisplay explicitly so that any pending
errors are reported as XCloseDisplay performs a final XSync operation.
XCloseDisplay can generate a BadGC error.
Xlib provides a function to permit the resources owned by a client to survive after the client's
connection is closed. To change a client's close-down mode, use XSetCloseDownMode.
XSetCloseDownMode (display, close_mode)
Display *display;
int close_mode;
display
Specifies the connection to the X server.
close_mode
Specifies the client close-down mode.
You
can pass
DestroyAll,
RetainPermanent, or RetainTemporary.
The XSetCloseDownMode defines what will happen to the client's resources at connection
close. A connection starts in DestroyAll mode. For information on what happens to the client's
resources when the close_mode argument is RetainPermanent or RetainTemporary, see sec-
tion 2.6.
XSetCloseDownMode can generate a BadValue error.
2.6. Using X Server Connection Close Operations
When the X server's connection to a client is closed either by an explicit call to XCloseDisplay
or by a process that exits, the X server performs the following automatic operations:

It disowns all selections owned by the client (see XSetSelectionOwner).

It performs an XUngrabPointer and XUngrabKeyboard if the client has actively
grabbed the pointer or the keyboard.

It performs an XUngrabServer if the client has grabbed the server.

It releases all passive grabs made by the client.

It marks all resources (including colormap entries) allocated by the client either as perma-
nent or temporary, depending on whether the close-down mode is RetainPermanent or
RetainTemporary. Howev er, this does not prevent other client applications from explic-
itly destroying the resources (see XSetCloseDownMode).
When the close-down mode is DestroyAll, the X server destroys all of a client's resources as fol-
lows:
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It examines each window in the client's sav e-set to determine if it is an inferior (subwin-
dow) of a window created by the client. (The save-set is a list of other clients' windows
that are referred to as save-set windows.) If so, the X server reparents the save-set window
to the closest ancestor so that the save-set window is not an inferior of a window created by
the client. The reparenting leaves unchanged the absolute coordinates (with respect to the
root window) of the upper-left outer corner of the save-set window.

It performs a MapWindow request on the save-set window if the save-set window is
unmapped. The X server does this even if the save-set window was not an inferior of a
window created by the client.

It destroys all windows created by the client.

It performs the appropriate free request on each nonwindow resource created by the client
in the server (for example, Font, Pixmap, Cursor, Colormap, and GContext).

It frees all colors and colormap entries allocated by a client application.
Additional processing occurs when the last connection to the X server closes. An X server goes
through a cycle of having no connections and having some connections. When the last connec-
tion to the X server closes as a result of a connection closing with the close_mode of DestroyAll,
the X server does the following:

It resets its state as if it had just been started. The X server begins by destroying all linger-
ing resources from clients that have terminated in RetainPermanent or RetainTempo-
rary
mode.

It deletes all but the predefined atom identifiers.

It deletes all properties on all root windows (see section 4.3).

It resets all device maps and attributes (for example, key click, bell volume, and accelera-
tion) as well as the access control list.

It restores the standard root tiles and cursors.

It restores the default font path.

It restores the input focus to state PointerRoot.
However, the X server does not reset if you close a connection with a close-down mode set to
RetainPermanent or RetainTemporary.
2.7. Using Xlib with Threads
On systems that have threads, support may be provided to permit multiple threads to use Xlib
concurrently.
To initialize support for concurrent threads, use XInitThreads.
Status XInitThreads( );
The XInitThreads function initializes Xlib support for concurrent threads. This function must
be the first Xlib function a multi-threaded program calls, and it must complete before any other
Xlib call is made. This function returns a nonzero status if initialization was successful; other-
wise, it returns zero. On systems that do not support threads, this function always returns zero.
It is only necessary to call this function if multiple threads might use Xlib concurrently. If all
calls to Xlib functions are protected by some other access mechanism (for example, a mutual
exclusion lock in a toolkit or through explicit client programming), Xlib thread initialization is
not required. It is recommended that single-threaded programs not call this function.
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To lock a display across several Xlib calls, use XLockDisplay.
void XLockDisplay(display)
Display *display;
display
Specifies the connection to the X server.
The XLockDisplay function locks out all other threads from using the specified display. Other
threads attempting to use the display will block until the display is unlocked by this thread.
Nested calls to XLockDisplay work correctly; the display will not actually be unlocked until
XUnlockDisplay has been called the same number of times as XLockDisplay. This function
has no effect unless Xlib was successfully initialized for threads using XInitThreads.
To unlock a display, use XUnlockDisplay.
void XUnlockDisplay(display)
Display *display;
display
Specifies the connection to the X server.
The XUnlockDisplay function allows other threads to use the specified display again. Any
threads that have blocked on the display are allowed to continue. Nested locking works correctly;
if XLockDisplay has been called multiple times by a thread, then XUnlockDisplay must be
called an equal number of times before the display is actually unlocked. This function has no
effect unless Xlib was successfully initialized for threads using XInitThreads.
2.8. Using Internal Connections
In addition to the connection to the X server, an Xlib implementation may require connections to
other kinds of servers (for example, to input method servers as described in chapter 13). Toolkits
and clients that use multiple displays, or that use displays in combination with other inputs, need
to obtain these additional connections to correctly block until input is available and need to pro-
cess that input when it is available. Simple clients that use a single display and block for input in
an Xlib event function do not need to use these facilities.
To track internal connections for a display, use XAddConnectionWatch.
typedef void (*XConnectionWatchProc) (display, client_data, fd, opening, watch_data)
Display *display;
XPointer client_data;
int fd;
Bool opening;
XPointer *watch_data;
Status XAddConnectionWatch (display, procedure, client_data)
Display *display;
XWatchProc procedure;
XPointer client_data;
display
Specifies the connection to the X server.
procedure
Specifies the procedure to be called.
client_data
Specifies the additional client data.
The XAddConnectionWatch function registers a procedure to be called each time Xlib opens or
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closes an internal connection for the specified display. The procedure is passed the display, the
specified client_data, the file descriptor for the connection, a Boolean indicating whether the con-
nection is being opened or closed, and a pointer to a location for private watch data. If opening is
True, the procedure can store a pointer to private data in the location pointed to by watch_data;
when the procedure is later called for this same connection and opening is False, the location
pointed to by watch_data will hold this same private data pointer.
This function can be called at any time after a display is opened. If internal connections already
exist, the registered procedure will immediately be called for each of them, before XAddConnec-
tionWatch
returns. XAddConnectionWatch returns a nonzero status if the procedure is suc-
cessfully registered; otherwise, it returns zero.
The registered procedure should not call any Xlib functions. If the procedure directly or indi-
rectly causes the state of internal connections or watch procedures to change, the result is not
defined. If Xlib has been initialized for threads, the procedure is called with the display locked
and the result of a call by the procedure to any Xlib function that locks the display is not defined
unless the executing thread has externally locked the display using XLockDisplay.
To stop tracking internal connections for a display, use XRemoveConnectionWatch.
Status XRemoveConnectionWatch (display, procedure, client_data)
Display *display;
XWatchProc procedure;
XPointer client_data;
display
Specifies the connection to the X server.
procedure
Specifies the procedure to be called.
client_data
Specifies the additional client data.
The XRemoveConnectionWatch function removes a previously registered connection watch
procedure. The client_data must match the client_data used when the procedure was initially reg-
istered.
To process input on an internal connection, use XProcessInternalConnection.
void XProcessInternalConnection(display, fd)
Display *display;
int fd;
display
Specifies the connection to the X server.
fd
Specifies the file descriptor.
The XProcessInternalConnection function processes input available on an internal connection.
This function should be called for an internal connection only after an operating system facility
(for example, select or poll) has indicated that input is available; otherwise, the effect is not
defined.
To obtain all of the current internal connections for a display, use
XInternalConnectionNumbers.
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Status XInternalConnectionNumbers(display, fd_return, count_return)
Display *display;
int **fd_return;
int *count_return;
display
Specifies the connection to the X server.
fd_return
Returns the file descriptors.
count_return
Returns the number of file descriptors.
The XInternalConnectionNumbers function returns a list of the file descriptors for all internal
connections currently open for the specified display. When the allocated list is no longer needed,
free it by using XFree. This functions returns a nonzero status if the list is successfully allo-
cated; otherwise, it returns zero.
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Chapter 3
Window Functions
In the X Window System, a window is a rectangular area on the screen that lets you view graphic
output. Client applications can display overlapping and nested windows on one or more screens
that are driven by X servers on one or more machines. Clients who want to create windows must
first connect their program to the X server by calling XOpenDisplay. This chapter begins with a
discussion of visual types and window attributes. The chapter continues with a discussion of the
Xlib functions you can use to:

Create windows

Destroy windows

Map windows

Unmap windows

Configure windows

Change window stacking order

Change window attributes
This chapter also identifies the window actions that may generate events.
Note that it is vital that your application conform to the established conventions for communicat-
ing with window managers for it to work well with the various window managers in use (see sec-
tion 14.1). Toolkits generally adhere to these conventions for you, relieving you of the burden.
Toolkits also often supersede many functions in this chapter with versions of their own. For more
information, refer to the documentation for the toolkit that you are using.
3.1. Visual Types
On some display hardware, it may be possible to deal with color resources in more than one way.
For example, you may be able to deal with a screen of either 12-bit depth with arbitrary mapping
of pixel to color (pseudo-color) or 24-bit depth with 8 bits of the pixel dedicated to each of red,
green, and blue. These different ways of dealing with the visual aspects of the screen are called
visuals. For each screen of the display, there may be a list of valid visual types supported at dif-
ferent depths of the screen. Because default windows and visual types are defined for each
screen, most simple applications need not deal with this complexity. Xlib provides macros and
functions that return the default root window, the default depth of the default root window, and
the default visual type (see sections 2.2.1 and 16.7).
Xlib uses an opaque Visual structure that contains information about the possible color mapping.
The visual utility functions (see section 16.7) use an XVisualInfo structure to return this infor-
mation to an application. The members of this structure pertinent to this discussion are class,
red_mask, green_mask, blue_mask, bits_per_rgb, and colormap_size. The class member speci-
fies one of the possible visual classes of the screen and can be StaticGray, StaticColor,
TrueColor, GrayScale, PseudoColor, or DirectColor.
The following concepts may serve to make the explanation of visual types clearer. The screen
can be color or grayscale, can have a colormap that is writable or read-only, and can also have a
colormap whose indices are decomposed into separate RGB pieces, provided one is not on a
grayscale screen. This leads to the following diagram:
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Color Gray-scale
R/O R/W R/O
R/W
Undecomposed Static Pseudo Static
Gray
Colormap Color
Color Gray
Scale
Decomposed True Direct
Colormap Color
Color
Conceptually, as each pixel is read out of video memory for display on the screen, it goes through
a look-up stage by indexing into a colormap. Colormaps can be manipulated arbitrarily on some
hardware, in limited ways on other hardware, and not at all on other hardware. The visual types
affect the colormap and the RGB values in the following ways:

For PseudoColor, a pixel value indexes a colormap to produce independent RGB values,
and the RGB values can be changed dynamically.

GrayScale is treated the same way as PseudoColor except that the primary that drives the
screen is undefined. Thus, the client should always store the same value for red, green, and
blue in the colormaps.

For DirectColor, a pixel value is decomposed into separate RGB subfields, and each sub-
field separately indexes the colormap for the corresponding value. The RGB values can be
changed dynamically.

TrueColor is treated the same way as DirectColor except that the colormap has prede-
fined, read-only RGB values. These RGB values are server dependent but provide linear or
near-linear ramps in each primary.

StaticColor is treated the same way as PseudoColor except that the colormap has prede-
fined, read-only, server-dependent RGB values.

StaticGray is treated the same way as StaticColor except that the RGB values are equal
for any single pixel value, thus resulting in shades of gray. StaticGray with a two-entry
colormap can be thought of as monochrome.
The red_mask, green_mask, and blue_mask members are only defined for DirectColor and
TrueColor. Each has one contiguous set of bits with no intersections. The bits_per_rgb member
specifies the log base 2 of the number of distinct color values (individually) of red, green, and
blue. Actual RGB values are unsigned 16-bit numbers. The colormap_size member defines the
number of available colormap entries in a newly created colormap. For DirectColor and
TrueColor, this is the size of an individual pixel subfield.
To obtain the visual ID from a Visual, use XVisualIDFromVisual.
VisualID XVisualIDFromVisual (visual)
Visual *visual;
visual
Specifies the visual type.
The XVisualIDFromVisual function returns the visual ID for the specified visual type.
3.2. Window Attributes
All InputOutput windows have a border width of zero or more pixels, an optional background,
an event suppression mask (which suppresses propagation of events from children), and a prop-
erty list (see section 4.3). The window border and background can be a solid color or a pattern,
called a tile. All windows except the root have a parent and are clipped by their parent. If a win-
dow is stacked on top of another window, it obscures that other window for the purpose of input.
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If a window has a background (almost all do), it obscures the other window for purposes of out-
put. Attempts to output to the obscured area do nothing, and no input events (for example,
pointer motion) are generated for the obscured area.
Windows also have associated property lists (see section 4.3).
Both InputOutput and InputOnly windows have the following common attributes, which are
the only attributes of an InputOnly window:

win-gravity

event-mask

do-not-propagate-mask

override-redirect

cursor
If you specify any other attributes for an InputOnly window, a BadMatch error results.
InputOnly windows are used for controlling input events in situations where InputOutput win-
dows are unnecessary. InputOnly windows are invisible; can only be used to control such things
as cursors, input event generation, and grabbing; and cannot be used in any graphics requests.
Note that InputOnly windows cannot have InputOutput windows as inferiors.
Windows have borders of a programmable width and pattern as well as a background pattern or
tile. Pixel values can be used for solid colors. The background and border pixmaps can be
destroyed immediately after creating the window if no further explicit references to them are to be
made. The pattern can either be relative to the parent or absolute. If ParentRelative, the par-
ent's background is used.
When windows are first created, they are not visible (not mapped) on the screen. Any output to a
window that is not visible on the screen and that does not have backing store will be discarded.
An application may wish to create a window long before it is mapped to the screen. When a win-
dow is eventually mapped to the screen (using XMapWindow), the X server generates an
Expose ev ent for the window if backing store has not been maintained.
A window manager can override your choice of size, border width, and position for a top-level
window. Your program must be prepared to use the actual size and position of the top window. It
is not acceptable for a client application to resize itself unless in direct response to a human com-
mand to do so. Instead, either your program should use the space given to it, or if the space is too
small for any useful work, your program might ask the user to resize the window. The border of
your top-level window is considered fair game for window managers.
To set an attribute of a window, set the appropriate member of the XSetWindowAttributes struc-
ture and OR in the corresponding value bitmask in your subsequent calls to XCreateWindow
and XChangeWindowAttributes, or use one of the other convenience functions that set the
appropriate attribute. The symbols for the value mask bits and the XSetWindowAttributes
structure are:
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/* Window attribute value mask bits */
#define
CWBackPixmap
(1L<<0)
#define
CWBackPixel
(1L<<1)
#define
CWBorderPixmap
(1L<<2)
#define
CWBorderPixel
(1L<<3)
#define
CWBitGravity
(1L<<4)
#define
CWWinGravity
(1L<<5)
#define
CWBackingStore
(1L<<6)
#define
CWBackingPlanes
(1L<<7)
#define
CWBackingPixel
(1L<<8)
#define
CWOverrideRedirect
(1L<<9)
#define
CWSaveUnder
(1L<<10)
#define
CWEventMask
(1L<<11)
#define
CWDontPropagate
(1L<<12)
#define
CWColormap
(1L<<13)
#define
CWCursor
(1L<<14)
/* Values */
typedef struct {
Pixmap background_pixmap;
/* background, None, or ParentRelative */
unsigned long background_pixel; /* background pixel */
Pixmap border_pixmap;
/* border of the window or CopyFromParent */
unsigned long border_pixel; /* border pixel value */
int bit_gravity; /* one of bit gravity values */
int win_gravity; /* one of the window gravity values */
int backing_store;
/* NotUseful, WhenMapped, Always */
unsigned long backing_planes;
/* planes to be preserved if possible */
unsigned long backing_pixel; /* value to use in restoring planes */
Bool save_under; /* should bits under be saved? (popups) */
long event_mask; /* set of events that should be saved */
long do_not_propagate_mask; /* set of events that should not propagate */
Bool override_redirect; /* boolean value for override_redirect */
Colormap colormap;
/* color map to be associated with window */
Cursor cursor;
/* cursor to be displayed (or None) */
} XSetWindowAttributes;
The following lists the defaults for each window attribute and indicates whether the attribute is
applicable to InputOutput and InputOnly windows:
Attribute
Default
InputOutput
InputOnly
background-pixmap
None
Yes
No
background-pixel Undefined
Yes
No
border-pixmap
CopyFromParent
Yes
No
border-pixel Undefined
Yes
No
bit-gravity
ForgetGravity
Yes
No
win-gravity
NorthWestGravity
Yes
Yes
backing-store
NotUseful
Yes
No
backing-planes All ones Yes No
backing-pixel zero
Yes
No
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Attribute
Default
InputOutput
InputOnly
save-under
False
Yes
No
ev ent-mask empty set Yes Yes
do-not-propagate-mask empty set Yes Yes
override-redirect
False
Yes
Yes
colormap
CopyFromParent
Yes
No
cursor
None
Yes
Yes
3.2.1. Background Attribute
Only InputOutput windows can have a background. You can set the background of an
InputOutput window by using a pixel or a pixmap.
The background-pixmap attribute of a window specifies the pixmap to be used for a window's
background. This pixmap can be of any size, although some sizes may be faster than others. The
background-pixel attribute of a window specifies a pixel value used to paint a window's back-
ground in a single color.
You can set the background-pixmap to a pixmap, None (default), or ParentRelative. You can
set the background-pixel of a window to any pixel value (no default). If you specify a back-
ground-pixel, it overrides either the default background-pixmap or any value you may have set in
the background-pixmap. A pixmap of an undefined size that is filled with the background-pixel is
used for the background. Range checking is not performed on the background pixel; it simply is
truncated to the appropriate number of bits.
If you set the background-pixmap, it overrides the default. The background-pixmap and the win-
dow must have the same depth, or a BadMatch error results. If you set background-pixmap to
None, the window has no defined background. If you set the background-pixmap to
ParentRelative:

The parent window's background-pixmap is used. The child window, howev er, must have
the same depth as its parent, or a BadMatch error results.

If the parent window has a background-pixmap of None, the window also has a back-
ground-pixmap of None.

A copy of the parent window's background-pixmap is not made. The parent's background-
pixmap is examined each time the child window's background-pixmap is required.

The background tile origin always aligns with the parent window's background tile origin.
If the background-pixmap is not ParentRelative, the background tile origin is the child
window's origin.
Setting a new background, whether by setting background-pixmap or background-pixel, overrides
any previous background. The background-pixmap can be freed immediately if no further
explicit reference is made to it (the X server will keep a copy to use when needed). If you later
draw into the pixmap used for the background, what happens is undefined because the X imple-
mentation is free to make a copy of the pixmap or to use the same pixmap.
When no valid contents are available for regions of a window and either the regions are visible or
the server is maintaining backing store, the server automatically tiles the regions with the win-
dow's background unless the window has a background of None. If the background is None, the
previous screen contents from other windows of the same depth as the window are simply left in
place as long as the contents come from the parent of the window or an inferior of the parent.
Otherwise, the initial contents of the exposed regions are undefined. Expose ev ents are then gen-
erated for the regions, even if the background-pixmap is None (see section 10.9).
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3.2.2. Border Attribute
Only InputOutput windows can have a border. You can set the border of an InputOutput win-
dow by using a pixel or a pixmap.
The border-pixmap attribute of a window specifies the pixmap to be used for a window's border.
The border-pixel attribute of a window specifies a pixmap of undefined size filled with that pixel
be used for a window's border. Range checking is not performed on the background pixel; it sim-
ply is truncated to the appropriate number of bits. The border tile origin is always the same as the
background tile origin.
You can also set the border-pixmap to a pixmap of any size (some may be faster than others) or to
CopyFromParent (default). You can set the border-pixel to any pixel value (no default).
If you set a border-pixmap, it overrides the default. The border-pixmap and the window must
have the same depth, or a BadMatch error results. If you set the border-pixmap to
CopyFromParent, the parent window's border-pixmap is copied. Subsequent changes to the
parent window's border attribute do not affect the child window. Howev er, the child window
must have the same depth as the parent window, or a BadMatch error results.
The border-pixmap can be freed immediately if no further explicit reference is made to it. If you
later draw into the pixmap used for the border, what happens is undefined because the X imple-
mentation is free either to make a copy of the pixmap or to use the same pixmap. If you specify a
border-pixel, it overrides either the default border-pixmap or any value you may have set in the
border-pixmap. All pixels in the window's border will be set to the border-pixel. Setting a new
border, whether by setting border-pixel or by setting border-pixmap, overrides any previous bor-
der.
Output to a window is always clipped to the inside of the window. Therefore, graphics operations
never affect the window border.
3.2.3. Gravity Attributes
The bit gravity of a window defines which region of the window should be retained when an
InputOutput window is resized. The default value for the bit-gravity attribute is
ForgetGravity. The window gravity of a window allows you to define how the InputOutput or
InputOnly window should be repositioned if its parent is resized. The default value for the win-
gravity attribute is NorthWestGravity.
If the inside width or height of a window is not changed and if the window is moved or its border
is changed, then the contents of the window are not lost but move with the window. Changing the
inside width or height of the window causes its contents to be moved or lost (depending on the
bit-gravity of the window) and causes children to be reconfigured (depending on their win-grav-
ity). For a change of width and height, the (x, y) pairs are defined:
Gravity Direction Coordinates
NorthWestGravity
(0, 0)
NorthGravity
(Width/2, 0)
NorthEastGravity
(Width, 0)
WestGravity
(0, Height/2)
CenterGravity
(Width/2, Height/2)
EastGravity
(Width, Height/2)
SouthWestGravity
(0, Height)
SouthGravity
(Width/2, Height)
SouthEastGravity
(Width, Height)
When a window with one of these bit-gravity values is resized, the corresponding pair defines the
change in position of each pixel in the window. When a window with one of these win-gravities
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has its parent window resized, the corresponding pair defines the change in position of the win-
dow within the parent. When a window is so repositioned, a GravityNotify ev ent is generated
(see section 10.10.5).
A bit-gravity of StaticGravity indicates that the contents or origin should not move relative to
the origin of the root window. If the change in size of the window is coupled with a change in
position (x, y), then for bit-gravity the change in position of each pixel is (-x, -y), and for win-
gravity the change in position of a child when its parent is so resized is (-x, -y). Note that Stat-
icGravity
still only takes effect when the width or height of the window is changed, not when the
window is moved.
A bit-gravity of ForgetGravity indicates that the window's contents are always discarded after a
size change, even if a backing store or save under has been requested. The window is tiled with
its background and zero or more Expose ev ents are generated. If no background is defined, the
existing screen contents are not altered. Some X servers may also ignore the specified bit-gravity
and always generate Expose ev ents.
The contents and borders of inferiors are not affected by their parent's bit-gravity. A server is
permitted to ignore the specified bit-gravity and use Forget instead.
A win-gravity of UnmapGravity is like NorthWestGravity (the window is not moved), except
the child is also unmapped when the parent is resized, and an UnmapNotify ev ent is generated.
3.2.4. Backing Store Attribute
Some implementations of the X server may choose to maintain the contents of InputOutput
windows. If the X server maintains the contents of a window, the off-screen saved pixels are
known as backing store. The backing store advises the X server on what to do with the contents
of a window. The backing-store attribute can be set to NotUseful (default), WhenMapped, or
Always.
A backing-store attribute of NotUseful advises the X server that maintaining contents is unneces-
sary, although some X implementations may still choose to maintain contents and, therefore, not
generate Expose ev ents. A backing-store attribute of WhenMapped advises the X server that
maintaining contents of obscured regions when the window is mapped would be beneficial. In
this case, the server may generate an Expose ev ent when the window is created. A backing-store
attribute of Always advises the X server that maintaining contents even when the window is
unmapped would be beneficial. Even if the window is larger than its parent, this is a request to
the X server to maintain complete contents, not just the region within the parent window bound-
aries. While the X server maintains the window's contents, Expose ev ents normally are not gen-
erated, but the X server may stop maintaining contents at any time.
When the contents of obscured regions of a window are being maintained, regions obscured by
noninferior windows are included in the destination of graphics requests (and source, when the
window is the source). However, regions obscured by inferior windows are not included.
3.2.5. Save Under Flag
Some server implementations may preserve contents of InputOutput windows under other
InputOutput windows. This is not the same as preserving the contents of a window for you.
You may get better visual appeal if transient windows (for example, pop-up menus) request that
the system preserve the screen contents under them, so the temporarily obscured applications do
not have to repaint.
You can set the save-under flag to True or False (default). If save-under is True, the X server is
advised that, when this window is mapped, saving the contents of windows it obscures would be
beneficial.
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3.2.6. Backing Planes and Backing Pixel Attributes
You can set backing planes to indicate (with bits set to 1) which bit planes of an InputOutput
window hold dynamic data that must be preserved in backing store and during save unders. The
default value for the backing-planes attribute is all bits set to 1. You can set backing pixel to
specify what bits to use in planes not covered by backing planes. The default value for the back-
ing-pixel attribute is all bits set to 0. The X server is free to save only the specified bit planes in
the backing store or the save under and is free to regenerate the remaining planes with the speci-
fied pixel value. Any extraneous bits in these values (that is, those bits beyond the specified depth
of the window) may be simply ignored. If you request backing store or save unders, you should
use these members to minimize the amount of off-screen memory required to store your window.
3.2.7. Event Mask and Do Not Propagate Mask Attributes
The event mask defines which events the client is interested in for this InputOutput or Inpu-
tOnly
window (or, for some event types, inferiors of this window). The ev ent mask is the bitwise
inclusive OR of zero or more of the valid event mask bits. You can specify that no maskable
ev ents are reported by setting NoEventMask (default).
The do-not-propagate-mask attribute defines which events should not be propagated to ancestor
windows when no client has the event type selected in this InputOutput or InputOnly window.
The do-not-propagate-mask is the bitwise inclusive OR of zero or more of the following masks:
KeyPress, KeyRelease, ButtonPress, ButtonRelease, PointerMotion, Button1Motion,
Button2Motion, Button3Motion, Button4Motion, Button5Motion, and ButtonMotion. You
can specify that all events are propagated by setting NoEventMask (default).
3.2.8. Override Redirect Flag
To control window placement or to add decoration, a window manager often needs to intercept
(redirect) any map or configure request. Pop-up windows, however, often need to be mapped
without a window manager getting in the way. To control whether an InputOutput or Inpu-
tOnly
window is to ignore these structure control facilities, use the override-redirect flag.
The override-redirect flag specifies whether map and configure requests on this window should
override a SubstructureRedirectMask on the parent. You can set the override-redirect flag to
True or False (default). Window managers use this information to avoid tampering with pop-up
windows (see also chapter 14).
3.2.9. Colormap Attribute
The colormap attribute specifies which colormap best reflects the true colors of the InputOutput
window. The colormap must have the same visual type as the window, or a BadMatch error
results. X servers capable of supporting multiple hardware colormaps can use this information,
and window managers can use it for calls to XInstallColormap. You can set the colormap
attribute to a colormap or to CopyFromParent (default).
If you set the colormap to CopyFromParent, the parent window's colormap is copied and used
by its child. However, the child window must have the same visual type as the parent, or a Bad-
Match
error results. The parent window must not have a colormap of None, or a BadMatch
error results. The colormap is copied by sharing the colormap object between the child and par-
ent, not by making a complete copy of the colormap contents. Subsequent changes to the parent
window's colormap attribute do not affect the child window.
3.2.10. Cursor Attribute
The cursor attribute specifies which cursor is to be used when the pointer is in the InputOutput
or InputOnly window. You can set the cursor to a cursor or None (default).
If you set the cursor to None, the parent's cursor is used when the pointer is in the InputOutput
or InputOnly window, and any change in the parent's cursor will cause an immediate change in
the displayed cursor. By calling XFreeCursor, the cursor can be freed immediately as long as
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no further explicit reference to it is made.
3.3. Creating Windows
Xlib provides basic ways for creating windows, and toolkits often supply higher-level functions
specifically for creating and placing top-level windows, which are discussed in the appropriate
toolkit documentation. If you do not use a toolkit, however, you must provide some standard
information or hints for the window manager by using the Xlib inter-client communication func-
tions (see chapter 14).
If you use Xlib to create your own top-level windows (direct children of the root window), you
must observe the following rules so that all applications interact reasonably across the different
styles of window management:

You must never fight with the window manager for the size or placement of your top-level
window.

You must be able to deal with whatever size window you get, even if this means that your
application just prints a message like ``Please make me bigger'' in its window.

You should only attempt to resize or move top-level windows in direct response to a user
request. If a request to change the size of a top-level window fails, you must be prepared to
live with what you get. You are free to resize or move the children of top-level windows as
necessary. (Toolkits often have facilities for automatic relayout.)

If you do not use a toolkit that automatically sets standard window properties, you should
set these properties for top-level windows before mapping them.
For further information, see chapter 14 and the Inter-Client Communication Conventions Manual.
XCreateWindow is the more general function that allows you to set specific window attributes
when you create a window. XCreateSimpleWindow creates a window that inherits its attributes
from its parent window.
The X server acts as if InputOnly windows do not exist for the purposes of graphics requests,
exposure processing, and VisibilityNotify ev ents. An InputOnly window cannot be used as a
drawable (that is, as a source or destination for graphics requests). InputOnly and InputOutput
windows act identically in other respects (properties, grabs, input control, and so on). Extension
packages can define other classes of windows.
To create an unmapped window and set its window attributes, use XCreateWindow.
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Window XCreateWindow(display, parent, x, y, width, height, border_width, depth,
class, visual, valuemask, attributes)
Display *display;
Window parent;
int x, y;
unsigned int width, height;
unsigned int border_width;
int depth;
unsigned int class;
Visual *visual;
unsigned long valuemask;
XSetWindowAttributes *attributes;
display
Specifies the connection to the X server.
parent
Specifies the parent window.
x
y
Specify the x and y coordinates, which are the top-left outside corner of the creat-
ed window's borders and are relative to the inside of the parent window's bor-
ders.
width
height
Specify the width and height, which are the created window's inside dimensions
and do not include the created window's borders. The dimensions must be
nonzero, or a BadValue error results.
border_width
Specifies the width of the created window's border in pixels.
depth
Specifies the window's depth. A depth of CopyFromParent means the depth is
taken from the parent.
class
Specifies the created window's class. You can pass InputOutput, InputOnly,
or CopyFromParent. A class of CopyFromParent means the class is taken
from the parent.
visual
Specifies the visual type. A visual of CopyFromParent means the visual type is
taken from the parent.
valuemask
Specifies which window attributes are defined in the attributes argument. This
mask is the bitwise inclusive OR of the valid attribute mask bits. If valuemask is
zero, the attributes are ignored and are not referenced.
attributes
Specifies the structure from which the values (as specified by the value mask) are
to be taken. The value mask should have the appropriate bits set to indicate
which attributes have been set in the structure.
The XCreateWindow function creates an unmapped subwindow for a specified parent window,
returns the window ID of the created window, and causes the X server to generate a CreateNo-
tify
ev ent. The created window is placed on top in the stacking order with respect to siblings.
The coordinate system has the X axis horizontal and the Y axis vertical with the origin [0, 0] at
the upper-left corner. Coordinates are integral, in terms of pixels, and coincide with pixel centers.
Each window and pixmap has its own coordinate system. For a window, the origin is inside the
border at the inside, upper-left corner.
The border_width for an InputOnly window must be zero, or a BadMatch error results. For
class InputOutput, the visual type and depth must be a combination supported for the screen, or
a BadMatch error results. The depth need not be the same as the parent, but the parent must not
be a window of class InputOnly, or a BadMatch error results. For an InputOnly window, the
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depth must be zero, and the visual must be one supported by the screen. If either condition is not
met, a BadMatch error results. The parent window, howev er, may have any depth and class. If
you specify any inv alid window attribute for a window, a BadMatch error results.
The created window is not yet displayed (mapped) on the user's display. To display the window,
call XMapWindow. The new window initially uses the same cursor as its parent. A new cursor
can be defined for the new window by calling XDefineCursor. The window will not be visible
on the screen unless it and all of its ancestors are mapped and it is not obscured by any of its
ancestors.
XCreateWindow can generate BadAlloc, BadColor, BadCursor, BadMatch, BadPixmap,
BadValue, and BadWindow errors.
To create an unmapped InputOutput subwindow of a giv en parent window, use
XCreateSimpleWindow.
Window XCreateSimpleWindow(display, parent, x, y, width, height, border_width,
border, background)
Display *display;
Window parent;
int x, y;
unsigned int width, height;
unsigned int border_width;
unsigned long border;
unsigned long background;
display
Specifies the connection to the X server.
parent
Specifies the parent window.
x
y
Specify the x and y coordinates, which are the top-left outside corner of the new
window's borders and are relative to the inside of the parent window's borders.
width
height
Specify the width and height, which are the created window's inside dimensions
and do not include the created window's borders. The dimensions must be
nonzero, or a BadValue error results.
border_width
Specifies the width of the created window's border in pixels.
border
Specifies the border pixel value of the window.
background
Specifies the background pixel value of the window.
The XCreateSimpleWindow function creates an unmapped InputOutput subwindow for a
specified parent window, returns the window ID of the created window, and causes the X server to
generate a CreateNotify ev ent. The created window is placed on top in the stacking order with
respect to siblings. Any part of the window that extends outside its parent window is clipped.
The border_width for an InputOnly window must be zero, or a BadMatch error results. XCre-
ateSimpleWindow
inherits its depth, class, and visual from its parent. All other window
attributes, except background and border, hav e their default values.
XCreateSimpleWindow can generate BadAlloc, BadMatch, BadValue, and BadWindow
errors.
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3.4. Destroying Windows
Xlib provides functions that you can use to destroy a window or destroy all subwindows of a win-
dow.
To destroy a window and all of its subwindows, use XDestroyWindow.
XDestroyWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XDestroyWindow function destroys the specified window as well as all of its subwindows
and causes the X server to generate a DestroyNotify ev ent for each window. The window should
never be referenced again. If the window specified by the w argument is mapped, it is unmapped
automatically. The ordering of the DestroyNotify ev ents is such that for any giv en window being
destroyed, DestroyNotify is generated on any inferiors of the window before being generated on
the window itself. The ordering among siblings and across subhierarchies is not otherwise con-
strained. If the window you specified is a root window, no windows are destroyed. Destroying a
mapped window will generate Expose ev ents on other windows that were obscured by the win-
dow being destroyed.
XDestroyWindow can generate a BadWindow error.
To destroy all subwindows of a specified window, use XDestroySubwindows.
XDestroySubwindows (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XDestroySubwindows function destroys all inferior windows of the specified window, in
bottom-to-top stacking order. It causes the X server to generate a DestroyNotify ev ent for each
window. If any mapped subwindows were actually destroyed, XDestroySubwindows causes the
X server to generate Expose ev ents on the specified window. This is much more efficient than
deleting many windows one at a time because much of the work need be performed only once for
all of the windows, rather than for each window. The subwindows should never be referenced
again.
XDestroySubwindows can generate a BadWindow error.
3.5. Mapping Windows
A window is considered mapped if an XMapWindow call has been made on it. It may not be
visible on the screen for one of the following reasons:

It is obscured by another opaque window.

One of its ancestors is not mapped.

It is entirely clipped by an ancestor.
Expose ev ents are generated for the window when part or all of it becomes visible on the screen.
A client receives the Expose ev ents only if it has asked for them. Windows retain their position
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in the stacking order when they are unmapped.
A window manager may want to control the placement of subwindows. If SubstructureRedi-
rectMask
has been selected by a window manager on a parent window (usually a root window),
a map request initiated by other clients on a child window is not performed, and the window man-
ager is sent a MapRequest ev ent. However, if the override-redirect flag on the child had been set
to True (usually only on pop-up menus), the map request is performed.
A tiling window manager might decide to reposition and resize other clients' windows and then
decide to map the window to its final location. A window manager that wants to provide decora-
tion might reparent the child into a frame first. For further information, see sections 3.2.8 and
10.10. Only a single client at a time can select for SubstructureRedirectMask.
Similarly, a single client can select for ResizeRedirectMask on a parent window. Then, any
attempt to resize the window by another client is suppressed, and the client receives a Resiz-
eRequest
ev ent.
To map a given window, use XMapWindow.
XMapWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XMapWindow function maps the window and all of its subwindows that have had map
requests. Mapping a window that has an unmapped ancestor does not display the window but
marks it as eligible for display when the ancestor becomes mapped. Such a window is called
unviewable. When all its ancestors are mapped, the window becomes viewable and will be visi-
ble on the screen if it is not obscured by another window. This function has no effect if the win-
dow is already mapped.
If the override-redirect of the window is False and if some other client has selected Substructur-
eRedirectMask
on the parent window, then the X server generates a MapRequest ev ent, and the
XMapWindow function does not map the window. Otherwise, the window is mapped, and the X
server generates a MapNotify ev ent.
If the window becomes viewable and no earlier contents for it are remembered, the X server tiles
the window with its background. If the window's background is undefined, the existing screen
contents are not altered, and the X server generates zero or more Expose ev ents. If backing-store
was maintained while the window was unmapped, no Expose ev ents are generated. If backing-
store will now be maintained, a full-window exposure is always generated. Otherwise, only visi-
ble regions may be reported. Similar tiling and exposure take place for any newly viewable infe-
riors.
If the window is an InputOutput window, XMapWindow generates Expose ev ents on each
InputOutput window that it causes to be displayed. If the client maps and paints the window
and if the client begins processing events, the window is painted twice. To avoid this, first ask for
Expose ev ents and then map the window, so the client processes input events as usual. The event
list will include Expose for each window that has appeared on the screen. The client's normal
response to an Expose ev ent should be to repaint the window. This method usually leads to sim-
pler programs and to proper interaction with window managers.
XMapWindow can generate a BadWindow error.
To map and raise a window, use XMapRaised.
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XMapRaised (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XMapRaised function essentially is similar to XMapWindow in that it maps the window
and all of its subwindows that have had map requests. However, it also raises the specified win-
dow to the top of the stack. For additional information, see XMapWindow.
XMapRaised can generate multiple BadWindow errors.
To map all subwindows for a specified window, use XMapSubwindows.
XMapSubwindows (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XMapSubwindows function maps all subwindows for a specified window in top-to-bottom
stacking order. The X server generates Expose ev ents on each newly displayed window. This
may be much more efficient than mapping many windows one at a time because the server needs
to perform much of the work only once, for all of the windows, rather than for each window.
XMapSubwindows can generate a BadWindow error.
3.6. Unmapping Windows
Xlib provides functions that you can use to unmap a window or all subwindows.
To unmap a window, use XUnmapWindow.
XUnmapWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XUnmapWindow function unmaps the specified window and causes the X server to gener-
ate an UnmapNotify ev ent. If the specified window is already unmapped, XUnmapWindow
has no effect. Normal exposure processing on formerly obscured windows is performed. Any
child window will no longer be visible until another map call is made on the parent. In other
words, the subwindows are still mapped but are not visible until the parent is mapped. Unmap-
ping a window will generate Expose ev ents on windows that were formerly obscured by it.
XUnmapWindow can generate a BadWindow error.
To unmap all subwindows for a specified window, use XUnmapSubwindows.
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XUnmapSubwindows (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XUnmapSubwindows function unmaps all subwindows for the specified window in bottom-
to-top stacking order. It causes the X server to generate an UnmapNotify ev ent on each subwin-
dow and Expose ev ents on formerly obscured windows. Using this function is much more effi-
cient than unmapping multiple windows one at a time because the server needs to perform much
of the work only once, for all of the windows, rather than for each window.
XUnmapSubwindows can generate a BadWindow error.
3.7. Configuring Windows
Xlib provides functions that you can use to move a window, resize a window, move and resize a
window, or change a window's border width. To change one of these parameters, set the appro-
priate member of the XWindowChanges structure and OR in the corresponding value mask in
subsequent calls to XConfigureWindow. The symbols for the value mask bits and the XWin-
dowChanges
structure are:
/* Configure window value mask bits */
#define
CWX
(1<<0)
#define
CWY
(1<<1)
#define
CWWidth
(1<<2)
#define
CWHeight
(1<<3)
#define
CWBorderWidth
(1<<4)
#define
CWSibling
(1<<5)
#define
CWStackMode
(1<<6)
/* Values */
typedef struct {
int x, y;
int width, height;
int border_width;
Window sibling;
int stack_mode;
} XWindowChanges;
The x and y members are used to set the window's x and y coordinates, which are relative to the
parent's origin and indicate the position of the upper-left outer corner of the window. The width
and height members are used to set the inside size of the window, not including the border, and
must be nonzero, or a BadValue error results. Attempts to configure a root window hav e no
effect.
The border_width member is used to set the width of the border in pixels. Note that setting just
the border width leaves the outer-left corner of the window in a fixed position but moves the abso-
lute position of the window's origin. If you attempt to set the border-width attribute of an Inpu-
tOnly
window nonzero, a BadMatch error results.
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The sibling member is used to set the sibling window for stacking operations. The stack_mode
member is used to set how the window is to be restacked and can be set to Above, Below, TopIf,
BottomIf, or Opposite.
If the override-redirect flag of the window is False and if some other client has selected Sub-
structureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and
no further processing is performed. Otherwise, if some other client has selected ResizeRedirect-
Mask
on the window and the inside width or height of the window is being changed, a Resiz-
eRequest
ev ent is generated, and the current inside width and height are used instead. Note that
the override-redirect flag of the window has no effect on ResizeRedirectMask and that Sub-
structureRedirectMask
on the parent has precedence over ResizeRedirectMask on the win-
dow.
When the geometry of the window is changed as specified, the window is restacked among sib-
lings, and a ConfigureNotify ev ent is generated if the state of the window actually changes.
GravityNotify ev ents are generated after ConfigureNotify ev ents. If the inside width or height
of the window has actually changed, children of the window are affected as specified.
If a window's size actually changes, the window's subwindows move according to their window
gravity. Depending on the window's bit gravity, the contents of the window also may be moved
(see section 3.2.3).
If regions of the window were obscured but now are not, exposure processing is performed on
these formerly obscured windows, including the window itself and its inferiors. As a result of
increasing the width or height, exposure processing is also performed on any new regions of the
window and any regions where window contents are lost.
The restack check (specifically, the computation for BottomIf, TopIf, and Opposite) is per-
formed with respect to the window's final size and position (as controlled by the other arguments
of the request), not its initial position. If a sibling is specified without a stack_mode, a Bad-
Match
error results.
If a sibling and a stack_mode are specified, the window is restacked as follows:
Above
The window is placed just above the sibling.
Below
The window is placed just below the sibling.
TopIf
If the sibling occludes the window, the window is placed at the top of the stack.
BottomIf
If the window occludes the sibling, the window is placed at the bottom of the
stack.
Opposite
If the sibling occludes the window, the window is placed at the top of the stack.
If the window occludes the sibling, the window is placed at the bottom of the
stack.
If a stack_mode is specified but no sibling is specified, the window is restacked as follows:
Above
The window is placed at the top of the stack.
Below
The window is placed at the bottom of the stack.
TopIf
If any sibling occludes the window, the window is placed at the top of the stack.
BottomIf
If the window occludes any sibling, the window is placed at the bottom of the
stack.
Opposite
If any sibling occludes the window, the window is placed at the top of the stack.
If the window occludes any sibling, the window is placed at the bottom of the
stack.
Attempts to configure a root window hav e no effect.
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To configure a window's size, location, stacking, or border, use XConfigureWindow.
XConfigureWindow(display, w, value_mask, values)
Display *display;
Window w;
unsigned int value_mask;
XWindowChanges *values;
display
Specifies the connection to the X server.
w
Specifies the window to be reconfigured.
value_mask
Specifies which values are to be set using information in the values structure.
This mask is the bitwise inclusive OR of the valid configure window values bits.
values
Specifies the XWindowChanges structure.
The XConfigureWindow function uses the values specified in the XWindowChanges structure
to reconfigure a window's size, position, border, and stacking order. Values not specified are
taken from the existing geometry of the window.
If a sibling is specified without a stack_mode or if the window is not actually a sibling, a Bad-
Match
error results. Note that the computations for BottomIf, TopIf, and Opposite are per-
formed with respect to the window's final geometry (as controlled by the other arguments passed
to XConfigureWindow), not its initial geometry. Any backing store contents of the window, its
inferiors, and other newly visible windows are either discarded or changed to reflect the current
screen contents (depending on the implementation).
XConfigureWindow can generate BadMatch, BadValue, and BadWindow errors.
To move a window without changing its size, use XMoveWindow.
XMoveWindow(display, w, x, y)
Display *display;
Window w;
int x, y;
display
Specifies the connection to the X server.
w
Specifies the window to be moved.
x
y
Specify the x and y coordinates, which define the new location of the top-left pix-
el of the window's border or the window itself if it has no border.
The XMoveWindow function moves the specified window to the specified x and y coordinates,
but it does not change the window's size, raise the window, or change the mapping state of the
window. Moving a mapped window may or may not lose the window's contents depending on if
the window is obscured by nonchildren and if no backing store exists. If the contents of the win-
dow are lost, the X server generates Expose ev ents. Moving a mapped window generates
Expose ev ents on any formerly obscured windows.
If the override-redirect flag of the window is False and some other client has selected Substruc-
tureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and no fur-
ther processing is performed. Otherwise, the window is moved.
XMoveWindow can generate a BadWindow error.
To change a window's size without changing the upper-left coordinate, use XResizeWindow.
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XResizeWindow(display, w, width, height)
Display *display;
Window w;
unsigned int width, height;
display
Specifies the connection to the X server.
w
Specifies the window.
width
height
Specify the width and height, which are the interior dimensions of the window
after the call completes.
The XResizeWindow function changes the inside dimensions of the specified window, not
including its borders. This function does not change the window's upper-left coordinate or the
origin and does not restack the window. Changing the size of a mapped window may lose its con-
tents and generate Expose ev ents. If a mapped window is made smaller, changing its size gener-
ates Expose ev ents on windows that the mapped window formerly obscured.
If the override-redirect flag of the window is False and some other client has selected Substruc-
tureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and no fur-
ther processing is performed. If either width or height is zero, a BadValue error results.
XResizeWindow can generate BadValue and BadWindow errors.
To change the size and location of a window, use XMoveResizeWindow.
XMoveResizeWindow(display, w, x, y, width, height)
Display *display;
Window w;
int x, y;
unsigned int width, height;
display
Specifies the connection to the X server.
w
Specifies the window to be reconfigured.
x
y
Specify the x and y coordinates, which define the new position of the window rel-
ative to its parent.
width
height
Specify the width and height, which define the interior size of the window.
The XMoveResizeWindow function changes the size and location of the specified window with-
out raising it. Moving and resizing a mapped window may generate an Expose ev ent on the win-
dow. Depending on the new size and location parameters, moving and resizing a window may
generate Expose ev ents on windows that the window formerly obscured.
If the override-redirect flag of the window is False and some other client has selected Substruc-
tureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and no fur-
ther processing is performed. Otherwise, the window size and location are changed.
XMoveResizeWindow can generate BadValue and BadWindow errors.
To change the border width of a given window, use XSetWindowBorderWidth.
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XSetWindowBorderWidth (display, w, width)
Display *display;
Window w;
unsigned int width;
display
Specifies the connection to the X server.
w
Specifies the window.
width
Specifies the width of the window border.
The XSetWindowBorderWidth function sets the specified window's border width to the speci-
fied width.
XSetWindowBorderWidth can generate a BadWindow error.
3.8. Changing Window Stacking Order
Xlib provides functions that you can use to raise, lower, circulate, or restack windows.
To raise a window so that no sibling window obscures it, use XRaiseWindow.
XRaiseWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XRaiseWindow function raises the specified window to the top of the stack so that no sib-
ling window obscures it. If the windows are regarded as overlapping sheets of paper stacked on a
desk, then raising a window is analogous to moving the sheet to the top of the stack but leaving its
x and y location on the desk constant. Raising a mapped window may generate Expose ev ents
for the window and any mapped subwindows that were formerly obscured.
If the override-redirect attribute of the window is False and some other client has selected Sub-
structureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and
no processing is performed. Otherwise, the window is raised.
XRaiseWindow can generate a BadWindow error.
To lower a window so that it does not obscure any sibling windows, use XLowerWindow.
XLowerWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XLowerWindow function lowers the specified window to the bottom of the stack so that it
does not obscure any sibling windows. If the windows are regarded as overlapping sheets of
paper stacked on a desk, then lowering a window is analogous to moving the sheet to the bottom
of the stack but leaving its x and y location on the desk constant. Lowering a mapped window
will generate Expose ev ents on any windows it formerly obscured.
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If the override-redirect attribute of the window is False and some other client has selected Sub-
structureRedirectMask
on the parent, the X server generates a ConfigureRequest ev ent, and
no processing is performed. Otherwise, the window is lowered to the bottom of the stack.
XLowerWindow can generate a BadWindow error.
To circulate a subwindow up or down, use XCirculateSubwindows.
XCirculateSubwindows (display, w, direction)
Display *display;
Window w;
int direction;
display
Specifies the connection to the X server.
w
Specifies the window.
direction
Specifies the direction (up or down) that you want to circulate the window. You
can pass RaiseLowest or LowerHighest.
The XCirculateSubwindows function circulates children of the specified window in the speci-
fied direction. If you specify RaiseLowest, XCirculateSubwindows raises the lowest mapped
child (if any) that is occluded by another child to the top of the stack. If you specify
LowerHighest, XCirculateSubwindows lowers the highest mapped child (if any) that occludes
another child to the bottom of the stack. Exposure processing is then performed on formerly
obscured windows. If some other client has selected SubstructureRedirectMask on the win-
dow, the X server generates a CirculateRequest ev ent, and no further processing is performed.
If a child is actually restacked, the X server generates a CirculateNotify ev ent.
XCirculateSubwindows can generate BadValue and BadWindow errors.
To raise the lowest mapped child of a window that is partially or completely occluded by another
child, use XCirculateSubwindowsUp.
XCirculateSubwindowsUp (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XCirculateSubwindowsUp function raises the lowest mapped child of the specified window
that is partially or completely occluded by another child. Completely unobscured children are not
affected. This is a convenience function equivalent to XCirculateSubwindows with RaiseLow-
est
specified.
XCirculateSubwindowsUp can generate a BadWindow error.
To lower the highest mapped child of a window that partially or completely occludes another
child, use XCirculateSubwindowsDown.
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XCirculateSubwindowsDown (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XCirculateSubwindowsDown function lowers the highest mapped child of the specified
window that partially or completely occludes another child. Completely unobscured children are
not affected. This is a convenience function equivalent to XCirculateSubwindows with Lower-
Highest
specified.
XCirculateSubwindowsDown can generate a BadWindow error.
To restack a set of windows from top to bottom, use XRestackWindows.
XRestackWindows (display, windows, nwindows);
Display *display;
Window windows[];
int nwindows;
display
Specifies the connection to the X server.
windows
Specifies an array containing the windows to be restacked.
nwindows
Specifies the number of windows to be restacked.
The XRestackWindows function restacks the windows in the order specified, from top to bot-
tom. The stacking order of the first window in the windows array is unaffected, but the other win-
dows in the array are stacked underneath the first window, in the order of the array. The stacking
order of the other windows is not affected. For each window in the window array that is not a
child of the specified window, a BadMatch error results.
If the override-redirect attribute of a window is False and some other client has selected Sub-
structureRedirectMask
on the parent, the X server generates ConfigureRequest ev ents for
each window whose override-redirect flag is not set, and no further processing is performed. Oth-
erwise, the windows will be restacked in top-to-bottom order.
XRestackWindows can generate a BadWindow error.
3.9. Changing Window Attributes
Xlib provides functions that you can use to set window attributes. XChangeWindowAttributes
is the more general function that allows you to set one or more window attributes provided by the
XSetWindowAttributes structure. The other functions described in this section allow you to set
one specific window attribute, such as a window's background.
To change one or more attributes for a given window, use XChangeWindowAttributes.
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XChangeWindowAttributes (display, w, valuemask, attributes)
Display *display;
Window w;
unsigned long valuemask;
XSetWindowAttributes *attributes;
display
Specifies the connection to the X server.
w
Specifies the window.
valuemask
Specifies which window attributes are defined in the attributes argument. This
mask is the bitwise inclusive OR of the valid attribute mask bits. If valuemask is
zero, the attributes are ignored and are not referenced. The values and restric-
tions are the same as for XCreateWindow.
attributes
Specifies the structure from which the values (as specified by the value mask) are
to be taken. The value mask should have the appropriate bits set to indicate
which attributes have been set in the structure (see section 3.2).
Depending on the valuemask, the XChangeWindowAttributes function uses the window
attributes in the XSetWindowAttributes structure to change the specified window attributes.
Changing the background does not cause the window contents to be changed. To repaint the win-
dow and its background, use XClearWindow. Setting the border or changing the background
such that the border tile origin changes causes the border to be repainted. Changing the back-
ground of a root window to None or ParentRelative restores the default background pixmap.
Changing the border of a root window to CopyFromParent restores the default border pixmap.
Changing the win-gravity does not affect the current position of the window. Changing the back-
ing-store of an obscured window to WhenMapped or Always, or changing the backing-planes,
backing-pixel, or save-under of a mapped window may have no immediate effect. Changing the
colormap of a window (that is, defining a new map, not changing the contents of the existing
map) generates a ColormapNotify ev ent. Changing the colormap of a visible window may have
no immediate effect on the screen because the map may not be installed (see
XInstallColormap). Changing the cursor of a root window to None restores the default cursor.
Whenever possible, you are encouraged to share colormaps.
Multiple clients can select input on the same window. Their event masks are maintained sepa-
rately. When an event is generated, it is reported to all interested clients. However, only one
client at a time can select for SubstructureRedirectMask, ResizeRedirectMask, and
ButtonPressMask. If a client attempts to select any of these event masks and some other client
has already selected one, a BadAccess error results. There is only one do-not-propagate-mask
for a window, not one per client.
XChangeWindowAttributes can generate BadAccess, BadColor, BadCursor, BadMatch,
BadPixmap, BadValue, and BadWindow errors.
To set the background of a window to a giv en pixel, use XSetWindowBackground.
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XSetWindowBackground (display, w, background_pixel)
Display *display;
Window w;
unsigned long background_pixel;
display
Specifies the connection to the X server.
w
Specifies the window.
background_pixel
Specifies the pixel that is to be used for the background.
The XSetWindowBackground function sets the background of the window to the specified pixel
value. Changing the background does not cause the window contents to be changed. XSetWin-
dowBackground
uses a pixmap of undefined size filled with the pixel value you passed. If you
try to change the background of an InputOnly window, a BadMatch error results.
XSetWindowBackground can generate BadMatch and BadWindow errors.
To set the background of a window to a giv en pixmap, use XSetWindowBackgroundPixmap.
XSetWindowBackgroundPixmap (display, w, background_pixmap)
Display *display;
Window w;
Pixmap background_pixmap;
display
Specifies the connection to the X server.
w
Specifies the window.
background_pixmap
Specifies the background pixmap, ParentRelative, or None.
The XSetWindowBackgroundPixmap function sets the background pixmap of the window to
the specified pixmap. The background pixmap can immediately be freed if no further explicit ref-
erences to it are to be made. If ParentRelative is specified, the background pixmap of the win-
dow's parent is used, or on the root window, the default background is restored. If you try to
change the background of an InputOnly window, a BadMatch error results. If the background
is set to None, the window has no defined background.
XSetWindowBackgroundPixmap can generate BadMatch, BadPixmap, and BadWindow
errors.
Note
XSetWindowBackground and XSetWindowBackgroundPixmap do not change
the current contents of the window.
To change and repaint a window's border to a given pixel, use XSetWindowBorder.
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XSetWindowBorder (display, w, border_pixel)
Display *display;
Window w;
unsigned long border_pixel;
display
Specifies the connection to the X server.
w
Specifies the window.
border_pixel
Specifies the entry in the colormap.
The XSetWindowBorder function sets the border of the window to the pixel value you specify.
If you attempt to perform this on an InputOnly window, a BadMatch error results.
XSetWindowBorder can generate BadMatch and BadWindow errors.
To change and repaint the border tile of a given window, use XSetWindowBorderPixmap.
XSetWindowBorderPixmap (display, w, border_pixmap)
Display *display;
Window w;
Pixmap border_pixmap;
display
Specifies the connection to the X server.
w
Specifies the window.
border_pixmap Specifies the border pixmap or CopyFromParent.
The XSetWindowBorderPixmap function sets the border pixmap of the window to the pixmap
you specify. The border pixmap can be freed immediately if no further explicit references to it
are to be made. If you specify CopyFromParent, a copy of the parent window's border pixmap
is used. If you attempt to perform this on an InputOnly window, a BadMatch error results.
XSetWindowBorderPixmap can generate BadMatch, BadPixmap, and BadWindow errors.
To set the colormap of a given window, use XSetWindowColormap.
XSetWindowColormap (display, w, colormap)
Display *display;
Window w;
Colormap colormap;
display
Specifies the connection to the X server.
w
Specifies the window.
colormap
Specifies the colormap.
The XSetWindowColormap function sets the specified colormap of the specified window. The
colormap must have the same visual type as the window, or a BadMatch error results.
XSetWindowColormap can generate BadColor, BadMatch, and BadWindow errors.
To define which cursor will be used in a window, use XDefineCursor.
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XDefineCursor (display, w, cursor)
Display *display;
Window w;
Cursor cursor;
display
Specifies the connection to the X server.
w
Specifies the window.
cursor
Specifies the cursor that is to be displayed or None.
If a cursor is set, it will be used when the pointer is in the window. If the cursor is None, it is
equivalent to XUndefineCursor.
XDefineCursor can generate BadCursor and BadWindow errors.
To undefine the cursor in a given window, use XUndefineCursor.
XUndefineCursor (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XUndefineCursor function undoes the effect of a previous XDefineCursor for this win-
dow. When the pointer is in the window, the parent's cursor will now be used. On the root win-
dow, the default cursor is restored.
XUndefineCursor can generate a BadWindow error.
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Chapter 4
Window Information Functions
After you connect the display to the X server and create a window, you can use the Xlib window
information functions to:

Obtain information about a window

Translate screen coordinates

Manipulate property lists

Obtain and change window properties

Manipulate selections
4.1. Obtaining Window Information
Xlib provides functions that you can use to obtain information about the window tree, the win-
dow's current attributes, the window's current geometry, or the current pointer coordinates.
Because they are most frequently used by window managers, these functions all return a status to
indicate whether the window still exists.
To obtain the parent, a list of children, and number of children for a given window, use
XQueryTree.
Status XQueryTree (display, w, root_return, parent_return, children_return, nchildren_return)
Display *display;
Window w;
Window *root_return;
Window *parent_return;
Window **children_return;
unsigned int *nchildren_return;
display
Specifies the connection to the X server.
w
Specifies the window whose list of children, root, parent, and number of children
you want to obtain.
root_return
Returns the root window.
parent_return
Returns the parent window.
children_return Returns the list of children.
nchildren_returnReturns the number of children.
The XQueryTree function returns the root ID, the parent window ID, a pointer to the list of chil-
dren windows (NULL when there are no children), and the number of children in the list for the
specified window. The children are listed in current stacking order, from bottom-most (first) to
top-most (last). XQueryTree returns zero if it fails and nonzero if it succeeds. To free a non-
NULL children list when it is no longer needed, use XFree.
XQueryTree can generate a BadWindow error.
To obtain the current attributes of a given window, use XGetWindowAttributes.
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Status XGetWindowAttributes (display, w, window_attributes_return)
Display *display;
Window w;
XWindowAttributes *window_attributes_return;
display
Specifies the connection to the X server.
w
Specifies the window whose current attributes you want to obtain.
window_attributes_return
Returns the specified window's attributes in the XWindowAttributes structure.
The XGetWindowAttributes function returns the current attributes for the specified window to
an XWindowAttributes structure.
typedef struct {
int x, y;
/* location of window */
int width, height;
/* width and height of window */
int border_width;
/* border width of window */
int depth;
/* depth of window */
Visual *visual;
/* the associated visual structure */
Window root; /* root of screen containing window */
int class;
/* InputOutput, InputOnly*/
int bit_gravity; /* one of the bit gravity values */
int win_gravity; /* one of the window gravity values */
int backing_store;
/* NotUseful, WhenMapped, Always */
unsigned long backing_planes;
/* planes to be preserved if possible */
unsigned long backing_pixel; /* value to be used when restoring planes */
Bool save_under; /* boolean, should bits under be saved? */
Colormap colormap;
/* color map to be associated with window */
Bool map_installed;
/* boolean, is color map currently installed*/
int map_state;
/* IsUnmapped, IsUnviewable, IsViewable */
long all_event_masks; /* set of events all people have interest in*/
long your_event_mask; /* my event mask */
long do_not_propagate_mask; /* set of events that should not propagate */
Bool override_redirect; /* boolean value for override-redirect */
Screen *screen;
/* back pointer to correct screen */
} XWindowAttributes;
The x and y members are set to the upper-left outer corner relative to the parent window's origin.
The width and height members are set to the inside size of the window, not including the border.
The border_width member is set to the window's border width in pixels. The depth member is set
to the depth of the window (that is, bits per pixel for the object). The visual member is a pointer
to the screen's associated Visual structure. The root member is set to the root window of the
screen containing the window. The class member is set to the window's class and can be either
InputOutput or InputOnly.
The bit_gravity member is set to the window's bit gravity and can be one of the following:
ForgetGravity
EastGravity
NorthWestGravity
SouthWestGravity
NorthGravity
SouthGravity
NorthEastGravity
SouthEastGravity
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WestGravity
StaticGravity
CenterGravity
The win_gravity member is set to the window's window gravity and can be one of the following:
UnmapGravity
EastGravity
NorthWestGravity
SouthWestGravity
NorthGravity
SouthGravity
NorthEastGravity
SouthEastGravity
WestGravity
StaticGravity
CenterGravity
For additional information on gravity, see section 3.2.3.
The backing_store member is set to indicate how the X server should maintain the contents of a
window and can be WhenMapped, Always, or NotUseful. The backing_planes member is set
to indicate (with bits set to 1) which bit planes of the window hold dynamic data that must be pre-
served in backing_stores and during save_unders. The backing_pixel member is set to indicate
what values to use for planes not set in backing_planes.
The save_under member is set to True or False. The colormap member is set to the colormap
for the specified window and can be a colormap ID or None. The map_installed member is set to
indicate whether the colormap is currently installed and can be True or False. The map_state
member is set to indicate the state of the window and can be IsUnmapped, IsUnviewable, or
IsViewable. IsUnviewable is used if the window is mapped but some ancestor is unmapped.
The all_event_masks member is set to the bitwise inclusive OR of all event masks selected on the
window by all clients. The your_event_mask member is set to the bitwise inclusive OR of all
ev ent masks selected by the querying client. The do_not_propagate_mask member is set to the
bitwise inclusive OR of the set of events that should not propagate.
The override_redirect member is set to indicate whether this window overrides structure control
facilities and can be True or False. Window manager clients should ignore the window if this
member is True.
The screen member is set to a screen pointer that gives you a back pointer to the correct screen.
This makes it easier to obtain the screen information without having to loop over the root window
fields to see which field matches.
XGetWindowAttributes can generate BadDrawable and BadWindow errors.
To obtain the current geometry of a given drawable, use XGetGeometry.
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Status XGetGeometry(display, d, root_return, x_return, y_return, width_return,
height_return, border_width_return, depth_return)
Display *display;
Drawable d;
Window *root_return;
int *x_return, *y_return;
unsigned int *width_return, *height_return;
unsigned int *border_width_return;
unsigned int *depth_return;
display
Specifies the connection to the X server.
d
Specifies the drawable, which can be a window or a pixmap.
root_return
Returns the root window.
x_return
y_return
Return the x and y coordinates that define the location of the drawable. For a
window, these coordinates specify the upper-left outer corner relative to its par-
ent's origin. For pixmaps, these coordinates are always zero.
width_return
height_return
Return the drawable's dimensions (width and height). For a window, these di-
mensions specify the inside size, not including the border.
border_width_return
Returns the border width in pixels. If the drawable is a pixmap, it returns zero.
depth_return
Returns the depth of the drawable (bits per pixel for the object).
The XGetGeometry function returns the root window and the current geometry of the drawable.
The geometry of the drawable includes the x and y coordinates, width and height, border width,
and depth. These are described in the argument list. It is legal to pass to this function a window
whose class is InputOnly.
XGetGeometry can generate a BadDrawable error.
4.2. Translating Screen Coordinates
Applications sometimes need to perform a coordinate transformation from the coordinate space of
one window to another window or need to determine which window the pointing device is in.
XTranslateCoordinates and XQueryPointer fulfill these needs (and avoid any race conditions)
by asking the X server to perform these operations.
To translate a coordinate in one window to the coordinate space of another window, use
XTranslateCoordinates.
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Bool XTranslateCoordinates (display, src_w, dest_w, src_x, src_y, dest_x_return,
dest_y_return, child_return)
Display *display;
Window src_w, dest_w;
int src_x, src_y;
int *dest_x_return, *dest_y_return;
Window *child_return;
display
Specifies the connection to the X server.
src_w
Specifies the source window.
dest_w
Specifies the destination window.
src_x
src_y
Specify the x and y coordinates within the source window.
dest_x_return
dest_y_return
Return the x and y coordinates within the destination window.
child_return
Returns the child if the coordinates are contained in a mapped child of the desti-
nation window.
If XTranslateCoordinates returns True, it takes the src_x and src_y coordinates relative to the
source window's origin and returns these coordinates to dest_x_return and dest_y_return relative
to the destination window's origin. If XTranslateCoordinates returns False, src_w and dest_w
are on different screens, and dest_x_return and dest_y_return are zero. If the coordinates are con-
tained in a mapped child of dest_w, that child is returned to child_return. Otherwise, child_return
is set to None.
XTranslateCoordinates can generate a BadWindow error.
To obtain the screen coordinates of the pointer or to determine the pointer coordinates relative to a
specified window, use XQueryPointer.
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Bool XQueryPointer(display, w, root_return, child_return, root_x_return, root_y_return,
win_x_return, win_y_return, mask_return)
Display *display;
Window w;
Window *root_return, *child_return;
int *root_x_return, *root_y_return;
int *win_x_return, *win_y_return;
unsigned int *mask_return;
display
Specifies the connection to the X server.
w
Specifies the window.
root_return
Returns the root window that the pointer is in.
child_return
Returns the child window that the pointer is located in, if any.
root_x_return
root_y_return
Return the pointer coordinates relative to the root window's origin.
win_x_return
win_y_return
Return the pointer coordinates relative to the specified window.
mask_return
Returns the current state of the modifier keys and pointer buttons.
The XQueryPointer function returns the root window the pointer is logically on and the pointer
coordinates relative to the root window's origin. If XQueryPointer returns False, the pointer is
not on the same screen as the specified window, and XQueryPointer returns None to
child_return and zero to win_x_return and win_y_return. If XQueryPointer returns True, the
pointer coordinates returned to win_x_return and win_y_return are relative to the origin of the
specified window. In this case, XQueryPointer returns the child that contains the pointer, if any,
or else None to child_return.
XQueryPointer returns the current logical state of the keyboard buttons and the modifier keys in
mask_return. It sets mask_return to the bitwise inclusive OR of one or more of the button or
modifier key bitmasks to match the current state of the mouse buttons and the modifier keys.
Note that the logical state of a device (as seen through Xlib) may lag the physical state if device
ev ent processing is frozen (see section 12.1).
XQueryPointer can generate a BadWindow error.
4.3. Properties and Atoms
A property is a collection of named, typed data. The window system has a set of predefined prop-
erties (for example, the name of a window, size hints, and so on), and users can define any other
arbitrary information and associate it with windows. Each property has a name, which is an ISO
Latin-1 string. For each named property, a unique identifier (atom) is associated with it. A prop-
erty also has a type, for example, string or integer. These types are also indicated using atoms, so
arbitrary new types can be defined. Data of only one type may be associated with a single prop-
erty name. Clients can store and retrieve properties associated with windows. For efficiency rea-
sons, an atom is used rather than a character string. XInternAtom can be used to obtain the
atom for property names.
A property is also stored in one of several possible formats. The X server can store the informa-
tion as 8-bit quantities, 16-bit quantities, or 32-bit quantities. This permits the X server to present
the data in the byte order that the client expects.
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Note
If you define further properties of complex type, you must encode and decode them
yourself. These functions must be carefully written if they are to be portable. For
further information about how to write a library extension, see appendix C.
The type of a property is defined by an atom, which allows for arbitrary extension in this type
scheme.
Certain property names are predefined in the server for commonly used functions. The atoms for
these properties are defined in <X11/Xatom.h>. To avoid name clashes with user symbols, the
#define name for each atom has the XA_ prefix. For an explanation of the functions that let you
get and set much of the information stored in these predefined properties, see chapter 14.
The core protocol imposes no semantics on these property names, but semantics are specified in
other X Consortium standards, such as the Inter-Client Communication Conventions Manual and
the X Logical Font Description Conventions.
You can use properties to communicate other information between applications. The functions
described in this section let you define new properties and get the unique atom IDs in your appli-
cations.
Although any particular atom can have some client interpretation within each of the name spaces,
atoms occur in five distinct name spaces within the protocol:

Selections

Property names

Property types

Font properties

Type of a ClientMessage ev ent (none are built into the X server)
The built-in selection property names are:
PRIMARY
SECONDARY
The built-in property names are:
CUT_BUFFER0 RESOURCE_MANAGER
CUT_BUFFER1 WM_CLASS
CUT_BUFFER2 WM_CLIENT_MACHINE
CUT_BUFFER3 WM_COLORMAP_WINDOWS
CUT_BUFFER4 WM_COMMAND
CUT_BUFFER5 WM_HINTS
CUT_BUFFER6 WM_ICON_NAME
CUT_BUFFER7 WM_ICON_SIZE
RGB_BEST_MAP WM_NAME
RGB_BLUE_MAP WM_NORMAL_HINTS
RGB_DEFAULT_MAP WM_PROT OCOLS
RGB_GRAY_MAP WM_STATE
RGB_GREEN_MAP WM_TRANSIENT_FOR
RGB_RED_MAP WM_ZOOM_HINTS
The built-in property types are:
ARC POINT
AT OM
RGB_COLOR_MAP
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BITMAP RECTANGLE
CARDINAL STRING
COLORMAP VISUALID
CURSOR WINDOW
DRAWABLE WM_HINTS
FONT WM_SIZE_HINTS
INTEGER
PIXMAP
The built-in font property names are:
MIN_SPACE
STRIKEOUT_DESCENT
NORM_SPACE
STRIKEOUT_ASCENT
MAX_SPACE
ITALIC_ANGLE
END_SPACE
X_HEIGHT
SUPERSCRIPT_X QUAD_WIDTH
SUPERSCRIPT_Y WEIGHT
SUBSCRIPT_X POINT_SIZE
SUBSCRIPT_Y RESOLUTION
UNDERLINE_POSITION COPYRIGHT
UNDERLINE_THICKNESS NOTICE
FONT_NAME FAMILY_NAME
FULL_NAME CAP_HEIGHT
For further information about font properties, see section 8.5.
To return an atom for a given name, use XInternAtom.
Atom XInternAtom(display, atom_name, only_if_exists)
Display *display;
char *atom_name;
Bool only_if_exists;
display
Specifies the connection to the X server.
atom_name
Specifies the name associated with the atom you want returned.
only_if_exists
Specifies a Boolean value that indicates whether the atom must be created.
The XInternAtom function returns the atom identifier associated with the specified atom_name
string. If only_if_exists is False, the atom is created if it does not exist. Therefore, XInter-
nAtom
can return None. If the atom name is not in the Host Portable Character Encoding, the
result is implementation-dependent. Uppercase and lowercase matter; the strings ``thing'',
``Thing'', and ``thinG'' all designate different atoms. The atom will remain defined even after the
client's connection closes. It will become undefined only when the last connection to the X
server closes.
XInternAtom can generate BadAlloc and BadValue errors.
To return atoms for an array of names, use XInternAtoms.
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Status XInternAtoms(display, names, count, only_if_exists, atoms_return)
Display *display;
char **names;
int count;
Bool only_if_exists;
Atom *atoms_return;
display
Specifies the connection to the X server.
names
Specifies the array of atom names.
count
Specifies the number of atom names in the array.
only_if_exists
Specifies a Boolean value that indicates whether the atom must be created.
atoms_return
Returns the atoms.
The XInternAtoms function returns the atom identifiers associated with the specified names.
The atoms are stored in the atoms_return array supplied by the caller. Calling this function is
equivalent to calling XInternAtom for each of the names in turn with the specified value of
only_if_exists, but this function minimizes the number of round-trip protocol exchanges between
the client and the X server.
This function returns a nonzero status if atoms are returned for all of the names; otherwise, it
returns zero.
XInternAtoms can generate BadAlloc and BadValue errors.
To return a name for a given atom identifier, use XGetAtomName.
char *XGetAtomName(display, atom)
Display *display;
Atom atom;
display
Specifies the connection to the X server.
atom
Specifies the atom for the property name you want returned.
The XGetAtomName function returns the name associated with the specified atom. If the data
returned by the server is in the Latin Portable Character Encoding, then the returned string is in
the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. To
free the resulting string, call XFree.
XGetAtomName can generate a BadAtom error.
To return the names for an array of atom identifiers, use XGetAtomNames.
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Status XGetAtomNames(display, atoms, count, names_return)
Display *display;
Atom *atoms;
int count;
char **names_return;
display
Specifies the connection to the X server.
atoms
Specifies the array of atoms.
count
Specifies the number of atoms in the array.
names_return
Returns the atom names.
The XGetAtomNames function returns the names associated with the specified atoms. The
names are stored in the names_return array supplied by the caller. Calling this function is equiv-
alent to calling XGetAtomName for each of the atoms in turn, but this function minimizes the
number of round-trip protocol exchanges between the client and the X server.
This function returns a nonzero status if names are returned for all of the atoms; otherwise, it
returns zero.
XGetAtomNames can generate a BadAtom error.
4.4. Obtaining and Changing Window Properties
You can attach a property list to every window. Each property has a name, a type, and a value
(see section 4.3). The value is an array of 8-bit, 16-bit, or 32-bit quantities, whose interpretation
is left to the clients. The type char is used to represent 8-bit quantities, the type short is used to
represent 16-bit quantities, and the type long is used to represent 32-bit quantities.
Xlib provides functions that you can use to obtain, change, update, or interchange window prop-
erties. In addition, Xlib provides other utility functions for inter-client communication (see chap-
ter 14).
To obtain the type, format, and value of a property of a given window, use
XGetWindowProperty.
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int XGetWindowProperty (display, w, property, long_offset, long_length, delete, req_type,
actual_type_return, actual_format_return, nitems_return, bytes_after_return,
prop_return)
Display *display;
Window w;
Atom property;
long long_offset, long_length;
Bool delete;
Atom req_type;
Atom *actual_type_return;
int *actual_format_return;
unsigned long *nitems_return;
unsigned long *bytes_after_return;
unsigned char **prop_return;
display
Specifies the connection to the X server.
w
Specifies the window whose property you want to obtain.
property
Specifies the property name.
long_offset
Specifies the offset in the specified property (in 32-bit quantities) where the data
is to be retrieved.
long_length
Specifies the length in 32-bit multiples of the data to be retrieved.
delete
Specifies a Boolean value that determines whether the property is deleted.
req_type
Specifies the atom identifier associated with the property type or
AnyPropertyType.
actual_type_return
Returns the atom identifier that defines the actual type of the property.
actual_format_return
Returns the actual format of the property.
nitems_return
Returns the actual number of 8-bit, 16-bit, or 32-bit items stored in the prop_re-
turn data.
bytes_after_return
Returns the number of bytes remaining to be read in the property if a partial read
was performed.
prop_return
Returns the data in the specified format.
The XGetWindowProperty function returns the actual type of the property; the actual format of
the property; the number of 8-bit, 16-bit, or 32-bit items transferred; the number of bytes remain-
ing to be read in the property; and a pointer to the data actually returned. XGetWindowProp-
erty
sets the return arguments as follows:

If the specified property does not exist for the specified window, XGetWindowProperty
returns None to actual_type_return and the value zero to actual_format_return and
bytes_after_return. The nitems_return argument is empty. In this case, the delete argument
is ignored.

If the specified property exists but its type does not match the specified type, XGetWin-
dowProperty returns the actual property type to actual_type_return, the actual property
format (never zero) to actual_format_return, and the property length in bytes (even if the
actual_format_return is 16 or 32) to bytes_after_return. It also ignores the delete argument.
The nitems_return argument is empty.
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If the specified property exists and either you assign AnyPropertyType to the req_type
argument or the specified type matches the actual property type, XGetWindowProperty
returns the actual property type to actual_type_return and the actual property format (never
zero) to actual_format_return. It also returns a value to bytes_after_return and
nitems_return, by defining the following values:
N = actual length of the stored property in bytes
(even if the format is 16 or 32)
I = 4 * long_offset
T = N - I
L = MINIMUM(T, 4 * long_length)
A = N - (I + L)
The returned value starts at byte index I in the property (indexing from zero), and its length
in bytes is L. If the value for long_offset causes L to be negative, a BadValue error results.
The value of bytes_after_return is A, giving the number of trailing unread bytes in the
stored property.
If the returned format is 8, the returned data is represented as a char array. If the returned format
is 16, the returned data is represented as a short array and should be cast to that type to obtain the
elements. If the returned format is 32, the returned data is represented as a long array and should
be cast to that type to obtain the elements.
XGetWindowProperty always allocates one extra byte in prop_return (even if the property is
zero length) and sets it to zero so that simple properties consisting of characters do not have to be
copied into yet another string before use.
If delete is True and bytes_after_return is zero, XGetWindowProperty deletes the property
from the window and generates a PropertyNotify ev ent on the window.
The function returns Success if it executes successfully. To free the resulting data, use XFree.
XGetWindowProperty can generate BadAtom, BadValue, and BadWindow errors.
To obtain a given window's property list, use XListProperties.
Atom *XListProperties(display, w, num_prop_return)
Display *display;
Window w;
int *num_prop_return;
display
Specifies the connection to the X server.
w
Specifies the window whose property list you want to obtain.
num_prop_returnReturns the length of the properties array.
The XListProperties function returns a pointer to an array of atom properties that are defined for
the specified window or returns NULL if no properties were found. To free the memory allocated
by this function, use XFree.
XListProperties can generate a BadWindow error.
To change a property of a given window, use XChangeProperty.
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XChangeProperty (display, w, property, type, format, mode, data, nelements)
Display *display;
Window w;
Atom property, type;
int format;
int mode;
unsigned char *data;
int nelements;
display
Specifies the connection to the X server.
w
Specifies the window whose property you want to change.
property
Specifies the property name.
type
Specifies the type of the property. The X server does not interpret the type but
simply passes it back to an application that later calls XGetWindowProperty.
format
Specifies whether the data should be viewed as a list of 8-bit, 16-bit, or 32-bit
quantities. Possible values are 8, 16, and 32. This information allows the X serv-
er to correctly perform byte-swap operations as necessary. If the format is 16-bit
or 32-bit, you must explicitly cast your data pointer to an (unsigned char *) in the
call to XChangeProperty.
mode
Specifies the mode of the operation.
You can pass PropModeReplace,
PropModePrepend, or PropModeAppend.
data
Specifies the property data.
nelements
Specifies the number of elements of the specified data format.
The XChangeProperty function alters the property for the specified window and causes the X
server to generate a PropertyNotify ev ent on that window. XChangeProperty performs the fol-
lowing:

If mode is PropModeReplace, XChangeProperty discards the previous property value
and stores the new data.

If mode is PropModePrepend or PropModeAppend, XChangeProperty inserts the
specified data before the beginning of the existing data or onto the end of the existing data,
respectively. The type and format must match the existing property value, or a BadMatch
error results. If the property is undefined, it is treated as defined with the correct type and
format with zero-length data.
If the specified format is 8, the property data must be a char array. If the specified format is 16,
the property data must be a short array. If the specified format is 32, the property data must be a
long array.
The lifetime of a property is not tied to the storing client. Properties remain until explicitly
deleted, until the window is destroyed, or until the server resets. For a discussion of what hap-
pens when the connection to the X server is closed, see section 2.6. The maximum size of a prop-
erty is server dependent and can vary dynamically depending on the amount of memory the server
has available. (If there is insufficient space, a BadAlloc error results.)
XChangeProperty can generate BadAlloc, BadAtom, BadMatch, BadValue, and BadWin-
dow errors.
To rotate a window's property list, use XRotateWindowProperties.
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XRotateWindowProperties (display, w, properties, num_prop, npositions)
Display *display;
Window w;
Atom properties[] ;
int num_prop;
int npositions;
display
Specifies the connection to the X server.
w
Specifies the window.
properties
Specifies the array of properties that are to be rotated.
num_prop
Specifies the length of the properties array.
npositions
Specifies the rotation amount.
The XRotateWindowProperties function allows you to rotate properties on a window and
causes the X server to generate PropertyNotify ev ents. If the property names in the properties
array are viewed as being numbered starting from zero and if there are num_prop property names
in the list, then the value associated with property name I becomes the value associated with prop-
erty name (I + npositions) mod N for all I from zero to N - 1. The effect is to rotate the states by
npositions places around the virtual ring of property names (right for positive npositions, left for
negative npositions). If npositions mod N is nonzero, the X server generates a PropertyNotify
ev ent for each property in the order that they are listed in the array. If an atom occurs more than
once in the list or no property with that name is defined for the window, a BadMatch error
results. If a BadAtom or BadMatch error results, no properties are changed.
XRotateWindowProperties can generate BadAtom, BadMatch, and BadWindow errors.
To delete a property on a given window, use XDeleteProperty.
XDeleteProperty (display, w, property)
Display *display;
Window w;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window whose property you want to delete.
property
Specifies the property name.
The XDeleteProperty function deletes the specified property only if the property was defined on
the specified window and causes the X server to generate a PropertyNotify ev ent on the window
unless the property does not exist.
XDeleteProperty can generate BadAtom and BadWindow errors.
4.5. Selections
Selections are one method used by applications to exchange data. By using the property mecha-
nism, applications can exchange data of arbitrary types and can negotiate the type of the data. A
selection can be thought of as an indirect property with a dynamic type. That is, rather than hav-
ing the property stored in the X server, the property is maintained by some client (the owner). A
selection is global in nature (considered to belong to the user but be maintained by clients) rather
than being private to a particular window subhierarchy or a particular set of clients.
Xlib provides functions that you can use to set, get, or request conversion of selections. This
allows applications to implement the notion of current selection, which requires that notification
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be sent to applications when they no longer own the selection. Applications that support selection
often highlight the current selection and so must be informed when another application has
acquired the selection so that they can unhighlight the selection.
When a client asks for the contents of a selection, it specifies a selection target type. This target
type can be used to control the transmitted representation of the contents. For example, if the
selection is ``the last thing the user clicked on'' and that is currently an image, then the target type
might specify whether the contents of the image should be sent in XY format or Z format.
The target type can also be used to control the class of contents transmitted, for example, asking
for the ``looks'' (fonts, line spacing, indentation, and so forth) of a paragraph selection, not the
text of the paragraph. The target type can also be used for other purposes. The protocol does not
constrain the semantics.
To set the selection owner, use XSetSelectionOwner.
XSetSelectionOwner (display, selection, owner, time)
Display *display;
Atom selection;
Window owner;
Time time;
display
Specifies the connection to the X server.
selection
Specifies the selection atom.
owner
Specifies the owner of the specified selection atom. You can pass a window or
None.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XSetSelectionOwner function changes the owner and last-change time for the specified
selection and has no effect if the specified time is earlier than the current last-change time of the
specified selection or is later than the current X server time. Otherwise, the last-change time is
set to the specified time, with CurrentTime replaced by the current server time. If the owner
window is specified as None, then the owner of the selection becomes None (that is, no owner).
Otherwise, the owner of the selection becomes the client executing the request.
If the new owner (whether a client or None) is not the same as the current owner of the selection
and the current owner is not None, the current owner is sent a SelectionClear ev ent. If the client
that is the owner of a selection is later terminated (that is, its connection is closed) or if the owner
window it has specified in the request is later destroyed, the owner of the selection automatically
reverts to None, but the last-change time is not affected. The selection atom is uninterpreted by
the X server. XGetSelectionOwner returns the owner window, which is reported in Selection-
Request
and SelectionClear ev ents. Selections are global to the X server.
XSetSelectionOwner can generate BadAtom and BadWindow errors.
To return the selection owner, use XGetSelectionOwner.
Window XGetSelectionOwner (display, selection)
Display *display;
Atom selection;
display
Specifies the connection to the X server.
selection
Specifies the selection atom whose owner you want returned.
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currently owns the specified selection. If no selection was specified, the function returns the con-
stant None. If None is returned, there is no owner for the selection.
XGetSelectionOwner can generate a BadAtom error.
To request conversion of a selection, use XConvertSelection.
XConvertSelection (display, selection, target, property, requestor, time)
Display *display;
Atom selection, target;
Atom property;
Window requestor;
Time time;
display
Specifies the connection to the X server.
selection
Specifies the selection atom.
target
Specifies the target atom.
property
Specifies the property name. You also can pass None.
requestor
Specifies the requestor.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
XConvertSelection requests that the specified selection be converted to the specified target type:

If the specified selection has an owner, the X server sends a SelectionRequest ev ent to that
owner.

If no owner for the specified selection exists, the X server generates a SelectionNotify
ev ent to the requestor with property None.
The arguments are passed on unchanged in either of the events. There are two predefined selec-
tion atoms: PRIMARY and SECONDARY.
XConvertSelection can generate BadAtom and BadWindow errors.
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Chapter 5
Pixmap and Cursor Functions
Once you have connected to an X server, you can use the Xlib functions to:

Create and free pixmaps

Create, recolor, and free cursors
5.1. Creating and Freeing Pixmaps
Pixmaps can only be used on the screen on which they were created. Pixmaps are off-screen
resources that are used for various operations, such as defining cursors as tiling patterns or as the
source for certain raster operations. Most graphics requests can operate either on a window or on
a pixmap. A bitmap is a single bit-plane pixmap.
To create a pixmap of a given size, use XCreatePixmap.
Pixmap XCreatePixmap(display, d, width, height, depth)
Display *display;
Drawable d;
unsigned int width, height;
unsigned int depth;
display
Specifies the connection to the X server.
d
Specifies which screen the pixmap is created on.
width
height
Specify the width and height, which define the dimensions of the pixmap.
depth
Specifies the depth of the pixmap.
The XCreatePixmap function creates a pixmap of the width, height, and depth you specified and
returns a pixmap ID that identifies it. It is valid to pass an InputOnly window to the drawable
argument. The width and height arguments must be nonzero, or a BadValue error results. The
depth argument must be one of the depths supported by the screen of the specified drawable, or a
BadValue error results.
The server uses the specified drawable to determine on which screen to create the pixmap. The
pixmap can be used only on this screen and only with other drawables of the same depth (see
XCopyPlane for an exception to this rule). The initial contents of the pixmap are undefined.
XCreatePixmap can generate BadAlloc, BadDrawable, and BadValue errors.
To free all storage associated with a specified pixmap, use XFreePixmap.
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XFreePixmap (display, pixmap)
Display *display;
Pixmap pixmap;
display
Specifies the connection to the X server.
pixmap
Specifies the pixmap.
The XFreePixmap function first deletes the association between the pixmap ID and the pixmap.
Then, the X server frees the pixmap storage when there are no references to it. The pixmap
should never be referenced again.
XFreePixmap can generate a BadPixmap error.
5.2. Creating, Recoloring, and Freeing Cursors
Each window can have a different cursor defined for it. Whenever the pointer is in a visible win-
dow, it is set to the cursor defined for that window. If no cursor was defined for that window, the
cursor is the one defined for the parent window.
From X's perspective, a cursor consists of a cursor source, mask, colors, and a hotspot. The mask
pixmap determines the shape of the cursor and must be a depth of one. The source pixmap must
have a depth of one, and the colors determine the colors of the source. The hotspot defines the
point on the cursor that is reported when a pointer event occurs. There may be limitations
imposed by the hardware on cursors as to size and whether a mask is implemented.
XQueryBestCursor can be used to find out what sizes are possible. There is a standard font for
creating cursors, but Xlib provides functions that you can use to create cursors from an arbitrary
font or from bitmaps.
To create a cursor from the standard cursor font, use XCreateFontCursor.
#include <X11/cursorfont.h>
Cursor XCreateFontCursor (display, shape)
Display *display;
unsigned int shape;
display
Specifies the connection to the X server.
shape
Specifies the shape of the cursor.
X provides a set of standard cursor shapes in a special font named cursor. Applications are
encouraged to use this interface for their cursors because the font can be customized for the indi-
vidual display type. The shape argument specifies which glyph of the standard fonts to use.
The hotspot comes from the information stored in the cursor font. The initial colors of a cursor
are a black foreground and a white background (see XRecolorCursor). For further information
about cursor shapes, see appendix B.
XCreateFontCursor can generate BadAlloc and BadValue errors.
To create a cursor from font glyphs, use XCreateGlyphCursor.
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Cursor XCreateGlyphCursor(display, source_font, mask_font, source_char, mask_char,
foreground_color, background_color)
Display *display;
Font source_font, mask_font;
unsigned int source_char, mask_char;
XColor *foreground_color;
XColor *background_color;
display
Specifies the connection to the X server.
source_font
Specifies the font for the source glyph.
mask_font
Specifies the font for the mask glyph or None.
source_char
Specifies the character glyph for the source.
mask_char
Specifies the glyph character for the mask.
foreground_colorSpecifies the RGB values for the foreground of the source.
background_color
Specifies the RGB values for the background of the source.
The XCreateGlyphCursor function is similar to XCreatePixmapCursor except that the source
and mask bitmaps are obtained from the specified font glyphs. The source_char must be a
defined glyph in source_font, or a BadValue error results. If mask_font is given, mask_char
must be a defined glyph in mask_font, or a BadValue error results. The mask_font and character
are optional. The origins of the source_char and mask_char (if defined) glyphs are positioned
coincidently and define the hotspot. The source_char and mask_char need not have the same
bounding box metrics, and there is no restriction on the placement of the hotspot relative to the
bounding boxes. If no mask_char is given, all pixels of the source are displayed. You can free
the fonts immediately by calling XFreeFont if no further explicit references to them are to be
made.
For 2-byte matrix fonts, the 16-bit value should be formed with the byte1 member in the most sig-
nificant byte and the byte2 member in the least significant byte.
XCreateGlyphCursor can generate BadAlloc, BadFont, and BadValue errors.
To create a cursor from two bitmaps, use XCreatePixmapCursor.
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Cursor XCreatePixmapCursor(display, source, mask, foreground_color, background_color, x, y)
Display *display;
Pixmap source;
Pixmap mask;
XColor *foreground_color;
XColor *background_color;
unsigned int x, y;
display
Specifies the connection to the X server.
source
Specifies the shape of the source cursor.
mask
Specifies the cursor's source bits to be displayed or None.
foreground_colorSpecifies the RGB values for the foreground of the source.
background_color
Specifies the RGB values for the background of the source.
x
y
Specify the x and y coordinates, which indicate the hotspot relative to the
source's origin.
The XCreatePixmapCursor function creates a cursor and returns the cursor ID associated with
it. The foreground and background RGB values must be specified using foreground_color and
background_color, even if the X server only has a StaticGray or GrayScale screen. The fore-
ground color is used for the pixels set to 1 in the source, and the background color is used for the
pixels set to 0. Both source and mask, if specified, must have depth one (or a BadMatch error
results) but can have any root. The mask argument defines the shape of the cursor. The pixels set
to 1 in the mask define which source pixels are displayed, and the pixels set to 0 define which pix-
els are ignored. If no mask is given, all pixels of the source are displayed. The mask, if present,
must be the same size as the pixmap defined by the source argument, or a BadMatch error
results. The hotspot must be a point within the source, or a BadMatch error results.
The components of the cursor can be transformed arbitrarily to meet display limitations. The
pixmaps can be freed immediately if no further explicit references to them are to be made. Sub-
sequent drawing in the source or mask pixmap has an undefined effect on the cursor. The X
server might or might not make a copy of the pixmap.
XCreatePixmapCursor can generate BadAlloc and BadPixmap errors.
To determine useful cursor sizes, use XQueryBestCursor.
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Status XQueryBestCursor(display, d, width, height, width_return, height_return)
Display *display;
Drawable d;
unsigned int width, height;
unsigned int *width_return, *height_return;
display
Specifies the connection to the X server.
d
Specifies the drawable, which indicates the screen.
width
height
Specify the width and height of the cursor that you want the size information for.
width_return
height_return
Return the best width and height that is closest to the specified width and height.
Some displays allow larger cursors than other displays. The XQueryBestCursor function pro-
vides a way to find out what size cursors are actually possible on the display. It returns the largest
size that can be displayed. Applications should be prepared to use smaller cursors on displays
that cannot support large ones.
XQueryBestCursor can generate a BadDrawable error.
To change the color of a given cursor, use XRecolorCursor.
XRecolorCursor (display, cursor, foreground_color, background_color)
Display *display;
Cursor cursor;
XColor *foreground_color, *background_color;
display
Specifies the connection to the X server.
cursor
Specifies the cursor.
foreground_colorSpecifies the RGB values for the foreground of the source.
background_color
Specifies the RGB values for the background of the source.
The XRecolorCursor function changes the color of the specified cursor, and if the cursor is
being displayed on a screen, the change is visible immediately. The pixel members of the
XColor structures are ignored; only the RGB values are used.
XRecolorCursor can generate a BadCursor error.
To free (destroy) a given cursor, use XFreeCursor.
XFreeCursor (display, cursor)
Display *display;
Cursor cursor;
display
Specifies the connection to the X server.
cursor
Specifies the cursor.
The XFreeCursor function deletes the association between the cursor resource ID and the speci-
fied cursor. The cursor storage is freed when no other resource references it. The specified cursor
ID should not be referred to again.
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XFreeCursor can generate a BadCursor error.
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Chapter 6
Color Management Functions
Each X window always has an associated colormap that provides a level of indirection between
pixel values and colors displayed on the screen. Xlib provides functions that you can use to
manipulate a colormap. The X protocol defines colors using values in the RGB color space. The
RGB color space is device dependent; rendering an RGB value on differing output devices typi-
cally results in different colors. Xlib also provides a means for clients to specify color using
device-independent color spaces for consistent results across devices. Xlib supports device-inde-
pendent color spaces derivable from the CIE XYZ color space. This includes the CIE XYZ, xyY,
L*u*v*, and L*a*b* color spaces as well as the TekHVC color space.
This chapter discusses how to:

Create, copy, and destroy a colormap

Specify colors by name or value

Allocate, modify, and free color cells

Read entries in a colormap

Convert between color spaces

Control aspects of color conversion

Query the color gamut of a screen

Add new color spaces
All functions, types, and symbols in this chapter with the prefix ``Xcms'' are defined in
<X11/Xcms.h>. The remaining functions and types are defined in <X11/Xlib.h>.
Functions in this chapter manipulate the representation of color on the screen. For each possible
value that a pixel can take in a window, there is a color cell in the colormap. For example, if a
window is 4 bits deep, pixel values 0 through 15 are defined. A colormap is a collection of color
cells. A color cell consists of a triple of red, green, and blue (RGB) values. The hardware
imposes limits on the number of significant bits in these values. As each pixel is read out of dis-
play memory, the pixel is looked up in a colormap. The RGB value of the cell determines what
color is displayed on the screen. On a grayscale display with a black-and-white monitor, the val-
ues are combined to determine the brightness on the screen.
Typically, an application allocates color cells or sets of color cells to obtain the desired colors.
The client can allocate read-only cells. In which case, the pixel values for these colors can be
shared among multiple applications, and the RGB value of the cell cannot be changed. If the
client allocates read/write cells, they are exclusively owned by the client, and the color associated
with the pixel value can be changed at will. Cells must be allocated (and, if read/write, initialized
with an RGB value) by a client to obtain desired colors. The use of pixel value for an unallocated
cell results in an undefined color.
Because colormaps are associated with windows, X supports displays with multiple colormaps
and, indeed, different types of colormaps. If there are insufficient colormap resources in the dis-
play, some windows will display in their true colors, and others will display with incorrect colors.
A window manager usually controls which windows are displayed in their true colors if more
than one colormap is required for the color resources the applications are using. At any time,
there is a set of installed colormaps for a screen. Windows using one of the installed colormaps
display with true colors, and windows using other colormaps generally display with incorrect col-
ors. You can control the set of installed colormaps by using XInstallColormap and
XUninstallColormap.
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Colormaps are local to a particular screen. Screens always have a default colormap, and pro-
grams typically allocate cells out of this colormap. Generally, you should not write applications
that monopolize color resources. Although some hardware supports multiple colormaps installed
at one time, many of the hardware displays built today support only a single installed colormap,
so the primitives are written to encourage sharing of colormap entries between applications.
The DefaultColormap macro returns the default colormap. The DefaultVisual macro returns
the default visual type for the specified screen. Possible visual types are StaticGray,
GrayScale, StaticColor, PseudoColor, TrueColor, or DirectColor (see section 3.1).
6.1. Color Structures
Functions that operate only on RGB color space values use an XColor structure, which contains:
typedef struct {
unsigned long pixel; /* pixel value */
unsigned short red, green, blue; /* rgb values */
char flags;
/* DoRed, DoGreen, DoBlue */
char pad;
} XColor;
The red, green, and blue values are always in the range 0 to 65535 inclusive, independent of the
number of bits actually used in the display hardware. The server scales these values down to the
range used by the hardware. Black is represented by (0,0,0), and white is represented by
(65535,65535,65535). In some functions, the flags member controls which of the red, green, and
blue members is used and can be the inclusive OR of zero or more of DoRed, DoGreen, and
DoBlue.
Functions that operate on all color space values use an XcmsColor structure. This structure con-
tains a union of substructures, each supporting color specification encoding for a particular color
space. Like the XColor structure, the XcmsColor structure contains pixel and color specifica-
tion information (the spec member in the XcmsColor structure).
typedef unsigned long XcmsColorFormat;/* Color Specification Format */
typedef struct {
union {
XcmsRGB RGB;
XcmsRGBi RGBi;
XcmsCIEXYZ CIEXYZ;
XcmsCIEuvY CIEuvY;
XcmsCIExyY CIExyY;
XcmsCIELab CIELab;
XcmsCIELuv CIELuv;
XcmsTekHVC TekHVC;
XcmsPad Pad;
} spec;
unsigned long pixel;
XcmsColorFormat format;
} XcmsColor; /* Xcms Color Structure */
Because the color specification can be encoded for the various color spaces, encoding for the spec
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member is identified by the format member, which is of type XcmsColorFormat. The following
macros define standard formats.
#define
XcmsUndefinedFormat
0x00000000
#define
XcmsCIEXYZFormat
0x00000001
/* CIE XYZ */
#define
XcmsCIEuvYFormat
0x00000002
/* CIE u'v'Y */
#define
XcmsCIExyYFormat
0x00000003
/* CIE xyY */
#define
XcmsCIELabFormat
0x00000004
/* CIE L*a*b* */
#define
XcmsCIELuvFormat
0x00000005
/* CIE L*u*v* */
#define
XcmsTekHVCFormat
0x00000006
/* TekHVC */
#define
XcmsRGBFormat
0x80000000
/* RGB Device */
#define
XcmsRGBiFormat
0x80000001
/* RGB Intensity */
Formats for device-independent color spaces are distinguishable from those for device-dependent
spaces by the 32nd bit. If this bit is set, it indicates that the color specification is in a device-
dependent form; otherwise, it is in a device-independent form. If the 31st bit is set, this indicates
that the color space has been added to Xlib at run time (see section 6.12.4). The format value for
a color space added at run time may be different each time the program is executed. If references
to such a color space must be made outside the client (for example, storing a color specification in
a file), then reference should be made by color space string prefix (see XcmsFormatOfPrefix
and XcmsPrefixOfFormat).
Data types that describe the color specification encoding for the various color spaces are defined
as follows:
typedef double XcmsFloat;
typedef struct {
unsigned short red;
/* 0x0000 to 0xffff */
unsigned short green;
/* 0x0000 to 0xffff */
unsigned short blue;
/* 0x0000 to 0xffff */
} XcmsRGB; /* RGB Device */
typedef struct {
XcmsFloat red;
/* 0.0 to 1.0 */
XcmsFloat green;
/* 0.0 to 1.0 */
XcmsFloat blue;
/* 0.0 to 1.0 */
} XcmsRGBi; /* RGB Intensity */
typedef struct {
XcmsFloat X;
XcmsFloat Y;
/* 0.0 to 1.0 */
XcmsFloat Z;
} XcmsCIEXYZ; /* CIE XYZ */
typedef struct {
XcmsFloat u_prime;
/* 0.0 to ~0.6 */
XcmsFloat v_prime;
/* 0.0 to ~0.6 */
XcmsFloat Y;
/* 0.0 to 1.0 */
} XcmsCIEuvY;
/* CIE u'v'Y */
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typedef struct {
XcmsFloat x;
/* 0.0 to ~.75 */
XcmsFloat y;
/* 0.0 to ~.85 */
XcmsFloat Y;
/* 0.0 to 1.0 */
} XcmsCIExyY;
/* CIE xyY */
typedef struct {
XcmsFloat L_star;
/* 0.0 to 100.0 */
XcmsFloat a_star;
XcmsFloat b_star;
} XcmsCIELab; /* CIE L*a*b* */
typedef struct {
XcmsFloat L_star;
/* 0.0 to 100.0 */
XcmsFloat u_star;
XcmsFloat v_star;
} XcmsCIELuv; /* CIE L*u*v* */
typedef struct {
XcmsFloat H;
/* 0.0 to 360.0 */
XcmsFloat V;
/* 0.0 to 100.0 */
XcmsFloat C;
/* 0.0 to 100.0 */
} XcmsTekHVC; /* TekHVC */
typedef struct {
XcmsFloat pad0;
XcmsFloat pad1;
XcmsFloat pad2;
XcmsFloat pad3;
} XcmsPad; /* four doubles */
The device-dependent formats provided allow color specification in:

RGB Intensity (XcmsRGBi)
Red, green, and blue linear intensity values, floating-point values from 0.0 to 1.0, where 1.0
indicates full intensity, 0.5 half intensity, and so on.

RGB Device (XcmsRGB)
Red, green, and blue values appropriate for the specified output device. XcmsRGB values
are of type unsigned short, scaled from 0 to 65535 inclusive, and are interchangeable with
the red, green, and blue values in an XColor structure.
It is important to note that RGB Intensity values are not gamma corrected values. In contrast,
RGB Device values generated as a result of converting color specifications are always gamma
corrected, and RGB Device values acquired as a result of querying a colormap or passed in by the
client are assumed by Xlib to be gamma corrected. The term RGB value in this manual always
refers to an RGB Device value.
6.2. Color Strings
Xlib provides a mechanism for using string names for colors. A color string may either contain
an abstract color name or a numerical color specification. Color strings are case-insensitive.
Color strings are used in the following functions:
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XAllocNamedColor

XcmsAllocNamedColor

XLookupColor

XcmsLookupColor

XParseColor

XStoreNamedColor
Xlib supports the use of abstract color names, for example, red or blue. A value for this abstract
name is obtained by searching one or more color name databases. Xlib first searches zero or
more client-side databases; the number, location, and content of these databases is implementa-
tion-dependent and might depend on the current locale. If the name is not found, Xlib then looks
for the color in the X server's database. If the color name is not in the Host Portable Character
Encoding, the result is implementation-dependent.
A numerical color specification consists of a color space name and a set of values in the following
syntax:
<color_space_name>:<value>/.../<value>
The following are examples of valid color strings.
"CIEXYZ:0.3227/0.28133/0.2493"
"RGBi:1.0/0.0/0.0"
"rgb:00/ff/00"
"CIELuv:50.0/0.0/0.0"
The syntax and semantics of numerical specifications are given for each standard color space in
the following sections.
6.2.1. RGB Device String Specification
An RGB Device specification is identified by the prefix ``rgb:'' and conforms to the following
syntax:
rgb:<red>/<green>/<blue>
<red>, <green>, <blue> := h | hh | hhh | hhhh
h
:= single hexadecimal digits (case insignificant)
Note that h indicates the value scaled in 4 bits, hh the value scaled in 8 bits, hhh the value scaled
in 12 bits, and hhhh the value scaled in 16 bits, respectively.
Typical examples are the strings ``rgb:ea/75/52'' and ``rgb:ccc/320/320'', but mixed numbers of
hexadecimal digit strings (``rgb:ff/a5/0'' and ``rgb:ccc/32/0'') are also allowed.
For backward compatibility, an older syntax for RGB Device is supported, but its continued use is
not encouraged. The syntax is an initial sharp sign character followed by a numeric specification,
in one of the following formats:
#RGB (4 bits each)
#RRGGBB (8 bits each)
#RRRGGGBBB (12 bits each)
#RRRRGGGGBBBB (16 bits each)
The R, G, and B represent single hexadecimal digits. When fewer than 16 bits each are specified,
they represent the most significant bits of the value (unlike the ``rgb:'' syntax, in which values are
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scaled). For example, the string ``#3a7'' is the same as ``#3000a0007000''.
6.2.2. RGB Intensity String Specification
An RGB intensity specification is identified by the prefix ``rgbi:'' and conforms to the following
syntax:
rgbi:<red>/<green>/<blue>
Note that red, green, and blue are floating-point values between 0.0 and 1.0, inclusive. The input
format for these values is an optional sign, a string of numbers possibly containing a decimal
point, and an optional exponent field containing an E or e followed by a possibly signed integer
string.
6.2.3. Device-Independent String Specifications
The standard device-independent string specifications have the following syntax:
CIEXYZ:<X>/<Y>/<Z>
CIEuvY:<u>/<v>/<Y>
CIExyY:<x>/<y>/<Y>
CIELab:<L>/<a>/<b>
CIELuv:<L>/<u>/<v>
TekHVC:<H>/<V>/<C>
All of the values (C, H, V, X, Y, Z, a, b, u, v, y, x) are floating-point values. The syntax for these
values is an optional plus or minus sign, a string of digits possibly containing a decimal point, and
an optional exponent field consisting of an ``E'' or ``e'' followed by an optional plus or minus fol-
lowed by a string of digits.
6.3. Color Conversion Contexts and Gamut Mapping
When Xlib converts device-independent color specifications into device-dependent specifications
and vice versa, it uses knowledge about the color limitations of the screen hardware. This infor-
mation, typically called the device profile, is available in a Color Conversion Context (CCC).
Because a specified color may be outside the color gamut of the target screen and the white point
associated with the color specification may differ from the white point inherent to the screen, Xlib
applies gamut mapping when it encounters certain conditions:

Gamut compression occurs when conversion of device-independent color specifications to
device-dependent color specifications results in a color out of the target screen's gamut.

White adjustment occurs when the inherent white point of the screen differs from the white
point assumed by the client.
Gamut handling methods are stored as callbacks in the CCC, which in turn are used by the color
space conversion routines. Client data is also stored in the CCC for each callback. The CCC also
contains the white point the client assumes to be associated with color specifications (that is, the
Client White Point). The client can specify the gamut handling callbacks and client data as well
as the Client White Point. Xlib does not preclude the X client from performing other forms of
gamut handling (for example, gamut expansion); however, Xlib does not provide direct support
for gamut handling other than white adjustment and gamut compression.
Associated with each colormap is an initial CCC transparently generated by Xlib. Therefore,
when you specify a colormap as an argument to an Xlib function, you are indirectly specifying a
CCC. There is a default CCC associated with each screen. Newly created CCCs inherit attributes
from the default CCC, so the default CCC attributes can be modified to affect new CCCs.
Xcms functions in which gamut mapping can occur return Status and have specific status values
defined for them, as follows:
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XcmsFailure indicates that the function failed.

XcmsSuccess indicates that the function succeeded. In addition, if the function performed
any color conversion, the colors did not need to be compressed.

XcmsSuccessWithCompression indicates the function performed color conversion and at
least one of the colors needed to be compressed. The gamut compression method is deter-
mined by the gamut compression procedure in the CCC that is specified directly as a func-
tion argument or in the CCC indirectly specified by means of the colormap argument.
6.4. Creating, Copying, and Destroying Colormaps
To create a colormap for a screen, use XCreateColormap.
Colormap XCreateColormap(display, w, visual, alloc)
Display *display;
Window w;
Visual *visual;
int alloc;
display
Specifies the connection to the X server.
w
Specifies the window on whose screen you want to create a colormap.
visual
Specifies a visual type supported on the screen. If the visual type is not one sup-
ported by the screen, a BadMatch error results.
alloc
Specifies the colormap entries to be allocated. You can pass AllocNone or
AllocAll.
The XCreateColormap function creates a colormap of the specified visual type for the screen on
which the specified window resides and returns the colormap ID associated with it. Note that the
specified window is only used to determine the screen.
The initial values of the colormap entries are undefined for the visual classes GrayScale,
PseudoColor, and DirectColor. For StaticGray, StaticColor, and TrueColor, the entries
have defined values, but those values are specific to the visual and are not defined by X. For
StaticGray, StaticColor, and TrueColor, alloc must be AllocNone, or a BadMatch error
results. For the other visual classes, if alloc is AllocNone, the colormap initially has no allocated
entries, and clients can allocate them. For information about the visual types, see section 3.1.
If alloc is AllocAll, the entire colormap is allocated writable. The initial values of all allocated
entries are undefined. For GrayScale and PseudoColor, the effect is as if an XAllocColorCells
call returned all pixel values from zero to N - 1, where N is the colormap entries value in the
specified visual. For DirectColor, the effect is as if an XAllocColorPlanes call returned a pixel
value of zero and red_mask, green_mask, and blue_mask values containing the same bits as the
corresponding masks in the specified visual. However, in all cases, none of these entries can be
freed by using XFreeColors.
XCreateColormap can generate BadAlloc, BadMatch, BadValue, and BadWindow errors.
To create a new colormap when the allocation out of a previously shared colormap has failed
because of resource exhaustion, use XCopyColormapAndFree.
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Colormap XCopyColormapAndFree (display, colormap)
Display *display;
Colormap colormap;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
The XCopyColormapAndFree function creates a colormap of the same visual type and for the
same screen as the specified colormap and returns the new colormap ID. It also moves all of the
client's existing allocation from the specified colormap to the new colormap with their color val-
ues intact and their read-only or writable characteristics intact and frees those entries in the speci-
fied colormap. Color values in other entries in the new colormap are undefined. If the specified
colormap was created by the client with alloc set to AllocAll, the new colormap is also created
with AllocAll, all color values for all entries are copied from the specified colormap, and then all
entries in the specified colormap are freed. If the specified colormap was not created by the client
with AllocAll, the allocations to be moved are all those pixels and planes that have been allocated
by the client using XAllocColor, XAllocNamedColor, XAllocColorCells, or XAllocColor-
Planes
and that have not been freed since they were allocated.
XCopyColormapAndFree can generate BadAlloc and BadColor errors.
To destroy a colormap, use XFreeColormap.
XFreeColormap (display, colormap)
Display *display;
Colormap colormap;
display
Specifies the connection to the X server.
colormap
Specifies the colormap that you want to destroy.
The XFreeColormap function deletes the association between the colormap resource ID and the
colormap and frees the colormap storage. However, this function has no effect on the default col-
ormap for a screen. If the specified colormap is an installed map for a screen, it is uninstalled
(see XUninstallColormap). If the specified colormap is defined as the colormap for a window
(by XCreateWindow, XSetWindowColormap, or XChangeWindowAttributes), XFreeCol-
ormap
changes the colormap associated with the window to None and generates a Colormap-
Notify
ev ent. X does not define the colors displayed for a window with a colormap of None.
XFreeColormap can generate a BadColor error.
6.5. Mapping Color Names to Values
To map a color name to an RGB value, use XLookupColor.
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Status XLookupColor(display, colormap, color_name, exact_def_return, screen_def_return)
Display *display;
Colormap colormap;
char *color_name;
XColor *exact_def_return, *screen_def_return;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_name
Specifies the color name string (for example, red) whose color definition struc-
ture you want returned.
exact_def_returnReturns the exact RGB values.
screen_def_return
Returns the closest RGB values provided by the hardware.
The XLookupColor function looks up the string name of a color with respect to the screen asso-
ciated with the specified colormap. It returns both the exact color values and the closest values
provided by the screen with respect to the visual type of the specified colormap. If the color
name is not in the Host Portable Character Encoding, the result is implementation-dependent.
Use of uppercase or lowercase does not matter. XLookupColor returns nonzero if the name is
resolved; otherwise, it returns zero.
XLookupColor can generate a BadColor error.
To map a color name to the exact RGB value, use XParseColor.
Status XParseColor (display, colormap, spec, exact_def_return)
Display *display;
Colormap colormap;
char *spec;
XColor *exact_def_return;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
spec
Specifies the color name string; case is ignored.
exact_def_returnReturns the exact color value for later use and sets the DoRed, DoGreen, and
DoBlue flags.
The XParseColor function looks up the string name of a color with respect to the screen associ-
ated with the specified colormap. It returns the exact color value. If the color name is not in the
Host Portable Character Encoding, the result is implementation-dependent. Use of uppercase or
lowercase does not matter. XParseColor returns nonzero if the name is resolved; otherwise, it
returns zero.
XParseColor can generate a BadColor error.
To map a color name to a value in an arbitrary color space, use XcmsLookupColor.
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Status XcmsLookupColor(display, colormap, color_string, color_exact_return, color_screen_return,
result_format)
Display *display;
Colormap colormap;
char *color_string;
XcmsColor *color_exact_return, *color_screen_return;
XcmsColorFormat result_format;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_string
Specifies the color string.
color_exact_return
Returns the color specification parsed from the color string or parsed from the
corresponding string found in a color-name database.
color_screen_return
Returns the color that can be reproduced on the screen.
result_format
Specifies the color format for the returned color specifications (color_screen_re-
turn and color_exact_return arguments). If the format is XcmsUndefinedFor-
mat
and the color string contains a numerical color specification, the specifica-
tion is returned in the format used in that numerical color specification. If the
format is XcmsUndefinedFormat and the color string contains a color name, the
specification is returned in the format used to store the color in the database.
The XcmsLookupColor function looks up the string name of a color with respect to the screen
associated with the specified colormap. It returns both the exact color values and the closest val-
ues provided by the screen with respect to the visual type of the specified colormap. The values
are returned in the format specified by result_format. If the color name is not in the Host Portable
Character Encoding, the result is implementation-dependent. Use of uppercase or lowercase does
not matter. XcmsLookupColor returns XcmsSuccess or XcmsSuccessWithCompression if
the name is resolved; otherwise, it returns XcmsFailure. If XcmsSuccessWithCompression is
returned, the color specification returned in color_screen_return is the result of gamut compres-
sion.
6.6. Allocating and Freeing Color Cells
There are two ways of allocating color cells: explicitly as read-only entries, one pixel value at a
time, or read/write, where you can allocate a number of color cells and planes simultaneously. A
read-only cell has its RGB value set by the server. Read/write cells do not have defined colors
initially; functions described in the next section must be used to store values into them. Although
it is possible for any client to store values into a read/write cell allocated by another client,
read/write cells normally should be considered private to the client that allocated them.
Read-only colormap cells are shared among clients. The server counts each allocation and free-
ing of the cell by clients. When the last client frees a shared cell, the cell is finally deallocated. If
a single client allocates the same read-only cell multiple times, the server counts each such alloca-
tion, not just the first one.
To allocate a read-only color cell with an RGB value, use XAllocColor.
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Status XAllocColor(display, colormap, screen_in_out)
Display *display;
Colormap colormap;
XColor *screen_in_out;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
screen_in_out
Specifies and returns the values actually used in the colormap.
The XAllocColor function allocates a read-only colormap entry corresponding to the closest
RGB value supported by the hardware. XAllocColor returns the pixel value of the color closest
to the specified RGB elements supported by the hardware and returns the RGB value actually
used. The corresponding colormap cell is read-only. In addition, XAllocColor returns nonzero
if it succeeded or zero if it failed. Multiple clients that request the same effective RGB value can
be assigned the same read-only entry, thus allowing entries to be shared. When the last client
deallocates a shared cell, it is deallocated. XAllocColor does not use or affect the flags in the
XColor structure.
XAllocColor can generate a BadColor error.
To allocate a read-only color cell with a color in arbitrary format, use XcmsAllocColor.
Status XcmsAllocColor(display, colormap, color_in_out, result_format)
Display *display;
Colormap colormap;
XcmsColor *color_in_out;
XcmsColorFormat result_format;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_in_out
Specifies the color to allocate and returns the pixel and color that is actually used
in the colormap.
result_format
Specifies the color format for the returned color specification.
The XcmsAllocColor function is similar to XAllocColor except the color can be specified in
any format. The XcmsAllocColor function ultimately calls XAllocColor to allocate a read-only
color cell (colormap entry) with the specified color. XcmsAllocColor first converts the color
specified to an RGB value and then passes this to XAllocColor. XcmsAllocColor returns the
pixel value of the color cell and the color specification actually allocated. This returned color
specification is the result of converting the RGB value returned by XAllocColor into the format
specified with the result_format argument. If there is no interest in a returned color specification,
unnecessary computation can be bypassed if result_format is set to XcmsRGBFormat. The cor-
responding colormap cell is read-only. If this routine returns XcmsFailure, the color_in_out
color specification is left unchanged.
XcmsAllocColor can generate a BadColor error.
To allocate a read-only color cell using a color name and return the closest color supported by the
hardware in RGB format, use XAllocNamedColor.
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Status XAllocNamedColor(display, colormap, color_name, screen_def_return, exact_def_return)
Display *display;
Colormap colormap;
char *color_name;
XColor *screen_def_return, *exact_def_return;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_name
Specifies the color name string (for example, red) whose color definition struc-
ture you want returned.
screen_def_return
Returns the closest RGB values provided by the hardware.
exact_def_returnReturns the exact RGB values.
The XAllocNamedColor function looks up the named color with respect to the screen that is
associated with the specified colormap. It returns both the exact database definition and the clos-
est color supported by the screen. The allocated color cell is read-only. The pixel value is
returned in screen_def_return. If the color name is not in the Host Portable Character Encoding,
the result is implementation-dependent. Use of uppercase or lowercase does not matter. If
screen_def_return and exact_def_return point to the same structure, the pixel field will be set cor-
rectly, but the color values are undefined. XAllocNamedColor returns nonzero if a cell is allo-
cated; otherwise, it returns zero.
XAllocNamedColor can generate a BadColor error.
To allocate a read-only color cell using a color name and return the closest color supported by the
hardware in an arbitrary format, use XcmsAllocNamedColor.
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Status XcmsAllocNamedColor(display, colormap, color_string, color_screen_return, color_exact_return,
result_format)
Display *display;
Colormap colormap;
char *color_string;
XcmsColor *color_screen_return;
XcmsColor *color_exact_return;
XcmsColorFormat result_format;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_string
Specifies the color string whose color definition structure is to be returned.
color_screen_return
Returns the pixel value of the color cell and color specification that actually is
stored for that cell.
color_exact_return
Returns the color specification parsed from the color string or parsed from the
corresponding string found in a color-name database.
result_format
Specifies the color format for the returned color specifications (color_screen_re-
turn and color_exact_return arguments). If the format is XcmsUndefinedFor-
mat
and the color string contains a numerical color specification, the specifica-
tion is returned in the format used in that numerical color specification. If the
format is XcmsUndefinedFormat and the color string contains a color name, the
specification is returned in the format used to store the color in the database.
The XcmsAllocNamedColor function is similar to XAllocNamedColor except that the color
returned can be in any format specified. This function ultimately calls XAllocColor to allocate a
read-only color cell with the color specified by a color string. The color string is parsed into an
XcmsColor structure (see XcmsLookupColor), converted to an RGB value, and finally passed
to XAllocColor. If the color name is not in the Host Portable Character Encoding, the result is
implementation-dependent. Use of uppercase or lowercase does not matter.
This function returns both the color specification as a result of parsing (exact specification) and
the actual color specification stored (screen specification). This screen specification is the result
of converting the RGB value returned by XAllocColor into the format specified in result_format.
If there is no interest in a returned color specification, unnecessary computation can be bypassed
if result_format is set to XcmsRGBFormat. If color_screen_return and color_exact_return point
to the same structure, the pixel field will be set correctly, but the color values are undefined.
XcmsAllocNamedColor can generate a BadColor error.
To allocate read/write color cell and color plane combinations for a PseudoColor model, use
XAllocColorCells.
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Status XAllocColorCells(display, colormap, contig, plane_masks_return, nplanes,
pixels_return, npixels)
Display *display;
Colormap colormap;
Bool contig;
unsigned long plane_masks_return[];
unsigned int nplanes;
unsigned long pixels_return[];
unsigned int npixels;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
contig
Specifies a Boolean value that indicates whether the planes must be contiguous.
plane_mask_return
Returns an array of plane masks.
nplanes
Specifies the number of plane masks that are to be returned in the plane masks ar-
ray.
pixels_return
Returns an array of pixel values.
npixels
Specifies the number of pixel values that are to be returned in the pixels_return
array.
The XAllocColorCells function allocates read/write color cells. The number of colors must be
positive and the number of planes nonnegative, or a BadValue error results. If ncolors and
nplanes are requested, then ncolors pixels and nplane plane masks are returned. No mask will
have any bits set to 1 in common with any other mask or with any of the pixels. By ORing
together each pixel with zero or more masks, ncolors * 2nplanes distinct pixels can be produced.
All of these are allocated writable by the request. For GrayScale or PseudoColor, each mask
has exactly one bit set to 1. For DirectColor, each has exactly three bits set to 1. If contig is
True and if all masks are ORed together, a single contiguous set of bits set to 1 will be formed
for GrayScale or PseudoColor and three contiguous sets of bits set to 1 (one within each pixel
subfield) for DirectColor. The RGB values of the allocated entries are undefined. XAllocCol-
orCells
returns nonzero if it succeeded or zero if it failed.
XAllocColorCells can generate BadColor and BadValue errors.
To allocate read/write color resources for a DirectColor model, use XAllocColorPlanes.
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Status XAllocColorPlanes(display, colormap, contig, pixels_return, ncolors, nreds, ngreens,
nblues, rmask_return, gmask_return, bmask_return)
Display *display;
Colormap colormap;
Bool contig;
unsigned long pixels_return[];
int ncolors;
int nreds, ngreens, nblues;
unsigned long *rmask_return, *gmask_return, *bmask_return;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
contig
Specifies a Boolean value that indicates whether the planes must be contiguous.
pixels_return
Returns an array of pixel values. XAllocColorPlanes returns the pixel values in
this array.
ncolors
Specifies the number of pixel values that are to be returned in the pixels_return
array.
nreds
ngreens
nblues
Specify the number of red, green, and blue planes. The value you pass must be
nonnegative.
rmask_return
gmask_return
bmask_return
Return bit masks for the red, green, and blue planes.
The specified ncolors must be positive; and nreds, ngreens, and nblues must be nonnegative, or a
BadValue error results. If ncolors colors, nreds reds, ngreens greens, and nblues blues are
requested, ncolors pixels are returned; and the masks have nreds, ngreens, and nblues bits set to 1,
respectively. If contig is True, each mask will have a contiguous set of bits set to 1. No mask
will have any bits set to 1 in common with any other mask or with any of the pixels. For
DirectColor, each mask will lie within the corresponding pixel subfield. By ORing together sub-
sets of masks with each pixel value, ncolors * 2(nreds+ngreens+nblues) distinct pixel values can be pro-
duced. All of these are allocated by the request. However, in the colormap, there are only ncol-
ors * 2nreds independent red entries, ncolors * 2ngreens independent green entries, and ncolors *
2nblues independent blue entries. This is true even for PseudoColor. When the colormap entry of
a pixel value is changed (using XStoreColors, XStoreColor, or XStoreNamedColor), the pixel
is decomposed according to the masks, and the corresponding independent entries are updated.
XAllocColorPlanes returns nonzero if it succeeded or zero if it failed.
XAllocColorPlanes can generate BadColor and BadValue errors.
To free colormap cells, use XFreeColors.
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XFreeColors (display, colormap, pixels, npixels, planes)
Display *display;
Colormap colormap;
unsigned long pixels[];
int npixels;
unsigned long planes;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
pixels
Specifies an array of pixel values that map to the cells in the specified colormap.
npixels
Specifies the number of pixels.
planes
Specifies the planes you want to free.
The XFreeColors function frees the cells represented by pixels whose values are in the pixels
array. The planes argument should not have any bits set to 1 in common with any of the pixels.
The set of all pixels is produced by ORing together subsets of the planes argument with the pix-
els. The request frees all of these pixels that were allocated by the client (using XAllocColor,
XAllocNamedColor, XAllocColorCells, and XAllocColorPlanes). Note that freeing an indi-
vidual pixel obtained from XAllocColorPlanes may not actually allow it to be reused until all of
its related pixels are also freed. Similarly, a read-only entry is not actually freed until it has been
freed by all clients, and if a client allocates the same read-only entry multiple times, it must free
the entry that many times before the entry is actually freed.
All specified pixels that are allocated by the client in the colormap are freed, even if one or more
pixels produce an error. If a specified pixel is not a valid index into the colormap, a BadValue
error results. If a specified pixel is not allocated by the client (that is, is unallocated or is only
allocated by another client) or if the colormap was created with all entries writable (by passing
AllocAll to XCreateColormap), a BadAccess error results. If more than one pixel is in error,
the one that gets reported is arbitrary.
XFreeColors can generate BadAccess, BadColor, and BadValue errors.
6.7. Modifying and Querying Colormap Cells
To store an RGB value in a single colormap cell, use XStoreColor.
XStoreColor (display, colormap, color)
Display *display;
Colormap colormap;
XColor *color;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color
Specifies the pixel and RGB values.
The XStoreColor function changes the colormap entry of the pixel value specified in the pixel
member of the XColor structure. You specified this value in the pixel member of the XColor
structure. This pixel value must be a read/write cell and a valid index into the colormap. If a
specified pixel is not a valid index into the colormap, a BadValue error results. XStoreColor
also changes the red, green, and/or blue color components. You specify which color components
are to be changed by setting DoRed, DoGreen, and/or DoBlue in the flags member of the
XColor structure. If the colormap is an installed map for its screen, the changes are visible
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immediately.
XStoreColor can generate BadAccess, BadColor, and BadValue errors.
To store multiple RGB values in multiple colormap cells, use XStoreColors.
XStoreColors (display, colormap, color, ncolors)
Display *display;
Colormap colormap;
XColor color[];
int ncolors;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color
Specifies an array of color definition structures to be stored.
ncolors
Specifies the number of XColor structures in the color definition array.
The XStoreColors function changes the colormap entries of the pixel values specified in the
pixel members of the XColor structures. You specify which color components are to be changed
by setting DoRed, DoGreen, and/or DoBlue in the flags member of the XColor structures. If
the colormap is an installed map for its screen, the changes are visible immediately. XStoreCol-
ors
changes the specified pixels if they are allocated writable in the colormap by any client, even
if one or more pixels generates an error. If a specified pixel is not a valid index into the colormap,
a BadValue error results. If a specified pixel either is unallocated or is allocated read-only, a
BadAccess error results. If more than one pixel is in error, the one that gets reported is arbitrary.
XStoreColors can generate BadAccess, BadColor, and BadValue errors.
To store a color of arbitrary format in a single colormap cell, use XcmsStoreColor.
Status XcmsStoreColor(display, colormap, color)
Display *display;
Colormap colormap;
XcmsColor *color;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color
Specifies the color cell and the color to store. Values specified in this XcmsCol-
or
structure remain unchanged on return.
The XcmsStoreColor function converts the color specified in the XcmsColor structure into
RGB values. It then uses this RGB specification in an XColor structure, whose three flags
(DoRed, DoGreen, and DoBlue) are set, in a call to XStoreColor to change the color cell spec-
ified by the pixel member of the XcmsColor structure. This pixel value must be a valid index for
the specified colormap, and the color cell specified by the pixel value must be a read/write cell. If
the pixel value is not a valid index, a BadValue error results. If the color cell is unallocated or is
allocated read-only, a BadAccess error results. If the colormap is an installed map for its screen,
the changes are visible immediately.
Note that XStoreColor has no return value; therefore, an XcmsSuccess return value from this
function indicates that the conversion to RGB succeeded and the call to XStoreColor was made.
To obtain the actual color stored, use XcmsQueryColor. Because of the screen's hardware limi-
tations or gamut compression, the color stored in the colormap may not be identical to the color
specified.
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XcmsStoreColor can generate BadAccess, BadColor, and BadValue errors.
To store multiple colors of arbitrary format in multiple colormap cells, use XcmsStoreColors.
Status XcmsStoreColors(display, colormap, colors, ncolors, compression_flags_return)
Display *display;
Colormap colormap;
XcmsColor colors[];
int ncolors;
Bool compression_flags_return[];
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
colors
Specifies the color specification array of XcmsColor structures, each specifying
a color cell and the color to store in that cell. Values specified in the array remain
unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return
Returns an array of Boolean values indicating compression status. If a non-
NULL pointer is supplied, each element of the array is set to True if the corre-
sponding color was compressed and False otherwise. Pass NULL if the com-
pression status is not useful.
The XcmsStoreColors function converts the colors specified in the array of XcmsColor struc-
tures into RGB values and then uses these RGB specifications in XColor structures, whose three
flags (DoRed, DoGreen, and DoBlue) are set, in a call to XStoreColors to change the color
cells specified by the pixel member of the corresponding XcmsColor structure. Each pixel value
must be a valid index for the specified colormap, and the color cell specified by each pixel value
must be a read/write cell. If a pixel value is not a valid index, a BadValue error results. If a
color cell is unallocated or is allocated read-only, a BadAccess error results. If more than one
pixel is in error, the one that gets reported is arbitrary. If the colormap is an installed map for its
screen, the changes are visible immediately.
Note that XStoreColors has no return value; therefore, an XcmsSuccess return value from this
function indicates that conversions to RGB succeeded and the call to XStoreColors was made.
To obtain the actual colors stored, use XcmsQueryColors. Because of the screen's hardware
limitations or gamut compression, the colors stored in the colormap may not be identical to the
colors specified.
XcmsStoreColors can generate BadAccess, BadColor, and BadValue errors.
To store a color specified by name in a single colormap cell, use XStoreNamedColor.
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XStoreNamedColor (display, colormap, color, pixel, flags)
Display *display;
Colormap colormap;
char *color;
unsigned long pixel;
int flags;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color
Specifies the color name string (for example, red).
pixel
Specifies the entry in the colormap.
flags
Specifies which red, green, and blue components are set.
The XStoreNamedColor function looks up the named color with respect to the screen associated
with the colormap and stores the result in the specified colormap. The pixel argument determines
the entry in the colormap. The flags argument determines which of the red, green, and blue com-
ponents are set. You can set this member to the bitwise inclusive OR of the bits DoRed,
DoGreen, and DoBlue. If the color name is not in the Host Portable Character Encoding, the
result is implementation-dependent. Use of uppercase or lowercase does not matter. If the speci-
fied pixel is not a valid index into the colormap, a BadValue error results. If the specified pixel
either is unallocated or is allocated read-only, a BadAccess error results.
XStoreNamedColor can generate BadAccess, BadColor, BadName, and BadValue errors.
The XQueryColor and XQueryColors functions take pixel values in the pixel member of
XColor structures and store in the structures the RGB values for those pixels from the specified
colormap. The values returned for an unallocated entry are undefined. These functions also set
the flags member in the XColor structure to all three colors. If a pixel is not a valid index into
the specified colormap, a BadValue error results. If more than one pixel is in error, the one that
gets reported is arbitrary.
To query the RGB value of a single colormap cell, use XQueryColor.
XQueryColor (display, colormap, def_in_out)
Display *display;
Colormap colormap;
XColor *def_in_out;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
def_in_out
Specifies and returns the RGB values for the pixel specified in the structure.
The XQueryColor function returns the current RGB value for the pixel in the XColor structure
and sets the DoRed, DoGreen, and DoBlue flags.
XQueryColor can generate BadColor and BadValue errors.
To query the RGB values of multiple colormap cells, use XQueryColors.
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XQueryColors (display, colormap, defs_in_out, ncolors)
Display *display;
Colormap colormap;
XColor defs_in_out[];
int ncolors;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
defs_in_out
Specifies and returns an array of color definition structures for the pixel specified
in the structure.
ncolors
Specifies the number of XColor structures in the color definition array.
The XQueryColors function returns the RGB value for each pixel in each XColor structure and
sets the DoRed, DoGreen, and DoBlue flags in each structure.
XQueryColors can generate BadColor and BadValue errors.
To query the color of a single colormap cell in an arbitrary format, use XcmsQueryColor.
Status XcmsQueryColor(display, colormap, color_in_out, result_format)
Display *display;
Colormap colormap;
XcmsColor *color_in_out;
XcmsColorFormat result_format;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
color_in_out
Specifies the pixel member that indicates the color cell to query. The color speci-
fication stored for the color cell is returned in this XcmsColor structure.
result_format
Specifies the color format for the returned color specification.
The XcmsQueryColor function obtains the RGB value for the pixel value in the pixel member
of the specified XcmsColor structure and then converts the value to the target format as specified
by the result_format argument. If the pixel is not a valid index in the specified colormap, a Bad-
Value
error results.
XcmsQueryColor can generate BadColor and BadValue errors.
To query the color of multiple colormap cells in an arbitrary format, use XcmsQueryColors.
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Status XcmsQueryColors(display, colormap, colors_in_out, ncolors, result_format)
Display *display;
Colormap colormap;
XcmsColor colors_in_out[];
unsigned int ncolors;
XcmsColorFormat result_format;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
colors_in_out
Specifies an array of XcmsColor structures, each pixel member indicating the
color cell to query. The color specifications for the color cells are returned in
these structures.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
result_format
Specifies the color format for the returned color specification.
The XcmsQueryColors function obtains the RGB values for pixel values in the pixel members
of XcmsColor structures and then converts the values to the target format as specified by the
result_format argument. If a pixel is not a valid index into the specified colormap, a BadValue
error results. If more than one pixel is in error, the one that gets reported is arbitrary.
XcmsQueryColors can generate BadColor and BadValue errors.
6.8. Color Conversion Context Functions
This section describes functions to create, modify, and query Color Conversion Contexts (CCCs).
Associated with each colormap is an initial CCC transparently generated by Xlib. Therefore,
when you specify a colormap as an argument to a function, you are indirectly specifying a CCC.
The CCC attributes that can be modified by the X client are:

Client White Point

Gamut compression procedure and client data

White point adjustment procedure and client data
The initial values for these attributes are implementation specific. The CCC attributes for subse-
quently created CCCs can be defined by changing the CCC attributes of the default CCC. There
is a default CCC associated with each screen.
6.8.1. Getting and Setting the Color Conversion Context of a Colormap
To obtain the CCC associated with a colormap, use XcmsCCCOfColormap.
XcmsCCC XcmsCCCOfColormap(display, colormap)
Display *display;
Colormap colormap;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
The XcmsCCCOfColormap function returns the CCC associated with the specified colormap.
Once obtained, the CCC attributes can be queried or modified. Unless the CCC associated with
the specified colormap is changed with XcmsSetCCCOfColormap, this CCC is used when the
specified colormap is used as an argument to color functions.
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To change the CCC associated with a colormap, use XcmsSetCCCOfColormap.
XcmsCCC XcmsSetCCCOfColormap(display, colormap, ccc)
Display *display;
Colormap colormap;
XcmsCCC ccc;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
ccc
Specifies the CCC.
The XcmsSetCCCOfColormap function changes the CCC associated with the specified col-
ormap. It returns the CCC previously associated with the colormap. If they are not used again in
the application, CCCs should be freed by calling XcmsFreeCCC. Sev eral colormaps may share
the same CCC without restriction; this includes the CCCs generated by Xlib with each colormap.
Xlib, however, creates a new CCC with each new colormap.
6.8.2. Obtaining the Default Color Conversion Context
You can change the default CCC attributes for subsequently created CCCs by changing the CCC
attributes of the default CCC. A default CCC is associated with each screen.
To obtain the default CCC for a screen, use XcmsDefaultCCC.
XcmsCCC XcmsDefaultCCC (display, screen_number)
Display *display;
int screen_number;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
The XcmsDefaultCCC function returns the default CCC for the specified screen. Its visual is
the default visual of the screen. Its initial gamut compression and white point adjustment proce-
dures as well as the associated client data are implementation specific.
6.8.3. Color Conversion Context Macros
Applications should not directly modify any part of the XcmsCCC. The following lists the C
language macros, their corresponding function equivalents for other language bindings, and what
data they both can return.
DisplayOfCCC (ccc)
XcmsCCC ccc;
Display *XcmsDisplayOfCCC(ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
Both return the display associated with the specified CCC.
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VisualOfCCC (ccc)
XcmsCCC ccc;
Visual *XcmsVisualOfCCC (ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
Both return the visual associated with the specified CCC.
ScreenNumberOfCCC (ccc)
XcmsCCC ccc;
int XcmsScreenNumberOfCCC(ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
Both return the number of the screen associated with the specified CCC.
ScreenWhitePointOfCCC (ccc)
XcmsCCC ccc;
XcmsColor *XcmsScreenWhitePointOfCCC(ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
Both return the white point of the screen associated with the specified CCC.
ClientWhitePointOfCCC (ccc)
XcmsCCC ccc;
XcmsColor *XcmsClientWhitePointOfCCC(ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
Both return the Client White Point of the specified CCC.
6.8.4. Modifying Attributes of a Color Conversion Context
To set the Client White Point in the CCC, use XcmsSetWhitePoint.
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Status XcmsSetWhitePoint(ccc, color)
XcmsCCC ccc;
XcmsColor *color;
ccc
Specifies the CCC.
color
Specifies the new Client White Point.
The XcmsSetWhitePoint function changes the Client White Point in the specified CCC. Note
that the pixel member is ignored and that the color specification is left unchanged upon return.
The format for the new white point must be XcmsCIEXYZFormat, XcmsCIEuvYFormat,
XcmsCIExyYFormat, or XcmsUndefinedFormat. If the color argument is NULL, this func-
tion sets the format component of the Client White Point specification to
XcmsUndefinedFormat, indicating that the Client White Point is assumed to be the same as the
Screen White Point.
This function returns nonzero status if the format for the new white point is valid; otherwise, it
returns zero.
To set the gamut compression procedure and corresponding client data in a specified CCC, use
XcmsSetCompressionProc.
XcmsCompressionProc XcmsSetCompressionProc(ccc, compression_proc, client_data)
XcmsCCC ccc;
XcmsCompressionProc compression_proc;
XPointer client_data;
ccc
Specifies the CCC.
compression_proc
Specifies the gamut compression procedure that is to be applied when a color lies
outside the screen's color gamut. If NULL is specified and a function using this
CCC must convert a color specification to a device-dependent format and en-
counters a color that lies outside the screen's color gamut, that function will re-
turn XcmsFailure.
client_data
Specifies client data for the gamut compression procedure or NULL.
The XcmsSetCompressionProc function first sets the gamut compression procedure and client
data in the specified CCC with the newly specified procedure and client data and then returns the
old procedure.
To set the white point adjustment procedure and corresponding client data in a specified CCC, use
XcmsSetWhiteAdjustProc.
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XcmsWhiteAdjustProc XcmsSetWhiteAdjustProc(ccc, white_adjust_proc, client_data)
XcmsCCC ccc;
XcmsWhiteAdjustProc white_adjust_proc;
XPointer client_data;
ccc
Specifies the CCC.
white_adjust_proc
Specifies the white point adjustment procedure.
client_data
Specifies client data for the white point adjustment procedure or NULL.
The XcmsSetWhiteAdjustProc function first sets the white point adjustment procedure and
client data in the specified CCC with the newly specified procedure and client data and then
returns the old procedure.
6.8.5. Creating and Freeing a Color Conversion Context
You can explicitly create a CCC within your application by calling XcmsCreateCCC. These
created CCCs can then be used by those functions that explicitly call for a CCC argument. Old
CCCs that will not be used by the application should be freed using XcmsFreeCCC.
To create a CCC, use XcmsCreateCCC.
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XcmsCCC XcmsCreateCCC(display, screen_number, visual, client_white_point, compression_proc,
compression_client_data, white_adjust_proc, white_adjust_client_data)
Display *display;
int screen_number;
Visual *visual;
XcmsColor *client_white_point;
XcmsCompressionProc compression_proc;
XPointer compression_client_data;
XcmsWhiteAdjustProc white_adjust_proc;
XPointer white_adjust_client_data;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
visual
Specifies the visual type.
client_white_point
Specifies the Client White Point. If NULL is specified, the Client White Point is
to be assumed to be the same as the Screen White Point. Note that the pixel
member is ignored.
compression_proc
Specifies the gamut compression procedure that is to be applied when a color lies
outside the screen's color gamut. If NULL is specified and a function using this
CCC must convert a color specification to a device-dependent format and en-
counters a color that lies outside the screen's color gamut, that function will re-
turn XcmsFailure.
compression_client_data
Specifies client data for use by the gamut compression procedure or NULL.
white_adjust_proc
Specifies the white adjustment procedure that is to be applied when the Client
White Point differs from the Screen White Point. NULL indicates that no white
point adjustment is desired.
white_adjust_client_data
Specifies client data for use with the white point adjustment procedure or NULL.
The XcmsCreateCCC function creates a CCC for the specified display, screen, and visual.
To free a CCC, use XcmsFreeCCC.
void XcmsFreeCCC(ccc)
XcmsCCC ccc;
ccc
Specifies the CCC.
The XcmsFreeCCC function frees the memory used for the specified CCC. Note that default
CCCs and those currently associated with colormaps are ignored.
6.9. Converting between Color Spaces
To convert an array of color specifications in arbitrary color formats to a single destination for-
mat, use XcmsConvertColors.
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Status XcmsConvertColors (ccc, colors_in_out, ncolors, target_format, compression_flags_return)
XcmsCCC ccc;
XcmsColor colors_in_out[];
unsigned int ncolors;
XcmsColorFormat target_format;
Bool compression_flags_return[];
ccc
Specifies the CCC. If conversion is between device-independent color spaces on-
ly (for example, TekHVC to CIELuv), the CCC is necessary only to specify the
Client White Point.
colors_in_out
Specifies an array of color specifications. Pixel members are ignored and remain
unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
target_format
Specifies the target color specification format.
compression_flags_return
Returns an array of Boolean values indicating compression status. If a non-
NULL pointer is supplied, each element of the array is set to True if the corre-
sponding color was compressed and False otherwise. Pass NULL if the com-
pression status is not useful.
The XcmsConvertColors function converts the color specifications in the specified array of
XcmsColor structures from their current format to a single target format, using the specified
CCC. When the return value is XcmsFailure, the contents of the color specification array are left
unchanged.
The array may contain a mixture of color specification formats (for example, 3 CIE XYZ, 2 CIE
Luv, and so on). When the array contains both device-independent and device-dependent color
specifications and the target_format argument specifies a device-dependent format (for example,
XcmsRGBiFormat, XcmsRGBFormat), all specifications are converted to CIE XYZ format
and then to the target device-dependent format.
6.10. Callback Functions
This section describes the gamut compression and white point adjustment callbacks.
The gamut compression procedure specified in the CCC is called when an attempt to convert a
color specification from XcmsCIEXYZ to a device-dependent format (typically XcmsRGBi)
results in a color that lies outside the screen's color gamut. If the gamut compression procedure
requires client data, this data is passed via the gamut compression client data in the CCC.
During color specification conversion between device-independent and device-dependent color
spaces, if a white point adjustment procedure is specified in the CCC, it is triggered when the
Client White Point and Screen White Point differ. If required, the client data is obtained from the
CCC.
6.10.1. Prototype Gamut Compression Procedure
The gamut compression callback interface must adhere to the following:
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typedef Status (*XcmsCompressionProc ) (ccc, colors_in_out, ncolors, index, compression_flags_return)
XcmsCCC ccc;
XcmsColor colors_in_out[];
unsigned int ncolors;
unsigned int index;
Bool compression_flags_return[];
ccc
Specifies the CCC.
colors_in_out
Specifies an array of color specifications. Pixel members should be ignored and
must remain unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
index
Specifies the index into the array of XcmsColor structures for the encountered
color specification that lies outside the screen's color gamut. Valid values are 0
(for the first element) to ncolors - 1.
compression_flags_return
Returns an array of Boolean values for indicating compression status. If a non-
NULL pointer is supplied and a color at a given index is compressed, then True
should be stored at the corresponding index in this array; otherwise, the array
should not be modified.
When implementing a gamut compression procedure, consider the following rules and assump-
tions:

The gamut compression procedure can attempt to compress one or multiple specifications
at a time.

When called, elements 0 to index - 1 in the color specification array can be assumed to fall
within the screen's color gamut. In addition, these color specifications are already in some
device-dependent format (typically XcmsRGBi). If any modifications are made to these
color specifications, they must be in their initial device-dependent format upon return.

When called, the element in the color specification array specified by the index argument
contains the color specification outside the screen's color gamut encountered by the calling
routine. In addition, this color specification can be assumed to be in XcmsCIEXYZ.
Upon return, this color specification must be in XcmsCIEXYZ.

When called, elements from index to ncolors - 1 in the color specification array may or
may not fall within the screen's color gamut. In addition, these color specifications can be
assumed to be in XcmsCIEXYZ. If any modifications are made to these color specifica-
tions, they must be in XcmsCIEXYZ upon return.

The color specifications passed to the gamut compression procedure have already been
adjusted to the Screen White Point. This means that at this point the color specification's
white point is the Screen White Point.

If the gamut compression procedure uses a device-independent color space not initially
accessible for use in the color management system, use XcmsAddColorSpace to ensure
that it is added.
6.10.2. Supplied Gamut Compression Procedures
The following equations are useful in describing gamut compression functions:
CIELab Psychometric Chroma = sqrt(a_star2 + b_star2)
b_star
CIELab Psychometric Hue = tan-1

a_star
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CIELuv Psychometric Chroma = sqrt(u_star2 + v_star2)
v_star
CIELuv Psychometric Hue = tan-1 u_star
The gamut compression callback procedures provided by Xlib are as follows:

XcmsCIELabClipL
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing or increasing CIE metric lightness (L*) in the CIE L*a*b* color space until the
color is within the gamut. If the Psychometric Chroma of the color specification is beyond
maximum for the Psychometric Hue Angle, then while maintaining the same Psychometric
Hue Angle, the color will be clipped to the CIE L*a*b* coordinates of maximum Psycho-
metric Chroma. See XcmsCIELabQueryMaxC. No client data is necessary.

XcmsCIELabClipab
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing Psychometric Chroma, while maintaining Psychometric Hue Angle, until the
color is within the gamut. No client data is necessary.

XcmsCIELabClipLab
This brings the encountered out-of-gamut color specification into the screen's color gamut
by replacing it with CIE L*a*b* coordinates that fall within the color gamut while main-
taining the original Psychometric Hue Angle and whose vector to the original coordinates
is the shortest attainable. No client data is necessary.

XcmsCIELuvClipL
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing or increasing CIE metric lightness (L*) in the CIE L*u*v* color space until the
color is within the gamut. If the Psychometric Chroma of the color specification is beyond
maximum for the Psychometric Hue Angle, then, while maintaining the same Psychometric
Hue Angle, the color will be clipped to the CIE L*u*v* coordinates of maximum Psycho-
metric Chroma. See XcmsCIELuvQueryMaxC. No client data is necessary.

XcmsCIELuvClipuv
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing Psychometric Chroma, while maintaining Psychometric Hue Angle, until the
color is within the gamut. No client data is necessary.

XcmsCIELuvClipLuv
This brings the encountered out-of-gamut color specification into the screen's color gamut
by replacing it with CIE L*u*v* coordinates that fall within the color gamut while main-
taining the original Psychometric Hue Angle and whose vector to the original coordinates
is the shortest attainable. No client data is necessary.

XcmsTekHVCClipV
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing or increasing the Value dimension in the TekHVC color space until the color is
within the gamut. If Chroma of the color specification is beyond maximum for the particu-
lar Hue, then, while maintaining the same Hue, the color will be clipped to the Value and
Chroma coordinates that represent maximum Chroma for that particular Hue. No client
data is necessary.

XcmsTekHVCClipC
This brings the encountered out-of-gamut color specification into the screen's color gamut
by reducing the Chroma dimension in the TekHVC color space until the color is within the
gamut. No client data is necessary.
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XcmsTekHVCClipVC
This brings the encountered out-of-gamut color specification into the screen's color gamut
by replacing it with TekHVC coordinates that fall within the color gamut while maintaining
the original Hue and whose vector to the original coordinates is the shortest attainable. No
client data is necessary.
6.10.3. Prototype White Point Adjustment Procedure
The white point adjustment procedure interface must adhere to the following:
typedef Status (*XcmsWhiteAdjustProc ) (ccc, initial_white_point, target_white_point, target_format,
colors_in_out, ncolors, compression_flags_return)
XcmsCCC ccc;
XcmsColor *initial_white_point;
XcmsColor *target_white_point;
XcmsColorFormat target_format;
XcmsColor colors_in_out[];
unsigned int ncolors;
Bool compression_flags_return[];
ccc
Specifies the CCC.
initial_white_point
Specifies the initial white point.
target_white_point
Specifies the target white point.
target_format
Specifies the target color specification format.
colors_in_out
Specifies an array of color specifications. Pixel members should be ignored and
must remain unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return
Returns an array of Boolean values for indicating compression status. If a non-
NULL pointer is supplied and a color at a given index is compressed, then True
should be stored at the corresponding index in this array; otherwise, the array
should not be modified.
6.10.4. Supplied White Point Adjustment Procedures
White point adjustment procedures provided by Xlib are as follows:

XcmsCIELabWhiteShiftColors
This uses the CIE L*a*b* color space for adjusting the chromatic character of colors to
compensate for the chromatic differences between the source and destination white points.
This procedure simply converts the color specifications to XcmsCIELab using the source
white point and then converts to the target specification format using the destination's white
point. No client data is necessary.

XcmsCIELuvWhiteShiftColors
This uses the CIE L*u*v* color space for adjusting the chromatic character of colors to
compensate for the chromatic differences between the source and destination white points.
This procedure simply converts the color specifications to XcmsCIELuv using the source
white point and then converts to the target specification format using the destination's white
point. No client data is necessary.
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XcmsTekHVCWhiteShiftColors
This uses the TekHVC color space for adjusting the chromatic character of colors to com-
pensate for the chromatic differences between the source and destination white points. This
procedure simply converts the color specifications to XcmsTekHVC using the source
white point and then converts to the target specification format using the destination's white
point. An advantage of this procedure over those previously described is an attempt to min-
imize hue shift. No client data is necessary.
From an implementation point of view, these white point adjustment procedures convert the color
specifications to a device-independent but white-point-dependent color space (for example, CIE
L*u*v*, CIE L*a*b*, TekHVC) using one white point and then converting those specifications to
the target color space using another white point. In other words, the specification goes in the
color space with one white point but comes out with another white point, resulting in a chromatic
shift based on the chromatic displacement between the initial white point and target white point.
The CIE color spaces that are assumed to be white-point-independent are CIE u'v'Y, CIE XYZ,
and CIE xyY. When developing a custom white point adjustment procedure that uses a device-
independent color space not initially accessible for use in the color management system, use
XcmsAddColorSpace to ensure that it is added.
As an example, if the CCC specifies a white point adjustment procedure and if the Client White
Point and Screen White Point differ, the XcmsAllocColor function will use the white point
adjustment procedure twice:

Once to convert to XcmsRGB

A second time to convert from XcmsRGB
For example, assume the specification is in XcmsCIEuvY and the adjustment procedure is
XcmsCIELuvWhiteShiftColors. During conversion to XcmsRGB, the call to XcmsAlloc-
Color results in the following series of color specification conversions:

From XcmsCIEuvY to XcmsCIELuv using the Client White Point

From XcmsCIELuv to XcmsCIEuvY using the Screen White Point

From XcmsCIEuvY to XcmsCIEXYZ (CIE u'v'Y and XYZ are white-point-independent
color spaces)

From XcmsCIEXYZ to XcmsRGBi

From XcmsRGBi to XcmsRGB
The resulting RGB specification is passed to XAllocColor, and the RGB specification returned
by XAllocColor is converted back to XcmsCIEuvY by reversing the color conversion sequence.
6.11. Gamut Querying Functions
This section describes the gamut querying functions that Xlib provides. These functions allow
the client to query the boundary of the screen's color gamut in terms of the CIE L*a*b*, CIE
L*u*v*, and TekHVC color spaces. Functions are also provided that allow you to query the color
specification of:

White (full-intensity red, green, and blue)

Red (full-intensity red while green and blue are zero)

Green (full-intensity green while red and blue are zero)

Blue (full-intensity blue while red and green are zero)

Black (zero-intensity red, green, and blue)
The white point associated with color specifications passed to and returned from these gamut
querying functions is assumed to be the Screen White Point. This is a reasonable assumption,
because the client is trying to query the screen's color gamut.
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The following naming convention is used for the Max and Min functions:
Xcms<color_space>QueryMax<dimensions>
Xcms<color_space>QueryMin<dimensions>
The <dimensions> consists of a letter or letters that identify the dimensions of the color space that
are not fixed. For example, XcmsTekHVCQueryMaxC is given a fixed Hue and Value for
which maximum Chroma is found.
6.11.1. Red, Green, and Blue Queries
To obtain the color specification for black (zero-intensity red, green, and blue), use
XcmsQueryBlack.
Status XcmsQueryBlack(ccc, target_format, color_return)
XcmsCCC ccc;
XcmsColorFormat target_format;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
target_format
Specifies the target color specification format.
color_return
Returns the color specification in the specified target format for zero-intensity
red, green, and blue. The white point associated with the returned color specifi-
cation is the Screen White Point. The value returned in the pixel member is un-
defined.
The XcmsQueryBlack function returns the color specification in the specified target format for
zero-intensity red, green, and blue.
To obtain the color specification for blue (full-intensity blue while red and green are zero), use
XcmsQueryBlue.
Status XcmsQueryBlue(ccc, target_format, color_return)
XcmsCCC ccc;
XcmsColorFormat target_format;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
target_format
Specifies the target color specification format.
color_return
Returns the color specification in the specified target format for full-intensity
blue while red and green are zero. The white point associated with the returned
color specification is the Screen White Point. The value returned in the pixel
member is undefined.
The XcmsQueryBlue function returns the color specification in the specified target format for
full-intensity blue while red and green are zero.
To obtain the color specification for green (full-intensity green while red and blue are zero), use
XcmsQueryGreen.
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Status XcmsQueryGreen(ccc, target_format, color_return)
XcmsCCC ccc;
XcmsColorFormat target_format;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
target_format
Specifies the target color specification format.
color_return
Returns the color specification in the specified target format for full-intensity
green while red and blue are zero. The white point associated with the returned
color specification is the Screen White Point. The value returned in the pixel
member is undefined.
The XcmsQueryGreen function returns the color specification in the specified target format for
full-intensity green while red and blue are zero.
To obtain the color specification for red (full-intensity red while green and blue are zero), use
XcmsQueryRed.
Status XcmsQueryRed(ccc, target_format, color_return)
XcmsCCC ccc;
XcmsColorFormat target_format;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
target_format
Specifies the target color specification format.
color_return
Returns the color specification in the specified target format for full-intensity red
while green and blue are zero. The white point associated with the returned color
specification is the Screen White Point. The value returned in the pixel member
is undefined.
The XcmsQueryRed function returns the color specification in the specified target format for
full-intensity red while green and blue are zero.
To obtain the color specification for white (full-intensity red, green, and blue), use
XcmsQueryWhite.
Status XcmsQueryWhite(ccc, target_format, color_return)
XcmsCCC ccc;
XcmsColorFormat target_format;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
target_format
Specifies the target color specification format.
color_return
Returns the color specification in the specified target format for full-intensity red,
green, and blue. The white point associated with the returned color specification
is the Screen White Point. The value returned in the pixel member is undefined.
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The XcmsQueryWhite function returns the color specification in the specified target format for
full-intensity red, green, and blue.
6.11.2. CIELab Queries
The following equations are useful in describing the CIELab query functions:
CIELab Psychometric Chroma = sqrt(a_star2 + b_star2)
b_star
CIELab Psychometric Hue = tan-1

a_star
To obtain the CIE L*a*b* coordinates of maximum Psychometric Chroma for a given Psychome-
tric Hue Angle and CIE metric lightness (L*), use XcmsCIELabQueryMaxC.
Status XcmsCIELabQueryMaxC(ccc, hue_angle, L_star, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat L_star;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum chroma.
L_star
Specifies the lightness (L*) at which to find maximum chroma.
color_return
Returns the CIE L*a*b* coordinates of maximum chroma displayable by the
screen for the given hue angle and lightness. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELabQueryMaxC function, given a hue angle and lightness, finds the point of
maximum chroma displayable by the screen. It returns this point in CIE L*a*b* coordinates.
To obtain the CIE L*a*b* coordinates of maximum CIE metric lightness (L*) for a given Psycho-
metric Hue Angle and Psychometric Chroma, use XcmsCIELabQueryMaxL.
Status XcmsCIELabQueryMaxL(ccc, hue_angle, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum lightness.
chroma
Specifies the chroma at which to find maximum lightness.
color_return
Returns the CIE L*a*b* coordinates of maximum lightness displayable by the
screen for the given hue angle and chroma. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELabQueryMaxL function, given a hue angle and chroma, finds the point in CIE
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L*a*b* color space of maximum lightness (L*) displayable by the screen. It returns this point in
CIE L*a*b* coordinates. An XcmsFailure return value usually indicates that the given chroma
is beyond maximum for the given hue angle.
To obtain the CIE L*a*b* coordinates of maximum Psychometric Chroma for a given Psychome-
tric Hue Angle, use XcmsCIELabQueryMaxLC.
Status XcmsCIELabQueryMaxLC(ccc, hue_angle, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum chroma.
color_return
Returns the CIE L*a*b* coordinates of maximum chroma displayable by the
screen for the given hue angle. The white point associated with the returned col-
or specification is the Screen White Point. The value returned in the pixel mem-
ber is undefined.
The XcmsCIELabQueryMaxLC function, given a hue angle, finds the point of maximum
chroma displayable by the screen. It returns this point in CIE L*a*b* coordinates.
To obtain the CIE L*a*b* coordinates of minimum CIE metric lightness (L*) for a given Psycho-
metric Hue Angle and Psychometric Chroma, use XcmsCIELabQueryMinL.
Status XcmsCIELabQueryMinL(ccc, hue_angle, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find minimum lightness.
chroma
Specifies the chroma at which to find minimum lightness.
color_return
Returns the CIE L*a*b* coordinates of minimum lightness displayable by the
screen for the given hue angle and chroma. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELabQueryMinL function, given a hue angle and chroma, finds the point of mini-
mum lightness (L*) displayable by the screen. It returns this point in CIE L*a*b* coordinates.
An XcmsFailure return value usually indicates that the given chroma is beyond maximum for the
given hue angle.
6.11.3. CIELuv Queries
The following equations are useful in describing the CIELuv query functions:
CIELuv Psychometric Chroma = sqrt(u_star2 + v_star2)
v_star
CIELuv Psychometric Hue = tan-1 u_star
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To obtain the CIE L*u*v* coordinates of maximum Psychometric Chroma for a given Psychome-
tric Hue Angle and CIE metric lightness (L*), use XcmsCIELuvQueryMaxC.
Status XcmsCIELuvQueryMaxC(ccc, hue_angle, L_star, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat L_star;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum chroma.
L_star
Specifies the lightness (L*) at which to find maximum chroma.
color_return
Returns the CIE L*u*v* coordinates of maximum chroma displayable by the
screen for the given hue angle and lightness. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELuvQueryMaxC function, given a hue angle and lightness, finds the point of
maximum chroma displayable by the screen. It returns this point in CIE L*u*v* coordinates.
To obtain the CIE L*u*v* coordinates of maximum CIE metric lightness (L*) for a given Psycho-
metric Hue Angle and Psychometric Chroma, use XcmsCIELuvQueryMaxL.
Status XcmsCIELuvQueryMaxL(ccc, hue_angle, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum lightness.
L_star
Specifies the lightness (L*) at which to find maximum lightness.
color_return
Returns the CIE L*u*v* coordinates of maximum lightness displayable by the
screen for the given hue angle and chroma. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELuvQueryMaxL function, given a hue angle and chroma, finds the point in CIE
L*u*v* color space of maximum lightness (L*) displayable by the screen. It returns this point in
CIE L*u*v* coordinates. An XcmsFailure return value usually indicates that the given chroma
is beyond maximum for the given hue angle.
To obtain the CIE L*u*v* coordinates of maximum Psychometric Chroma for a given Psychome-
tric Hue Angle, use XcmsCIELuvQueryMaxLC.
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Status XcmsCIELuvQueryMaxLC(ccc, hue_angle, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find maximum chroma.
color_return
Returns the CIE L*u*v* coordinates of maximum chroma displayable by the
screen for the given hue angle. The white point associated with the returned col-
or specification is the Screen White Point. The value returned in the pixel mem-
ber is undefined.
The XcmsCIELuvQueryMaxLC function, given a hue angle, finds the point of maximum
chroma displayable by the screen. It returns this point in CIE L*u*v* coordinates.
To obtain the CIE L*u*v* coordinates of minimum CIE metric lightness (L*) for a given Psycho-
metric Hue Angle and Psychometric Chroma, use XcmsCIELuvQueryMinL.
Status XcmsCIELuvQueryMinL(ccc, hue_angle, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue_angle;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue_angle
Specifies the hue angle (in degrees) at which to find minimum lightness.
chroma
Specifies the chroma at which to find minimum lightness.
color_return
Returns the CIE L*u*v* coordinates of minimum lightness displayable by the
screen for the given hue angle and chroma. The white point associated with the
returned color specification is the Screen White Point. The value returned in the
pixel member is undefined.
The XcmsCIELuvQueryMinL function, given a hue angle and chroma, finds the point of mini-
mum lightness (L*) displayable by the screen. It returns this point in CIE L*u*v* coordinates.
An XcmsFailure return value usually indicates that the given chroma is beyond maximum for the
given hue angle.
6.11.4. TekHVC Queries
To obtain the maximum Chroma for a given Hue and Value, use XcmsTekHVCQueryMaxC.
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Status XcmsTekHVCQueryMaxC (ccc, hue, value, color_return)
XcmsCCC ccc;
XcmsFloat hue;
XcmsFloat value;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue
Specifies the Hue in which to find the maximum Chroma.
value
Specifies the Value in which to find the maximum Chroma.
color_return
Returns the maximum Chroma along with the actual Hue and Value at which the
maximum Chroma was found. The white point associated with the returned col-
or specification is the Screen White Point. The value returned in the pixel mem-
ber is undefined.
The XcmsTekHVCQueryMaxC function, given a Hue and Value, determines the maximum
Chroma in TekHVC color space displayable by the screen. It returns the maximum Chroma
along with the actual Hue and Value at which the maximum Chroma was found.
To obtain the maximum Value for a given Hue and Chroma, use XcmsTekHVCQueryMaxV.
Status XcmsTekHVCQueryMaxV (ccc, hue, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue
Specifies the Hue in which to find the maximum Value.
chroma
Specifies the chroma at which to find maximum Value.
color_return
Returns the maximum Value along with the Hue and Chroma at which the maxi-
mum Value was found. The white point associated with the returned color speci-
fication is the Screen White Point. The value returned in the pixel member is un-
defined.
The XcmsTekHVCQueryMaxV function, given a Hue and Chroma, determines the maximum
Value in TekHVC color space displayable by the screen. It returns the maximum Value and the
actual Hue and Chroma at which the maximum Value was found.
To obtain the maximum Chroma and Value at which it is reached for a specified Hue, use
XcmsTekHVCQueryMaxVC.
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Status XcmsTekHVCQueryMaxVC (ccc, hue, color_return)
XcmsCCC ccc;
XcmsFloat hue;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue
Specifies the Hue in which to find the maximum Chroma.
color_return
Returns the color specification in XcmsTekHVC for the maximum Chroma, the
Value at which that maximum Chroma is reached, and the actual Hue at which
the maximum Chroma was found. The white point associated with the returned
color specification is the Screen White Point. The value returned in the pixel
member is undefined.
The XcmsTekHVCQueryMaxVC function, given a Hue, determines the maximum Chroma in
TekHVC color space displayable by the screen and the Value at which that maximum Chroma is
reached. It returns the maximum Chroma, the Value at which that maximum Chroma is reached,
and the actual Hue for which the maximum Chroma was found.
To obtain a specified number of TekHVC specifications such that they contain maximum Values
for a specified Hue and the Chroma at which the maximum Values are reached, use
XcmsTekHVCQueryMaxVSamples.
Status XcmsTekHVCQueryMaxVSamples (ccc, hue, colors_return, nsamples)
XcmsCCC ccc;
XcmsFloat hue;
XcmsColor colors_return[];
unsigned int nsamples;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue
Specifies the Hue for maximum Chroma/Value samples.
nsamples
Specifies the number of samples.
colors_return
Returns nsamples of color specifications in XcmsTekHVC such that the Chroma
is the maximum attainable for the Value and Hue. The white point associated
with the returned color specification is the Screen White Point. The value re-
turned in the pixel member is undefined.
The XcmsTekHVCQueryMaxVSamples returns nsamples of maximum Value, the Chroma at
which that maximum Value is reached, and the actual Hue for which the maximum Chroma was
found. These sample points may then be used to plot the maximum Value/Chroma boundary of
the screen's color gamut for the specified Hue in TekHVC color space.
To obtain the minimum Value for a given Hue and Chroma, use XcmsTekHVCQueryMinV.
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Status XcmsTekHVCQueryMinV (ccc, hue, chroma, color_return)
XcmsCCC ccc;
XcmsFloat hue;
XcmsFloat chroma;
XcmsColor *color_return;
ccc
Specifies the CCC. The CCC's Client White Point and white point adjustment
procedures are ignored.
hue
Specifies the Hue in which to find the minimum Value.
value
Specifies the Value in which to find the minimum Value.
color_return
Returns the minimum Value and the actual Hue and Chroma at which the mini-
mum Value was found. The white point associated with the returned color speci-
fication is the Screen White Point. The value returned in the pixel member is un-
defined.
The XcmsTekHVCQueryMinV function, given a Hue and Chroma, determines the minimum
Value in TekHVC color space displayable by the screen. It returns the minimum Value and the
actual Hue and Chroma at which the minimum Value was found.
6.12. Color Management Extensions
The Xlib color management facilities can be extended in two ways:

Device-Independent Color Spaces
Device-independent color spaces that are derivable to CIE XYZ space can be added using
the XcmsAddColorSpace function.

Color Characterization Function Set
A Color Characterization Function Set consists of device-dependent color spaces and their
functions that convert between these color spaces and the CIE XYZ color space, bundled
together for a specific class of output devices. A function set can be added using the Xcm-
sAddFunctionSet
function.
6.12.1. Color Spaces
The CIE XYZ color space serves as the hub for all conversions between device-independent and
device-dependent color spaces. Therefore, the knowledge to convert an XcmsColor structure to
and from CIE XYZ format is associated with each color space. For example, conversion from
CIE L*u*v* to RGB requires the knowledge to convert from CIE L*u*v* to CIE XYZ and from
CIE XYZ to RGB. This knowledge is stored as an array of functions that, when applied in series,
will convert the XcmsColor structure to or from CIE XYZ format. This color specification con-
version mechanism facilitates the addition of color spaces.
Of course, when converting between only device-independent color spaces or only device-depen-
dent color spaces, shortcuts are taken whenever possible. For example, conversion from TekHVC
to CIE L*u*v* is performed by intermediate conversion to CIE u*v*Y and then to CIE L*u*v*,
thus bypassing conversion between CIE u*v*Y and CIE XYZ.
6.12.2. Adding Device-Independent Color Spaces
To add a device-independent color space, use XcmsAddColorSpace.
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Status XcmsAddColorSpace(color_space)
XcmsColorSpace *color_space;
color_space
Specifies the device-independent color space to add.
The XcmsAddColorSpace function makes a device-independent color space (actually an Xcms-
ColorSpace
structure) accessible by the color management system. Because format values for
unregistered color spaces are assigned at run time, they should be treated as private to the client.
If references to an unregistered color space must be made outside the client (for example, storing
color specifications in a file using the unregistered color space), then reference should be made by
color space prefix (see XcmsFormatOfPrefix and XcmsPrefixOfFormat).
If the XcmsColorSpace structure is already accessible in the color management system, Xcm-
sAddColorSpace
returns XcmsSuccess.
Note that added XcmsColorSpaces must be retained for reference by Xlib.
6.12.3. Querying Color Space Format and Prefix
To obtain the format associated with the color space associated with a specified color string pre-
fix, use XcmsFormatOfPrefix.
XcmsColorFormat XcmsFormatOfPrefix (prefix)
char *prefix;
prefix
Specifies the string that contains the color space prefix.
The XcmsFormatOfPrefix function returns the format for the specified color space prefix (for
example, the string ``CIEXYZ''). The prefix is case-insensitive. If the color space is not accessi-
ble in the color management system, XcmsFormatOfPrefix returns XcmsUndefinedFormat.
To obtain the color string prefix associated with the color space specified by a color format, use
XcmsPrefixOfFormat.
char *XcmsPrefixOfFormat (format)
XcmsColorFormat format;
format
Specifies the color specification format.
The XcmsPrefixOfFormat function returns the string prefix associated with the color specifica-
tion encoding specified by the format argument. Otherwise, if no encoding is found, it returns
NULL. The returned string must be treated as read-only.
6.12.4. Creating Additional Color Spaces
Color space specific information necessary for color space conversion and color string parsing is
stored in an XcmsColorSpace structure. Therefore, a new structure containing this information
is required for each additional color space. In the case of device-independent color spaces, a han-
dle to this new structure (that is, by means of a global variable) is usually made accessible to the
client program for use with the XcmsAddColorSpace function.
If a new XcmsColorSpace structure specifies a color space not registered with the X Consor-
tium, they should be treated as private to the client because format values for unregistered color
spaces are assigned at run time. If references to an unregistered color space must be made outside
the client (for example, storing color specifications in a file using the unregistered color space),
then reference should be made by color space prefix (see XcmsFormatOfPrefix and
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XcmsPrefixOfFormat).
typedef (*XcmsConversionProc)();
typedef XcmsConversionProc *XcmsFuncListPtr;
/* A NULL terminated list of function pointers*/
typedef struct _XcmsColorSpace {
char *prefix;
XcmsColorFormat format;
XcmsParseStringProc parseString;
XcmsFuncListPtr to_CIEXYZ;
XcmsFuncListPtr from_CIEXYZ;
int inverse_flag;
} XcmsColorSpace;
The prefix member specifies the prefix that indicates a color string is in this color space's string
format. For example, the strings ``ciexyz'' or ``CIEXYZ'' for CIE XYZ, and ``rgb'' or ``RGB''
for RGB. The prefix is case insensitive. The format member specifies the color specification for-
mat. Formats for unregistered color spaces are assigned at run time. The parseString member
contains a pointer to the function that can parse a color string into an XcmsColor structure. This
function returns an integer (int): nonzero if it succeeded and zero otherwise. The to_CIEXYZ
and from_CIEXYZ members contain pointers, each to a NULL terminated list of function point-
ers. When the list of functions is executed in series, it will convert the color specified in an Xcm-
sColor
structure from/to the current color space format to/from the CIE XYZ format. Each func-
tion returns an integer (int): nonzero if it succeeded and zero otherwise. The white point to be
associated with the colors is specified explicitly, even though white points can be found in the
CCC. The inverse_flag member, if nonzero, specifies that for each function listed in to_CIEXYZ,
its inverse function can be found in from_CIEXYZ such that:
Given: n = number of functions in each list
for each i, such that 0 <= i < n
from_CIEXYZ[n - i - 1] is the inverse of to_CIEXYZ[i].
This allows Xlib to use the shortest conversion path, thus bypassing CIE XYZ if possible (for
example, TekHVC to CIE L*u*v*).
6.12.5. Parse String Callback
The callback in the XcmsColorSpace structure for parsing a color string for the particular color
space must adhere to the following software interface specification:
typedef int (*XcmsParseStringProc) (color_string, color_return)
char *color_string;
XcmsColor *color_return;
color_string
Specifies the color string to parse.
color_return
Returns the color specification in the color space's format.
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6.12.6. Color Specification Conversion Callback
Callback functions in the XcmsColorSpace structure for converting a color specification
between device-independent spaces must adhere to the following software interface specification:
Status ConversionProc (ccc, white_point, colors_in_out, ncolors)
XcmsCCC ccc;
XcmsColor *white_point;
XcmsColor *colors_in_out;
unsigned int ncolors;
ccc
Specifies the CCC.
white_point
Specifies the white point associated with color specifications. The pixel member
should be ignored, and the entire structure remain unchanged upon return.
colors_in_out
Specifies an array of color specifications. Pixel members should be ignored and
must remain unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
Callback functions in the XcmsColorSpace structure for converting a color specification to or
from a device-dependent space must adhere to the following software interface specification:
Status ConversionProc (ccc, colors_in_out, ncolors, compression_flags_return)
XcmsCCC ccc;
XcmsColor *colors_in_out;
unsigned int ncolors;
Bool compression_flags_return[];
ccc
Specifies the CCC.
colors_in_out
Specifies an array of color specifications. Pixel members should be ignored and
must remain unchanged upon return.
ncolors
Specifies the number of XcmsColor structures in the color-specification array.
compression_flags_return
Returns an array of Boolean values for indicating compression status. If a non-
NULL pointer is supplied and a color at a given index is compressed, then True
should be stored at the corresponding index in this array; otherwise, the array
should not be modified.
Conversion functions are available globally for use by other color spaces. The conversion func-
tions provided by Xlib are:
Function Converts from Converts to
XcmsCIELabToCIEXYZ
XcmsCIELabFormat
XcmsCIEXYZFormat
XcmsCIELuvToCIEuvY
XcmsCIELuvFormat
XcmsCIEuvYFormat
XcmsCIEXYZToCIELab
XcmsCIEXYZFormat
XcmsCIELabFormat
XcmsCIEXYZToCIEuvY
XcmsCIEXYZFormat
XcmsCIEuvYFormat
XcmsCIEXYZToCIExyY
XcmsCIEXYZFormat
XcmsCIExyYFormat
XcmsCIEXYZToRGBi
XcmsCIEXYZFormat
XcmsRGBiFormat
XcmsCIEuvYToCIELuv
XcmsCIEuvYFormat
XcmsCIELabFormat
XcmsCIEuvYToCIEXYZ
XcmsCIEuvYFormat
XcmsCIEXYZFormat
XcmsCIEuvYToTekHVC
XcmsCIEuvYFormat
XcmsTekHVCFormat
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Function Converts from Converts to
XcmsCIExyYToCIEXYZ
XcmsCIExyYFormat
XcmsCIEXYZFormat
XcmsRGBToRGBi
XcmsRGBFormat
XcmsRGBiFormat
XcmsRGBiToCIEXYZ
XcmsRGBiFormat
XcmsCIEXYZFormat
XcmsRGBiToRGB
XcmsRGBiFormat
XcmsRGBFormat
XcmsTekHVCToCIEuvY
XcmsTekHVCFormat
XcmsCIEuvYFormat
6.12.7. Function Sets
Functions to convert between device-dependent color spaces and CIE XYZ may differ for differ-
ent classes of output devices (for example, color versus gray monitors). Therefore, the notion of a
Color Characterization Function Set has been developed. A function set consists of device-
dependent color spaces and the functions that convert color specifications between these device-
dependent color spaces and the CIE XYZ color space appropriate for a particular class of output
devices. The function set also contains a function that reads color characterization data off root
window properties. It is this characterization data that will differ between devices within a class
of output devices. For details about how color characterization data is stored in root window
properties, see the section on Device Color Characterization in the Inter-Client Communication
Conventions Manual
. The LINEAR_RGB function set is provided by Xlib and will support most
color monitors. Function sets may require data that differs from those needed for the LIN-
EAR_RGB function set. In that case, its corresponding data may be stored on different root win-
dow properties.
6.12.8. Adding Function Sets
To add a function set, use XcmsAddFunctionSet.
Status XcmsAddFunctionSet(function_set)
XcmsFunctionSet *function_set;
function_set
Specifies the function set to add.
The XcmsAddFunctionSet function adds a function set to the color management system. If the
function set uses device-dependent XcmsColorSpace structures not accessible in the color man-
agement system, XcmsAddFunctionSet adds them. If an added XcmsColorSpace structure is
for a device-dependent color space not registered with the X Consortium, they should be treated
as private to the client because format values for unregistered color spaces are assigned at run
time. If references to an unregistered color space must be made outside the client (for example,
storing color specifications in a file using the unregistered color space), then reference should be
made by color space prefix (see XcmsFormatOfPrefix and XcmsPrefixOfFormat).
Additional function sets should be added before any calls to other Xlib routines are made. If not,
the XcmsPerScrnInfo member of a previously created XcmsCCC does not have the opportunity
to initialize with the added function set.
6.12.9. Creating Additional Function Sets
The creation of additional function sets should be required only when an output device does not
conform to existing function sets or when additional device-dependent color spaces are necessary.
A function set consists primarily of a collection of device-dependent XcmsColorSpace struc-
tures and a means to read and store a screen's color characterization data. This data is stored in
an XcmsFunctionSet structure. A handle to this structure (that is, by means of global variable)
is usually made accessible to the client program for use with XcmsAddFunctionSet.
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If a function set uses new device-dependent XcmsColorSpace structures, they will be transpar-
ently processed into the color management system. Function sets can share an XcmsColorSpace
structure for a device-dependent color space. In addition, multiple XcmsColorSpace structures
are allowed for a device-dependent color space; however, a function set can reference only one of
them. These XcmsColorSpace structures will differ in the functions to convert to and from CIE
XYZ, thus tailored for the specific function set.
typedef struct _XcmsFunctionSet {
XcmsColorSpace **DDColorSpaces;
XcmsScreenInitProc screenInitProc;
XcmsScreenFreeProc screenFreeProc;
} XcmsFunctionSet;
The DDColorSpaces member is a pointer to a NULL terminated list of pointers to XcmsCol-
orSpace
structures for the device-dependent color spaces that are supported by the function set.
The screenInitProc member is set to the callback procedure (see the following interface specifica-
tion) that initializes the XcmsPerScrnInfo structure for a particular screen.
The screen initialization callback must adhere to the following software interface specification:
typedef Status (*XcmsScreenInitProc)(display, screen_number, screen_info)
Display *display;
int screen_number;
XcmsPerScrnInfo *screen_info;
display
Specifies the connection to the X server.
screen_number Specifies the appropriate screen number on the host server.
screen_info
Specifies the XcmsPerScrnInfo structure, which contains the per screen infor-
mation.
The screen initialization callback in the XcmsFunctionSet structure fetches the color characteri-
zation data (device profile) for the specified screen, typically off properties on the screen's root
window. It then initializes the specified XcmsPerScrnInfo structure. If successful, the proce-
dure fills in the XcmsPerScrnInfo structure as follows:

It sets the screenData member to the address of the created device profile data structure
(contents known only by the function set).

It next sets the screenWhitePoint member.

It next sets the functionSet member to the address of the XcmsFunctionSet structure.

It then sets the state member to XcmsInitSuccess and finally returns XcmsSuccess.
If unsuccessful, the procedure sets the state member to XcmsInitFailure and returns
XcmsFailure.
The XcmsPerScrnInfo structure contains:
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typedef struct _XcmsPerScrnInfo {
XcmsColor screenWhitePoint;
XPointer functionSet;
XPointer screenData;
unsigned char state;
char pad[3];
} XcmsPerScrnInfo;
The screenWhitePoint member specifies the white point inherent to the screen. The functionSet
member specifies the appropriate function set. The screenData member specifies the device pro-
file. The state member is set to one of the following:

XcmsInitNone indicates initialization has not been previously attempted.

XcmsInitFailure indicates initialization has been previously attempted but failed.

XcmsInitSuccess indicates initialization has been previously attempted and succeeded.
The screen free callback must adhere to the following software interface specification:
typedef void (*XcmsScreenFreeProc)(screenData)
XPointer screenData;
screenData
Specifies the data to be freed.
This function is called to free the screenData stored in an XcmsPerScrnInfo structure.
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Chapter 7
Graphics Context Functions
A number of resources are used when performing graphics operations in X. Most information
about performing graphics (for example, foreground color, background color, line style, and so
on) is stored in resources called graphics contexts (GCs). Most graphics operations (see chapter
8) take a GC as an argument. Although in theory the X protocol permits sharing of GCs between
applications, it is expected that applications will use their own GCs when performing operations.
Sharing of GCs is highly discouraged because the library may cache GC state.
Graphics operations can be performed to either windows or pixmaps, which collectively are
called drawables. Each drawable exists on a single screen. A GC is created for a specific screen
and drawable depth and can only be used with drawables of matching screen and depth.
This chapter discusses how to:

Manipulate graphics context/state

Use graphics context convenience functions
7.1. Manipulating Graphics Context/State
Most attributes of graphics operations are stored in GCs. These include line width, line style,
plane mask, foreground, background, tile, stipple, clipping region, end style, join style, and so on.
Graphics operations (for example, drawing lines) use these values to determine the actual drawing
operation. Extensions to X may add additional components to GCs. The contents of a GC are
private to Xlib.
Xlib implements a write-back cache for all elements of a GC that are not resource IDs to allow
Xlib to implement the transparent coalescing of changes to GCs. For example, a call to XSet-
Foreground
of a GC followed by a call to XSetLineAttributes results in only a single-change
GC protocol request to the server. GCs are neither expected nor encouraged to be shared between
client applications, so this write-back caching should present no problems. Applications cannot
share GCs without external synchronization. Therefore, sharing GCs between applications is
highly discouraged.
To set an attribute of a GC, set the appropriate member of the XGCValues structure and OR in
the corresponding value bitmask in your subsequent calls to XCreateGC. The symbols for the
value mask bits and the XGCValues structure are:
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/* GC attribute value mask bits */
#define
GCFunction
(1L<<0)
#define
GCPlaneMask
(1L<<1)
#define
GCForeground
(1L<<2)
#define
GCBackground
(1L<<3)
#define
GCLineWidth
(1L<<4)
#define
GCLineStyle
(1L<<5)
#define
GCCapStyle
(1L<<6)
#define
GCJoinStyle
(1L<<7)
#define
GCFillStyle
(1L<<8)
#define
GCFillRule
(1L<<9)
#define
GCTile
(1L<<10)
#define
GCStipple
(1L<<11)
#define
GCTileStipXOrigin
(1L<<12)
#define
GCTileStipYOrigin
(1L<<13)
#define
GCFont
(1L<<14)
#define
GCSubwindowMode
(1L<<15)
#define
GCGraphicsExposures
(1L<<16)
#define
GCClipXOrigin
(1L<<17)
#define
GCClipYOrigin
(1L<<18)
#define
GCClipMask
(1L<<19)
#define
GCDashOffset
(1L<<20)
#define
GCDashList
(1L<<21)
#define
GCArcMode
(1L<<22)
/* Values */
typedef struct {
int function;
/* logical operation */
unsigned long plane_mask;
/* plane mask */
unsigned long foreground; /* foreground pixel */
unsigned long background;
/* background pixel */
int line_width;
/* line width (in pixels) */
int line_style;
/* LineSolid, LineOnOffDash, LineDoubleDash */
int cap_style;
/* CapNotLast, CapButt, CapRound, CapProjecting */
int join_style;
/* JoinMiter, JoinRound, JoinBevel */
int fill_style;
/* FillSolid, FillTiled, FillStippled FillOpaqueStippled*/
int fill_rule;
/* EvenOddRule, WindingRule */
int arc_mode;
/* ArcChord, ArcPieSlice */
Pixmap tile;
/* tile pixmap for tiling operations */
Pixmap stipple;
/* stipple 1 plane pixmap for stippling */
int ts_x_origin;
/* offset for tile or stipple operations */
int ts_y_origin;
Font font;
/* default text font for text operations */
int subwindow_mode; /* ClipByChildren, IncludeInferiors */
Bool graphics_exposures; /* boolean, should exposures be generated */
int clip_x_origin;
/* origin for clipping */
int clip_y_origin;
Pixmap clip_mask;
/* bitmap clipping; other calls for rects */
int dash_offset; /* patterned/dashed line information */
char dashes;
} XGCValues;
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The default GC values are:
Component Default
function
GXcopy
plane_mask All ones
foreground 0
background 1
line_width 0
line_style
LineSolid
cap_style
CapButt
join_style
JoinMiter
fill_style
FillSolid
fill_rule
EvenOddRule
arc_mode
ArcPieSlice
tile Pixmap of unspecified size filled with foreground pixel
(that is, client specified pixel if any, else 0)
(subsequent changes to foreground do not affect this pixmap)
stipple Pixmap of unspecified size filled with ones
ts_x_origin 0
ts_y_origin 0
font <implementation dependent>
subwindow_mode
ClipByChildren
graphics_exposures
True
clip_x_origin 0
clip_y_origin 0
clip_mask
None
dash_offset 0
dashes 4 (that is, the list [4, 4])
Note that foreground and background are not set to any values likely to be useful in a window.
The function attributes of a GC are used when you update a section of a drawable (the destina-
tion) with bits from somewhere else (the source). The function in a GC defines how the new des-
tination bits are to be computed from the source bits and the old destination bits. GXcopy is typ-
ically the most useful because it will work on a color display, but special applications may use
other functions, particularly in concert with particular planes of a color display. The 16 GC func-
tions, defined in <X11/X.h>, are:
Function Name
Value Operation
GXclear
0x0
0
GXand
0x1
src AND dst
GXandReverse
0x2
src AND NOT dst
GXcopy
0x3
src
GXandInverted
0x4
(NOT src) AND dst
GXnoop
0x5
dst
GXxor
0x6
src XOR dst
GXor
0x7
src OR dst
GXnor
0x8
(NOT src) AND (NOT dst)
GXequiv
0x9
(NOT src) XOR dst
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Function Name
Value Operation
GXinvert
0xa
NOT dst
GXorReverse
0xb
src OR (NOT dst)
GXcopyInverted
0xc
NOT src
GXorInverted
0xd
(NOT src) OR dst
GXnand
0xe
(NOT src) OR (NOT dst)
GXset
0xf
1
Many graphics operations depend on either pixel values or planes in a GC. The planes attribute is
of type long, and it specifies which planes of the destination are to be modified, one bit per plane.
A monochrome display has only one plane and will be the least significant bit of the word. As
planes are added to the display hardware, they will occupy more significant bits in the plane
mask.
In graphics operations, given a source and destination pixel, the result is computed bitwise on cor-
responding bits of the pixels. That is, a Boolean operation is performed in each bit plane. The
plane_mask restricts the operation to a subset of planes. A macro constant AllPlanes can be used
to refer to all planes of the screen simultaneously. The result is computed by the following:
((src FUNC dst) AND plane-mask) OR (dst AND (NOT plane-mask))
Range checking is not performed on the values for foreground, background, or plane_mask. They
are simply truncated to the appropriate number of bits. The line-width is measured in pixels and
either can be greater than or equal to one (wide line) or can be the special value zero (thin line).
Wide lines are drawn centered on the path described by the graphics request. Unless otherwise
specified by the join-style or cap-style, the bounding box of a wide line with endpoints [x1, y1],
[x2, y2] and width w is a rectangle with vertices at the following real coordinates:
[x1-(w*sn/2), y1+(w*cs/2)], [x1+(w*sn/2), y1-(w*cs/2)],
[x2-(w*sn/2), y2+(w*cs/2)], [x2+(w*sn/2), y2-(w*cs/2)]
Here sn is the sine of the angle of the line, and cs is the cosine of the angle of the line. A pixel is
part of the line and so is drawn if the center of the pixel is fully inside the bounding box (which is
viewed as having infinitely thin edges). If the center of the pixel is exactly on the bounding box,
it is part of the line if and only if the interior is immediately to its right (x increasing direction).
Pixels with centers on a horizontal edge are a special case and are part of the line if and only if
the interior or the boundary is immediately below (y increasing direction) and the interior or the
boundary is immediately to the right (x increasing direction).
Thin lines (zero line-width) are one-pixel-wide lines drawn using an unspecified, device-depen-
dent algorithm. There are only two constraints on this algorithm.
1. If a line is drawn unclipped from [x1,y1] to [x2,y2] and if another line is drawn unclipped
from [x1+dx,y1+dy] to [x2+dx,y2+dy], a point [x,y] is touched by drawing the first line if
and only if the point [x+dx,y+dy] is touched by drawing the second line.
2. The effective set of points comprising a line cannot be affected by clipping. That is, a point
is touched in a clipped line if and only if the point lies inside the clipping region and the
point would be touched by the line when drawn unclipped.
A wide line drawn from [x1,y1] to [x2,y2] always draws the same pixels as a wide line drawn
from [x2,y2] to [x1,y1], not counting cap-style and join-style. It is recommended that this prop-
erty be true for thin lines, but this is not required. A line-width of zero may differ from a line-
width of one in which pixels are drawn. This permits the use of many manufacturers' line draw-
ing hardware, which may run many times faster than the more precisely specified wide lines.
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In general, drawing a thin line will be faster than drawing a wide line of width one. However,
because of their different drawing algorithms, thin lines may not mix well aesthetically with wide
lines. If it is desirable to obtain precise and uniform results across all displays, a client should
always use a line-width of one rather than a line-width of zero.
The line-style defines which sections of a line are drawn:
LineSolid
The full path of the line is drawn.
LineDoubleDash
The full path of the line is drawn, but the even dashes are filled differ-
ently from the odd dashes (see fill-style) with CapButt style used where
ev en and odd dashes meet.
LineOnOffDash
Only the even dashes are drawn, and cap-style applies to all internal ends
of the individual dashes, except CapNotLast is treated as CapButt.
The cap-style defines how the endpoints of a path are drawn:
CapNotLast
This is equivalent to CapButt except that for a line-width of zero the
final endpoint is not drawn.
CapButt
The line is square at the endpoint (perpendicular to the slope of the line)
with no projection beyond.
CapRound
The line has a circular arc with the diameter equal to the line-width, cen-
tered on the endpoint. (This is equivalent to CapButt for line-width of
zero).
CapProjecting
The line is square at the end, but the path continues beyond the endpoint
for a distance equal to half the line-width. (This is equivalent to Cap-
Butt
for line-width of zero).
The join-style defines how corners are drawn for wide lines:
JoinMiter
The outer edges of two lines extend to meet at an angle. However, if the
angle is less than 11 degrees, then a JoinBevel join-style is used instead.
JoinRound
The corner is a circular arc with the diameter equal to the line-width,
centered on the joinpoint.
JoinBevel
The corner has CapButt endpoint styles with the triangular notch filled.
For a line with coincident endpoints (x1=x2, y1=y2), when the cap-style is applied to both end-
points, the semantics depends on the line-width and the cap-style:
CapNotLast
thin
The results are device dependent, but the desired effect is that
nothing is drawn.
CapButt
thin
The results are device dependent, but the desired effect is that a
single pixel is drawn.
CapRound
thin
The results are the same as for CapButt/thin.
CapProjecting
thin
The results are the same as for CapButt/thin.
CapButt
wide
Nothing is drawn.
CapRound
wide
The closed path is a circle, centered at the endpoint, and with the
diameter equal to the line-width.
CapProjecting
wide
The closed path is a square, aligned with the coordinate axes,
centered at the endpoint, and with the sides equal to the line-
width.
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For a line with coincident endpoints (x1=x2, y1=y2), when the join-style is applied at one or both
endpoints, the effect is as if the line was removed from the overall path. However, if the total path
consists of or is reduced to a single point joined with itself, the effect is the same as when the cap-
style is applied at both endpoints.
The tile/stipple represents an infinite two-dimensional plane, with the tile/stipple replicated in all
dimensions. When that plane is superimposed on the drawable for use in a graphics operation,
the upper-left corner of some instance of the tile/stipple is at the coordinates within the drawable
specified by the tile/stipple origin. The tile/stipple and clip origins are interpreted relative to the
origin of whatever destination drawable is specified in a graphics request. The tile pixmap must
have the same root and depth as the GC, or a BadMatch error results. The stipple pixmap must
have depth one and must have the same root as the GC, or a BadMatch error results. For stipple
operations where the fill-style is FillStippled but not FillOpaqueStippled, the stipple pattern is
tiled in a single plane and acts as an additional clip mask to be ANDed with the clip-mask.
Although some sizes may be faster to use than others, any size pixmap can be used for tiling or
stippling.
The fill-style defines the contents of the source for line, text, and fill requests. For all text and fill
requests (for example, XDrawText, XDrawText16, XFillRectangle, XFillPolygon, and
XFillArc); for line requests with line-style LineSolid (for example, XDrawLine,
XDrawSegments, XDrawRectangle, XDrawArc); and for the even dashes for line requests
with line-style LineOnOffDash or LineDoubleDash, the following apply:
FillSolid
Foreground
FillTiled
Tile
FillOpaqueStippled
A tile with the same width and height as stipple, but with back-
ground everywhere stipple has a zero and with foreground every-
where stipple has a one
FillStippled
Foreground masked by stipple
When drawing lines with line-style LineDoubleDash, the odd dashes are controlled by the fill-
style in the following manner:
FillSolid
Background
FillTiled
Same as for even dashes
FillOpaqueStippled
Same as for even dashes
FillStippled
Background masked by stipple
Storing a pixmap in a GC might or might not result in a copy being made. If the pixmap is later
used as the destination for a graphics request, the change might or might not be reflected in the
GC. If the pixmap is used simultaneously in a graphics request both as a destination and as a tile
or stipple, the results are undefined.
For optimum performance, you should draw as much as possible with the same GC (without
changing its components). The costs of changing GC components relative to using different GCs
depend on the display hardware and the server implementation. It is quite likely that some
amount of GC information will be cached in display hardware and that such hardware can only
cache a small number of GCs.
The dashes value is actually a simplified form of the more general patterns that can be set with
XSetDashes. Specifying a value of N is equivalent to specifying the two-element list [N, N] in
XSetDashes. The value must be nonzero, or a BadValue error results.
The clip-mask restricts writes to the destination drawable. If the clip-mask is set to a pixmap, it
must have depth one and have the same root as the GC, or a BadMatch error results. If clip-
mask is set to None, the pixels are always drawn regardless of the clip origin. The clip-mask also
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can be set by calling the XSetClipRectangles or XSetRegion functions. Only pixels where the
clip-mask has a bit set to 1 are drawn. Pixels are not drawn outside the area covered by the clip-
mask or where the clip-mask has a bit set to 0. The clip-mask affects all graphics requests. The
clip-mask does not clip sources. The clip-mask origin is interpreted relative to the origin of what-
ev er destination drawable is specified in a graphics request.
You can set the subwindow-mode to ClipByChildren or IncludeInferiors. For
ClipByChildren, both source and destination windows are additionally clipped by all viewable
InputOutput children. For IncludeInferiors, neither source nor destination window is clipped
by inferiors. This will result in including subwindow contents in the source and drawing through
subwindow boundaries of the destination. The use of IncludeInferiors on a window of one
depth with mapped inferiors of differing depth is not illegal, but the semantics are undefined by
the core protocol.
The fill-rule defines what pixels are inside (drawn) for paths given in XFillPolygon requests and
can be set to EvenOddRule or WindingRule. For EvenOddRule, a point is inside if an infinite
ray with the point as origin crosses the path an odd number of times. For WindingRule, a point
is inside if an infinite ray with the point as origin crosses an unequal number of clockwise and
counterclockwise directed path segments. A clockwise directed path segment is one that crosses
the ray from left to right as observed from the point. A counterclockwise segment is one that
crosses the ray from right to left as observed from the point. The case where a directed line seg-
ment is coincident with the ray is uninteresting because you can simply choose a different ray that
is not coincident with a segment.
For both EvenOddRule and WindingRule, a point is infinitely small, and the path is an
infinitely thin line. A pixel is inside if the center point of the pixel is inside and the center point is
not on the boundary. If the center point is on the boundary, the pixel is inside if and only if the
polygon interior is immediately to its right (x increasing direction). Pixels with centers on a hori-
zontal edge are a special case and are inside if and only if the polygon interior is immediately
below (y increasing direction).
The arc-mode controls filling in the XFillArcs function and can be set to ArcPieSlice or
ArcChord. For ArcPieSlice, the arcs are pie-slice filled. For ArcChord, the arcs are chord
filled.
The graphics-exposure flag controls GraphicsExpose ev ent generation for XCopyArea and
XCopyPlane requests (and any similar requests defined by extensions).
To create a new GC that is usable on a given screen with a depth of drawable, use XCreateGC.
GC XCreateGC(display, d, valuemask, values)
Display *display;
Drawable d;
unsigned long valuemask;
XGCValues *values;
display
Specifies the connection to the X server.
d
Specifies the drawable.
valuemask
Specifies which components in the GC are to be set using the information in the
specified values structure. This argument is the bitwise inclusive OR of zero or
more of the valid GC component mask bits.
values
Specifies any values as specified by the valuemask.
The XCreateGC function creates a graphics context and returns a GC. The GC can be used with
any destination drawable having the same root and depth as the specified drawable. Use with
other drawables results in a BadMatch error.
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XCreateGC can generate BadAlloc, BadDrawable, BadFont, BadMatch, BadPixmap, and
BadValue errors.
To copy components from a source GC to a destination GC, use XCopyGC.
XCopyGC (display, src, valuemask, dest)
Display *display;
GC src, dest;
unsigned long valuemask;
display
Specifies the connection to the X server.
src
Specifies the components of the source GC.
valuemask
Specifies which components in the GC are to be copied to the destination GC.
This argument is the bitwise inclusive OR of zero or more of the valid GC com-
ponent mask bits.
dest
Specifies the destination GC.
The XCopyGC function copies the specified components from the source GC to the destination
GC. The source and destination GCs must have the same root and depth, or a BadMatch error
results. The valuemask specifies which component to copy, as for XCreateGC.
XCopyGC can generate BadAlloc, BadGC, and BadMatch errors.
To change the components in a given GC, use XChangeGC.
XChangeGC (display, gc, valuemask, values)
Display *display;
GC gc;
unsigned long valuemask;
XGCValues *values;
display
Specifies the connection to the X server.
gc
Specifies the GC.
valuemask
Specifies which components in the GC are to be changed using information in the
specified values structure. This argument is the bitwise inclusive OR of zero or
more of the valid GC component mask bits.
values
Specifies any values as specified by the valuemask.
The XChangeGC function changes the components specified by valuemask for the specified GC.
The values argument contains the values to be set. The values and restrictions are the same as for
XCreateGC. Changing the clip-mask overrides any previous XSetClipRectangles request on
the context. Changing the dash-offset or dash-list overrides any previous XSetDashes request on
the context. The order in which components are verified and altered is server dependent. If an
error is generated, a subset of the components may have been altered.
XChangeGC can generate BadAlloc, BadFont, BadGC, BadMatch, BadPixmap, and Bad-
Value errors.
To obtain components of a given GC, use XGetGCValues.
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Status XGetGCValues (display, gc, valuemask, values_return)
Display *display;
GC gc;
unsigned long valuemask;
XGCValues *values_return;
display
Specifies the connection to the X server.
gc
Specifies the GC.
valuemask
Specifies which components in the GC are to be returned in the values_return ar-
gument. This argument is the bitwise inclusive OR of zero or more of the valid
GC component mask bits.
values_return
Returns the GC values in the specified XGCValues structure.
The XGetGCValues function returns the components specified by valuemask for the specified
GC. If the valuemask contains a valid set of GC mask bits (GCFunction, GCPlaneMask,
GCForeground, GCBackground, GCLineWidth, GCLineStyle, GCCapStyle,
GCJoinStyle, GCFillStyle, GCFillRule, GCTile, GCStipple, GCTileStipXOrigin,
GCTileStipYOrigin, GCFont, GCSubwindowMode, GCGraphicsExposures,
GCClipXOrigin, GCCLipYOrigin, GCDashOffset, or GCArcMode) and no error occurs,
XGetGCValues sets the requested components in values_return and returns a nonzero status.
Otherwise, it returns a zero status. Note that the clip-mask and dash-list (represented by the
GCClipMask and GCDashList bits, respectively, in the valuemask) cannot be requested. Also
note that an invalid resource ID (with one or more of the three most significant bits set to 1) will
be returned for GCFont, GCTile, and GCStipple if the component has never been explicitly set
by the client.
To free a given GC, use XFreeGC.
XFreeGC (display, gc)
Display *display;
GC gc;
display
Specifies the connection to the X server.
gc
Specifies the GC.
The XFreeGC function destroys the specified GC as well as all the associated storage.
XFreeGC can generate a BadGC error.
To obtain the GContext resource ID for a given GC, use XGContextFromGC.
GContext XGContextFromGC (gc)
GC gc;
gc
Specifies the GC for which you want the resource ID.
Xlib usually defers sending changes to the components of a GC to the server until a graphics
function is actually called with that GC. This permits batching of component changes into a sin-
gle server request. In some circumstances, however, it may be necessary for the client to explic-
itly force sending the changes to the server. An example might be when a protocol extension uses
the GC indirectly, in such a way that the extension interface cannot know what GC will be used.
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To force sending GC component changes, use XFlushGC.
void XFlushGC(display, gc)
Display *display;
GC gc;
display
Specifies the connection to the X server.
gc
Specifies the GC.
7.2. Using Graphics Context Convenience Routines
This section discusses how to set the:

Foreground, background, plane mask, or function components

Line attributes and dashes components

Fill style and fill rule components

Fill tile and stipple components

Font component

Clip region component

Arc mode, subwindow mode, and graphics exposure components
7.2.1. Setting the Foreground, Background, Function, or Plane Mask
To set the foreground, background, plane mask, and function components for a given GC, use
XSetState.
XSetState (display, gc, foreground, background, function, plane_mask)
Display *display;
GC gc;
unsigned long foreground, background;
int function;
unsigned long plane_mask;
display
Specifies the connection to the X server.
gc
Specifies the GC.
foreground
Specifies the foreground you want to set for the specified GC.
background
Specifies the background you want to set for the specified GC.
function
Specifies the function you want to set for the specified GC.
plane_mask
Specifies the plane mask.
XSetState can generate BadAlloc, BadGC, and BadValue errors.
To set the foreground of a given GC, use XSetForeground.
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XSetForeground (display, gc, foreground)
Display *display;
GC gc;
unsigned long foreground;
display
Specifies the connection to the X server.
gc
Specifies the GC.
foreground
Specifies the foreground you want to set for the specified GC.
XSetForeground can generate BadAlloc and BadGC errors.
To set the background of a given GC, use XSetBackground.
XSetBackground (display, gc, background)
Display *display;
GC gc;
unsigned long background;
display
Specifies the connection to the X server.
gc
Specifies the GC.
background
Specifies the background you want to set for the specified GC.
XSetBackground can generate BadAlloc and BadGC errors.
To set the display function in a given GC, use XSetFunction.
XSetFunction (display, gc, function)
Display *display;
GC gc;
int function;
display
Specifies the connection to the X server.
gc
Specifies the GC.
function
Specifies the function you want to set for the specified GC.
XSetFunction can generate BadAlloc, BadGC, and BadValue errors.
To set the plane mask of a given GC, use XSetPlaneMask.
XSetPlaneMask (display, gc, plane_mask)
Display *display;
GC gc;
unsigned long plane_mask;
display
Specifies the connection to the X server.
gc
Specifies the GC.
plane_mask
Specifies the plane mask.
XSetPlaneMask can generate BadAlloc and BadGC errors.
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7.2.2. Setting the Line Attributes and Dashes
To set the line drawing components of a given GC, use XSetLineAttributes.
XSetLineAttributes (display, gc, line_width, line_style, cap_style, join_style)
Display *display;
GC gc;
unsigned int line_width;
int line_style;
int cap_style;
int join_style;
display
Specifies the connection to the X server.
gc
Specifies the GC.
line_width
Specifies the line-width you want to set for the specified GC.
line_style
Specifies the line-style you want to set for the specified GC. You can pass
LineSolid, LineOnOffDash, or LineDoubleDash.
cap_style
Specifies the line-style and cap-style you want to set for the specified GC. You
can pass CapNotLast, CapButt, CapRound, or CapProjecting.
join_style
Specifies the line join-style you want to set for the specified GC. You can pass
JoinMiter, JoinRound, or JoinBevel.
XSetLineAttributes can generate BadAlloc, BadGC, and BadValue errors.
To set the dash-offset and dash-list for dashed line styles of a given GC, use XSetDashes.
XSetDashes (display, gc, dash_offset, dash_list, n)
Display *display;
GC gc;
int dash_offset;
char dash_list[] ;
int n;
display
Specifies the connection to the X server.
gc
Specifies the GC.
dash_offset
Specifies the phase of the pattern for the dashed line-style you want to set for the
specified GC.
dash_list
Specifies the dash-list for the dashed line-style you want to set for the specified
GC.
n
Specifies the number of elements in dash_list.
The XSetDashes function sets the dash-offset and dash-list attributes for dashed line styles in the
specified GC. There must be at least one element in the specified dash_list, or a BadValue error
results. The initial and alternating elements (second, fourth, and so on) of the dash_list are the
ev en dashes, and the others are the odd dashes. Each element specifies a dash length in pixels.
All of the elements must be nonzero, or a BadValue error results. Specifying an odd-length list
is equivalent to specifying the same list concatenated with itself to produce an even-length list.
The dash-offset defines the phase of the pattern, specifying how many pixels into the dash-list the
pattern should actually begin in any single graphics request. Dashing is continuous through path
elements combined with a join-style but is reset to the dash-offset between each sequence of
joined lines.
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The unit of measure for dashes is the same for the ordinary coordinate system. Ideally, a dash
length is measured along the slope of the line, but implementations are only required to match
this ideal for horizontal and vertical lines. Failing the ideal semantics, it is suggested that the
length be measured along the major axis of the line. The major axis is defined as the x axis for
lines drawn at an angle of between -45 and +45 degrees or between 135 and 225 degrees from
the x axis. For all other lines, the major axis is the y axis.
XSetDashes can generate BadAlloc, BadGC, and BadValue errors.
7.2.3. Setting the Fill Style and Fill Rule
To set the fill-style of a given GC, use XSetFillStyle.
XSetFillStyle (display, gc, fill_style)
Display *display;
GC gc;
int fill_style;
display
Specifies the connection to the X server.
gc
Specifies the GC.
fill_style
Specifies the fill-style you want to set for the specified GC. You can pass
FillSolid, FillTiled, FillStippled, or FillOpaqueStippled.
XSetFillStyle can generate BadAlloc, BadGC, and BadValue errors.
To set the fill-rule of a given GC, use XSetFillRule.
XSetFillRule (display, gc, fill_rule)
Display *display;
GC gc;
int fill_rule;
display
Specifies the connection to the X server.
gc
Specifies the GC.
fill_rule
Specifies the fill-rule you want to set for the specified GC. You can pass Even-
OddRule or WindingRule.
XSetFillRule can generate BadAlloc, BadGC, and BadValue errors.
7.2.4. Setting the Fill Tile and Stipple
Some displays have hardware support for tiling or stippling with patterns of specific sizes. Tiling
and stippling operations that restrict themselves to those specific sizes run much faster than such
operations with arbitrary size patterns. Xlib provides functions that you can use to determine the
best size, tile, or stipple for the display as well as to set the tile or stipple shape and the tile or
stipple origin.
To obtain the best size of a tile, stipple, or cursor, use XQueryBestSize.
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Status XQueryBestSize(display, class, which_screen, width, height, width_return, height_return)
Display *display;
int class;
Drawable which_screen;
unsigned int width, height;
unsigned int *width_return, *height_return;
display
Specifies the connection to the X server.
class
Specifies the class that you are interested in.
You can pass TileShape,
CursorShape, or StippleShape.
which_screen
Specifies any drawable on the screen.
width
height
Specify the width and height.
width_return
height_return
Return the width and height of the object best supported by the display hardware.
The XQueryBestSize function returns the best or closest size to the specified size. For
CursorShape, this is the largest size that can be fully displayed on the screen specified by
which_screen. For TileShape, this is the size that can be tiled fastest. For StippleShape, this is
the size that can be stippled fastest. For CursorShape, the drawable indicates the desired screen.
For TileShape and StippleShape, the drawable indicates the screen and possibly the window
class and depth. An InputOnly window cannot be used as the drawable for TileShape or
StippleShape, or a BadMatch error results.
XQueryBestSize can generate BadDrawable, BadMatch, and BadValue errors.
To obtain the best fill tile shape, use XQueryBestTile.
Status XQueryBestTile (display, which_screen, width, height, width_return, height_return)
Display *display;
Drawable which_screen;
unsigned int width, height;
unsigned int *width_return, *height_return;
display
Specifies the connection to the X server.
which_screen
Specifies any drawable on the screen.
width
height
Specify the width and height.
width_return
height_return
Return the width and height of the object best supported by the display hardware.
The XQueryBestTile function returns the best or closest size, that is, the size that can be tiled
fastest on the screen specified by which_screen. The drawable indicates the screen and possibly
the window class and depth. If an InputOnly window is used as the drawable, a BadMatch
error results.
XQueryBestTile can generate BadDrawable and BadMatch errors.
To obtain the best stipple shape, use XQueryBestStipple.
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Status XQueryBestStipple(display, which_screen, width, height, width_return, height_return)
Display *display;
Drawable which_screen;
unsigned int width, height;
unsigned int *width_return, *height_return;
display
Specifies the connection to the X server.
which_screen
Specifies any drawable on the screen.
width
height
Specify the width and height.
width_return
height_return
Return the width and height of the object best supported by the display hardware.
The XQueryBestStipple function returns the best or closest size, that is, the size that can be stip-
pled fastest on the screen specified by which_screen. The drawable indicates the screen and pos-
sibly the window class and depth. If an InputOnly window is used as the drawable, a Bad-
Match
error results.
XQueryBestStipple can generate BadDrawable and BadMatch errors.
To set the fill tile of a given GC, use XSetTile.
XSetTile (display, gc, tile)
Display *display;
GC gc;
Pixmap tile;
display
Specifies the connection to the X server.
gc
Specifies the GC.
tile
Specifies the fill tile you want to set for the specified GC.
The tile and GC must have the same depth, or a BadMatch error results.
XSetTile can generate BadAlloc, BadGC, BadMatch, and BadPixmap errors.
To set the stipple of a given GC, use XSetStipple.
XSetStipple (display, gc, stipple)
Display *display;
GC gc;
Pixmap stipple;
display
Specifies the connection to the X server.
gc
Specifies the GC.
stipple
Specifies the stipple you want to set for the specified GC.
The stipple must have a depth of one, or a BadMatch error results.
XSetStipple can generate BadAlloc, BadGC, BadMatch, and BadPixmap errors.
To set the tile or stipple origin of a given GC, use XSetTSOrigin.
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XSetTSOrigin (display, gc, ts_x_origin, ts_y_origin)
Display *display;
GC gc;
int ts_x_origin, ts_y_origin;
display
Specifies the connection to the X server.
gc
Specifies the GC.
ts_x_origin
ts_y_origin
Specify the x and y coordinates of the tile and stipple origin.
When graphics requests call for tiling or stippling, the parent's origin will be interpreted relative
to whatever destination drawable is specified in the graphics request.
XSetTSOrigin can generate BadAlloc and BadGC errors.
7.2.5. Setting the Current Font
To set the current font of a given GC, use XSetFont.
XSetFont (display, gc, font)
Display *display;
GC gc;
Font font;
display
Specifies the connection to the X server.
gc
Specifies the GC.
font
Specifies the font.
XSetFont can generate BadAlloc, BadFont, and BadGC errors.
7.2.6. Setting the Clip Region
Xlib provides functions that you can use to set the clip-origin and the clip-mask or set the clip-
mask to a list of rectangles.
To set the clip-origin of a given GC, use XSetClipOrigin.
XSetClipOrigin (display, gc, clip_x_origin, clip_y_origin)
Display *display;
GC gc;
int clip_x_origin, clip_y_origin;
display
Specifies the connection to the X server.
gc
Specifies the GC.
clip_x_origin
clip_y_origin
Specify the x and y coordinates of the clip-mask origin.
The clip-mask origin is interpreted relative to the origin of whatever destination drawable is spec-
ified in the graphics request.
XSetClipOrigin can generate BadAlloc and BadGC errors.
To set the clip-mask of a given GC to the specified pixmap, use XSetClipMask.
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XSetClipMask (display, gc, pixmap)
Display *display;
GC gc;
Pixmap pixmap;
display
Specifies the connection to the X server.
gc
Specifies the GC.
pixmap
Specifies the pixmap or None.
If the clip-mask is set to None, the pixels are always drawn (regardless of the clip-origin).
XSetClipMask can generate BadAlloc, BadGC, BadMatch, and BadPixmap errors.
To set the clip-mask of a given GC to the specified list of rectangles, use XSetClipRectangles.
XSetClipRectangles (display, gc, clip_x_origin, clip_y_origin, rectangles, n, ordering)
Display *display;
GC gc;
int clip_x_origin, clip_y_origin;
XRectangle rectangles[] ;
int n;
int ordering;
display
Specifies the connection to the X server.
gc
Specifies the GC.
clip_x_origin
clip_y_origin
Specify the x and y coordinates of the clip-mask origin.
rectangles
Specifies an array of rectangles that define the clip-mask.
n
Specifies the number of rectangles.
ordering
Specifies the ordering relations on the rectangles. You can pass Unsorted,
YSorted, YXSorted, or YXBanded.
The XSetClipRectangles function changes the clip-mask in the specified GC to the specified list
of rectangles and sets the clip origin. The output is clipped to remain contained within the rectan-
gles. The clip-origin is interpreted relative to the origin of whatever destination drawable is spec-
ified in a graphics request. The rectangle coordinates are interpreted relative to the clip-origin.
The rectangles should be nonintersecting, or the graphics results will be undefined. Note that the
list of rectangles can be empty, which effectively disables output. This is the opposite of passing
None as the clip-mask in XCreateGC, XChangeGC, and XSetClipMask.
If known by the client, ordering relations on the rectangles can be specified with the ordering
argument. This may provide faster operation by the server. If an incorrect ordering is specified,
the X server may generate a BadMatch error, but it is not required to do so. If no error is gener-
ated, the graphics results are undefined. Unsorted means the rectangles are in arbitrary order.
YSorted means that the rectangles are nondecreasing in their Y origin. YXSorted additionally
constrains YSorted order in that all rectangles with an equal Y origin are nondecreasing in their
X origin. YXBanded additionally constrains YXSorted by requiring that, for every possible Y
scanline, all rectangles that include that scanline have an identical Y origins and Y extents.
XSetClipRectangles can generate BadAlloc, BadGC, BadMatch, and BadValue errors.
Xlib provides a set of basic functions for performing region arithmetic. For information about
these functions, see section 16.5.
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7.2.7. Setting the Arc Mode, Subwindow Mode, and Graphics Exposure
To set the arc mode of a given GC, use XSetArcMode.
XSetArcMode (display, gc, arc_mode)
Display *display;
GC gc;
int arc_mode;
display
Specifies the connection to the X server.
gc
Specifies the GC.
arc_mode
Specifies the arc mode. You can pass ArcChord or ArcPieSlice.
XSetArcMode can generate BadAlloc, BadGC, and BadValue errors.
To set the subwindow mode of a given GC, use XSetSubwindowMode.
XSetSubwindowMode (display, gc, subwindow_mode)
Display *display;
GC gc;
int subwindow_mode;
display
Specifies the connection to the X server.
gc
Specifies the GC.
subwindow_mode
Specifies the subwindow
mode. You can pass
ClipByChildren
or
IncludeInferiors.
XSetSubwindowMode can generate BadAlloc, BadGC, and BadValue errors.
To set the graphics-exposures flag of a given GC, use XSetGraphicsExposures.
XSetGraphicsExposures (display, gc, graphics_exposures)
Display *display;
GC gc;
Bool graphics_exposures;
display
Specifies the connection to the X server.
gc
Specifies the GC.
graphics_exposures
Specifies a Boolean value that indicates whether you want GraphicsExpose and
NoExpose ev ents to be reported when calling XCopyArea and XCopyPlane
with this GC.
XSetGraphicsExposures can generate BadAlloc, BadGC, and BadValue errors.
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Chapter 8
Graphics Functions
Once you have established a connection to a display, you can use the Xlib graphics functions to:

Clear and copy areas

Draw points, lines, rectangles, and arcs

Fill areas

Manipulate fonts

Draw text

Transfer images between clients and the server
If the same drawable and GC is used for each call, Xlib batches back-to-back calls to
XDrawPoint, XDrawLine, XDrawRectangle, XFillArc, and XFillRectangle. Note that this
reduces the total number of requests sent to the server.
8.1. Clearing Areas
Xlib provides functions that you can use to clear an area or the entire window. Because pixmaps
do not have defined backgrounds, they cannot be filled by using the functions described in this
section. Instead, to accomplish an analogous operation on a pixmap, you should use
XFillRectangle, which sets the pixmap to a known value.
To clear a rectangular area of a given window, use XClearArea.
XClearArea (display, w, x, y, width, height, exposures)
Display *display;
Window w;
int x, y;
unsigned int width, height;
Bool exposures;
display
Specifies the connection to the X server.
w
Specifies the window.
x
y
Specify the x and y coordinates, which are relative to the origin of the window
and specify the upper-left corner of the rectangle.
width
height
Specify the width and height, which are the dimensions of the rectangle.
exposures
Specifies a Boolean value that indicates if Expose ev ents are to be generated.
The XClearArea function paints a rectangular area in the specified window according to the
specified dimensions with the window's background pixel or pixmap. The subwindow-mode
effectively is ClipByChildren. If width is zero, it is replaced with the current width of the win-
dow minus x. If height is zero, it is replaced with the current height of the window minus y. If
the window has a defined background tile, the rectangle clipped by any children is filled with this
tile. If the window has background None, the contents of the window are not changed. In either
case, if exposures is True, one or more Expose ev ents are generated for regions of the rectangle
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that are either visible or are being retained in a backing store. If you specify a window whose
class is InputOnly, a BadMatch error results.
XClearArea can generate BadMatch, BadValue, and BadWindow errors.
To clear the entire area in a given window, use XClearWindow.
XClearWindow(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XClearWindow function clears the entire area in the specified window and is equivalent to
XClearArea (display, w, 0, 0, 0, 0, False). If the window has a defined background tile, the rect-
angle is tiled with a plane-mask of all ones and GXcopy function. If the window has background
None, the contents of the window are not changed. If you specify a window whose class is
InputOnly, a BadMatch error results.
XClearWindow can generate BadMatch and BadWindow errors.
8.2. Copying Areas
Xlib provides functions that you can use to copy an area or a bit plane.
To copy an area between drawables of the same root and depth, use XCopyArea.
XCopyArea (display, src, dest, gc, src_x, src_y, width, height, dest_x, dest_y)
Display *display;
Drawable src, dest;
GC gc;
int src_x, src_y;
unsigned int width, height;
int dest_x, dest_y;
display
Specifies the connection to the X server.
src
dest
Specify the source and destination rectangles to be combined.
gc
Specifies the GC.
src_x
src_y
Specify the x and y coordinates, which are relative to the origin of the source
rectangle and specify its upper-left corner.
width
height
Specify the width and height, which are the dimensions of both the source and
destination rectangles.
dest_x
dest_y
Specify the x and y coordinates, which are relative to the origin of the destination
rectangle and specify its upper-left corner.
The XCopyArea function combines the specified rectangle of src with the specified rectangle of
dest. The drawables must have the same root and depth, or a BadMatch error results.
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If regions of the source rectangle are obscured and have not been retained in backing store or if
regions outside the boundaries of the source drawable are specified, those regions are not copied.
Instead, the following occurs on all corresponding destination regions that are either visible or are
retained in backing store. If the destination is a window with a background other than None, cor-
responding regions of the destination are tiled with that background (with plane-mask of all ones
and GXcopy function). Regardless of tiling or whether the destination is a window or a pixmap,
if graphics-exposures is True, then GraphicsExpose ev ents for all corresponding destination
regions are generated. If graphics-exposures is True but no GraphicsExpose ev ents are gener-
ated, a NoExpose ev ent is generated. Note that by default graphics-exposures is True in new
GCs.
This function uses these GC components: function, plane-mask, subwindow-mode, graphics-
exposures, clip-x-origin, clip-y-origin, and clip-mask.
XCopyArea can generate BadDrawable, BadGC, and BadMatch errors.
To copy a single bit plane of a given drawable, use XCopyPlane.
XCopyPlane (display, src, dest, gc, src_x, src_y, width, height, dest_x, dest_y, plane)
Display *display;
Drawable src, dest;
GC gc;
int src_x, src_y;
unsigned int width, height;
int dest_x, dest_y;
unsigned long plane;
display
Specifies the connection to the X server.
src
dest
Specify the source and destination rectangles to be combined.
gc
Specifies the GC.
src_x
src_y
Specify the x and y coordinates, which are relative to the origin of the source
rectangle and specify its upper-left corner.
width
height
Specify the width and height, which are the dimensions of both the source and
destination rectangles.
dest_x
dest_y
Specify the x and y coordinates, which are relative to the origin of the destination
rectangle and specify its upper-left corner.
plane
Specifies the bit plane. You must set exactly one bit to 1.
The XCopyPlane function uses a single bit plane of the specified source rectangle combined
with the specified GC to modify the specified rectangle of dest. The drawables must have the
same root but need not have the same depth. If the drawables do not have the same root, a Bad-
Match
error results. If plane does not have exactly one bit set to 1 and the value of plane is not
less than 2n, where n is the depth of src, a BadValue error results.
Effectively, XCopyPlane forms a pixmap of the same depth as the rectangle of dest and with a
size specified by the source region. It uses the foreground/background pixels in the GC (fore-
ground everywhere the bit plane in src contains a bit set to 1, background everywhere the bit
plane in src contains a bit set to 0) and the equivalent of a CopyArea protocol request is per-
formed with all the same exposure semantics. This can also be thought of as using the specified
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region of the source bit plane as a stipple with a fill-style of FillOpaqueStippled for filling a
rectangular area of the destination.
This function uses these GC components: function, plane-mask, foreground, background, subwin-
dow-mode, graphics-exposures, clip-x-origin, clip-y-origin, and clip-mask.
XCopyPlane can generate BadDrawable, BadGC, BadMatch, and BadValue errors.
8.3. Drawing Points, Lines, Rectangles, and Arcs
Xlib provides functions that you can use to draw:

A single point or multiple points

A single line or multiple lines

A single rectangle or multiple rectangles

A single arc or multiple arcs
Some of the functions described in the following sections use these structures:
typedef struct {
short x1, y1, x2, y2;
} XSegment;
typedef struct {
short x, y;
} XPoint;
typedef struct {
short x, y;
unsigned short width, height;
} XRectangle;
typedef struct {
short x, y;
unsigned short width, height;
short angle1, angle2;
/* Degrees * 64 */
} XArc;
All x and y members are signed integers. The width and height members are 16-bit unsigned
integers. You should be careful not to generate coordinates and sizes out of the 16-bit ranges,
because the protocol only has 16-bit fields for these values.
8.3.1. Drawing Single and Multiple Points
To draw a single point in a given drawable, use XDrawPoint.
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XDrawPoint (display, d, gc, x, y)
Display *display;
Drawable d;
GC gc;
int x, y;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates where you want the point drawn.
To draw multiple points in a given drawable, use XDrawPoints.
XDrawPoints (display, d, gc, points, npoints, mode)
Display *display;
Drawable d;
GC gc;
XPoint *points;
int npoints;
int mode;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
points
Specifies an array of points.
npoints
Specifies the number of points in the array.
mode
Specifies the coordinate mode.
You
can pass
CoordModeOrigin
or
CoordModePrevious.
The XDrawPoint function uses the foreground pixel and function components of the GC to draw
a single point into the specified drawable; XDrawPoints draws multiple points this way. Coord-
ModeOrigin
treats all coordinates as relative to the origin, and CoordModePrevious treats all
coordinates after the first as relative to the previous point. XDrawPoints draws the points in the
order listed in the array.
Both functions use these GC components: function, plane-mask, foreground, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
XDrawPoint can generate BadDrawable, BadGC, and BadMatch errors. XDrawPoints can
generate BadDrawable, BadGC, BadMatch, and BadValue errors.
8.3.2. Drawing Single and Multiple Lines
To draw a single line between two points in a given drawable, use XDrawLine.
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XDrawLine (display, d, gc, x1, y1, x2, y2)
Display *display;
Drawable d;
GC gc;
int x1, y1, x2, y2;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x1
y1
x2
y2
Specify the points (x1, y1) and (x2, y2) to be connected.
To draw multiple lines in a given drawable, use XDrawLines.
XDrawLines (display, d, gc, points, npoints, mode)
Display *display;
Drawable d;
GC gc;
XPoint *points;
int npoints;
int mode;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
points
Specifies an array of points.
npoints
Specifies the number of points in the array.
mode
Specifies the coordinate mode.
You
can pass
CoordModeOrigin
or
CoordModePrevious.
To draw multiple, unconnected lines in a given drawable, use XDrawSegments.
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XDrawSegments (display, d, gc, segments, nsegments)
Display *display;
Drawable d;
GC gc;
XSegment *segments;
int nsegments;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
segments
Specifies an array of segments.
nsegments
Specifies the number of segments in the array.
The XDrawLine function uses the components of the specified GC to draw a line between the
specified set of points (x1, y1) and (x2, y2). It does not perform joining at coincident endpoints.
For any giv en line, XDrawLine does not draw a pixel more than once. If lines intersect, the
intersecting pixels are drawn multiple times.
The XDrawLines function uses the components of the specified GC to draw npoints-1 lines
between each pair of points (point[i], point[i+1]) in the array of XPoint structures. It draws the
lines in the order listed in the array. The lines join correctly at all intermediate points, and if the
first and last points coincide, the first and last lines also join correctly. For any giv en line,
XDrawLines does not draw a pixel more than once. If thin (zero line-width) lines intersect, the
intersecting pixels are drawn multiple times. If wide lines intersect, the intersecting pixels are
drawn only once, as though the entire PolyLine protocol request were a single, filled shape.
CoordModeOrigin treats all coordinates as relative to the origin, and CoordModePrevious
treats all coordinates after the first as relative to the previous point.
The XDrawSegments function draws multiple, unconnected lines. For each segment,
XDrawSegments draws a line between (x1, y1) and (x2, y2). It draws the lines in the order
listed in the array of XSegment structures and does not perform joining at coincident endpoints.
For any giv en line, XDrawSegments does not draw a pixel more than once. If lines intersect, the
intersecting pixels are drawn multiple times.
All three functions use these GC components: function, plane-mask, line-width, line-style, cap-
style, fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask. The XDrawLines
function also uses the join-style GC component. All three functions also use these GC mode-
dependent components: foreground, background, tile, stipple, tile-stipple-x-origin, tile-stipple-y-
origin, dash-offset, and dash-list.
XDrawLine, XDrawLines, and XDrawSegments can generate BadDrawable, BadGC, and
BadMatch errors. XDrawLines also can generate BadValue errors.
8.3.3. Drawing Single and Multiple Rectangles
To draw the outline of a single rectangle in a given drawable, use XDrawRectangle.
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XDrawRectangle (display, d, gc, x, y, width, height)
Display *display;
Drawable d;
GC gc;
int x, y;
unsigned int width, height;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which specify the upper-left corner of the rectan-
gle.
width
height
Specify the width and height, which specify the dimensions of the rectangle.
To draw the outline of multiple rectangles in a given drawable, use XDrawRectangles.
XDrawRectangles (display, d, gc, rectangles, nrectangles)
Display *display;
Drawable d;
GC gc;
XRectangle rectangles[];
int nrectangles;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
rectangles
Specifies an array of rectangles.
nrectangles
Specifies the number of rectangles in the array.
The XDrawRectangle and XDrawRectangles functions draw the outlines of the specified rect-
angle or rectangles as if a five-point PolyLine protocol request were specified for each rectangle:
[x,y] [x+width,y] [x+width,y+height] [x,y+height] [x,y]
For the specified rectangle or rectangles, these functions do not draw a pixel more than once.
XDrawRectangles draws the rectangles in the order listed in the array. If rectangles intersect,
the intersecting pixels are drawn multiple times.
Both functions use these GC components: function, plane-mask, line-width, line-style, cap-style,
join-style, fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask. They also use
these GC mode-dependent components: foreground, background, tile, stipple, tile-stipple-x-ori-
gin, tile-stipple-y-origin, dash-offset, and dash-list.
XDrawRectangle and XDrawRectangles can generate BadDrawable, BadGC, and Bad-
Match errors.
8.3.4. Drawing Single and Multiple Arcs
To draw a single arc in a given drawable, use XDrawArc.
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XDrawArc (display, d, gc, x, y, width, height, angle1, angle2)
Display *display;
Drawable d;
GC gc;
int x, y;
unsigned int width, height;
int angle1, angle2;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the drawable
and specify the upper-left corner of the bounding rectangle.
width
height
Specify the width and height, which are the major and minor axes of the arc.
angle1
Specifies the start of the arc relative to the three-o'clock position from the center,
in units of degrees * 64.
angle2
Specifies the path and extent of the arc relative to the start of the arc, in units of
degrees * 64.
To draw multiple arcs in a given drawable, use XDrawArcs.
XDrawArcs (display, d, gc, arcs, narcs)
Display *display;
Drawable d;
GC gc;
XArc *arcs;
int narcs;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
arcs
Specifies an array of arcs.
narcs
Specifies the number of arcs in the array.
XDrawArc draws a single circular or elliptical arc, and XDrawArcs draws multiple circular or
elliptical arcs. Each arc is specified by a rectangle and two angles. The center of the circle or
ellipse is the center of the rectangle, and the major and minor axes are specified by the width and
height. Positive angles indicate counterclockwise motion, and negative angles indicate clockwise
motion. If the magnitude of angle2 is greater than 360 degrees, XDrawArc or XDrawArcs
truncates it to 360 degrees.
For an arc specified as [ x, y, width, height, angle1, angle2], the origin of the major and minor
axes is at [x + width , y + height ], and the infinitely thin path describing the entire circle or
2
2
ellipse intersects the horizontal axis at [x, y + height ] and [x + width, y + height ] and intersects
2
2
the vertical axis at [x + width , y] and [x + width , y + height]. These coordinates can be frac-
2
2
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tional and so are not truncated to discrete coordinates. The path should be defined by the ideal
mathematical path. For a wide line with line-width lw, the bounding outlines for filling are given
by the two infinitely thin paths consisting of all points whose perpendicular distance from the
path of the circle/ellipse is equal to lw/2 (which may be a fractional value). The cap-style and
join-style are applied the same as for a line corresponding to the tangent of the circle/ellipse at the
endpoint.
For an arc specified as [ x, y, width, height, angle1, angle2], the angles must be specified in the
effectively skewed coordinate system of the ellipse (for a circle, the angles and coordinate sys-
tems are identical). The relationship between these angles and angles expressed in the normal
coordinate system of the screen (as measured with a protractor) is as follows:

width
skewed-angle = atan
+
tan(normal-angle) *
adjust
height
The skewed-angle and normal-angle are expressed in radians (rather than in degrees scaled by 64)

in the range [0, 2 ] and where atan returns a value in the range [-
,
] and adjust is:
2
2

0
for normal-angle in the range [0,
]
2


3
for normal-angle in the range [
,
]
2
2
3
2
for normal-angle in the range [
, 2 ]
2
For any giv en arc, XDrawArc and XDrawArcs do not draw a pixel more than once. If two arcs
join correctly and if the line-width is greater than zero and the arcs intersect, XDrawArc and
XDrawArcs do not draw a pixel more than once. Otherwise, the intersecting pixels of intersect-
ing arcs are drawn multiple times. Specifying an arc with one endpoint and a clockwise extent
draws the same pixels as specifying the other endpoint and an equivalent counterclockwise extent,
except as it affects joins.
If the last point in one arc coincides with the first point in the following arc, the two arcs will join
correctly. If the first point in the first arc coincides with the last point in the last arc, the two arcs
will join correctly. By specifying one axis to be zero, a horizontal or vertical line can be drawn.
Angles are computed based solely on the coordinate system and ignore the aspect ratio.
Both functions use these GC components: function, plane-mask, line-width, line-style, cap-style,
join-style, fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask. They also use
these GC mode-dependent components: foreground, background, tile, stipple, tile-stipple-x-ori-
gin, tile-stipple-y-origin, dash-offset, and dash-list.
XDrawArc and XDrawArcs can generate BadDrawable, BadGC, and BadMatch errors.
8.4. Filling Areas
Xlib provides functions that you can use to fill:

A single rectangle or multiple rectangles

A single polygon

A single arc or multiple arcs
8.4.1. Filling Single and Multiple Rectangles
To fill a single rectangular area in a given drawable, use XFillRectangle.
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XFillRectangle (display, d, gc, x, y, width, height)
Display *display;
Drawable d;
GC gc;
int x, y;
unsigned int width, height;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the drawable
and specify the upper-left corner of the rectangle.
width
height
Specify the width and height, which are the dimensions of the rectangle to be
filled.
To fill multiple rectangular areas in a given drawable, use XFillRectangles.
XFillRectangles (display, d, gc, rectangles, nrectangles)
Display *display;
Drawable d;
GC gc;
XRectangle *rectangles;
int nrectangles;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
rectangles
Specifies an array of rectangles.
nrectangles
Specifies the number of rectangles in the array.
The XFillRectangle and XFillRectangles functions fill the specified rectangle or rectangles as if
a four-point FillPolygon protocol request were specified for each rectangle:
[x,y] [x+width,y] [x+width,y+height] [x,y+height]
Each function uses the x and y coordinates, width and height dimensions, and GC you specify.
XFillRectangles fills the rectangles in the order listed in the array. For any giv en rectangle,
XFillRectangle and XFillRectangles do not draw a pixel more than once. If rectangles inter-
sect, the intersecting pixels are drawn multiple times.
Both functions use these GC components: function, plane-mask, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask. They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin, and tile-stipple-y-origin.
XFillRectangle and XFillRectangles can generate BadDrawable, BadGC, and BadMatch
errors.
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8.4.2. Filling a Single Polygon
To fill a polygon area in a given drawable, use XFillPolygon.
XFillPolygon (display, d, gc, points, npoints, shape, mode)
Display *display;
Drawable d;
GC gc;
XPoint *points;
int npoints;
int shape;
int mode;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
points
Specifies an array of points.
npoints
Specifies the number of points in the array.
shape
Specifies a shape that helps the server to improve performance. You can pass
Complex, Convex, or Nonconvex.
mode
Specifies the coordinate mode.
You
can pass
CoordModeOrigin
or
CoordModePrevious.
XFillPolygon fills the region closed by the specified path. The path is closed automatically if the
last point in the list does not coincide with the first point. XFillPolygon does not draw a pixel of
the region more than once. CoordModeOrigin treats all coordinates as relative to the origin, and
CoordModePrevious treats all coordinates after the first as relative to the previous point.
Depending on the specified shape, the following occurs:

If shape is Complex, the path may self-intersect. Note that contiguous coincident points in
the path are not treated as self-intersection.

If shape is Convex, for every pair of points inside the polygon, the line segment connecting
them does not intersect the path. If known by the client, specifying Convex can improve
performance. If you specify Convex for a path that is not convex, the graphics results are
undefined.

If shape is Nonconvex, the path does not self-intersect, but the shape is not wholly convex.
If known by the client, specifying Nonconvex instead of Complex may improve perfor-
mance. If you specify Nonconvex for a self-intersecting path, the graphics results are
undefined.
The fill-rule of the GC controls the filling behavior of self-intersecting polygons.
This function uses these GC components: function, plane-mask, fill-style, fill-rule, subwindow-
mode, clip-x-origin, clip-y-origin, and clip-mask. It also uses these GC mode-dependent compo-
nents: foreground, background, tile, stipple, tile-stipple-x-origin, and tile-stipple-y-origin.
XFillPolygon can generate BadDrawable, BadGC, BadMatch, and BadValue errors.
8.4.3. Filling Single and Multiple Arcs
To fill a single arc in a given drawable, use XFillArc.
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XFillArc (display, d, gc, x, y, width, height, angle1, angle2)
Display *display;
Drawable d;
GC gc;
int x, y;
unsigned int width, height;
int angle1, angle2;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the drawable
and specify the upper-left corner of the bounding rectangle.
width
height
Specify the width and height, which are the major and minor axes of the arc.
angle1
Specifies the start of the arc relative to the three-o'clock position from the center,
in units of degrees * 64.
angle2
Specifies the path and extent of the arc relative to the start of the arc, in units of
degrees * 64.
To fill multiple arcs in a given drawable, use XFillArcs.
XFillArcs (display, d, gc, arcs, narcs)
Display *display;
Drawable d;
GC gc;
XArc *arcs;
int narcs;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
arcs
Specifies an array of arcs.
narcs
Specifies the number of arcs in the array.
For each arc, XFillArc or XFillArcs fills the region closed by the infinitely thin path described
by the specified arc and, depending on the arc-mode specified in the GC, one or two line seg-
ments. For ArcChord, the single line segment joining the endpoints of the arc is used. For
ArcPieSlice, the two line segments joining the endpoints of the arc with the center point are
used. XFillArcs fills the arcs in the order listed in the array. For any giv en arc, XFillArc and
XFillArcs do not draw a pixel more than once. If regions intersect, the intersecting pixels are
drawn multiple times.
Both functions use these GC components: function, plane-mask, fill-style, arc-mode, subwindow-
mode, clip-x-origin, clip-y-origin, and clip-mask. They also use these GC mode-dependent com-
ponents: foreground, background, tile, stipple, tile-stipple-x-origin, and tile-stipple-y-origin.
XFillArc and XFillArcs can generate BadDrawable, BadGC, and BadMatch errors.
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8.5. Font Metrics
A font is a graphical description of a set of characters that are used to increase efficiency when-
ev er a set of small, similar sized patterns are repeatedly used.
This section discusses how to:

Load and free fonts

Obtain and free font names

Compute character string sizes

Compute logical extents

Query character string sizes
The X server loads fonts whenever a program requests a new font. The server can cache fonts for
quick lookup. Fonts are global across all screens in a server. Sev eral levels are possible when
dealing with fonts. Most applications simply use XLoadQueryFont to load a font and query the
font metrics.
Characters in fonts are regarded as masks. Except for image text requests, the only pixels modi-
fied are those in which bits are set to 1 in the character. This means that it makes sense to draw
text using stipples or tiles (for example, many menus gray-out unusable entries).
The XFontStruct structure contains all of the information for the font and consists of the font-
specific information as well as a pointer to an array of XCharStruct structures for the characters
contained in the font. The XFontStruct, XFontProp, and XCharStruct structures contain:
typedef struct {
short lbearing;
/* origin to left edge of raster */
short rbearing;
/* origin to right edge of raster */
short width;
/* advance to next char's origin */
short ascent;
/* baseline to top edge of raster */
short descent;
/* baseline to bottom edge of raster */
unsigned short attributes; /* per char flags (not predefined) */
} XCharStruct;
typedef struct {
Atom name;
unsigned long card32;
} XFontProp;
typedef struct {
/* normal 16 bit characters are two bytes */
unsigned char byte1;
unsigned char byte2;
} XChar2b;
typedef struct {
XExtData *ext_data; /* hook for extension to hang data */
Font fid;
/* Font id for this font */
unsigned direction;
/* hint about the direction font is painted */
unsigned min_char_or_byte2;
/* first character */
unsigned max_char_or_byte2;
/* last character */
unsigned min_byte1;
/* first row that exists */
unsigned max_byte1;
/* last row that exists */
Bool all_chars_exist; /* flag if all characters have nonzero size */
unsigned default_char; /* char to print for undefined character */
int n_properties;
/* how many properties there are */
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XFontProp *properties;
/* pointer to array of additional properties */
XCharStruct min_bounds;
/* minimum bounds over all existing char */
XCharStruct max_bounds;
/* maximum bounds over all existing char */
XCharStruct *per_char;
/* first_char to last_char information */
int ascent;
/* logical extent above baseline for spacing */
int descent;
/* logical descent below baseline for spacing */
} XFontStruct;
X supports single byte/character, two bytes/character matrix, and 16-bit character text operations.
Note that any of these forms can be used with a font, but a single byte/character text request can
only specify a single byte (that is, the first row of a 2-byte font). You should view 2-byte fonts as
a two-dimensional matrix of defined characters: byte1 specifies the range of defined rows and
byte2 defines the range of defined columns of the font. Single byte/character fonts have one row
defined, and the byte2 range specified in the structure defines a range of characters.
The bounding box of a character is defined by the XCharStruct of that character. When charac-
ters are absent from a font, the default_char is used. When fonts have all characters of the same
size, only the information in the XFontStruct min and max bounds are used.
The members of the XFontStruct have the following semantics:

The direction member can be either FontLeftToRight or FontRightToLeft. It is just a
hint as to whether most XCharStruct elements have a positive (FontLeftToRight) or a
negative (FontRightToLeft) character width metric. The core protocol defines no support
for vertical text.

If the min_byte1 and max_byte1 members are both zero, min_char_or_byte2 specifies the
linear character index corresponding to the first element of the per_char array, and
max_char_or_byte2 specifies the linear character index of the last element.
If either min_byte1 or max_byte1 are nonzero, both min_char_or_byte2 and
max_char_or_byte2 are less than 256, and the 2-byte character index values corresponding
to the per_char array element N (counting from 0) are:
byte1 = N/D + min_byte1
byte2 = N\D + min_char_or_byte2
where:
D = max_char_or_byte2 - min_char_or_byte2 + 1
/ = integer division
\ = integer modulus

If the per_char pointer is NULL, all glyphs between the first and last character indexes
inclusive hav e the same information, as given by both min_bounds and max_bounds.

If all_chars_exist is True, all characters in the per_char array have nonzero bounding
boxes.

The default_char member specifies the character that will be used when an undefined or
nonexistent character is printed. The default_char is a 16-bit character (not a 2-byte charac-
ter). For a font using 2-byte matrix format, the default_char has byte1 in the most-signifi-
cant byte and byte2 in the least significant byte. If the default_char itself specifies an unde-
fined or nonexistent character, no printing is performed for an undefined or nonexistent
character.

The min_bounds and max_bounds members contain the most extreme values of each indi-
vidual XCharStruct component over all elements of this array (and ignore nonexistent
characters). The bounding box of the font (the smallest rectangle enclosing the shape
obtained by superimposing all of the characters at the same origin [x,y]) has its upper-left
coordinate at:
[x + min_bounds.lbearing, y - max_bounds.ascent]
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Its width is:
max_bounds.rbearing - min_bounds.lbearing
Its height is:
max_bounds.ascent + max_bounds.descent

The ascent member is the logical extent of the font above the baseline that is used for deter-
mining line spacing. Specific characters may extend beyond this.

The descent member is the logical extent of the font at or below the baseline that is used for
determining line spacing. Specific characters may extend beyond this.

If the baseline is at Y-coordinate y, the logical extent of the font is inclusive between the
Y-coordinate values (y - font.ascent) and (y + font.descent - 1). Typically, the minimum
interline spacing between rows of text is given by ascent + descent.
For a character origin at [x,y], the bounding box of a character (that is, the smallest rectangle that
encloses the character's shape) described in terms of XCharStruct components is a rectangle
with its upper-left corner at:
[x + lbearing, y - ascent]
Its width is:
rbearing - lbearing
Its height is:
ascent + descent
The origin for the next character is defined to be:
[x + width, y]
The lbearing member defines the extent of the left edge of the character ink from the origin. The
rbearing member defines the extent of the right edge of the character ink from the origin. The
ascent member defines the extent of the top edge of the character ink from the origin. The
descent member defines the extent of the bottom edge of the character ink from the origin. The
width member defines the logical width of the character.
Note that the baseline (the y position of the character origin) is logically viewed as being the
scanline just below nondescending characters. When descent is zero, only pixels with Y-coordi-
nates less than y are drawn, and the origin is logically viewed as being coincident with the left
edge of a nonkerned character. When lbearing is zero, no pixels with X-coordinate less than x are
drawn. Any of the XCharStruct metric members could be negative. If the width is negative, the
next character will be placed to the left of the current origin.
The X protocol does not define the interpretation of the attributes member in the XCharStruct
structure. A nonexistent character is represented with all members of its XCharStruct set to
zero.
A font is not guaranteed to have any properties. The interpretation of the property value (for
example, long or unsigned long) must be derived from a priori knowledge of the property. A
basic set of font properties is specified in the X Consortium standard X Logical Font Description
Conventions
.
8.5.1. Loading and Freeing Fonts
Xlib provides functions that you can use to load fonts, get font information, unload fonts, and free
font information. A few font functions use a GContext resource ID or a font ID interchangeably.
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To load a given font, use XLoadFont.
Font XLoadFont (display, name)
Display *display;
char *name;
display
Specifies the connection to the X server.
name
Specifies the name of the font, which is a null-terminated string.
The XLoadFont function loads the specified font and returns its associated font ID. If the font
name is not in the Host Portable Character Encoding, the result is implementation-dependent.
Use of uppercase or lowercase does not matter. When the characters ``?'' and ``*'' are used in a
font name, a pattern match is performed and any matching font is used. In the pattern, the ``?''
character will match any single character, and the ``*'' character will match any number of char-
acters. A structured format for font names is specified in the X Consortium standard X Logical
Font Description Conventions
. If XLoadFont was unsuccessful at loading the specified font, a
BadName error results. Fonts are not associated with a particular screen and can be stored as a
component of any GC. When the font is no longer needed, call XUnloadFont.
XLoadFont can generate BadAlloc and BadName errors.
To return information about an available font, use XQueryFont.
XFontStruct *XQueryFont (display, font_ID)
Display *display;
XID font_ID;
display
Specifies the connection to the X server.
font_ID
Specifies the font ID or the GContext ID.
The XQueryFont function returns a pointer to the XFontStruct structure, which contains infor-
mation associated with the font. You can query a font or the font stored in a GC. The font ID
stored in the XFontStruct structure will be the GContext ID, and you need to be careful when
using this ID in other functions (see XGContextFromGC). If the font does not exist, XQuery-
Font
returns NULL. To free this data, use XFreeFontInfo.
To perform a XLoadFont and XQueryFont in a single operation, use XLoadQueryFont.
XFontStruct *XLoadQueryFont (display, name)
Display *display;
char *name;
display
Specifies the connection to the X server.
name
Specifies the name of the font, which is a null-terminated string.
The XLoadQueryFont function provides the most common way for accessing a font. XLoad-
QueryFont
both opens (loads) the specified font and returns a pointer to the appropriate
XFontStruct structure. If the font name is not in the Host Portable Character Encoding, the
result is implementation-dependent. If the font does not exist, XLoadQueryFont returns NULL.
XLoadQueryFont can generate a BadAlloc error.
To unload the font and free the storage used by the font structure that was allocated by
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XQueryFont or XLoadQueryFont, use XFreeFont.
XFreeFont (display, font_struct)
Display *display;
XFontStruct *font_struct;
display
Specifies the connection to the X server.
font_struct
Specifies the storage associated with the font.
The XFreeFont function deletes the association between the font resource ID and the specified
font and frees the XFontStruct structure. The font itself will be freed when no other resource
references it. The data and the font should not be referenced again.
XFreeFont can generate a BadFont error.
To return a given font property, use XGetFontProperty.
Bool XGetFontProperty (font_struct, atom, value_return)
XFontStruct *font_struct;
Atom atom;
unsigned long *value_return;
font_struct
Specifies the storage associated with the font.
atom
Specifies the atom for the property name you want returned.
value_return
Returns the value of the font property.
Given the atom for that property, the XGetFontProperty function returns the value of the speci-
fied font property. XGetFontProperty also returns False if the property was not defined or
True if it was defined. A set of predefined atoms exists for font properties, which can be found
in <X11/Xatom.h>. This set contains the standard properties associated with a font. Although it
is not guaranteed, it is likely that the predefined font properties will be present.
To unload a font that was loaded by XLoadFont, use XUnloadFont.
XUnloadFont (display, font)
Display *display;
Font font;
display
Specifies the connection to the X server.
font
Specifies the font.
The XUnloadFont function deletes the association between the font resource ID and the speci-
fied font. The font itself will be freed when no other resource references it. The font should not
be referenced again.
XUnloadFont can generate a BadFont error.
8.5.2. Obtaining and Freeing Font Names and Information
You obtain font names and information by matching a wildcard specification when querying a
font type for a list of available sizes and so on.
To return a list of the available font names, use XListFonts.
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char **XListFonts (display, pattern, maxnames, actual_count_return)
Display *display;
char *pattern;
int maxnames;
int *actual_count_return;
display
Specifies the connection to the X server.
pattern
Specifies the null-terminated pattern string that can contain wildcard characters.
maxnames
Specifies the maximum number of names to be returned.
actual_count_return
Returns the actual number of font names.
The XListFonts function returns an array of available font names (as controlled by the font
search path; see XSetFontPath) that match the string you passed to the pattern argument. The
pattern string can contain any characters, but each asterisk (*) is a wildcard for any number of
characters, and each question mark (?) is a wildcard for a single character. If the pattern string is
not in the Host Portable Character Encoding, the result is implementation-dependent. Use of
uppercase or lowercase does not matter. Each returned string is null-terminated. If the data
returned by the server is in the Latin Portable Character Encoding, then the returned strings are in
the Host Portable Character Encoding. Otherwise, the result is implementation-dependent. If
there are no matching font names, XListFonts returns NULL. The client should call XFree-
FontNames
when finished with the result to free the memory.
To free a font name array, use XFreeFontNames.
XFreeFontNames (list)
char *list[];
list
Specifies the array of strings you want to free.
The XFreeFontNames function frees the array and strings returned by XListFonts or
XListFontsWithInfo.
To obtain the names and information about available fonts, use XListFontsWithInfo.
char **XListFontsWithInfo (display, pattern, maxnames, count_return, info_return)
Display *display;
char *pattern;
int maxnames;
int *count_return;
XFontStruct **info_return;
display
Specifies the connection to the X server.
pattern
Specifies the null-terminated pattern string that can contain wildcard characters.
maxnames
Specifies the maximum number of names to be returned.
count_return
Returns the actual number of matched font names.
info_return
Returns the font information.
The XListFontsWithInfo function returns a list of font names that match the specified pattern
and their associated font information. The list of names is limited to size specified by maxnames.
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The information returned for each font is identical to what XLoadQueryFont would return
except that the per-character metrics are not returned. The pattern string can contain any charac-
ters, but each asterisk (*) is a wildcard for any number of characters, and each question mark (?)
is a wildcard for a single character. If the pattern string is not in the Host Portable Character
Encoding, the result is implementation-dependent. Use of uppercase or lowercase does not mat-
ter. Each returned string is null-terminated. If the data returned by the server is in the Latin
Portable Character Encoding, then the returned strings are in the Host Portable Character Encod-
ing. Otherwise, the result is implementation-dependent. If there are no matching font names,
XListFontsWithInfo returns NULL.
To free only the allocated name array, the client should call XFreeFontNames. To free both the
name array and the font information array or to free just the font information array, the client
should call XFreeFontInfo.
To free font structures and font names, use XFreeFontInfo.
XFreeFontInfo(names, free_info, actual_count)
char **names;
XFontStruct *free_info;
int actual_count;
names
Specifies the list of font names.
free_info
Specifies the font information.
actual_count
Specifies the actual number of font names.
The XFreeFontInfo function frees a font structure or an array of font structures and optionally
an array of font names. If NULL is passed for names, no font names are freed. If a font structure
for an open font (returned by XLoadQueryFont) is passed, the structure is freed, but the font is
not closed; use XUnloadFont to close the font.
8.5.3. Computing Character String Sizes
Xlib provides functions that you can use to compute the width, the logical extents, and the server
information about 8-bit and 2-byte text strings. The width is computed by adding the character
widths of all the characters. It does not matter if the font is an 8-bit or 2-byte font. These func-
tions return the sum of the character metrics in pixels.
To determine the width of an 8-bit character string, use XTextWidth.
int XTextWidth (font_struct, string, count)
XFontStruct *font_struct;
char *string;
int count;
font_struct
Specifies the font used for the width computation.
string
Specifies the character string.
count
Specifies the character count in the specified string.
To determine the width of a 2-byte character string, use XTextWidth16.
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int XTextWidth16 (font_struct, string, count)
XFontStruct *font_struct;
XChar2b *string;
int count;
font_struct
Specifies the font used for the width computation.
string
Specifies the character string.
count
Specifies the character count in the specified string.
8.5.4. Computing Logical Extents
To compute the bounding box of an 8-bit character string in a given font, use XTextExtents.
XTextExtents (font_struct, string, nchars, direction_return, font_ascent_return,
font_descent_return, overall_return)
XFontStruct *font_struct;
char *string;
int nchars;
int *direction_return;
int *font_ascent_return, *font_descent_return;
XCharStruct *overall_return;
font_struct
Specifies the XFontStruct structure.
string
Specifies the character string.
nchars
Specifies the number of characters in the character string.
direction_returnReturns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return
Returns the font ascent.
font_descent_return
Returns the font descent.
overall_return Returns the overall size in the specified XCharStruct structure.
To compute the bounding box of a 2-byte character string in a given font, use XTextExtents16.
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XTextExtents16 (font_struct, string, nchars, direction_return, font_ascent_return,
font_descent_return, overall_return)
XFontStruct *font_struct;
XChar2b *string;
int nchars;
int *direction_return;
int *font_ascent_return, *font_descent_return;
XCharStruct *overall_return;
font_struct
Specifies the XFontStruct structure.
string
Specifies the character string.
nchars
Specifies the number of characters in the character string.
direction_returnReturns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return
Returns the font ascent.
font_descent_return
Returns the font descent.
overall_return Returns the overall size in the specified XCharStruct structure.
The XTextExtents and XTextExtents16 functions perform the size computation locally and,
thereby, avoid the round-trip overhead of XQueryTextExtents and XQueryTextExtents16.
Both functions return an XCharStruct structure, whose members are set to the values as follows.
The ascent member is set to the maximum of the ascent metrics of all characters in the string.
The descent member is set to the maximum of the descent metrics. The width member is set to
the sum of the character-width metrics of all characters in the string. For each character in the
string, let W be the sum of the character-width metrics of all characters preceding it in the string.
Let L be the left-side-bearing metric of the character plus W. Let R be the right-side-bearing met-
ric of the character plus W. The lbearing member is set to the minimum L of all characters in the
string. The rbearing member is set to the maximum R.
For fonts defined with linear indexing rather than 2-byte matrix indexing, each XChar2b struc-
ture is interpreted as a 16-bit number with byte1 as the most significant byte. If the font has no
defined default character, undefined characters in the string are taken to have all zero metrics.
8.5.5. Querying Character String Sizes
To query the server for the bounding box of an 8-bit character string in a given font, use
XQueryTextExtents.
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XQueryTextExtents (display, font_ID, string, nchars, direction_return, font_ascent_return,
font_descent_return, overall_return)
Display *display;
XID font_ID;
char *string;
int nchars;
int *direction_return;
int *font_ascent_return, *font_descent_return;
XCharStruct *overall_return;
display
Specifies the connection to the X server.
font_ID
Specifies either the font ID or the GContext ID that contains the font.
string
Specifies the character string.
nchars
Specifies the number of characters in the character string.
direction_returnReturns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return
Returns the font ascent.
font_descent_return
Returns the font descent.
overall_return Returns the overall size in the specified XCharStruct structure.
To query the server for the bounding box of a 2-byte character string in a given font, use
XQueryTextExtents16.
XQueryTextExtents16 (display, font_ID, string, nchars, direction_return, font_ascent_return,
font_descent_return, overall_return)
Display *display;
XID font_ID;
XChar2b *string;
int nchars;
int *direction_return;
int *font_ascent_return, *font_descent_return;
XCharStruct *overall_return;
display
Specifies the connection to the X server.
font_ID
Specifies either the font ID or the GContext ID that contains the font.
string
Specifies the character string.
nchars
Specifies the number of characters in the character string.
direction_returnReturns the value of the direction hint (FontLeftToRight or FontRightToLeft).
font_ascent_return
Returns the font ascent.
font_descent_return
Returns the font descent.
overall_return Returns the overall size in the specified XCharStruct structure.
The XQueryTextExtents and XQueryTextExtents16 functions return the bounding box of the
specified 8-bit and 16-bit character string in the specified font or the font contained in the speci-
fied GC. These functions query the X server and, therefore, suffer the round-trip overhead that is
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avoided by XTextExtents and XTextExtents16. Both functions return a XCharStruct struc-
ture, whose members are set to the values as follows.
The ascent member is set to the maximum of the ascent metrics of all characters in the string.
The descent member is set to the maximum of the descent metrics. The width member is set to
the sum of the character-width metrics of all characters in the string. For each character in the
string, let W be the sum of the character-width metrics of all characters preceding it in the string.
Let L be the left-side-bearing metric of the character plus W. Let R be the right-side-bearing met-
ric of the character plus W. The lbearing member is set to the minimum L of all characters in the
string. The rbearing member is set to the maximum R.
For fonts defined with linear indexing rather than 2-byte matrix indexing, each XChar2b struc-
ture is interpreted as a 16-bit number with byte1 as the most significant byte. If the font has no
defined default character, undefined characters in the string are taken to have all zero metrics.
Characters with all zero metrics are ignored. If the font has no defined default_char, the unde-
fined characters in the string are also ignored.
XQueryTextExtents and XQueryTextExtents16 can generate BadFont and BadGC errors.
8.6. Drawing Text
This section discusses how to draw:

Complex text

Text characters

Image text characters
The fundamental text functions XDrawText and XDrawText16 use the following structures:
typedef struct {
char *chars;
/* pointer to string */
int nchars;
/* number of characters */
int delta;
/* delta between strings */
Font font;
/* Font to print it in, None don't change */
} XTe xtItem;
typedef struct {
XChar2b *chars;
/* pointer to two-byte characters */
int nchars;
/* number of characters */
int delta;
/* delta between strings */
Font font;
/* font to print it in, None don't change */
} XTe xtItem16;
If the font member is not None, the font is changed before printing and also is stored in the GC.
If an error was generated during text drawing, the previous items may have been drawn. The
baseline of the characters are drawn starting at the x and y coordinates that you pass in the text
drawing functions.
For example, consider the background rectangle drawn by XDrawImageString. If you want the
upper-left corner of the background rectangle to be at pixel coordinate (x,y), pass the (x,y +
ascent) as the baseline origin coordinates to the text functions. The ascent is the font ascent, as
given in the XFontStruct structure. If you want the lower-left corner of the background rectan-
gle to be at pixel coordinate (x,y), pass the (x,y - descent + 1) as the baseline origin coordinates
to the text functions. The descent is the font descent, as given in the XFontStruct structure.
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8.6.1. Drawing Complex Text
To draw 8-bit characters in a given drawable, use XDrawText.
XDrawText(display, d, gc, x, y, items, nitems)
Display *display;
Drawable d;
GC gc;
int x, y;
XTextItem *items;
int nitems;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
items
Specifies an array of text items.
nitems
Specifies the number of text items in the array.
To draw 2-byte characters in a given drawable, use XDrawText16.
XDrawText16 (display, d, gc, x, y, items, nitems)
Display *display;
Drawable d;
GC gc;
int x, y;
XTextItem16 *items;
int nitems;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
items
Specifies an array of text items.
nitems
Specifies the number of text items in the array.
The XDrawText16 function is similar to XDrawText except that it uses 2-byte or 16-bit charac-
ters. Both functions allow complex spacing and font shifts between counted strings.
Each text item is processed in turn. A font member other than None in an item causes the font to
be stored in the GC and used for subsequent text. A text element delta specifies an additional
change in the position along the x axis before the string is drawn. The delta is always added to
the character origin and is not dependent on any characteristics of the font. Each character image,
as defined by the font in the GC, is treated as an additional mask for a fill operation on the draw-
able. The drawable is modified only where the font character has a bit set to 1. If a text item gen-
erates a BadFont error, the previous text items may have been drawn.
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For fonts defined with linear indexing rather than 2-byte matrix indexing, each XChar2b struc-
ture is interpreted as a 16-bit number with byte1 as the most significant byte.
Both functions use these GC components: function, plane-mask, fill-style, font, subwindow-
mode, clip-x-origin, clip-y-origin, and clip-mask. They also use these GC mode-dependent com-
ponents: foreground, background, tile, stipple, tile-stipple-x-origin, and tile-stipple-y-origin.
XDrawText and XDrawText16 can generate BadDrawable, BadFont, BadGC, and Bad-
Match errors.
8.6.2. Drawing Text Characters
To draw 8-bit characters in a given drawable, use XDrawString.
XDrawString (display, d, gc, x, y, string, length)
Display *display;
Drawable d;
GC gc;
int x, y;
char *string;
int length;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
string
Specifies the character string.
length
Specifies the number of characters in the string argument.
To draw 2-byte characters in a given drawable, use XDrawString16.
XDrawString16 (display, d, gc, x, y, string, length)
Display *display;
Drawable d;
GC gc;
int x, y;
XChar2b *string;
int length;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
string
Specifies the character string.
length
Specifies the number of characters in the string argument.
Each character image, as defined by the font in the GC, is treated as an additional mask for a fill
operation on the drawable. The drawable is modified only where the font character has a bit set to
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1. For fonts defined with 2-byte matrix indexing and used with XDrawString16, each byte is
used as a byte2 with a byte1 of zero.
Both functions use these GC components: function, plane-mask, fill-style, font, subwindow-
mode, clip-x-origin, clip-y-origin, and clip-mask. They also use these GC mode-dependent com-
ponents: foreground, background, tile, stipple, tile-stipple-x-origin, and tile-stipple-y-origin.
XDrawString and XDrawString16 can generate BadDrawable, BadGC, and BadMatch
errors.
8.6.3. Drawing Image Text Characters
Some applications, in particular terminal emulators, need to print image text in which both the
foreground and background bits of each character are painted. This prevents annoying flicker on
many displays.
To draw 8-bit image text characters in a given drawable, use XDrawImageString.
XDrawImageString (display, d, gc, x, y, string, length)
Display *display;
Drawable d;
GC gc;
int x, y;
char *string;
int length;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
string
Specifies the character string.
length
Specifies the number of characters in the string argument.
To draw 2-byte image text characters in a given drawable, use XDrawImageString16.
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XDrawImageString16 (display, d, gc, x, y, string, length)
Display *display;
Drawable d;
GC gc;
int x, y;
XChar2b *string;
int length;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates, which are relative to the origin of the specified
drawable and define the origin of the first character.
string
Specifies the character string.
length
Specifies the number of characters in the string argument.
The XDrawImageString16 function is similar to XDrawImageString except that it uses 2-byte
or 16-bit characters. Both functions also use both the foreground and background pixels of the
GC in the destination.
The effect is first to fill a destination rectangle with the background pixel defined in the GC and
then to paint the text with the foreground pixel. The upper-left corner of the filled rectangle is at:
[x, y - font-ascent]
The width is:
overall-width
The height is:
font-ascent + font-descent
The overall-width, font-ascent, and font-descent are as would be returned by XQueryTextEx-
tents
using gc and string. The function and fill-style defined in the GC are ignored for these
functions. The effective function is GXcopy, and the effective fill-style is FillSolid.
For fonts defined with 2-byte matrix indexing and used with XDrawImageString, each byte is
used as a byte2 with a byte1 of zero.
Both functions use these GC components: plane-mask, foreground, background, font, subwin-
dow-mode, clip-x-origin, clip-y-origin, and clip-mask.
XDrawImageString and XDrawImageString16 can generate BadDrawable, BadGC, and
BadMatch errors.
8.7. Transferring Images between Client and Server
Xlib provides functions that you can use to transfer images between a client and the server.
Because the server may require diverse data formats, Xlib provides an image object that fully
describes the data in memory and that provides for basic operations on that data. You should ref-
erence the data through the image object rather than referencing the data directly. Howev er, some
implementations of the Xlib library may efficiently deal with frequently used data formats by
replacing functions in the procedure vector with special case functions. Supported operations
include destroying the image, getting a pixel, storing a pixel, extracting a subimage of an image,
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and adding a constant to an image (see section 16.8).
All the image manipulation functions discussed in this section make use of the XImage structure,
which describes an image as it exists in the client's memory.
typedef struct _XImage {
int width, height;
/* size of image */
int xoffset; /* number of pixels offset in X direction */
int format;
/* XYBitmap, XYPixmap, ZPixmap */
char *data;
/* pointer to image data */
int byte_order;
/* data byte order, LSBFirst, MSBFirst */
int bitmap_unit;
/* quant. of scanline 8, 16, 32 */
int bitmap_bit_order;
/* LSBFirst, MSBFirst */
int bitmap_pad;
/* 8, 16, 32 either XY or ZPixmap */
int depth;
/* depth of image */
int bytes_per_line;
/* accelerator to next scanline */
int bits_per_pixel; /* bits per pixel (ZPixmap) */
unsigned long red_mask;
/* bits in z arrangement */
unsigned long green_mask;
unsigned long blue_mask;
XPointer obdata;
/* hook for the object routines to hang on */
struct funcs {
/* image manipulation routines */
struct _XImage *(*create_image)();
int (*destroy_image)();
unsigned long (*get_pixel)();
int (*put_pixel)();
struct _XImage *(*sub_image)();
int (*add_pixel)();
} f;
} XImage;
To initialize the image manipulation routines of an image structure, use XInitImage.
Status XInitImage(image)
XImage *image;
ximage
Specifies the image.
The XInitImage function initializes the internal image manipulation routines of an image struc-
ture, based on the values of the various structure members. All fields other than the manipulation
routines must already be initialized. If the bytes_per_line member is zero, XInitImage will
assume the image data is contiguous in memory and set the bytes_per_line member to an appro-
priate value based on the other members; otherwise, the value of bytes_per_line is not changed.
All of the manipulation routines are initialized to functions that other Xlib image manipulation
functions need to operate on the type of image specified by the rest of the structure.
This function must be called for any image constructed by the client before passing it to any other
Xlib function. Image structures created or returned by Xlib do not need to be initialized in this
fashion.
This function returns a nonzero status if initialization of the structure is successful. It returns zero
if it detected some error or inconsistency in the structure, in which case the image is not changed.
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To combine an image with a rectangle of a drawable on the display, use XPutImage.
XPutImage (display, d, gc, image, src_x, src_y, dest_x, dest_y, width, height)
Display *display;
Drawable d;
GC gc;
XImage *image;
int src_x, src_y;
int dest_x, dest_y;
unsigned int width, height;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
image
Specifies the image you want combined with the rectangle.
src_x
Specifies the offset in X from the left edge of the image defined by the XImage
structure.
src_y
Specifies the offset in Y from the top edge of the image defined by the XImage
structure.
dest_x
dest_y
Specify the x and y coordinates, which are relative to the origin of the drawable
and are the coordinates of the subimage.
width
height
Specify the width and height of the subimage, which define the dimensions of the
rectangle.
The XPutImage function combines an image with a rectangle of the specified drawable. The
section of the image defined by the src_x, src_y, width, and height arguments is drawn on the
specified part of the drawable. If XYBitmap format is used, the depth of the image must be one,
or a BadMatch error results. The foreground pixel in the GC defines the source for the one bits
in the image, and the background pixel defines the source for the zero bits. For XYPixmap and
ZPixmap, the depth of the image must match the depth of the drawable, or a BadMatch error
results.
If the characteristics of the image (for example, byte_order and bitmap_unit) differ from what the
server requires, XPutImage automatically makes the appropriate conversions.
This function uses these GC components: function, plane-mask, subwindow-mode, clip-x-origin,
clip-y-origin, and clip-mask. It also uses these GC mode-dependent components: foreground and
background.
XPutImage can generate BadDrawable, BadGC, BadMatch, and BadValue errors.
To return the contents of a rectangle in a given drawable on the display, use XGetImage. This
function specifically supports rudimentary screen dumps.
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XImage *XGetImage(display, d, x, y, width, height, plane_mask, format)
Display *display;
Drawable d;
int x, y;
unsigned int width, height;
unsigned long plane_mask;
int format;
display
Specifies the connection to the X server.
d
Specifies the drawable.
x
y
Specify the x and y coordinates, which are relative to the origin of the drawable
and define the upper-left corner of the rectangle.
width
height
Specify the width and height of the subimage, which define the dimensions of the
rectangle.
plane_mask
Specifies the plane mask.
format
Specifies the format for the image. You can pass XYPixmap or ZPixmap.
The XGetImage function returns a pointer to an XImage structure. This structure provides you
with the contents of the specified rectangle of the drawable in the format you specify. If the for-
mat argument is XYPixmap, the image contains only the bit planes you passed to the
plane_mask argument. If the plane_mask argument only requests a subset of the planes of the
display, the depth of the returned image will be the number of planes requested. If the format
argument is ZPixmap, XGetImage returns as zero the bits in all planes not specified in the
plane_mask argument. The function performs no range checking on the values in plane_mask
and ignores extraneous bits.
XGetImage returns the depth of the image to the depth member of the XImage structure. The
depth of the image is as specified when the drawable was created, except when getting a subset of
the planes in XYPixmap format, when the depth is given by the number of bits set to 1 in
plane_mask.
If the drawable is a pixmap, the given rectangle must be wholly contained within the pixmap, or a
BadMatch error results. If the drawable is a window, the window must be viewable, and it must
be the case that if there were no inferiors or overlapping windows, the specified rectangle of the
window would be fully visible on the screen and wholly contained within the outside edges of the
window, or a BadMatch error results. Note that the borders of the window can be included and
read with this request. If the window has backing-store, the backing-store contents are returned
for regions of the window that are obscured by noninferior windows. If the window does not
have backing-store, the returned contents of such obscured regions are undefined. The returned
contents of visible regions of inferiors of a different depth than the specified window's depth are
also undefined. The pointer cursor image is not included in the returned contents. If a problem
occurs, XGetImage returns NULL.
XGetImage can generate BadDrawable, BadMatch, and BadValue errors.
To copy the contents of a rectangle on the display to a location within a preexisting image struc-
ture, use XGetSubImage.
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XImage *XGetSubImage(display, d, x, y, width, height, plane_mask, format, dest_image, dest_x,
dest_y)
Display *display;
Drawable d;
int x, y;
unsigned int width, height;
unsigned long plane_mask;
int format;
XImage *dest_image;
int dest_x, dest_y;
display
Specifies the connection to the X server.
d
Specifies the drawable.
x
y
Specify the x and y coordinates, which are relative to the origin of the drawable
and define the upper-left corner of the rectangle.
width
height
Specify the width and height of the subimage, which define the dimensions of the
rectangle.
plane_mask
Specifies the plane mask.
format
Specifies the format for the image. You can pass XYPixmap or ZPixmap.
dest_image
Specifies the destination image.
dest_x
dest_y
Specify the x and y coordinates, which are relative to the origin of the destination
rectangle, specify its upper-left corner, and determine where the subimage is
placed in the destination image.
The XGetSubImage function updates dest_image with the specified subimage in the same man-
ner as XGetImage. If the format argument is XYPixmap, the image contains only the bit planes
you passed to the plane_mask argument. If the format argument is ZPixmap, XGetSubImage
returns as zero the bits in all planes not specified in the plane_mask argument. The function per-
forms no range checking on the values in plane_mask and ignores extraneous bits. As a con-
venience, XGetSubImage returns a pointer to the same XImage structure specified by
dest_image.
The depth of the destination XImage structure must be the same as that of the drawable. If the
specified subimage does not fit at the specified location on the destination image, the right and
bottom edges are clipped. If the drawable is a pixmap, the given rectangle must be wholly con-
tained within the pixmap, or a BadMatch error results. If the drawable is a window, the window
must be viewable, and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen and wholly contained
within the outside edges of the window, or a BadMatch error results. If the window has back-
ing-store, then the backing-store contents are returned for regions of the window that are obscured
by noninferior windows. If the window does not have backing-store, the returned contents of
such obscured regions are undefined. The returned contents of visible regions of inferiors of a
different depth than the specified window's depth are also undefined. If a problem occurs, XGet-
SubImage
returns NULL.
XGetSubImage can generate BadDrawable, BadGC, BadMatch, and BadValue errors.
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Chapter 9
Window and Session Manager Functions
Although it is difficult to categorize functions as exclusively for an application, a window man-
ager, or a session manager, the functions in this chapter are most often used by window managers
and session managers. It is not expected that these functions will be used by most application
programs. Xlib provides management functions to:

Change the parent of a window

Control the lifetime of a window

Manage installed colormaps

Set and retrieve the font search path

Grab the server

Kill a client

Control the screen saver

Control host access
9.1. Changing the Parent of a Window
To change a window's parent to another window on the same screen, use XReparentWindow.
There is no way to move a window between screens.
XReparentWindow(display, w, parent, x, y)
Display *display;
Window w;
Window parent;
int x, y;
display
Specifies the connection to the X server.
w
Specifies the window.
parent
Specifies the parent window.
x
y
Specify the x and y coordinates of the position in the new parent window.
If the specified window is mapped, XReparentWindow automatically performs an UnmapWin-
dow
request on it, removes it from its current position in the hierarchy, and inserts it as the child
of the specified parent. The window is placed in the stacking order on top with respect to sibling
windows.
After reparenting the specified window, XReparentWindow causes the X server to generate a
ReparentNotify ev ent. The override_redirect member returned in this event is set to the win-
dow's corresponding attribute. Window manager clients usually should ignore this window if this
member is set to True. Finally, if the specified window was originally mapped, the X server
automatically performs a MapWindow request on it.
The X server performs normal exposure processing on formerly obscured windows. The X server
might not generate Expose ev ents for regions from the initial UnmapWindow request that are
immediately obscured by the final MapWindow request. A BadMatch error results if:
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The new parent window is not on the same screen as the old parent window.

The new parent window is the specified window or an inferior of the specified window.

The new parent is InputOnly, and the window is not.

The specified window has a ParentRelative background, and the new parent window is not
the same depth as the specified window.
XReparentWindow can generate BadMatch and BadWindow errors.
9.2. Controlling the Lifetime of a Window
The save-set of a client is a list of other clients' windows that, if they are inferiors of one of the
client's windows at connection close, should not be destroyed and should be remapped if they are
unmapped. For further information about close-connection processing, see section 2.6. To allow
an application's window to survive when a window manager that has reparented a window fails,
Xlib provides the save-set functions that you can use to control the longevity of subwindows that
are normally destroyed when the parent is destroyed. For example, a window manager that wants
to add decoration to a window by adding a frame might reparent an application's window. When
the frame is destroyed, the application's window should not be destroyed but be returned to its
previous place in the window hierarchy.
The X server automatically removes windows from the save-set when they are destroyed.
To add or remove a window from the client's sav e-set, use XChangeSaveSet.
XChangeSaveSet (display, w, change_mode)
Display *display;
Window w;
int change_mode;
display
Specifies the connection to the X server.
w
Specifies the window that you want to add to or delete from the client's sav e-set.
change_mode
Specifies the mode. You can pass SetModeInsert or SetModeDelete.
Depending on the specified mode, XChangeSaveSet either inserts or deletes the specified win-
dow from the client's sav e-set. The specified window must have been created by some other
client, or a BadMatch error results.
XChangeSaveSet can generate BadMatch, BadValue, and BadWindow errors.
To add a window to the client's sav e-set, use XAddToSaveSet.
XAddToSaveSet (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window that you want to add to the client's sav e-set.
The XAddToSaveSet function adds the specified window to the client's sav e-set. The specified
window must have been created by some other client, or a BadMatch error results.
XAddToSaveSet can generate BadMatch and BadWindow errors.
To remove a window from the client's sav e-set, use XRemoveFromSaveSet.
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XRemoveFromSaveSet (display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window that you want to delete from the client's sav e-set.
The XRemoveFromSaveSet function removes the specified window from the client's sav e-set.
The specified window must have been created by some other client, or a BadMatch error results.
XRemoveFromSaveSet can generate BadMatch and BadWindow errors.
9.3. Managing Installed Colormaps
The X server maintains a list of installed colormaps. Windows using these colormaps are guaran-
teed to display with correct colors; windows using other colormaps may or may not display with
correct colors. Xlib provides functions that you can use to install a colormap, uninstall a col-
ormap, and obtain a list of installed colormaps.
At any time, there is a subset of the installed maps that is viewed as an ordered list and is called
the required list. The length of the required list is at most M, where M is the minimum number of
installed colormaps specified for the screen in the connection setup. The required list is main-
tained as follows. When a colormap is specified to XInstallColormap, it is added to the head of
the list; the list is truncated at the tail, if necessary, to keep its length to at most M. When a col-
ormap is specified to XUninstallColormap and it is in the required list, it is removed from the
list. A colormap is not added to the required list when it is implicitly installed by the X server,
and the X server cannot implicitly uninstall a colormap that is in the required list.
To install a colormap, use XInstallColormap.
XInstallColormap (display, colormap)
Display *display;
Colormap colormap;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
The XInstallColormap function installs the specified colormap for its associated screen. All
windows associated with this colormap immediately display with true colors. You associated the
windows with this colormap when you created them by calling XCreateWindow,
XCreateSimpleWindow, XChangeWindowAttributes, or XSetWindowColormap.
If the specified colormap is not already an installed colormap, the X server generates a Col-
ormapNotify
ev ent on each window that has that colormap. In addition, for every other col-
ormap that is installed as a result of a call to XInstallColormap, the X server generates a Col-
ormapNotify
ev ent on each window that has that colormap.
XInstallColormap can generate a BadColor error.
To uninstall a colormap, use XUninstallColormap.
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XUninstallColormap (display, colormap)
Display *display;
Colormap colormap;
display
Specifies the connection to the X server.
colormap
Specifies the colormap.
The XUninstallColormap function removes the specified colormap from the required list for its
screen. As a result, the specified colormap might be uninstalled, and the X server might implic-
itly install or uninstall additional colormaps. Which colormaps get installed or uninstalled is
server dependent except that the required list must remain installed.
If the specified colormap becomes uninstalled, the X server generates a ColormapNotify ev ent
on each window that has that colormap. In addition, for every other colormap that is installed or
uninstalled as a result of a call to XUninstallColormap, the X server generates a ColormapNo-
tify
ev ent on each window that has that colormap.
XUninstallColormap can generate a BadColor error.
To obtain a list of the currently installed colormaps for a given screen, use
XListInstalledColormaps.
Colormap *XListInstalledColormaps(display, w, num_return)
Display *display;
Window w;
int *num_return;
display
Specifies the connection to the X server.
w
Specifies the window that determines the screen.
num_return
Returns the number of currently installed colormaps.
The XListInstalledColormaps function returns a list of the currently installed colormaps for the
screen of the specified window. The order of the colormaps in the list is not significant and is no
explicit indication of the required list. When the allocated list is no longer needed, free it by
using XFree.
XListInstalledColormaps can generate a BadWindow error.
9.4. Setting and Retrieving the Font Search Path
The set of fonts available from a server depends on a font search path. Xlib provides functions to
set and retrieve the search path for a server.
To set the font search path, use XSetFontPath.
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XSetFontPath (display, directories, ndirs)
Display *display;
char **directories;
int ndirs;
display
Specifies the connection to the X server.
directories
Specifies the directory path used to look for a font. Setting the path to the empty
list restores the default path defined for the X server.
ndirs
Specifies the number of directories in the path.
The XSetFontPath function defines the directory search path for font lookup. There is only one
search path per X server, not one per client. The encoding and interpretation of the strings are
implementation-dependent, but typically they specify directories or font servers to be searched in
the order listed. An X server is permitted to cache font information internally; for example, it
might cache an entire font from a file and not check on subsequent opens of that font to see if the
underlying font file has changed. However, when the font path is changed, the X server is guaran-
teed to flush all cached information about fonts for which there currently are no explicit resource
IDs allocated. The meaning of an error from this request is implementation-dependent.
XSetFontPath can generate a BadValue error.
To get the current font search path, use XGetFontPath.
char **XGetFontPath (display, npaths_return)
Display *display;
int *npaths_return;
display
Specifies the connection to the X server.
npaths_return
Returns the number of strings in the font path array.
The XGetFontPath function allocates and returns an array of strings containing the search path.
The contents of these strings are implementation-dependent and are not intended to be interpreted
by client applications. When it is no longer needed, the data in the font path should be freed by
using XFreeFontPath.
To free data returned by XGetFontPath, use XFreeFontPath.
XFreeFontPath (list)
char **list;
list
Specifies the array of strings you want to free.
The XFreeFontPath function frees the data allocated by XGetFontPath.
9.5. Grabbing the Server
Xlib provides functions that you can use to grab and ungrab the server. These functions can be
used to control processing of output on other connections by the window system server. While
the server is grabbed, no processing of requests or close downs on any other connection will
occur. A client closing its connection automatically ungrabs the server. Although grabbing the
server is highly discouraged, it is sometimes necessary.
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To grab the server, use XGrabServer.
XGrabServer (display)
Display *display;
display
Specifies the connection to the X server.
The XGrabServer function disables processing of requests and close downs on all other connec-
tions than the one this request arrived on. You should not grab the X server any more than is
absolutely necessary.
To ungrab the server, use XUngrabServer.
XUngrabServer (display)
Display *display;
display
Specifies the connection to the X server.
The XUngrabServer function restarts processing of requests and close downs on other connec-
tions. You should avoid grabbing the X server as much as possible.
9.6. Killing Clients
Xlib provides a function to cause the connection to a client to be closed and its resources to be
destroyed. To destroy a client, use XKillClient.
XKillClient (display, resource)
Display *display;
XID resource;
display
Specifies the connection to the X server.
resource
Specifies any resource associated with the client that you want to destroy or
AllTemporary.
The XKillClient function forces a close down of the client that created the resource if a valid
resource is specified. If the client has already terminated in either RetainPermanent or Retain-
Temporary
mode, all of the client's resources are destroyed. If AllTemporary is specified, the
resources of all clients that have terminated in RetainTemporary are destroyed (see section 2.5).
This permits implementation of window manager facilities that aid debugging. A client can set
its close-down mode to RetainTemporary. If the client then crashes, its windows would not be
destroyed. The programmer can then inspect the application's window tree and use the window
manager to destroy the zombie windows.
XKillClient can generate a BadValue error.
9.7. Controlling the Screen Saver
Xlib provides functions that you can use to set or reset the mode of the screen saver, to force or
activate the screen saver, or to obtain the current screen saver values.
To set the screen saver mode, use XSetScreenSaver.
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XSetScreenSaver(display, timeout, interval, prefer_blanking, allow_exposures)
Display *display;
int timeout, interval;
int prefer_blanking;
int allow_exposures;
display
Specifies the connection to the X server.
timeout
Specifies the timeout, in seconds, until the screen saver turns on.
interval
Specifies the interval, in seconds, between screen saver alterations.
prefer_blanking Specifies how to enable screen blanking. You can pass DontPreferBlanking,
PreferBlanking, or DefaultBlanking.
allow_exposuresSpecifies the screen save control values. You can pass DontAllowExposures,
AllowExposures, or DefaultExposures.
Timeout and interval are specified in seconds. A timeout of 0 disables the screen saver (but an
activated screen saver is not deactivated), and a timeout of -1 restores the default. Other negative
values generate a BadValue error. If the timeout value is nonzero, XSetScreenSaver enables the
screen saver. An interval of 0 disables the random-pattern motion. If no input from devices
(keyboard, mouse, and so on) is generated for the specified number of timeout seconds once the
screen saver is enabled, the screen saver is activated.
For each screen, if blanking is preferred and the hardware supports video blanking, the screen
simply goes blank. Otherwise, if either exposures are allowed or the screen can be regenerated
without sending Expose ev ents to clients, the screen is tiled with the root window background
tile randomly re-origined each interval seconds. Otherwise, the screens' state do not change, and
the screen saver is not activated. The screen saver is deactivated, and all screen states are restored
at the next keyboard or pointer input or at the next call to XForceScreenSaver with mode
ScreenSaverReset.
If the server-dependent screen saver method supports periodic change, the interval argument
serves as a hint about how long the change period should be, and zero hints that no periodic
change should be made. Examples of ways to change the screen include scrambling the colormap
periodically, moving an icon image around the screen periodically, or tiling the screen with the
root window background tile, randomly re-origined periodically.
XSetScreenSaver can generate a BadValue error.
To force the screen saver on or off, use XForceScreenSaver.
XForceScreenSaver(display, mode)
Display *display;
int mode;
display
Specifies the connection to the X server.
mode
Specifies the mode that is to be applied. You can pass ScreenSaverActive or
ScreenSaverReset.
If the specified mode is ScreenSaverActive and the screen saver currently is deactivated,
XForceScreenSaver activates the screen saver even if the screen saver had been disabled with a
timeout of zero. If the specified mode is ScreenSaverReset and the screen saver currently is
enabled, XForceScreenSaver deactivates the screen saver if it was activated, and the activation
timer is reset to its initial state (as if device input had been received).
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XForceScreenSaver can generate a BadValue error.
To activate the screen saver, use XActivateScreenSaver.
XActivateScreenSaver(display)
Display *display;
display
Specifies the connection to the X server.
To reset the screen saver, use XResetScreenSaver.
XResetScreenSaver(display)
Display *display;
display
Specifies the connection to the X server.
To get the current screen saver values, use XGetScreenSaver.
XGetScreenSaver(display, timeout_return, interval_return, prefer_blanking_return,
allow_exposures_return)
Display *display;
int *timeout_return, *interval_return;
int *prefer_blanking_return;
int *allow_exposures_return;
display
Specifies the connection to the X server.
timeout_return Returns the timeout, in seconds, until the screen saver turns on.
interval_return Returns the interval between screen saver inv ocations.
prefer_blanking_return
Returns the current screen blanking preference (DontPreferBlanking,
PreferBlanking, or DefaultBlanking).
allow_exposures_return
Returns the current screen save control value (DontAllowExposures,
AllowExposures, or DefaultExposures).
9.8. Controlling Host Access
This section discusses how to:

Add, get, or remove hosts from the access control list

Change, enable, or disable access
X does not provide any protection on a per-window basis. If you find out the resource ID of a
resource, you can manipulate it. To provide some minimal level of protection, however, connec-
tions are permitted only from machines you trust. This is adequate on single-user workstations
but obviously breaks down on timesharing machines. Although provisions exist in the X protocol
for proper connection authentication, the lack of a standard authentication server leaves host-level
access control as the only common mechanism.
The initial set of hosts allowed to open connections typically consists of:

The host the window system is running on.
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On POSIX-conformant systems, each host listed in the /etc/X?.hosts file. The ? indicates
the number of the display. This file should consist of host names separated by newlines.
DECnet nodes must terminate in :: to distinguish them from Internet hosts.
If a host is not in the access control list when the access control mechanism is enabled and if the
host attempts to establish a connection, the server refuses the connection. To change the access
list, the client must reside on the same host as the server and/or must have been granted permis-
sion in the initial authorization at connection setup.
Servers also can implement other access control policies in addition to or in place of this host
access facility. For further information about other access control implementations, see ``X Win-
dow System Protocol.''
9.8.1. Adding, Getting, or Removing Hosts
Xlib provides functions that you can use to add, get, or remove hosts from the access control list.
All the host access control functions use the XHostAddress structure, which contains:
typedef struct {
int family; /* for example FamilyInternet */
int length;
/* length of address, in bytes */
char *address;
/* pointer to where to find the address */
} XHostAddress;
The family member specifies which protocol address family to use (for example, TCP/IP or DEC-
net) and can be FamilyInternet, FamilyDECnet, or FamilyChaos. The length member speci-
fies the length of the address in bytes. The address member specifies a pointer to the address.
For TCP/IP, the address should be in network byte order. For the DECnet family, the server per-
forms no automatic swapping on the address bytes. A Phase IV address is 2 bytes long. The first
byte contains the least significant 8 bits of the node number. The second byte contains the most
significant 2 bits of the node number in the least significant 2 bits of the byte and the area in the
most significant 6 bits of the byte.
To add a single host, use XAddHost.
XAddHost (display, host)
Display *display;
XHostAddress *host;
display
Specifies the connection to the X server.
host
Specifies the host that is to be added.
The XAddHost function adds the specified host to the access control list for that display. The
server must be on the same host as the client issuing the command, or a BadAccess error results.
XAddHost can generate BadAccess and BadValue errors.
To add multiple hosts at one time, use XAddHosts.
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XAddHosts (display, hosts, num_hosts)
Display *display;
XHostAddress *hosts;
int num_hosts;
display
Specifies the connection to the X server.
hosts
Specifies each host that is to be added.
num_hosts
Specifies the number of hosts.
The XAddHosts function adds each specified host to the access control list for that display. The
server must be on the same host as the client issuing the command, or a BadAccess error results.
XAddHosts can generate BadAccess and BadValue errors.
To obtain a host list, use XListHosts.
XHostAddress *XListHosts(display, nhosts_return, state_return)
Display *display;
int *nhosts_return;
Bool *state_return;
display
Specifies the connection to the X server.
nhosts_return
Returns the number of hosts currently in the access control list.
state_return
Returns the state of the access control.
The XListHosts function returns the current access control list as well as whether the use of the
list at connection setup was enabled or disabled. XListHosts allows a program to find out what
machines can make connections. It also returns a pointer to a list of host structures that were allo-
cated by the function. When no longer needed, this memory should be freed by calling XFree.
To remove a single host, use XRemoveHost.
XRemoveHost (display, host)
Display *display;
XHostAddress *host;
display
Specifies the connection to the X server.
host
Specifies the host that is to be removed.
The XRemoveHost function removes the specified host from the access control list for that dis-
play. The server must be on the same host as the client process, or a BadAccess error results. If
you remove your machine from the access list, you can no longer connect to that server, and this
operation cannot be reversed unless you reset the server.
XRemoveHost can generate BadAccess and BadValue errors.
To remove multiple hosts at one time, use XRemoveHosts.
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XRemoveHosts (display, hosts, num_hosts)
Display *display;
XHostAddress *hosts;
int num_hosts;
display
Specifies the connection to the X server.
hosts
Specifies each host that is to be removed.
num_hosts
Specifies the number of hosts.
The XRemoveHosts function removes each specified host from the access control list for that
display. The X server must be on the same host as the client process, or a BadAccess error
results. If you remove your machine from the access list, you can no longer connect to that
server, and this operation cannot be reversed unless you reset the server.
XRemoveHosts can generate BadAccess and BadValue errors.
9.8.2. Changing, Enabling, or Disabling Access Control
Xlib provides functions that you can use to enable, disable, or change access control.
For these functions to execute successfully, the client application must reside on the same host as
the X server and/or have been given permission in the initial authorization at connection setup.
To change access control, use XSetAccessControl.
XSetAccessControl (display, mode)
Display *display;
int mode;
display
Specifies the connection to the X server.
mode
Specifies the mode. You can pass EnableAccess or DisableAccess.
The XSetAccessControl function either enables or disables the use of the access control list at
each connection setup.
XSetAccessControl can generate BadAccess and BadValue errors.
To enable access control, use XEnableAccessControl.
XEnableAccessControl (display)
Display *display;
display
Specifies the connection to the X server.
The XEnableAccessControl function enables the use of the access control list at each connec-
tion setup.
XEnableAccessControl can generate a BadAccess error.
To disable access control, use XDisableAccessControl.
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XDisableAccessControl (display)
Display *display;
display
Specifies the connection to the X server.
The XDisableAccessControl function disables the use of the access control list at each connec-
tion setup.
XDisableAccessControl can generate a BadAccess error.
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Chapter 10
Events
A client application communicates with the X server through the connection you establish with
the XOpenDisplay function. A client application sends requests to the X server over this con-
nection. These requests are made by the Xlib functions that are called in the client application.
Many Xlib functions cause the X server to generate events, and the user's typing or moving the
pointer can generate events asynchronously. The X server returns events to the client on the same
connection.
This chapter discusses the following topics associated with events:

Event types

Event structures

Event masks

Event processing
Functions for handling events are dealt with in the next chapter.
10.1. Event Types
An event is data generated asynchronously by the X server as a result of some device activity or
as side effects of a request sent by an Xlib function. Device-related events propagate from the
source window to ancestor windows until some client application has selected that event type or
until the event is explicitly discarded. The X server generally sends an event to a client applica-
tion only if the client has specifically asked to be informed of that event type, typically by setting
the event-mask attribute of the window. The mask can also be set when you create a window or
by changing the window's event-mask. You can also mask out events that would propagate to
ancestor windows by manipulating the do-not-propagate mask of the window's attributes. How-
ev er, MappingNotify ev ents are always sent to all clients.
An event type describes a specific event generated by the X server. For each event type, a corre-
sponding constant name is defined in <X11/X.h>, which is used when referring to an event type.
The following table lists the event category and its associated event type or types. The processing
associated with these events is discussed in section 10.5.
Event Category
Event Type
Ke yboard events
KeyPress, KeyRelease
Pointer events
ButtonPress, ButtonRelease, MotionNotify
Window crossing events
EnterNotify, LeaveNotify
Input focus events
FocusIn, FocusOut
Ke ymap state notification event
KeymapNotify
Exposure events
Expose, GraphicsExpose, NoExpose
Structure control events
CirculateRequest, ConfigureRequest, MapRequest,
ResizeRequest
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Event Category
Event Type
Window state notification events
CirculateNotify, ConfigureNotify, CreateNotify,
DestroyNotify, GravityNotify, MapNotify,
MappingNotify, ReparentNotify, UnmapNotify,
VisibilityNotify
Colormap state notification event
ColormapNotify
Client communication events
ClientMessage, PropertyNotify, SelectionClear,
SelectionNotify, SelectionRequest
10.2. Event Structures
For each event type, a corresponding structure is declared in <X11/Xlib.h>. All the event struc-
tures have the following common members:
typedef struct {
int type;
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
} XAnyEvent;
The type member is set to the event type constant name that uniquely identifies it. For example,
when the X server reports a GraphicsExpose ev ent to a client application, it sends an XGraph-
icsExposeEvent
structure with the type member set to GraphicsExpose. The display member is
set to a pointer to the display the event was read on. The send_event member is set to True if the
ev ent came from a SendEvent protocol request. The serial member is set from the serial number
reported in the protocol but expanded from the 16-bit least-significant bits to a full 32-bit value.
The window member is set to the window that is most useful to toolkit dispatchers.
The X server can send events at any time in the input stream. Xlib stores any events received
while waiting for a reply in an event queue for later use. Xlib also provides functions that allow
you to check events in the event queue (see section 11.3).
In addition to the individual structures declared for each event type, the XEvent structure is a
union of the individual structures declared for each event type. Depending on the type, you
should access members of each event by using the XEvent union.
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typedef union _XEvent {
int type;
/* must not be changed */
XAnyEvent xany;
XKeyEvent xkey;
XButtonEvent xbutton;
XMotionEvent xmotion;
XCrossingEvent xcrossing;
XFocusChangeEvent xfocus;
XExposeEvent xexpose;
XGraphicsExposeEvent xgraphicsexpose;
XNoExposeEvent xnoexpose;
XVisibilityEvent xvisibility;
XCreateWindowEvent xcreatewindow;
XDestroyWindowEvent xdestroywindow;
XUnmapEvent xunmap;
XMapEvent xmap;
XMapRequestEvent xmaprequest;
XReparentEvent xreparent;
XConfigureEvent xconfigure;
XGravityEvent xgravity;
XResizeRequestEvent xresizerequest;
XConfigureRequestEvent xconfigurerequest;
XCirculateEvent xcirculate;
XCirculateRequestEvent xcirculaterequest;
XPropertyEvent xproperty;
XSelectionClearEvent xselectionclear;
XSelectionRequestEvent xselectionrequest;
XSelectionEvent xselection;
XColormapEvent xcolormap;
XClientMessageEvent xclient;
XMappingEvent xmapping;
XErrorEvent xerror;
XKeymapEvent xkeymap;
long pad[24];
} XEvent;
An XEvent structure's first entry always is the type member, which is set to the event type. The
second member always is the serial number of the protocol request that generated the event. The
third member always is send_event, which is a Bool that indicates if the event was sent by a dif-
ferent client. The fourth member always is a display, which is the display that the event was read
from. Except for keymap events, the fifth member always is a window, which has been carefully
selected to be useful to toolkit dispatchers. To avoid breaking toolkits, the order of these first five
entries is not to change. Most events also contain a time member, which is the time at which an
ev ent occurred. In addition, a pointer to the generic event must be cast before it is used to access
any other information in the structure.
10.3. Event Masks
Clients select event reporting of most events relative to a window. To do this, pass an event mask
to an Xlib event-handling function that takes an event_mask argument. The bits of the event
mask are defined in <X11/X.h>. Each bit in the event mask maps to an event mask name, which
describes the event or events you want the X server to return to a client application.
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Unless the client has specifically asked for them, most events are not reported to clients when
they are generated. Unless the client suppresses them by setting graphics-exposures in the GC to
False, GraphicsExpose and NoExpose are reported by default as a result of XCopyPlane and
XCopyArea. SelectionClear, SelectionRequest, SelectionNotify, or ClientMessage cannot
be masked. Selection-related ev ents are only sent to clients cooperating with selections (see sec-
tion 4.5). When the keyboard or pointer mapping is changed, MappingNotify is always sent to
clients.
The following table lists the event mask constants you can pass to the event_mask argument and
the circumstances in which you would want to specify the event mask:
Event Mask
Circumstances
NoEventMask
No events wanted
KeyPressMask
Ke yboard down events wanted
KeyReleaseMask
Ke yboard up events wanted
ButtonPressMask
Pointer button down events wanted
ButtonReleaseMask
Pointer button up events wanted
EnterWindowMask
Pointer window entry events wanted
LeaveWindowMask
Pointer window leave events wanted
PointerMotionMask
Pointer motion events wanted
PointerMotionHintMask
Pointer motion hints wanted
Button1MotionMask
Pointer motion while button 1 down
Button2MotionMask
Pointer motion while button 2 down
Button3MotionMask
Pointer motion while button 3 down
Button4MotionMask
Pointer motion while button 4 down
Button5MotionMask
Pointer motion while button 5 down
ButtonMotionMask
Pointer motion while any button down
KeymapStateMask
Ke yboard state wanted at window entry and focus in
ExposureMask
Any exposure wanted
VisibilityChangeMask
Any change in visibility wanted
StructureNotifyMask
Any change in window structure wanted
ResizeRedirectMask
Redirect resize of this window
SubstructureNotifyMask
Substructure notification wanted
SubstructureRedirectMask
Redirect structure requests on children
FocusChangeMask
Any change in input focus wanted
PropertyChangeMask
Any change in property wanted
ColormapChangeMask
Any change in colormap wanted
OwnerGrabButtonMask
Automatic grabs should activate with owner_events set
to True
10.4. Event Processing Overview
The event reported to a client application during event processing depends on which event masks
you provide as the event-mask attribute for a window. For some event masks, there is a one-to-
one correspondence between the event mask constant and the event type constant. For example,
if you pass the event mask ButtonPressMask, the X server sends back only ButtonPress ev ents.
Most events contain a time member, which is the time at which an event occurred.
In other cases, one event mask constant can map to several event type constants. For example, if
you pass the event mask SubstructureNotifyMask, the X server can send back
CirculateNotify, ConfigureNotify, CreateNotify, DestroyNotify, GravityNotify,
MapNotify, ReparentNotify, or UnmapNotify ev ents.
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In another case, two event masks can map to one event type. For example, if you pass either
PointerMotionMask or ButtonMotionMask, the X server sends back a MotionNotify ev ent.
The following table lists the event mask, its associated event type or types, and the structure name
associated with the event type. Some of these structures actually are typedefs to a generic struc-
ture that is shared between two event types. Note that N.A. appears in columns for which the
information is not applicable.
Event Mask
Event Type Structure
Generic Structure
ButtonMotionMask MotionNotify
XPointerMovedEvent XMotionEvent
Button1MotionMask
Button2MotionMask
Button3MotionMask
Button4MotionMask
Button5MotionMask
ButtonPressMask ButtonPress
XButtonPressedEvent XButtonEvent
ButtonReleaseMask ButtonRelease
XButtonReleasedEvent XButtonEvent
ColormapChangeMask ColormapNotify
XColormapEvent
EnterWindowMask EnterNotify
XEnterWindowEvent XCrossingEvent
LeaveWindowMask LeaveNotify XLeaveWindowEvent XCrossingEvent
ExposureMask Expose
XExposeEvent
GCGraphicsExposures in GC
GraphicsExpose XGraphicsExposeEvent
NoExpose XNoExposeEvent
FocusChangeMask FocusIn XFocusInEvent XFocusChangeEvent
FocusOut XFocusOutEvent XFocusChangeEvent
Ke ymapStateMask KeymapNotify XKeymapEvent
Ke yPressMask KeyPress XKeyPressedEvent XKeyEvent
Ke yReleaseMask KeyRelease XKeyReleasedEvent XKeyEvent
OwnerGrabButtonMask N.A.
N.A.
PointerMotionMask MotionNotify
XPointerMovedEvent XMotionEvent
PointerMotionHintMask N.A.
N.A.
PropertyChangeMask PropertyNotify
XPropertyEvent
ResizeRedirectMask ResizeRequest
XResizeRequestEvent
StructureNotifyMask CirculateNotify
XCirculateEvent
ConfigureNotify XConfigureEvent
DestroyNotify XDestroyWindowEvent
GravityNotify XGravityEvent
MapNotify XMapEvent
ReparentNotify XReparentEvent
UnmapNotify XUnmapEvent
SubstructureNotifyMask CirculateNotify
XCirculateEvent
ConfigureNotify XConfigureEvent
CreateNotify XCreateWindowEvent
DestroyNotify XDestroyWindowEvent
GravityNotify XGravityEvent
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Event Mask
Event Type Structure
Generic Structure
MapNotify XMapEvent
ReparentNotify XReparentEvent
UnmapNotify XUnmapEvent
SubstructureRedirectMask CirculateRequest
XCirculateRequestEvent
ConfigureRequest XConfigureRequestEvent
MapRequest XMapRequestEvent
N.A. ClientMessage
XClientMessageEvent
N.A. MappingNotify
XMappingEvent
N.A. SelectionClear
XSelectionClearEvent
N.A. SelectionNotify
XSelectionEvent
N.A. SelectionRequest
XSelectionRequestEvent
VisibilityChangeMask VisibilityNotify XVisibilityEvent
The sections that follow describe the processing that occurs when you select the different event
masks. The sections are organized according to these processing categories:

Keyboard and pointer events

Window crossing events

Input focus events

Keymap state notification events

Exposure events

Window state notification events

Structure control events

Colormap state notification events

Client communication events
10.5. Keyboard and Pointer Events
This section discusses:

Pointer button events

Keyboard and pointer events
10.5.1. Pointer Button Events
The following describes the event processing that occurs when a pointer button press is processed
with the pointer in some window w and when no active pointer grab is in progress.
The X server searches the ancestors of w from the root down, looking for a passive grab to acti-
vate. If no matching passive grab on the button exists, the X server automatically starts an active
grab for the client receiving the event and sets the last-pointer-grab time to the current server
time. The effect is essentially equivalent to an XGrabButton with these client passed argu-
ments:
Argument Value
w
The event window
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Argument Value
event_mask
The client's selected pointer events on the event window
pointer_mode
GrabModeAsync
keyboard_mode
GrabModeAsync
owner_events
True, if the client has selected OwnerGrabButton-
Mask on the event window, otherwise False
confine_to
None
cursor
None
The active grab is automatically terminated when the logical state of the pointer has all buttons
released. Clients can modify the active grab by calling XUngrabPointer and
XChangeActivePointerGrab.
10.5.2. Keyboard and Pointer Events
This section discusses the processing that occurs for the keyboard events KeyPress and KeyRe-
lease
and the pointer events ButtonPress, ButtonRelease, and MotionNotify. For information
about the keyboard event-handling utilities, see chapter 11.
The X server reports KeyPress or KeyRelease ev ents to clients wanting information about keys
that logically change state. Note that these events are generated for all keys, even those mapped
to modifier bits. The X server reports ButtonPress or ButtonRelease ev ents to clients wanting
information about buttons that logically change state.
The X server reports MotionNotify ev ents to clients wanting information about when the pointer
logically moves. The X server generates this event whenever the pointer is moved and the pointer
motion begins and ends in the window. The granularity of MotionNotify ev ents is not guaran-
teed, but a client that selects this event type is guaranteed to receive at least one event when the
pointer moves and then rests.
The generation of the logical changes lags the physical changes if device event processing is
frozen.
To receive KeyPress, KeyRelease, ButtonPress, and ButtonRelease ev ents, set
KeyPressMask, KeyReleaseMask, ButtonPressMask, and ButtonReleaseMask bits in the
ev ent-mask attribute of the window.
To receive MotionNotify ev ents, set one or more of the following event masks bits in the event-
mask attribute of the window.

Button1MotionMask - Button5MotionMask
The client application receives MotionNotify ev ents only when one or more of the speci-
fied buttons is pressed.

ButtonMotionMask
The client application receives MotionNotify ev ents only when at least one button is
pressed.

PointerMotionMask
The client application receives MotionNotify ev ents independent of the state of the pointer
buttons.

PointerMotionHintMask
If PointerMotionHintMask is selected in combination with one or more of the above
masks, the X server is free to send only one MotionNotify ev ent (with the is_hint member
of the XPointerMovedEvent structure set to NotifyHint) to the client for the event win-
dow, until either the key or button state changes, the pointer leaves the event window, or the
client calls XQueryPointer or XGetMotionEvents. The server still may send
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MotionNotify ev ents without is_hint set to NotifyHint.
The source of the event is the viewable window that the pointer is in. The window used by the X
server to report these events depends on the window's position in the window hierarchy and
whether any intervening window prohibits the generation of these events. Starting with the
source window, the X server searches up the window hierarchy until it locates the first window
specified by a client as having an interest in these events. If one of the intervening windows has
its do-not-propagate-mask set to prohibit generation of the event type, the events of those types
will be suppressed. Clients can modify the actual window used for reporting by performing
active grabs and, in the case of keyboard events, by using the focus window.
The structures for these event types contain:
typedef struct {
int type;
/* ButtonPress or ButtonRelease */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window; /* ``ev ent'' window it is reported relative to */
Window root; /* root window that the event occurred on */
Window subwindow; /* child window */
Time time;
/* milliseconds */
int x, y;
/* pointer x, y coordinates in event window */
int x_root, y_root;
/* coordinates relative to root */
unsigned int state;
/* key or button mask */
unsigned int button; /* detail */
Bool same_screen;
/* same screen flag */
} XButtonEvent;
typedef XButtonEvent XButtonPressedEvent;
typedef XButtonEvent XButtonReleasedEvent;
typedef struct {
int type;
/* KeyPress or KeyRelease */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window; /* ``ev ent'' window it is reported relative to */
Window root; /* root window that the event occurred on */
Window subwindow; /* child window */
Time time;
/* milliseconds */
int x, y;
/* pointer x, y coordinates in event window */
int x_root, y_root;
/* coordinates relative to root */
unsigned int state;
/* key or button mask */
unsigned int keycode; /* detail */
Bool same_screen;
/* same screen flag */
} XKe yEvent;
typedef XKeyEvent XKeyPressedEvent;
typedef XKeyEvent XKeyReleasedEvent;
typedef struct {
int type;
/* MotionNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
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Window window; /* ``ev ent'' window reported relative to */
Window root; /* root window that the event occurred on */
Window subwindow; /* child window */
Time time;
/* milliseconds */
int x, y;
/* pointer x, y coordinates in event window */
int x_root, y_root;
/* coordinates relative to root */
unsigned int state;
/* key or button mask */
char is_hint;
/* detail */
Bool same_screen;
/* same screen flag */
} XMotionEvent;
typedef XMotionEvent XPointerMovedEvent;
These structures have the following common members: window, root, subwindow, time, x, y,
x_root, y_root, state, and same_screen. The window member is set to the window on which the
ev ent was generated and is referred to as the event window. As long as the conditions previously
discussed are met, this is the window used by the X server to report the event. The root member
is set to the source window's root window. The x_root and y_root members are set to the
pointer's coordinates relative to the root window's origin at the time of the event.
The same_screen member is set to indicate whether the event window is on the same screen as the
root window and can be either True or False. If True, the event and root windows are on the
same screen. If False, the event and root windows are not on the same screen.
If the source window is an inferior of the event window, the subwindow member of the structure
is set to the child of the event window that is the source window or the child of the event window
that is an ancestor of the source window. Otherwise, the X server sets the subwindow member to
None. The time member is set to the time when the event was generated and is expressed in mil-
liseconds.
If the event window is on the same screen as the root window, the x and y members are set to the
coordinates relative to the event window's origin. Otherwise, these members are set to zero.
The state member is set to indicate the logical state of the pointer buttons and modifier keys just
prior to the event, which is the bitwise inclusive OR of one or more of the button or modifier key
masks: Button1Mask, Button2Mask, Button3Mask, Button4Mask, Button5Mask,
ShiftMask, LockMask, ControlMask, Mod1Mask, Mod2Mask, Mod3Mask, Mod4Mask,
and Mod5Mask.
Each of these structures also has a member that indicates the detail. For the XKeyPressedEvent
and XKeyReleasedEvent structures, this member is called a keycode. It is set to a number that
represents a physical key on the keyboard. The keycode is an arbitrary representation for any key
on the keyboard (see sections 12.7 and 16.1).
For the XButtonPressedEvent and XButtonReleasedEvent structures, this member is called
button. It represents the pointer button that changed state and can be the Button1, Button2,
Button3, Button4, or Button5 value. For the XPointerMovedEvent structure, this member is
called is_hint. It can be set to NotifyNormal or NotifyHint.
Some of the symbols mentioned in this section have fixed values, as follows:
Symbol Value
Button1MotionMask
(1L<<8)
Button2MotionMask
(1L<<9)
Button3MotionMask
(1L<<10)
Button4MotionMask
(1L<<11)
Button5MotionMask
(1L<<12)
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Symbol Value
Button1Mask
(1<<8)
Button2Mask
(1<<9)
Button3Mask
(1<<10)
Button4Mask
(1<<11)
Button5Mask
(1<<12)
ShiftMask
(1<<0)
LockMask
(1<<1)
ControlMask
(1<<2)
Mod1Mask
(1<<3)
Mod2Mask
(1<<4)
Mod3Mask
(1<<5)
Mod4Mask
(1<<6)
Mod5Mask
(1<<7)
Button1
1
Button2
2
Button3
3
Button4
4
Button5
5
10.6. Window Entry/Exit Events
This section describes the processing that occurs for the window crossing events EnterNotify
and LeaveNotify. If a pointer motion or a window hierarchy change causes the pointer to be in a
different window than before, the X server reports EnterNotify or LeaveNotify ev ents to clients
who have selected for these events. All EnterNotify and LeaveNotify ev ents caused by a hierar-
chy change are generated after any hierarchy event (UnmapNotify, MapNotify,
ConfigureNotify, GravityNotify, CirculateNotify) caused by that change; however, the X pro-
tocol does not constrain the ordering of EnterNotify and LeaveNotify ev ents with respect to
FocusOut, VisibilityNotify, and Expose ev ents.
This contrasts with MotionNotify ev ents, which are also generated when the pointer moves but
only when the pointer motion begins and ends in a single window. An EnterNotify or LeaveNo-
tify
ev ent also can be generated when some client application calls XGrabPointer and
XUngrabPointer.
To receive EnterNotify or LeaveNotify ev ents, set the EnterWindowMask or LeaveWindow-
Mask
bits of the event-mask attribute of the window.
The structure for these event types contains:
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typedef struct {
int type;
/* EnterNotify or LeaveNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window; /* ``ev ent'' window reported relative to */
Window root; /* root window that the event occurred on */
Window subwindow; /* child window */
Time time;
/* milliseconds */
int x, y;
/* pointer x, y coordinates in event window */
int x_root, y_root;
/* coordinates relative to root */
int mode;
/* NotifyNormal, NotifyGrab, NotifyUngrab */
int detail;
/*
* NotifyAncestor, NotifyVirtual, NotifyInferior,
* NotifyNonlinear,NotifyNonlinearVirtual
*/
Bool same_screen;
/* same screen flag */
Bool focus;
/* boolean focus */
unsigned int state;
/* key or button mask */
} XCrossingEvent;
typedef XCrossingEvent XEnterWindowEvent;
typedef XCrossingEvent XLeaveWindowEvent;
The window member is set to the window on which the EnterNotify or LeaveNotify ev ent was
generated and is referred to as the event window. This is the window used by the X server to
report the event, and is relative to the root window on which the event occurred. The root mem-
ber is set to the root window of the screen on which the event occurred.
For a LeaveNotify ev ent, if a child of the event window contains the initial position of the
pointer, the subwindow component is set to that child. Otherwise, the X server sets the subwin-
dow member to None. For an EnterNotify ev ent, if a child of the event window contains the
final pointer position, the subwindow component is set to that child or None.
The time member is set to the time when the event was generated and is expressed in millisec-
onds. The x and y members are set to the coordinates of the pointer position in the event window.
This position is always the pointer's final position, not its initial position. If the event window is
on the same screen as the root window, x and y are the pointer coordinates relative to the event
window's origin. Otherwise, x and y are set to zero. The x_root and y_root members are set to
the pointer's coordinates relative to the root window's origin at the time of the event.
The same_screen member is set to indicate whether the event window is on the same screen as the
root window and can be either True or False. If True, the event and root windows are on the
same screen. If False, the event and root windows are not on the same screen.
The focus member is set to indicate whether the event window is the focus window or an inferior
of the focus window. The X server can set this member to either True or False. If True, the
ev ent window is the focus window or an inferior of the focus window. If False, the event win-
dow is not the focus window or an inferior of the focus window.
The state member is set to indicate the state of the pointer buttons and modifier keys just prior to
the event. The X server can set this member to the bitwise inclusive OR of one or more of the
button or modifier key masks: Button1Mask, Button2Mask, Button3Mask, Button4Mask,
Button5Mask, ShiftMask, LockMask, ControlMask, Mod1Mask, Mod2Mask,
Mod3Mask, Mod4Mask, Mod5Mask.
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The mode member is set to indicate whether the events are normal events, pseudo-motion events
when a grab activates, or pseudo-motion events when a grab deactivates. The X server can set
this member to NotifyNormal, NotifyGrab, or NotifyUngrab.
The detail member is set to indicate the notify detail and can be NotifyAncestor, NotifyVirtual,
NotifyInferior, NotifyNonlinear, or NotifyNonlinearVirtual.
10.6.1. Normal Entry/Exit Events
EnterNotify and LeaveNotify ev ents are generated when the pointer moves from one window to
another window. Normal events are identified by XEnterWindowEvent or XLeaveWindow-
Event
structures whose mode member is set to NotifyNormal.

When the pointer moves from window A to window B and A is an inferior of B, the X
server does the following:
-
It generates a LeaveNotify ev ent on window A, with the detail member of the
XLeaveWindowEvent structure set to NotifyAncestor.
-
It generates a LeaveNotify ev ent on each window between window A and window
B, exclusive, with the detail member of each XLeaveWindowEvent structure set to
NotifyVirtual.
-
It generates an EnterNotify ev ent on window B, with the detail member of the XEn-
terWindowEvent
structure set to NotifyInferior.

When the pointer moves from window A to window B and B is an inferior of A, the X
server does the following:
-
It generates a LeaveNotify ev ent on window A, with the detail member of the
XLeaveWindowEvent structure set to NotifyInferior.
-
It generates an EnterNotify ev ent on each window between window A and window
B, exclusive, with the detail member of each XEnterWindowEvent structure set to
NotifyVirtual.
-
It generates an EnterNotify ev ent on window B, with the detail member of the XEn-
terWindowEvent
structure set to NotifyAncestor.

When the pointer moves from window A to window B and window C is their least common
ancestor, the X server does the following:
-
It generates a LeaveNotify ev ent on window A, with the detail member of the
XLeaveWindowEvent structure set to NotifyNonlinear.
-
It generates a LeaveNotify ev ent on each window between window A and window
C, exclusive, with the detail member of each XLeaveWindowEvent structure set to
NotifyNonlinearVirtual.
-
It generates an EnterNotify ev ent on each window between window C and window
B, exclusive, with the detail member of each XEnterWindowEvent structure set to
NotifyNonlinearVirtual.
-
It generates an EnterNotify ev ent on window B, with the detail member of the XEn-
terWindowEvent
structure set to NotifyNonlinear.

When the pointer moves from window A to window B on different screens, the X server
does the following:
-
It generates a LeaveNotify ev ent on window A, with the detail member of the
XLeaveWindowEvent structure set to NotifyNonlinear.
-
If window A is not a root window, it generates a LeaveNotify ev ent on each window
above window A up to and including its root, with the detail member of each
XLeaveWindowEvent structure set to NotifyNonlinearVirtual.
-
If window B is not a root window, it generates an EnterNotify ev ent on each win-
dow from window B's root down to but not including window B, with the detail
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member of each XEnterWindowEvent structure set to NotifyNonlinearVirtual.
-
It generates an EnterNotify ev ent on window B, with the detail member of the XEn-
terWindowEvent
structure set to NotifyNonlinear.
10.6.2. Grab and Ungrab Entry/Exit Events
Pseudo-motion mode EnterNotify and LeaveNotify ev ents are generated when a pointer grab
activates or deactivates. Events in which the pointer grab activates are identified by XEnterWin-
dowEvent
or XLeaveWindowEvent structures whose mode member is set to NotifyGrab.
Events in which the pointer grab deactivates are identified by XEnterWindowEvent or
XLeaveWindowEvent structures whose mode member is set to NotifyUngrab (see
XGrabPointer).

When a pointer grab activates after any initial warp into a confine_to window and before
generating any actual ButtonPress ev ent that activates the grab, G is the grab_window for
the grab, and P is the window the pointer is in, the X server does the following:
-
It generates EnterNotify and LeaveNotify ev ents (see section 10.6.1) with the mode
members of the XEnterWindowEvent and XLeaveWindowEvent structures set to
NotifyGrab. These events are generated as if the pointer were to suddenly warp
from its current position in P to some position in G. However, the pointer does not
warp, and the X server uses the pointer position as both the initial and final positions
for the events.

When a pointer grab deactivates after generating any actual ButtonRelease ev ent that
deactivates the grab, G is the grab_window for the grab, and P is the window the pointer is
in, the X server does the following:
-
It generates EnterNotify and LeaveNotify ev ents (see section 10.6.1) with the mode
members of the XEnterWindowEvent and XLeaveWindowEvent structures set to
NotifyUngrab. These events are generated as if the pointer were to suddenly warp
from some position in G to its current position in P. Howev er, the pointer does not
warp, and the X server uses the current pointer position as both the initial and final
positions for the events.
10.7. Input Focus Events
This section describes the processing that occurs for the input focus events FocusIn and
FocusOut. The X server can report FocusIn or FocusOut ev ents to clients wanting information
about when the input focus changes. The keyboard is always attached to some window (typically,
the root window or a top-level window), which is called the focus window. The focus window
and the position of the pointer determine the window that receives keyboard input. Clients may
need to know when the input focus changes to control highlighting of areas on the screen.
To receive FocusIn or FocusOut ev ents, set the FocusChangeMask bit in the event-mask
attribute of the window.
The structure for these event types contains:
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typedef struct {
int type;
/* FocusIn or FocusOut */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window; /* window of event */
int mode;
/* NotifyNormal, NotifyGrab, NotifyUngrab */
int detail;
/*
* NotifyAncestor, NotifyVirtual, NotifyInferior,
* NotifyNonlinear,NotifyNonlinearVirtual, NotifyPointer,
* NotifyPointerRoot, NotifyDetailNone
*/
} XFocusChangeEvent;
typedef XFocusChangeEvent XFocusInEvent;
typedef XFocusChangeEvent XFocusOutEvent;
The window member is set to the window on which the FocusIn or FocusOut ev ent was gener-
ated. This is the window used by the X server to report the event. The mode member is set to
indicate whether the focus events are normal focus events, focus events while grabbed, focus
ev ents when a grab activates, or focus events when a grab deactivates. The X server can set the
mode member to NotifyNormal, NotifyWhileGrabbed, NotifyGrab, or NotifyUngrab.
All FocusOut ev ents caused by a window unmap are generated after any UnmapNotify ev ent;
however, the X protocol does not constrain the ordering of FocusOut ev ents with respect to gen-
erated EnterNotify, LeaveNotify, VisibilityNotify, and Expose ev ents.
Depending on the event mode, the detail member is set to indicate the notify detail and can be
NotifyAncestor, NotifyVirtual, NotifyInferior, NotifyNonlinear, NotifyNonlinearVirtual,
NotifyPointer, NotifyPointerRoot, or NotifyDetailNone.
10.7.1. Normal Focus Events and Focus Events While Grabbed
Normal focus events are identified by XFocusInEvent or XFocusOutEvent structures whose
mode member is set to NotifyNormal. Focus events while grabbed are identified by XFocusIn-
Event
or XFocusOutEvent structures whose mode member is set to NotifyWhileGrabbed.
The X server processes normal focus and focus events while grabbed according to the following:

When the focus moves from window A to window B, A is an inferior of B, and the pointer
is in window P, the X server does the following:
-
It generates a FocusOut ev ent on window A, with the detail member of the XFocu-
sOutEvent
structure set to NotifyAncestor.
-
It generates a FocusOut ev ent on each window between window A and window B,
exclusive, with the detail member of each XFocusOutEvent structure set to
NotifyVirtual.
-
It generates a FocusIn ev ent on window B, with the detail member of the XFocu-
sOutEvent
structure set to NotifyInferior.
-
If window P is an inferior of window B but window P is not window A or an inferior
or ancestor of window A, it generates a FocusIn ev ent on each window below win-
dow B, down to and including window P, with the detail member of each XFocusIn-
Event
structure set to NotifyPointer.

When the focus moves from window A to window B, B is an inferior of A, and the pointer
is in window P, the X server does the following:
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-
If window P is an inferior of window A but P is not an inferior of window B or an
ancestor of B, it generates a FocusOut ev ent on each window from window P up to
but not including window A, with the detail member of each XFocusOutEvent
structure set to NotifyPointer.
-
It generates a FocusOut ev ent on window A, with the detail member of the XFocu-
sOutEvent
structure set to NotifyInferior.
-
It generates a FocusIn ev ent on each window between window A and window B,
exclusive, with the detail member of each XFocusInEvent structure set to
NotifyVirtual.
-
It generates a FocusIn ev ent on window B, with the detail member of the XFocusIn-
Event
structure set to NotifyAncestor.

When the focus moves from window A to window B, window C is their least common
ancestor, and the pointer is in window P, the X server does the following:
-
If window P is an inferior of window A, it generates a FocusOut ev ent on each win-
dow from window P up to but not including window A, with the detail member of the
XFocusOutEvent structure set to NotifyPointer.
-
It generates a FocusOut ev ent on window A, with the detail member of the XFocu-
sOutEvent
structure set to NotifyNonlinear.
-
It generates a FocusOut ev ent on each window between window A and window C,
exclusive, with the detail member of each XFocusOutEvent structure set to
NotifyNonlinearVirtual.
-
It generates a FocusIn ev ent on each window between C and B, exclusive, with the
detail member of each XFocusInEvent structure set to NotifyNonlinearVirtual.
-
It generates a FocusIn ev ent on window B, with the detail member of the XFocusIn-
Event
structure set to NotifyNonlinear.
-
If window P is an inferior of window B, it generates a FocusIn ev ent on each win-
dow below window B down to and including window P, with the detail member of
the XFocusInEvent structure set to NotifyPointer.

When the focus moves from window A to window B on different screens and the pointer is
in window P, the X server does the following:
-
If window P is an inferior of window A, it generates a FocusOut ev ent on each win-
dow from window P up to but not including window A, with the detail member of
each XFocusOutEvent structure set to NotifyPointer.
-
It generates a FocusOut ev ent on window A, with the detail member of the XFocu-
sOutEvent
structure set to NotifyNonlinear.
-
If window A is not a root window, it generates a FocusOut ev ent on each window
above window A up to and including its root, with the detail member of each XFocu-
sOutEvent
structure set to NotifyNonlinearVirtual.
-
If window B is not a root window, it generates a FocusIn ev ent on each window
from window B's root down to but not including window B, with the detail member
of each XFocusInEvent structure set to NotifyNonlinearVirtual.
-
It generates a FocusIn ev ent on window B, with the detail member of each XFo-
cusInEvent
structure set to NotifyNonlinear.
-
If window P is an inferior of window B, it generates a FocusIn ev ent on each win-
dow below window B down to and including window P, with the detail member of
each XFocusInEvent structure set to NotifyPointer.

When the focus moves from window A to PointerRoot (events sent to the window under
the pointer) or None (discard), and the pointer is in window P, the X server does the fol-
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-
If window P is an inferior of window A, it generates a FocusOut ev ent on each win-
dow from window P up to but not including window A, with the detail member of
each XFocusOutEvent structure set to NotifyPointer.
-
It generates a FocusOut ev ent on window A, with the detail member of the XFocu-
sOutEvent
structure set to NotifyNonlinear.
-
If window A is not a root window, it generates a FocusOut ev ent on each window
above window A up to and including its root, with the detail member of each XFocu-
sOutEvent
structure set to NotifyNonlinearVirtual.
-
It generates a FocusIn ev ent on the root window of all screens, with the detail mem-
ber of each XFocusInEvent structure set to NotifyPointerRoot (or
NotifyDetailNone).
-
If the new focus is PointerRoot, it generates a FocusIn ev ent on each window from
window P's root down to and including window P, with the detail member of each
XFocusInEvent structure set to NotifyPointer.

When the focus moves from PointerRoot (events sent to the window under the pointer) or
None to window A, and the pointer is in window P, the X server does the following:
-
If the old focus is PointerRoot, it generates a FocusOut ev ent on each window
from window P up to and including window P's root, with the detail member of each
XFocusOutEvent structure set to NotifyPointer.
-
It generates a FocusOut ev ent on all root windows, with the detail member of each
XFocusOutEvent structure set to NotifyPointerRoot (or NotifyDetailNone).
-
If window A is not a root window, it generates a FocusIn ev ent on each window
from window A's root down to but not including window A, with the detail member
of each XFocusInEvent structure set to NotifyNonlinearVirtual.
-
It generates a FocusIn ev ent on window A, with the detail member of the XFo-
cusInEvent
structure set to NotifyNonlinear.
-
If window P is an inferior of window A, it generates a FocusIn ev ent on each win-
dow below window A down to and including window P, with the detail member of
each XFocusInEvent structure set to NotifyPointer.

When the focus moves from PointerRoot (events sent to the window under the pointer) to
None (or vice versa), and the pointer is in window P, the X server does the following:
-
If the old focus is PointerRoot, it generates a FocusOut ev ent on each window
from window P up to and including window P's root, with the detail member of each
XFocusOutEvent structure set to NotifyPointer.
-
It generates a FocusOut ev ent on all root windows, with the detail member of each
XFocusOutEvent structure set to either NotifyPointerRoot or NotifyDetailNone.
-
It generates a FocusIn ev ent on all root windows, with the detail member of each
XFocusInEvent structure set to NotifyDetailNone or NotifyPointerRoot.
-
If the new focus is PointerRoot, it generates a FocusIn ev ent on each window from
window P's root down to and including window P, with the detail member of each
XFocusInEvent structure set to NotifyPointer.
10.7.2. Focus Events Generated by Grabs
Focus events in which the keyboard grab activates are identified by XFocusInEvent or XFocu-
sOutEvent
structures whose mode member is set to NotifyGrab. Focus events in which the
keyboard grab deactivates are identified by XFocusInEvent or XFocusOutEvent structures
whose mode member is set to NotifyUngrab (see XGrabKeyboard).

When a keyboard grab activates before generating any actual KeyPress ev ent that activates
the grab, G is the grab_window, and F is the current focus, the X server does the following:
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-
It generates FocusIn and FocusOut ev ents, with the mode members of the XFo-
cusInEvent
and XFocusOutEvent structures set to NotifyGrab. These events are
generated as if the focus were to change from F to G.

When a keyboard grab deactivates after generating any actual KeyRelease ev ent that deac-
tivates the grab, G is the grab_window, and F is the current focus, the X server does the fol-
lowing:
-
It generates FocusIn and FocusOut ev ents, with the mode members of the XFo-
cusInEvent
and XFocusOutEvent structures set to NotifyUngrab. These events
are generated as if the focus were to change from G to F.
10.8. Key Map State Notification Events
The X server can report KeymapNotify ev ents to clients that want information about changes in
their keyboard state.
To receive KeymapNotify ev ents, set the KeymapStateMask bit in the event-mask attribute of
the window. The X server generates this event immediately after every EnterNotify and
FocusIn ev ent.
The structure for this event type contains:
/* generated on EnterWindow and FocusIn when KeymapState selected */
typedef struct {
int type;
/* KeymapNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
char key_vector[32];
} XKe ymapEvent;
The window member is not used but is present to aid some toolkits. The key_vector member is
set to the bit vector of the keyboard. Each bit set to 1 indicates that the corresponding key is cur-
rently pressed. The vector is represented as 32 bytes. Byte N (from 0) contains the bits for keys
8N to 8N + 7 with the least significant bit in the byte representing key 8N.
10.9. Exposure Events
The X protocol does not guarantee to preserve the contents of window regions when the windows
are obscured or reconfigured. Some implementations may preserve the contents of windows.
Other implementations are free to destroy the contents of windows when exposed. X expects
client applications to assume the responsibility for restoring the contents of an exposed window
region. (An exposed window region describes a formerly obscured window whose region
becomes visible.) Therefore, the X server sends Expose ev ents describing the window and the
region of the window that has been exposed. A naive client application usually redraws the entire
window. A more sophisticated client application redraws only the exposed region.
10.9.1. Expose Events
The X server can report Expose ev ents to clients wanting information about when the contents of
window regions have been lost. The circumstances in which the X server generates Expose
ev ents are not as definite as those for other events. However, the X server never generates
Expose ev ents on windows whose class you specified as InputOnly. The X server can generate
Expose ev ents when no valid contents are available for regions of a window and either the
regions are visible, the regions are viewable and the server is (perhaps newly) maintaining back-
ing store on the window, or the window is not viewable but the server is (perhaps newly) honoring
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the window's backing-store attribute of Always or WhenMapped. The regions decompose into
an (arbitrary) set of rectangles, and an Expose ev ent is generated for each rectangle. For any
given window, the X server guarantees to report contiguously all of the regions exposed by some
action that causes Expose ev ents, such as raising a window.
To receive Expose ev ents, set the ExposureMask bit in the event-mask attribute of the window.
The structure for this event type contains:
typedef struct {
int type;
/* Expose */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
int x, y;
int width, height;
int count;
/* if nonzero, at least this many more */
} XExposeEvent;
The window member is set to the exposed (damaged) window. The x and y members are set to
the coordinates relative to the window's origin and indicate the upper-left corner of the rectangle.
The width and height members are set to the size (extent) of the rectangle. The count member is
set to the number of Expose ev ents that are to follow. If count is zero, no more Expose ev ents
follow for this window. Howev er, if count is nonzero, at least that number of Expose ev ents (and
possibly more) follow for this window. Simple applications that do not want to optimize redis-
play by distinguishing between subareas of its window can just ignore all Expose ev ents with
nonzero counts and perform full redisplays on events with zero counts.
10.9.2. GraphicsExpose and NoExpose Events
The X server can report GraphicsExpose ev ents to clients wanting information about when a
destination region could not be computed during certain graphics requests: XCopyArea or
XCopyPlane. The X server generates this event whenever a destination region could not be
computed because of an obscured or out-of-bounds source region. In addition, the X server guar-
antees to report contiguously all of the regions exposed by some graphics request (for example,
copying an area of a drawable to a destination drawable).
The X server generates a NoExpose ev ent whenever a graphics request that might produce a
GraphicsExpose ev ent does not produce any. In other words, the client is really asking for a
GraphicsExpose ev ent but instead receives a NoExpose ev ent.
To receive GraphicsExpose or NoExpose ev ents, you must first set the graphics-exposure
attribute of the graphics context to True. You also can set the graphics-expose attribute when
creating a graphics context using XCreateGC or by calling XSetGraphicsExposures.
The structures for these event types contain:
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typedef struct {
int type;
/* GraphicsExpose */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Drawable drawable;
int x, y;
int width, height;
int count;
/* if nonzero, at least this many more */
int major_code;
/* core is CopyArea or CopyPlane */
int minor_code;
/* not defined in the core */
} XGraphicsExposeEvent;
typedef struct {
int type;
/* NoExpose */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Drawable drawable;
int major_code;
/* core is CopyArea or CopyPlane */
int minor_code;
/* not defined in the core */
} XNoExposeEvent;
Both structures have these common members: drawable, major_code, and minor_code. The
drawable member is set to the drawable of the destination region on which the graphics request
was to be performed. The major_code member is set to the graphics request initiated by the client
and can be either X_CopyArea or X_CopyPlane. If it is X_CopyArea, a call to XCopyArea
initiated the request. If it is X_CopyPlane, a call to XCopyPlane initiated the request. These
constants are defined in <X11/Xproto.h>. The minor_code member, like the major_code mem-
ber, indicates which graphics request was initiated by the client. However, the minor_code mem-
ber is not defined by the core X protocol and will be zero in these cases, although it may be used
by an extension.
The XGraphicsExposeEvent structure has these additional members: x, y, width, height, and
count. The x and y members are set to the coordinates relative to the drawable's origin and indi-
cate the upper-left corner of the rectangle. The width and height members are set to the size
(extent) of the rectangle. The count member is set to the number of GraphicsExpose ev ents to
follow. If count is zero, no more GraphicsExpose ev ents follow for this window. Howev er, if
count is nonzero, at least that number of GraphicsExpose ev ents (and possibly more) are to fol-
low for this window.
10.10. Window State Change Events
The following sections discuss:

CirculateNotify ev ents

ConfigureNotify ev ents

CreateNotify ev ents

DestroyNotify ev ents

GravityNotify ev ents

MapNotify ev ents
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MappingNotify ev ents

ReparentNotify ev ents

UnmapNotify ev ents

VisibilityNotify ev ents
10.10.1. CirculateNotify Events
The X server can report CirculateNotify ev ents to clients wanting information about when a
window changes its position in the stack. The X server generates this event type whenever a win-
dow is actually restacked as a result of a client application calling XCirculateSubwindows,
XCirculateSubwindowsUp, or XCirculateSubwindowsDown.
To receive CirculateNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute
of the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent win-
dow (in which case, circulating any child generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* CirculateNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
int place;
/* PlaceOnTop, PlaceOnBottom */
} XCirculateEvent;
The event member is set either to the restacked window or to its parent, depending on whether
StructureNotify or SubstructureNotify was selected. The window member is set to the win-
dow that was restacked. The place member is set to the window's position after the restack
occurs and is either PlaceOnTop or PlaceOnBottom. If it is PlaceOnTop, the window is now
on top of all siblings. If it is PlaceOnBottom, the window is now below all siblings.
10.10.2. ConfigureNotify Events
The X server can report ConfigureNotify ev ents to clients wanting information about actual
changes to a window's state, such as size, position, border, and stacking order. The X server gen-
erates this event type whenever one of the following configure window requests made by a client
application actually completes:

A window's size, position, border, and/or stacking order is reconfigured by calling
XConfigureWindow.

The window's position in the stacking order is changed by calling XLowerWindow,
XRaiseWindow, or XRestackWindows.

A window is moved by calling XMoveWindow.

A window's size is changed by calling XResizeWindow.

A window's size and location is changed by calling XMoveResizeWindow.

A window is mapped and its position in the stacking order is changed by calling
XMapRaised.

A window's border width is changed by calling XSetWindowBorderWidth.
To receive ConfigureNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute
of the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent
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window (in which case, configuring any child generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* ConfigureNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
int x, y;
int width, height;
int border_width;
Window above;
Bool override_redirect;
} XConfigureEvent;
The event member is set either to the reconfigured window or to its parent, depending on whether
StructureNotify or SubstructureNotify was selected. The window member is set to the win-
dow whose size, position, border, and/or stacking order was changed.
The x and y members are set to the coordinates relative to the parent window's origin and indicate
the position of the upper-left outside corner of the window. The width and height members are
set to the inside size of the window, not including the border. The border_width member is set to
the width of the window's border, in pixels.
The above member is set to the sibling window and is used for stacking operations. If the X
server sets this member to None, the window whose state was changed is on the bottom of the
stack with respect to sibling windows. However, if this member is set to a sibling window, the
window whose state was changed is placed on top of this sibling window.
The override_redirect member is set to the override-redirect attribute of the window. Window
manager clients normally should ignore this window if the override_redirect member is True.
10.10.3. CreateNotify Events
The X server can report CreateNotify ev ents to clients wanting information about creation of
windows. The X server generates this event whenever a client application creates a window by
calling XCreateWindow or XCreateSimpleWindow.
To receive CreateNotify ev ents, set the SubstructureNotifyMask bit in the event-mask attribute
of the window. Creating any children then generates an event.
The structure for the event type contains:
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typedef struct {
int type;
/* CreateNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window parent; /* parent of the window */
Window window; /* window id of window created */
int x, y;
/* window location */
int width, height;
/* size of window */
int border_width;
/* border width */
Bool override_redirect; /* creation should be overridden */
} XCreateWindowEvent;
The parent member is set to the created window's parent. The window member specifies the cre-
ated window. The x and y members are set to the created window's coordinates relative to the
parent window's origin and indicate the position of the upper-left outside corner of the created
window. The width and height members are set to the inside size of the created window (not
including the border) and are always nonzero. The border_width member is set to the width of
the created window's border, in pixels. The override_redirect member is set to the override-redi-
rect attribute of the window. Window manager clients normally should ignore this window if the
override_redirect member is True.
10.10.4. DestroyNotify Events
The X server can report DestroyNotify ev ents to clients wanting information about which win-
dows are destroyed. The X server generates this event whenever a client application destroys a
window by calling XDestroyWindow or XDestroySubwindows.
The ordering of the DestroyNotify ev ents is such that for any giv en window, DestroyNotify is
generated on all inferiors of the window before being generated on the window itself. The X pro-
tocol does not constrain the ordering among siblings and across subhierarchies.
To receive DestroyNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute of
the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent window
(in which case, destroying any child generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* DestroyNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
} XDestroyWindowEvent;
The event member is set either to the destroyed window or to its parent, depending on whether
StructureNotify or SubstructureNotify was selected. The window member is set to the win-
dow that is destroyed.
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10.10.5. GravityNotify Events
The X server can report GravityNotify ev ents to clients wanting information about when a win-
dow is moved because of a change in the size of its parent. The X server generates this event
whenever a client application actually moves a child window as a result of resizing its parent by
calling XConfigureWindow, XMoveResizeWindow, or XResizeWindow.
To receive GravityNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute of
the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent window
(in which case, any child that is moved because its parent has been resized generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* GravityNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
int x, y;
} XGravityEvent;
The event member is set either to the window that was moved or to its parent, depending on
whether StructureNotify or SubstructureNotify was selected. The window member is set to
the child window that was moved. The x and y members are set to the coordinates relative to the
new parent window's origin and indicate the position of the upper-left outside corner of the win-
dow.
10.10.6. MapNotify Events
The X server can report MapNotify ev ents to clients wanting information about which windows
are mapped. The X server generates this event type whenever a client application changes the
window's state from unmapped to mapped by calling XMapWindow, XMapRaised,
XMapSubwindows, XReparentWindow, or as a result of save-set processing.
To receive MapNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute of
the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent window
(in which case, mapping any child generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* MapNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
Bool override_redirect; /* boolean, is override set... */
} XMapEvent;
The event member is set either to the window that was mapped or to its parent, depending on
whether StructureNotify or SubstructureNotify was selected. The window member is set to
the window that was mapped. The override_redirect member is set to the override-redirect
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attribute of the window. Window manager clients normally should ignore this window if the
override-redirect attribute is True, because these events usually are generated from pop-ups,
which override structure control.
10.10.7. MappingNotify Events
The X server reports MappingNotify ev ents to all clients. There is no mechanism to express dis-
interest in this event. The X server generates this event type whenever a client application suc-
cessfully calls:

XSetModifierMapping to indicate which KeyCodes are to be used as modifiers

XChangeKeyboardMapping to change the keyboard mapping

XSetPointerMapping to set the pointer mapping
The structure for this event type contains:
typedef struct {
int type;
/* MappingNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window; /* unused */
int request;
/* one of MappingModifier, MappingKeyboard,
MappingPointer */
int first_keycode; /* first keycode */
int count;
/* defines range of change w. first_keycode*/
} XMappingEvent;
The request member is set to indicate the kind of mapping change that occurred and can be
MappingModifier, MappingKeyboard, or MappingPointer. If it is MappingModifier, the
modifier mapping was changed. If it is MappingKeyboard, the keyboard mapping was changed.
If it is MappingPointer, the pointer button mapping was changed. The first_keycode and count
members are set only if the request member was set to MappingKeyboard. The number in
first_keycode represents the first number in the range of the altered mapping, and count represents
the number of keycodes altered.
To update the client application's knowledge of the keyboard, you should call
XRefreshKeyboardMapping.
10.10.8. ReparentNotify Events
The X server can report ReparentNotify ev ents to clients wanting information about changing a
window's parent. The X server generates this event whenever a client application calls XRepar-
entWindow
and the window is actually reparented.
To receive ReparentNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute
of the window or the SubstructureNotifyMask bit in the event-mask attribute of either the old or
the new parent window (in which case, reparenting any child generates an event).
The structure for this event type contains:
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typedef struct {
int type;
/* ReparentNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
Window parent;
int x, y;
Bool override_redirect;
} XReparentEvent;
The event member is set either to the reparented window or to the old or the new parent, depend-
ing on whether StructureNotify or SubstructureNotify was selected. The window member is
set to the window that was reparented. The parent member is set to the new parent window. The
x and y members are set to the reparented window's coordinates relative to the new parent win-
dow's origin and define the upper-left outer corner of the reparented window. The override_redi-
rect member is set to the override-redirect attribute of the window specified by the window mem-
ber. Window manager clients normally should ignore this window if the override_redirect mem-
ber is True.
10.10.9. UnmapNotify Events
The X server can report UnmapNotify ev ents to clients wanting information about which win-
dows are unmapped. The X server generates this event type whenever a client application
changes the window's state from mapped to unmapped.
To receive UnmapNotify ev ents, set the StructureNotifyMask bit in the event-mask attribute of
the window or the SubstructureNotifyMask bit in the event-mask attribute of the parent window
(in which case, unmapping any child window generates an event).
The structure for this event type contains:
typedef struct {
int type;
/* UnmapNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window event;
Window window;
Bool from_configure;
} XUnmapEvent;
The event member is set either to the unmapped window or to its parent, depending on whether
StructureNotify or SubstructureNotify was selected. This is the window used by the X server
to report the event. The window member is set to the window that was unmapped. The
from_configure member is set to True if the event was generated as a result of a resizing of the
window's parent when the window itself had a win_gravity of UnmapGravity.
10.10.10. VisibilityNotify Events
The X server can report VisibilityNotify ev ents to clients wanting any change in the visibility of
the specified window. A region of a window is visible if someone looking at the screen can
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actually see it. The X server generates this event whenever the visibility changes state. However,
this event is never generated for windows whose class is InputOnly.
All VisibilityNotify ev ents caused by a hierarchy change are generated after any hierarchy event
(UnmapNotify, MapNotify, ConfigureNotify, GravityNotify, CirculateNotify) caused by
that change. Any VisibilityNotify ev ent on a given window is generated before any Expose
ev ents on that window, but it is not required that all VisibilityNotify ev ents on all windows be
generated before all Expose ev ents on all windows. The X protocol does not constrain the order-
ing of VisibilityNotify ev ents with respect to FocusOut, EnterNotify, and LeaveNotify ev ents.
To receive VisibilityNotify ev ents, set the VisibilityChangeMask bit in the event-mask attribute
of the window.
The structure for this event type contains:
typedef struct {
int type;
/* VisibilityNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
int state;
} XVisibilityEvent;
The window member is set to the window whose visibility state changes. The state member is set
to the state of the window's visibility and can be VisibilityUnobscured,
VisibilityPartiallyObscured, or VisibilityFullyObscured. The X server ignores all of a win-
dow's subwindows when determining the visibility state of the window and processes Visibili-
tyNotify
ev ents according to the following:

When the window changes state from partially obscured, fully obscured, or not viewable to
viewable and completely unobscured, the X server generates the event with the state mem-
ber of the XVisibilityEvent structure set to VisibilityUnobscured.

When the window changes state from viewable and completely unobscured or not viewable
to viewable and partially obscured, the X server generates the event with the state member
of the XVisibilityEvent structure set to VisibilityPartiallyObscured.

When the window changes state from viewable and completely unobscured, viewable and
partially obscured, or not viewable to viewable and fully obscured, the X server generates
the event with the state member of the XVisibilityEvent structure set to
VisibilityFullyObscured.
10.11. Structure Control Events
This section discusses:

CirculateRequest ev ents

ConfigureRequest ev ents

MapRequest ev ents

ResizeRequest ev ents
10.11.1. CirculateRequest Events
The X server can report CirculateRequest ev ents to clients wanting information about when
another client initiates a circulate window request on a specified window. The X server generates
this event type whenever a client initiates a circulate window request on a window and a subwin-
dow actually needs to be restacked. The client initiates a circulate window request on the window
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by calling XCirculateSubwindows, XCirculateSubwindowsUp, or
XCirculateSubwindowsDown.
To receive CirculateRequest ev ents, set the SubstructureRedirectMask in the event-mask
attribute of the window. Then, in the future, the circulate window request for the specified win-
dow is not executed, and thus, any subwindow's position in the stack is not changed. For exam-
ple, suppose a client application calls XCirculateSubwindowsUp to raise a subwindow to the
top of the stack. If you had selected SubstructureRedirectMask on the window, the X server
reports to you a CirculateRequest ev ent and does not raise the subwindow to the top of the
stack.
The structure for this event type contains:
typedef struct {
int type;
/* CirculateRequest */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window parent;
Window window;
int place;
/* PlaceOnTop, PlaceOnBottom */
} XCirculateRequestEvent;
The parent member is set to the parent window. The window member is set to the subwindow to
be restacked. The place member is set to what the new position in the stacking order should be
and is either PlaceOnTop or PlaceOnBottom. If it is PlaceOnTop, the subwindow should be
on top of all siblings. If it is PlaceOnBottom, the subwindow should be below all siblings.
10.11.2. ConfigureRequest Events
The X server can report ConfigureRequest ev ents to clients wanting information about when a
different client initiates a configure window request on any child of a specified window. The con-
figure window request attempts to reconfigure a window's size, position, border, and stacking
order. The X server generates this event whenever a different client initiates a configure window
request on a window by calling XConfigureWindow, XLowerWindow, XRaiseWindow,
XMapRaised, XMoveResizeWindow, XMoveWindow, XResizeWindow,
XRestackWindows, or XSetWindowBorderWidth.
To receive ConfigureRequest ev ents, set the SubstructureRedirectMask bit in the event-mask
attribute of the window. ConfigureRequest ev ents are generated when a ConfigureWindow
protocol request is issued on a child window by another client. For example, suppose a client
application calls XLowerWindow to lower a window. If you had selected SubstructureRedi-
rectMask
on the parent window and if the override-redirect attribute of the window is set to
False, the X server reports a ConfigureRequest ev ent to you and does not lower the specified
window.
The structure for this event type contains:
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typedef struct {
int type;
/* ConfigureRequest */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window parent;
Window window;
int x, y;
int width, height;
int border_width;
Window above;
int detail;
/* Above, Below, TopIf, BottomIf, Opposite */
unsigned long value_mask;
} XConfigureRequestEvent;
The parent member is set to the parent window. The window member is set to the window whose
size, position, border width, and/or stacking order is to be reconfigured. The value_mask member
indicates which components were specified in the ConfigureWindow protocol request. The cor-
responding values are reported as given in the request. The remaining values are filled in from
the current geometry of the window, except in the case of above (sibling) and detail (stack-mode),
which are reported as None and Above, respectively, if they are not given in the request.
10.11.3. MapRequest Events
The X server can report MapRequest ev ents to clients wanting information about a different
client's desire to map windows. A window is considered mapped when a map window request
completes. The X server generates this event whenever a different client initiates a map window
request on an unmapped window whose override_redirect member is set to False. Clients initiate
map window requests by calling XMapWindow, XMapRaised, or XMapSubwindows.
To receive MapRequest ev ents, set the SubstructureRedirectMask bit in the event-mask
attribute of the window. This means another client's attempts to map a child window by calling
one of the map window request functions is intercepted, and you are sent a MapRequest instead.
For example, suppose a client application calls XMapWindow to map a window. If you (usually
a window manager) had selected SubstructureRedirectMask on the parent window and if the
override-redirect attribute of the window is set to False, the X server reports a MapRequest
ev ent to you and does not map the specified window. Thus, this event gives your window man-
ager client the ability to control the placement of subwindows.
The structure for this event type contains:
typedef struct {
int type;
/* MapRequest */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window parent;
Window window;
} XMapRequestEvent;
The parent member is set to the parent window. The window member is set to the window to be
mapped.
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10.11.4. ResizeRequest Events
The X server can report ResizeRequest ev ents to clients wanting information about another
client's attempts to change the size of a window. The X server generates this event whenever
some other client attempts to change the size of the specified window by calling
XConfigureWindow, XResizeWindow, or XMoveResizeWindow.
To receive ResizeRequest ev ents, set the ResizeRedirect bit in the event-mask attribute of the
window. Any attempts to change the size by other clients are then redirected.
The structure for this event type contains:
typedef struct {
int type;
/* ResizeRequest */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
int width, height;
} XResizeRequestEvent;
The window member is set to the window whose size another client attempted to change. The
width and height members are set to the inside size of the window, excluding the border.
10.12. Colormap State Change Events
The X server can report ColormapNotify ev ents to clients wanting information about when the
colormap changes and when a colormap is installed or uninstalled. The X server generates this
ev ent type whenever a client application:

Changes the colormap member of the XSetWindowAttributes structure by calling
XChangeWindowAttributes, XFreeColormap, or XSetWindowColormap

Installs or uninstalls the colormap by calling XInstallColormap or XUninstallColormap
To receive ColormapNotify ev ents, set the ColormapChangeMask bit in the event-mask
attribute of the window.
The structure for this event type contains:
typedef struct {
int type;
/* ColormapNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
Colormap colormap;
/* colormap or None */
Bool new;
int state;
/* ColormapInstalled, ColormapUninstalled */
} XColormapEvent;
The window member is set to the window whose associated colormap is changed, installed, or
uninstalled. For a colormap that is changed, installed, or uninstalled, the colormap member is set
to the colormap associated with the window. For a colormap that is changed by a call to
XFreeColormap, the colormap member is set to None. The new member is set to indicate
whether the colormap for the specified window was changed or installed or uninstalled and can be
True or False. If it is True, the colormap was changed. If it is False, the colormap was
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installed or uninstalled. The state member is always set to indicate whether the colormap is
installed or uninstalled and can be ColormapInstalled or ColormapUninstalled.
10.13. Client Communication Events
This section discusses:

ClientMessage ev ents

PropertyNotify ev ents

SelectionClear ev ents

SelectionNotify ev ents

SelectionRequest ev ents
10.13.1. ClientMessage Events
The X server generates ClientMessage ev ents only when a client calls the function
XSendEvent.
The structure for this event type contains:
typedef struct {
int type;
/* ClientMessage */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
Atom message_type;
int format;
union {
char b[20];
short s[10];
long l[5];
} data;
} XClientMessageEvent;
The message_type member is set to an atom that indicates how the data should be interpreted by
the receiving client. The format member is set to 8, 16, or 32 and specifies whether the data
should be viewed as a list of bytes, shorts, or longs. The data member is a union that contains the
members b, s, and l. The b, s, and l members represent data of twenty 8-bit values, ten 16-bit val-
ues, and five 32-bit values. Particular message types might not make use of all these values. The
X server places no interpretation on the values in the window, message_type, or data members.
10.13.2. PropertyNotify Events
The X server can report PropertyNotify ev ents to clients wanting information about property
changes for a specified window.
To receive PropertyNotify ev ents, set the PropertyChangeMask bit in the event-mask attribute
of the window.
The structure for this event type contains:
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typedef struct {
int type;
/* PropertyNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
Atom atom;
Time time;
int state;
/* PropertyNewValue or PropertyDelete */
} XPropertyEvent;
The window member is set to the window whose associated property was changed. The atom
member is set to the property's atom and indicates which property was changed or desired. The
time member is set to the server time when the property was changed. The state member is set to
indicate whether the property was changed to a new value or deleted and can be PropertyNew-
Value
or PropertyDelete. The state member is set to PropertyNewValue when a property of
the window is changed using XChangeProperty or XRotateWindowProperties (even when
adding zero-length data using XChangeProperty) and when replacing all or part of a property
with identical data using XChangeProperty or XRotateWindowProperties. The state member
is set to PropertyDelete when a property of the window is deleted using XDeleteProperty or, if
the delete argument is True, XGetWindowProperty.
10.13.3. SelectionClear Events
The X server reports SelectionClear ev ents to the client losing ownership of a selection. The X
server generates this event type when another client asserts ownership of the selection by calling
XSetSelectionOwner.
The structure for this event type contains:
typedef struct {
int type;
/* SelectionClear */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window window;
Atom selection;
Time time;
} XSelectionClearEvent;
The selection member is set to the selection atom. The time member is set to the last change time
recorded for the selection. The window member is the window that was specified by the current
owner (the owner losing the selection) in its XSetSelectionOwner call.
10.13.4. SelectionRequest Events
The X server reports SelectionRequest ev ents to the owner of a selection. The X server gener-
ates this event whenever a client requests a selection conversion by calling XConvertSelection
for the owned selection.
The structure for this event type contains:
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typedef struct {
int type;
/* SelectionRequest */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window owner;
Window requestor;
Atom selection;
Atom target;
Atom property;
Time time;
} XSelectionRequestEvent;
The owner member is set to the window that was specified by the current owner in its XSetSelec-
tionOwner
call. The requestor member is set to the window requesting the selection. The selec-
tion member is set to the atom that names the selection. For example, PRIMARY is used to indi-
cate the primary selection. The target member is set to the atom that indicates the type the selec-
tion is desired in. The property member can be a property name or None. The time member is
set to the timestamp or CurrentTime value from the ConvertSelection request.
The owner should convert the selection based on the specified target type and send a Selection-
Notify
ev ent back to the requestor. A complete specification for using selections is given in the X
Consortium standard Inter-Client Communication Conventions Manual.
10.13.5. SelectionNotify Events
This event is generated by the X server in response to a ConvertSelection protocol request when
there is no owner for the selection. When there is an owner, it should be generated by the owner
of the selection by using XSendEvent. The owner of a selection should send this event to a
requestor when a selection has been converted and stored as a property or when a selection con-
version could not be performed (which is indicated by setting the property member to None).
If None is specified as the property in the ConvertSelection protocol request, the owner should
choose a property name, store the result as that property on the requestor window, and then send a
SelectionNotify giving that actual property name.
The structure for this event type contains:
typedef struct {
int type;
/* SelectionNotify */
unsigned long serial;
/* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;
/* Display the event was read from */
Window requestor;
Atom selection;
Atom target;
Atom property;
/* atom or None */
Time time;
} XSelectionEvent;
The requestor member is set to the window associated with the requestor of the selection. The
selection member is set to the atom that indicates the selection. For example, PRIMARY is used
for the primary selection. The target member is set to the atom that indicates the converted type.
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For example, PIXMAP is used for a pixmap. The property member is set to the atom that indi-
cates which property the result was stored on. If the conversion failed, the property member is set
to None. The time member is set to the time the conversion took place and can be a timestamp or
CurrentTime.
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Chapter 11
Event Handling Functions
This chapter discusses the Xlib functions you can use to:

Select events

Handle the output buffer and the event queue

Select events from the event queue

Send and get events

Handle protocol errors
Note
Some toolkits use their own event-handling functions and do not allow you to
interchange these event-handling functions with those in Xlib. For further
information, see the documentation supplied with the toolkit.
Most applications simply are event loops: they wait for an event, decide what to do with it,
execute some amount of code that results in changes to the display, and then wait for the next
ev ent.
11.1. Selecting Events
There are two ways to select the events you want reported to your client application. One way is
to set the event_mask member of the XSetWindowAttributes structure when you call XCre-
ateWindow
and XChangeWindowAttributes. Another way is to use XSelectInput.
XSelectInput (display, w, event_mask)
Display *display;
Window w;
long event_mask;
display
Specifies the connection to the X server.
w
Specifies the window whose events you are interested in.
event_mask
Specifies the event mask.
The XSelectInput function requests that the X server report the events associated with the speci-
fied event mask. Initially, X will not report any of these events. Events are reported relative to a
window. If a window is not interested in a device event, it usually propagates to the closest ances-
tor that is interested, unless the do_not_propagate mask prohibits it.
Setting the event-mask attribute of a window overrides any previous call for the same window but
not for other clients. Multiple clients can select for the same events on the same window with the
following restrictions:

Multiple clients can select events on the same window because their event masks are dis-
joint. When the X server generates an event, it reports it to all interested clients.

Only one client at a time can select CirculateRequest, ConfigureRequest, or MapRe-
quest ev ents, which are associated with the event mask SubstructureRedirectMask.

Only one client at a time can select a ResizeRequest ev ent, which is associated with the
ev ent mask ResizeRedirectMask.
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Only one client at a time can select a ButtonPress ev ent, which is associated with the
ev ent mask ButtonPressMask.
The server reports the event to all interested clients.
XSelectInput can generate a BadWindow error.
11.2. Handling the Output Buffer
The output buffer is an area used by Xlib to store requests. The functions described in this sec-
tion flush the output buffer if the function would block or not return an event. That is, all requests
residing in the output buffer that have not yet been sent are transmitted to the X server. These
functions differ in the additional tasks they might perform.
To flush the output buffer, use XFlush.
XFlush (display)
Display *display;
display
Specifies the connection to the X server.
The XFlush function flushes the output buffer. Most client applications need not use this func-
tion because the output buffer is automatically flushed as needed by calls to XPending,
XNextEvent, and XWindowEvent. Events generated by the server may be enqueued into the
library's event queue.
To flush the output buffer and then wait until all requests have been processed, use XSync.
XSync (display, discard)
Display *display;
Bool discard;
display
Specifies the connection to the X server.
discard
Specifies a Boolean value that indicates whether XSync discards all events on
the event queue.
The XSync function flushes the output buffer and then waits until all requests have been received
and processed by the X server. Any errors generated must be handled by the error handler. For
each protocol error received by Xlib, XSync calls the client application's error handling routine
(see section 11.8.2). Any events generated by the server are enqueued into the library's event
queue.
Finally, if you passed False, XSync does not discard the events in the queue. If you passed
True, XSync discards all events in the queue, including those events that were on the queue
before XSync was called. Client applications seldom need to call XSync.
11.3. Event Queue Management
Xlib maintains an event queue. However, the operating system also may be buffering data in its
network connection that is not yet read into the event queue.
To check the number of events in the event queue, use XEventsQueued.
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int XEventsQueued (display, mode)
Display *display;
int mode;
display
Specifies the connection to the X server.
mode
Specifies the mode. You can pass QueuedAlready, QueuedAfterFlush, or
QueuedAfterReading.
If mode is QueuedAlready, XEventsQueued returns the number of events already in the event
queue (and never performs a system call). If mode is QueuedAfterFlush, XEventsQueued
returns the number of events already in the queue if the number is nonzero. If there are no events
in the queue, XEventsQueued flushes the output buffer, attempts to read more events out of the
application's connection, and returns the number read. If mode is QueuedAfterReading,
XEventsQueued returns the number of events already in the queue if the number is nonzero. If
there are no events in the queue, XEventsQueued attempts to read more events out of the appli-
cation's connection without flushing the output buffer and returns the number read.
XEventsQueued always returns immediately without I/O if there are events already in the queue.
XEventsQueued with mode QueuedAfterFlush is identical in behavior to XPending.
XEventsQueued with mode QueuedAlready is identical to the XQLength function.
To return the number of events that are pending, use XPending.
int XPending(display)
Display *display;
display
Specifies the connection to the X server.
The XPending function returns the number of events that have been received from the X server
but hav e not been removed from the event queue. XPending is identical to XEventsQueued
with the mode QueuedAfterFlush specified.
11.4. Manipulating the Event Queue
Xlib provides functions that let you manipulate the event queue. This section discusses how to:

Obtain events, in order, and remove them from the queue

Peek at events in the queue without removing them

Obtain events that match the event mask or the arbitrary predicate procedures that you pro-
vide
11.4.1. Returning the Next Event
To get the next event and remove it from the queue, use XNextEvent.
XNextEvent (display, event_return)
Display *display;
XEvent *event_return;
display
Specifies the connection to the X server.
event_return
Returns the next event in the queue.
The XNextEvent function copies the first event from the event queue into the specified XEvent
structure and then removes it from the queue. If the event queue is empty, XNextEvent flushes
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the output buffer and blocks until an event is received.
To peek at the event queue, use XPeekEvent.
XPeekEvent (display, event_return)
Display *display;
XEvent *event_return;
display
Specifies the connection to the X server.
event_return
Returns a copy of the matched event's associated structure.
The XPeekEvent function returns the first event from the event queue, but it does not remove the
ev ent from the queue. If the queue is empty, XPeekEvent flushes the output buffer and blocks
until an event is received. It then copies the event into the client-supplied XEvent structure with-
out removing it from the event queue.
11.4.2. Selecting Events Using a Predicate Procedure
Each of the functions discussed in this section requires you to pass a predicate procedure that
determines if an event matches what you want. Your predicate procedure must decide if the event
is useful without calling any Xlib functions. If the predicate directly or indirectly causes the state
of the event queue to change, the result is not defined. If Xlib has been initialized for threads, the
predicate is called with the display locked and the result of a call by the predicate to any Xlib
function that locks the display is not defined unless the caller has first called XLockDisplay.
The predicate procedure and its associated arguments are:
Bool (*predicate)(display, event, arg)
Display *display;
XEvent *event;
XPointer arg;
display
Specifies the connection to the X server.
event
Specifies the XEvent structure.
arg
Specifies the argument passed in from the XIfEvent, XCheckIfEvent, or
XPeekIfEvent function.
The predicate procedure is called once for each event in the queue until it finds a match. After
finding a match, the predicate procedure must return True. If it did not find a match, it must
return False.
To check the event queue for a matching event and, if found, remove the event from the queue,
use XIfEvent.
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XIfEvent (display, event_return, predicate, arg)
Display *display;
XEvent *event_return;
Bool (*predicate)();
XPointer arg;
display
Specifies the connection to the X server.
event_return
Returns the matched event's associated structure.
predicate
Specifies the procedure that is to be called to determine if the next event in the
queue matches what you want.
arg
Specifies the user-supplied argument that will be passed to the predicate proce-
dure.
The XIfEvent function completes only when the specified predicate procedure returns True for
an event, which indicates an event in the queue matches. XIfEvent flushes the output buffer if it
blocks waiting for additional events. XIfEvent removes the matching event from the queue and
copies the structure into the client-supplied XEvent structure.
To check the event queue for a matching event without blocking, use XCheckIfEvent.
Bool XCheckIfEvent (display, event_return, predicate, arg)
Display *display;
XEvent *event_return;
Bool (*predicate)();
XPointer arg;
display
Specifies the connection to the X server.
event_return
Returns a copy of the matched event's associated structure.
predicate
Specifies the procedure that is to be called to determine if the next event in the
queue matches what you want.
arg
Specifies the user-supplied argument that will be passed to the predicate proce-
dure.
When the predicate procedure finds a match, XCheckIfEvent copies the matched event into the
client-supplied XEvent structure and returns True. (This event is removed from the queue.) If
the predicate procedure finds no match, XCheckIfEvent returns False, and the output buffer will
have been flushed. All earlier events stored in the queue are not discarded.
To check the event queue for a matching event without removing the event from the queue, use
XPeekIfEvent.
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XPeekIfEvent (display, event_return, predicate, arg)
Display *display;
XEvent *event_return;
Bool (*predicate)();
XPointer arg;
display
Specifies the connection to the X server.
event_return
Returns a copy of the matched event's associated structure.
predicate
Specifies the procedure that is to be called to determine if the next event in the
queue matches what you want.
arg
Specifies the user-supplied argument that will be passed to the predicate proce-
dure.
The XPeekIfEvent function returns only when the specified predicate procedure returns True
for an event. After the predicate procedure finds a match, XPeekIfEvent copies the matched
ev ent into the client-supplied XEvent structure without removing the event from the queue.
XPeekIfEvent flushes the output buffer if it blocks waiting for additional events.
11.4.3. Selecting Events Using a Window or Event Mask
The functions discussed in this section let you select events by window or event types, allowing
you to process events out of order.
To remove the next event that matches both a window and an event mask, use XWindowEvent.
XWindowEvent (display, w, event_mask, event_return)
Display *display;
Window w;
long event_mask;
XEvent *event_return;
display
Specifies the connection to the X server.
w
Specifies the window whose events you are interested in.
event_mask
Specifies the event mask.
event_return
Returns the matched event's associated structure.
The XWindowEvent function searches the event queue for an event that matches both the speci-
fied window and event mask. When it finds a match, XWindowEvent removes that event from
the queue and copies it into the specified XEvent structure. The other events stored in the queue
are not discarded. If a matching event is not in the queue, XWindowEvent flushes the output
buffer and blocks until one is received.
To remove the next event that matches both a window and an event mask (if any), use
XCheckWindowEvent. This function is similar to XWindowEvent except that it never blocks
and it returns a Bool indicating if the event was returned.
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Bool XCheckWindowEvent (display, w, event_mask, event_return)
Display *display;
Window w;
long event_mask;
XEvent *event_return;
display
Specifies the connection to the X server.
w
Specifies the window whose events you are interested in.
event_mask
Specifies the event mask.
event_return
Returns the matched event's associated structure.
The XCheckWindowEvent function searches the event queue and then the events available on
the server connection for the first event that matches the specified window and event mask. If it
finds a match, XCheckWindowEvent removes that event, copies it into the specified XEvent
structure, and returns True. The other events stored in the queue are not discarded. If the event
you requested is not available, XCheckWindowEvent returns False, and the output buffer will
have been flushed.
To remove the next event that matches an event mask, use XMaskEvent.
XMaskEvent (display, event_mask, event_return)
Display *display;
long event_mask;
XEvent *event_return;
display
Specifies the connection to the X server.
event_mask
Specifies the event mask.
event_return
Returns the matched event's associated structure.
The XMaskEvent function searches the event queue for the events associated with the specified
mask. When it finds a match, XMaskEvent removes that event and copies it into the specified
XEvent structure. The other events stored in the queue are not discarded. If the event you
requested is not in the queue, XMaskEvent flushes the output buffer and blocks until one is
received.
To return and remove the next event that matches an event mask (if any), use
XCheckMaskEvent. This function is similar to XMaskEvent except that it never blocks and it
returns a Bool indicating if the event was returned.
Bool XCheckMaskEvent (display, event_mask, event_return)
Display *display;
long event_mask;
XEvent *event_return;
display
Specifies the connection to the X server.
event_mask
Specifies the event mask.
event_return
Returns the matched event's associated structure.
The XCheckMaskEvent function searches the event queue and then any events available on the
server connection for the first event that matches the specified mask. If it finds a match,
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XCheckMaskEvent removes that event, copies it into the specified XEvent structure, and
returns True. The other events stored in the queue are not discarded. If the event you requested
is not available, XCheckMaskEvent returns False, and the output buffer will have been flushed.
To return and remove the next event in the queue that matches an event type, use
XCheckTypedEvent.
Bool XCheckTypedEvent (display, event_type, event_return)
Display *display;
int event_type;
XEvent *event_return;
display
Specifies the connection to the X server.
event_type
Specifies the event type to be compared.
event_return
Returns the matched event's associated structure.
The XCheckTypedEvent function searches the event queue and then any events available on the
server connection for the first event that matches the specified type. If it finds a match, XCheck-
TypedEvent
removes that event, copies it into the specified XEvent structure, and returns True.
The other events in the queue are not discarded. If the event is not available, XCheckTypedE-
vent
returns False, and the output buffer will have been flushed.
To return and remove the next event in the queue that matches an event type and a window, use
XCheckTypedWindowEvent.
Bool XCheckTypedWindowEvent (display, w, event_type, event_return)
Display *display;
Window w;
int event_type;
XEvent *event_return;
display
Specifies the connection to the X server.
w
Specifies the window.
event_type
Specifies the event type to be compared.
event_return
Returns the matched event's associated structure.
The XCheckTypedWindowEvent function searches the event queue and then any events avail-
able on the server connection for the first event that matches the specified type and window. If it
finds a match, XCheckTypedWindowEvent removes the event from the queue, copies it into the
specified XEvent structure, and returns True. The other events in the queue are not discarded.
If the event is not available, XCheckTypedWindowEvent returns False, and the output buffer
will have been flushed.
11.5. Putting an Event Back into the Queue
To push an event back into the event queue, use XPutBackEvent.
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XPutBackEvent (display, event)
Display *display;
XEvent *event;
display
Specifies the connection to the X server.
event
Specifies the event.
The XPutBackEvent function pushes an event back onto the head of the display's event queue
by copying the event into the queue. This can be useful if you read an event and then decide that
you would rather deal with it later. There is no limit to the number of times in succession that
you can call XPutBackEvent.
11.6. Sending Events to Other Applications
To send an event to a specified window, use XSendEvent. This function is often used in selec-
tion processing. For example, the owner of a selection should use XSendEvent to send a Selec-
tionNotify
ev ent to a requestor when a selection has been converted and stored as a property.
Status XSendEvent (display, w, propagate, event_mask, event_send)
Display *display;
Window w;
Bool propagate;
long event_mask;
XEvent *event_send;
display
Specifies the connection to the X server.
w
Specifies the window the event is to be sent to, or PointerWindow, or
InputFocus.
propagate
Specifies a Boolean value.
event_mask
Specifies the event mask.
event_send
Specifies the event that is to be sent.
The XSendEvent function identifies the destination window, determines which clients should
receive the specified events, and ignores any active grabs. This function requires you to pass an
ev ent mask. For a discussion of the valid event mask names, see section 10.3. This function uses
the w argument to identify the destination window as follows:

If w is PointerWindow, the destination window is the window that contains the pointer.

If w is InputFocus and if the focus window contains the pointer, the destination window is
the window that contains the pointer; otherwise, the destination window is the focus win-
dow.
To determine which clients should receive the specified events, XSendEvent uses the propagate
argument as follows:

If event_mask is the empty set, the event is sent to the client that created the destination
window. If that client no longer exists, no event is sent.

If propagate is False, the event is sent to every client selecting on destination any of the
ev ent types in the event_mask argument.

If propagate is True and no clients have selected on destination any of the event types in
ev ent-mask, the destination is replaced with the closest ancestor of destination for which
some client has selected a type in event-mask and for which no intervening window has
that type in its do-not-propagate-mask. If no such window exists or if the window is an
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ancestor of the focus window and InputFocus was originally specified as the destination,
the event is not sent to any clients. Otherwise, the event is reported to every client selecting
on the final destination any of the types specified in event_mask.
The event in the XEvent structure must be one of the core events or one of the events defined by
an extension (or a BadValue error results) so that the X server can correctly byte-swap the con-
tents as necessary. The contents of the event are otherwise unaltered and unchecked by the X
server except to force send_event to True in the forwarded event and to set the serial number in
the event correctly; therefore these fields and the display field are ignored by XSendEvent.
XSendEvent returns zero if the conversion to wire protocol format failed and returns nonzero
otherwise.
XSendEvent can generate BadValue and BadWindow errors.
11.7. Getting Pointer Motion History
Some X server implementations will maintain a more complete history of pointer motion than is
reported by event notification. The pointer position at each pointer hardware interrupt may be
stored in a buffer for later retrieval. This buffer is called the motion history buffer. For example,
a few applications, such as paint programs, want to have a precise history of where the pointer
traveled. However, this historical information is highly excessive for most applications.
To determine the approximate maximum number of elements in the motion buffer, use
XDisplayMotionBufferSize.
unsigned long XDisplayMotionBufferSize (display)
Display *display;
display
Specifies the connection to the X server.
The server may retain the recent history of the pointer motion and do so to a finer granularity than
is reported by MotionNotify ev ents. The XGetMotionEvents function makes this history avail-
able.
To get the motion history for a specified window and time, use XGetMotionEvents.
XTimeCoord *XGetMotionEvents (display, w, start, stop, nevents_return)
Display *display;
Window w;
Time start, stop;
int *nevents_return;
display
Specifies the connection to the X server.
w
Specifies the window.
start
stop
Specify the time interval in which the events are returned from the motion history
buffer. You can pass a timestamp or CurrentTime.
nevents_return Returns the number of events from the motion history buffer.
The XGetMotionEvents function returns all events in the motion history buffer that fall between
the specified start and stop times, inclusive, and that have coordinates that lie within the specified
window (including its borders) at its present placement. If the server does not support motion his-
tory, if the start time is later than the stop time, or if the start time is in the future, no events are
returned; XGetMotionEvents returns NULL. If the stop time is in the future, it is equivalent to
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specifying CurrentTime. The return type for this function is a structure defined as follows:
typedef struct {
Time time;
short x, y;
} XTimeCoord;
The time member is set to the time, in milliseconds. The x and y members are set to the coordi-
nates of the pointer and are reported relative to the origin of the specified window. To free the
data returned from this call, use XFree.
XGetMotionEvents can generate a BadWindow error.
11.8. Handling Protocol Errors
Xlib provides functions that you can use to enable or disable synchronization and to use the
default error handlers.
11.8.1. Enabling or Disabling Synchronization
When debugging X applications, it often is very convenient to require Xlib to behave syn-
chronously so that errors are reported as they occur. The following function lets you disable or
enable synchronous behavior. Note that graphics may occur 30 or more times more slowly when
synchronization is enabled. On POSIX-conformant systems, there is also a global variable _Xde-
bug
that, if set to nonzero before starting a program under a debugger, will force synchronous
library behavior.
After completing their work, all Xlib functions that generate protocol requests call what is known
as an after function. XSetAfterFunction sets which function is to be called.
int (*XSetAfterFunction(display, procedure))()
Display *display;
int (*procedure)();
display
Specifies the connection to the X server.
procedure
Specifies the procedure to be called.
The specified procedure is called with only a display pointer. XSetAfterFunction returns the
previous after function.
To enable or disable synchronization, use XSynchronize.
int (*XSynchronize(display, onoff))()
Display *display;
Bool onoff;
display
Specifies the connection to the X server.
onoff
Specifies a Boolean value that indicates whether to enable or disable synchro-
nization.
The XSynchronize function returns the previous after function. If onoff is True, XSynchronize
turns on synchronous behavior. If onoff is False, XSynchronize turns off synchronous behavior.
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11.8.2. Using the Default Error Handlers
There are two default error handlers in Xlib: one to handle typically fatal conditions (for example,
the connection to a display server dying because a machine crashed) and one to handle protocol
errors from the X server. These error handlers can be changed to user-supplied routines if you
prefer your own error handling and can be changed as often as you like. If either function is
passed a NULL pointer, it will reinvoke the default handler. The action of the default handlers is
to print an explanatory message and exit.
To set the error handler, use XSetErrorHandler.
int (*XSetErrorHandler(handler))()
int (*handler)(Display *, XErrorEvent *)
handler
Specifies the program's supplied error handler.
Xlib generally calls the program's supplied error handler whenever an error is received. It is not
called on BadName errors from OpenFont, LookupColor, or AllocNamedColor protocol
requests or on BadFont errors from a QueryFont protocol request. These errors generally are
reflected back to the program through the procedural interface. Because this condition is not
assumed to be fatal, it is acceptable for your error handler to return; the returned value is ignored.
However, the error handler should not call any functions (directly or indirectly) on the display that
will generate protocol requests or that will look for input events. The previous error handler is
returned.
The XErrorEvent structure contains:
typedef struct {
int type;
Display *display;
/* Display the event was read from */
unsigned long serial;
/* serial number of failed request */
unsigned char error_code;
/* error code of failed request */
unsigned char request_code;
/* Major op-code of failed request */
unsigned char minor_code;
/* Minor op-code of failed request */
XID resourceid;
/* resource id */
} XErrorEvent;
The serial member is the number of requests, starting from one, sent over the network connection
since it was opened. It is the number that was the value of NextRequest immediately before the
failing call was made. The request_code member is a protocol request of the procedure that
failed, as defined in <X11/Xproto.h>. The following error codes can be returned by the func-
tions described in this chapter:
Error Code
Description
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Error Code
Description
BadAccess
A client attempts to grab a key/button combination already
grabbed by another client.
A client attempts to free a colormap entry that it had not already
allocated or to free an entry in a colormap that was created with
all entries writable.
A client attempts to store into a read-only or unallocated col-
ormap entry.
A client attempts to modify the access control list from other
than the local (or otherwise authorized) host.
A client attempts to select an event type that another client has
already selected.
BadAlloc
The server fails to allocate the requested resource. Note that the
explicit listing of BadAlloc errors in requests only covers alloca-
tion errors at a very coarse level and is not intended to (nor can it
in practice hope to) cover all cases of a server running out of
allocation space in the middle of service. The semantics when a
server runs out of allocation space are left unspecified, but a
server may generate a BadAlloc error on any request for this
reason, and clients should be prepared to receive such errors and
handle or discard them.
BadAtom
A value for an atom argument does not name a defined atom.
BadColor
A value for a colormap argument does not name a defined col-
ormap.
BadCursor
A value for a cursor argument does not name a defined cursor.
BadDrawable
A value for a drawable argument does not name a defined win-
dow or pixmap.
BadFont
A value for a font argument does not name a defined font (or, in
some cases, GContext).
BadGC
A value for a GContext argument does not name a defined
GContext.
BadIDChoice
The value chosen for a resource identifier either is not included
in the range assigned to the client or is already in use. Under
normal circumstances, this cannot occur and should be consid-
ered a server or Xlib error.
BadImplementation
The server does not implement some aspect of the request. A
server that generates this error for a core request is deficient. As
such, this error is not listed for any of the requests, but clients
should be prepared to receive such errors and handle or discard
them.
BadLength
The length of a request is shorter or longer than that required to
contain the arguments. This is an internal Xlib or server error.
The length of a request exceeds the maximum length accepted by
the server.
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Error Code
Description
BadMatch
In a graphics request, the root and depth of the graphics context
do not match those of the drawable.
An InputOnly window is used as a drawable.
Some argument or pair of arguments has the correct type and
range, but it fails to match in some other way required by the
request.
An InputOnly window lacks this attribute.
BadName
A font or color of the specified name does not exist.
BadPixmap
A value for a pixmap argument does not name a defined pixmap.
BadRequest
The major or minor opcode does not specify a valid request.
This usually is an Xlib or server error.
BadValue
Some numeric value falls outside of the range of values accepted
by the request. Unless a specific range is specified for an argu-
ment, the full range defined by the argument's type is accepted.
Any argument defined as a set of alternatives typically can gener-
ate this error (due to the encoding).
BadWindow
A value for a window argument does not name a defined win-
dow.
Note
The BadAtom, BadColor, BadCursor, BadDrawable, BadFont, BadGC,
BadPixmap, and BadWindow errors are also used when the argument type is
extended by a set of fixed alternatives.
To obtain textual descriptions of the specified error code, use XGetErrorText.
XGetErrorText(display, code, buffer_return, length)
Display *display;
int code;
char *buffer_return;
int length;
display
Specifies the connection to the X server.
code
Specifies the error code for which you want to obtain a description.
buffer_return
Returns the error description.
length
Specifies the size of the buffer.
The XGetErrorText function copies a null-terminated string describing the specified error code
into the specified buffer. The returned text is in the encoding of the current locale. It is recom-
mended that you use this function to obtain an error description because extensions to Xlib may
define their own error codes and error strings.
To obtain error messages from the error database, use XGetErrorDatabaseText.
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XGetErrorDatabaseText(display, name, message, default_string, buffer_return, length)
Display *display;
char *name, *message;
char *default_string;
char *buffer_return;
int length;
display
Specifies the connection to the X server.
name
Specifies the name of the application.
message
Specifies the type of the error message.
default_string
Specifies the default error message if none is found in the database.
buffer_return
Returns the error description.
length
Specifies the size of the buffer.
The XGetErrorDatabaseText function returns a null-terminated message (or the default mes-
sage) from the error message database. Xlib uses this function internally to look up its error mes-
sages. The text in the default_string argument is assumed to be in the encoding of the current
locale, and the text stored in the buffer_return argument is in the encoding of the current locale.
The name argument should generally be the name of your application. The message argument
should indicate which type of error message you want. If the name and message are not in the
Host Portable Character Encoding, the result is implementation-dependent. Xlib uses three pre-
defined ``application names'' to report errors. In these names, uppercase and lowercase matter.
XProtoError The protocol error number is used as a string for the message argument.
XlibMessage These are the message strings that are used internally by the library.
XRequest For a core protocol request, the major request protocol number is used for the
message argument. For an extension request, the extension name (as given by
InitExtension) followed by a period (.) and the minor request protocol number is
used for the message argument. If no string is found in the error database, the
default_string is returned to the buffer argument.
To report an error to the user when the requested display does not exist, use XDisplayName.
char *XDisplayName(string)
char *string;
string
Specifies the character string.
The XDisplayName function returns the name of the display that XOpenDisplay would attempt
to use. If a NULL string is specified, XDisplayName looks in the environment for the display
and returns the display name that XOpenDisplay would attempt to use. This makes it easier to
report to the user precisely which display the program attempted to open when the initial connec-
tion attempt failed.
To handle fatal I/O errors, use XSetIOErrorHandler.
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int (*XSetIOErrorHandler(handler))()
int (*handler)(Display *);
handler
Specifies the program's supplied error handler.
The XSetIOErrorHandler sets the fatal I/O error handler. Xlib calls the program's supplied
error handler if any sort of system call error occurs (for example, the connection to the server was
lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O
error handler does return, the client process exits.
Note that the previous error handler is returned.
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Chapter 12
Input Device Functions
You can use the Xlib input device functions to:

Grab the pointer and individual buttons on the pointer

Grab the keyboard and individual keys on the keyboard

Resume event processing

Move the pointer

Set the input focus

Manipulate the keyboard and pointer settings

Manipulate the keyboard encoding
12.1. Pointer Grabbing
Xlib provides functions that you can use to control input from the pointer, which usually is a
mouse. Usually, as soon as keyboard and mouse events occur, the X server delivers them to the
appropriate client, which is determined by the window and input focus. The X server provides
sufficient control over event delivery to allow window managers to support mouse ahead and vari-
ous other styles of user interface. Many of these user interfaces depend on synchronous delivery
of events. The delivery of pointer and keyboard events can be controlled independently.
When mouse buttons or keyboard keys are grabbed, events will be sent to the grabbing client
rather than the normal client who would have received the event. If the keyboard or pointer is in
asynchronous mode, further mouse and keyboard events will continue to be processed. If the
keyboard or pointer is in synchronous mode, no further events are processed until the grabbing
client allows them (see XAllowEvents). The keyboard or pointer is considered frozen during
this interval. The ev ent that triggered the grab can also be replayed.
Note that the logical state of a device (as seen by client applications) may lag the physical state if
device event processing is frozen.
There are two kinds of grabs: active and passive. An active grab occurs when a single client
grabs the keyboard and/or pointer explicitly (see XGrabPointer and XGrabKeyboard). A pas-
sive grab occurs when clients grab a particular keyboard key or pointer button in a window, and
the grab will activate when the key or button is actually pressed. Passive grabs are convenient for
implementing reliable pop-up menus. For example, you can guarantee that the pop-up is mapped
before the up pointer button event occurs by grabbing a button requesting synchronous behavior.
The down event will trigger the grab and freeze further processing of pointer events until you
have the chance to map the pop-up window. You can then allow further event processing. The up
ev ent will then be correctly processed relative to the pop-up window.
For many operations, there are functions that take a time argument. The X server includes a
timestamp in various events. One special time, called CurrentTime, represents the current
server time. The X server maintains the time when the input focus was last changed, when the
keyboard was last grabbed, when the pointer was last grabbed, or when a selection was last
changed. Your application may be slow reacting to an event. You often need some way to spec-
ify that your request should not occur if another application has in the meanwhile taken control of
the keyboard, pointer, or selection. By providing the timestamp from the event in the request, you
can arrange that the operation not take effect if someone else has performed an operation in the
meanwhile.
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A timestamp is a time value, expressed in milliseconds. It typically is the time since the last
server reset. Timestamp values wrap around (after about 49.7 days). The server, giv en its current
time is represented by timestamp T, always interprets timestamps from clients by treating half of
the timestamp space as being later in time than T. One timestamp value, named CurrentTime, is
never generated by the server. This value is reserved for use in requests to represent the current
server time.
For many functions in this section, you pass pointer event mask bits. The valid pointer event
mask bits are: ButtonPressMask, ButtonReleaseMask, EnterWindowMask,
LeaveWindowMask, PointerMotionMask, PointerMotionHintMask, Button1MotionMask,
Button2MotionMask, Button3MotionMask, Button4MotionMask, Button5MotionMask,
ButtonMotionMask, and KeyMapStateMask. For other functions in this section, you pass
keymask bits. The valid keymask bits are: ShiftMask, LockMask, ControlMask, Mod1Mask,
Mod2Mask, Mod3Mask, Mod4Mask, and Mod5Mask.
To grab the pointer, use XGrabPointer.
int XGrabPointer(display, grab_window, owner_events, event_mask, pointer_mode,
keyboard_mode, confine_to, cursor, time)
Display *display;
Window grab_window;
Bool owner_events;
unsigned int event_mask;
int pointer_mode, keyboard_mode;
Window confine_to;
Cursor cursor;
Time time;
display
Specifies the connection to the X server.
grab_window
Specifies the grab window.
owner_events
Specifies a Boolean value that indicates whether the pointer events are to be re-
ported as usual or reported with respect to the grab window if selected by the
ev ent mask.
event_mask
Specifies which pointer events are reported to the client. The mask is the bitwise
inclusive OR of the valid pointer event mask bits.
pointer_mode
Specifies further processing of pointer events. You can pass GrabModeSync or
GrabModeAsync.
keyboard_mode Specifies further processing of keyboard events. You can pass GrabModeSync
or GrabModeAsync.
confine_to
Specifies the window to confine the pointer in or None.
cursor
Specifies the cursor that is to be displayed during the grab or None.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XGrabPointer function actively grabs control of the pointer and returns GrabSuccess if the
grab was successful. Further pointer events are reported only to the grabbing client. XGrab-
Pointer
overrides any active pointer grab by this client. If owner_events is False, all generated
pointer events are reported with respect to grab_window and are reported only if selected by
ev ent_mask. If owner_events is True and if a generated pointer event would normally be
reported to this client, it is reported as usual. Otherwise, the event is reported with respect to the
grab_window and is reported only if selected by event_mask. For either value of owner_events,
unreported events are discarded.
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If the pointer_mode is GrabModeAsync, pointer event processing continues as usual. If the
pointer is currently frozen by this client, the processing of events for the pointer is resumed. If
the pointer_mode is GrabModeSync, the state of the pointer, as seen by client applications,
appears to freeze, and the X server generates no further pointer events until the grabbing client
calls XAllowEvents or until the pointer grab is released. Actual pointer changes are not lost
while the pointer is frozen; they are simply queued in the server for later processing.
If the keyboard_mode is GrabModeAsync, keyboard event processing is unaffected by acti-
vation of the grab. If the keyboard_mode is GrabModeSync, the state of the keyboard, as seen
by client applications, appears to freeze, and the X server generates no further keyboard events
until the grabbing client calls XAllowEvents or until the pointer grab is released. Actual
keyboard changes are not lost while the pointer is frozen; they are simply queued in the server for
later processing.
If a cursor is specified, it is displayed regardless of what window the pointer is in. If None is
specified, the normal cursor for that window is displayed when the pointer is in grab_window or
one of its subwindows; otherwise, the cursor for grab_window is displayed.
If a confine_to window is specified, the pointer is restricted to stay contained in that window. The
confine_to window need have no relationship to the grab_window. If the pointer is not initially in
the confine_to window, it is warped automatically to the closest edge just before the grab activates
and enter/leave events are generated as usual. If the confine_to window is subsequently reconfig-
ured, the pointer is warped automatically, as necessary, to keep it contained in the window.
The time argument allows you to avoid certain circumstances that come up if applications take a
long time to respond or if there are long network delays. Consider a situation where you have
two applications, both of which normally grab the pointer when clicked on. If both applications
specify the timestamp from the event, the second application may wake up faster and successfully
grab the pointer before the first application. The first application then will get an indication that
the other application grabbed the pointer before its request was processed.
XGrabPointer generates EnterNotify and LeaveNotify ev ents.
Either if grab_window or confine_to window is not viewable or if the confine_to window lies
completely outside the boundaries of the root window, XGrabPointer fails and returns
GrabNotViewable. If the pointer is actively grabbed by some other client, it fails and returns
AlreadyGrabbed. If the pointer is frozen by an active grab of another client, it fails and returns
GrabFrozen. If the specified time is earlier than the last-pointer-grab time or later than the cur-
rent X server time, it fails and returns GrabInvalidTime. Otherwise, the last-pointer-grab time
is set to the specified time (CurrentTime is replaced by the current X server time).
XGrabPointer can generate BadCursor, BadValue, and BadWindow errors.
To ungrab the pointer, use XUngrabPointer.
XUngrabPointer (display, time)
Display *display;
Time time;
display
Specifies the connection to the X server.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XUngrabPointer function releases the pointer and any queued events if this client has
actively grabbed the pointer from XGrabPointer, XGrabButton, or from a normal button press.
XUngrabPointer does not release the pointer if the specified time is earlier than the last-pointer-
grab time or is later than the current X server time. It also generates EnterNotify and LeaveNo-
tify
ev ents. The X server performs an UngrabPointer request automatically if the event window
or confine_to window for an active pointer grab becomes not viewable or if window reconfigura-
tion causes the confine_to window to lie completely outside the boundaries of the root window.
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To change an active pointer grab, use XChangeActivePointerGrab.
XChangeActivePointerGrab (display, event_mask, cursor, time)
Display *display;
unsigned int event_mask;
Cursor cursor;
Time time;
display
Specifies the connection to the X server.
event_mask
Specifies which pointer events are reported to the client. The mask is the bitwise
inclusive OR of the valid pointer event mask bits.
cursor
Specifies the cursor that is to be displayed or None.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XChangeActivePointerGrab function changes the specified dynamic parameters if the
pointer is actively grabbed by the client and if the specified time is no earlier than the last-pointer-
grab time and no later than the current X server time. This function has no effect on the passive
parameters of an XGrabButton. The interpretation of event_mask and cursor is the same as
described in XGrabPointer.
XChangeActivePointerGrab can generate BadCursor and BadValue errors.
To grab a pointer button, use XGrabButton.
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XGrabButton (display, button, modifiers, grab_window, owner_events, event_mask,
pointer_mode, keyboard_mode, confine_to, cursor)
Display *display;
unsigned int button;
unsigned int modifiers;
Window grab_window;
Bool owner_events;
unsigned int event_mask;
int pointer_mode, keyboard_mode;
Window confine_to;
Cursor cursor;
display
Specifies the connection to the X server.
button
Specifies the pointer button that is to be grabbed or AnyButton.
modifiers
Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive
OR of the valid keymask bits.
grab_window
Specifies the grab window.
owner_events
Specifies a Boolean value that indicates whether the pointer events are to be re-
ported as usual or reported with respect to the grab window if selected by the
ev ent mask.
event_mask
Specifies which pointer events are reported to the client. The mask is the bitwise
inclusive OR of the valid pointer event mask bits.
pointer_mode
Specifies further processing of pointer events. You can pass GrabModeSync or
GrabModeAsync.
keyboard_mode Specifies further processing of keyboard events. You can pass GrabModeSync
or GrabModeAsync.
confine_to
Specifies the window to confine the pointer in or None.
cursor
Specifies the cursor that is to be displayed or None.
The XGrabButton function establishes a passive grab. In the future, the pointer is actively
grabbed (as for XGrabPointer), the last-pointer-grab time is set to the time at which the button
was pressed (as transmitted in the ButtonPress ev ent), and the ButtonPress ev ent is reported if
all of the following conditions are true:

The pointer is not grabbed, and the specified button is logically pressed when the specified
modifier keys are logically down, and no other buttons or modifier keys are logically down.

The grab_window contains the pointer.

The confine_to window (if any) is viewable.

A passive grab on the same button/key combination does not exist on any ancestor of
grab_window.
The interpretation of the remaining arguments is as for XGrabPointer. The active grab is termi-
nated automatically when the logical state of the pointer has all buttons released (independent of
the state of the logical modifier keys).
Note that the logical state of a device (as seen by client applications) may lag the physical state if
device event processing is frozen.
This request overrides all previous grabs by the same client on the same button/key combinations
on the same window. A modifiers of AnyModifier is equivalent to issuing the grab request for
all possible modifier combinations (including the combination of no modifiers). It is not required
that all modifiers specified have currently assigned KeyCodes. A button of AnyButton is
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equivalent to issuing the request for all possible buttons. Otherwise, it is not required that the
specified button currently be assigned to a physical button.
If some other client has already issued an XGrabButton with the same button/key combination
on the same window, a BadAccess error results. When using AnyModifier or AnyButton, the
request fails completely, and a BadAccess error results (no grabs are established) if there is a
conflicting grab for any combination. XGrabButton has no effect on an active grab.
XGrabButton can generate BadCursor, BadValue, and BadWindow errors.
To ungrab a pointer button, use XUngrabButton.
XUngrabButton (display, button, modifiers, grab_window)
Display *display;
unsigned int button;
unsigned int modifiers;
Window grab_window;
display
Specifies the connection to the X server.
button
Specifies the pointer button that is to be released or AnyButton.
modifiers
Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive
OR of the valid keymask bits.
grab_window
Specifies the grab window.
The XUngrabButton function releases the passive button/key combination on the specified win-
dow if it was grabbed by this client. A modifiers of AnyModifier is equivalent to issuing the
ungrab request for all possible modifier combinations, including the combination of no modifiers.
A button of AnyButton is equivalent to issuing the request for all possible buttons. XUngrab-
Button
has no effect on an active grab.
XUngrabButton can generate BadValue and BadWindow errors.
12.2. Keyboard Grabbing
Xlib provides functions that you can use to grab or ungrab the keyboard as well as allow events.
For many functions in this section, you pass keymask bits. The valid keymask bits are:
ShiftMask, LockMask, ControlMask, Mod1Mask, Mod2Mask, Mod3Mask, Mod4Mask,
and Mod5Mask.
To grab the keyboard, use XGrabKeyboard.
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int XGrabKeyboard (display, grab_window, owner_events, pointer_mode, keyboard_mode, time)
Display *display;
Window grab_window;
Bool owner_events;
int pointer_mode, keyboard_mode;
Time time;
display
Specifies the connection to the X server.
grab_window
Specifies the grab window.
owner_events
Specifies a Boolean value that indicates whether the keyboard events are to be re-
ported as usual.
pointer_mode
Specifies further processing of pointer events. You can pass GrabModeSync or
GrabModeAsync.
keyboard_mode Specifies further processing of keyboard events. You can pass GrabModeSync
or GrabModeAsync.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XGrabKeyboard function actively grabs control of the keyboard and generates FocusIn
and FocusOut ev ents. Further key events are reported only to the grabbing client. XGrabKey-
board
overrides any active keyboard grab by this client. If owner_events is False, all generated
key events are reported with respect to grab_window. If owner_events is True and if a generated
key event would normally be reported to this client, it is reported normally; otherwise, the event is
reported with respect to the grab_window. Both KeyPress and KeyRelease ev ents are always
reported, independent of any event selection made by the client.
If the keyboard_mode argument is GrabModeAsync, keyboard event processing continues as
usual. If the keyboard is currently frozen by this client, then processing of keyboard events is
resumed. If the keyboard_mode argument is GrabModeSync, the state of the keyboard (as seen
by client applications) appears to freeze, and the X server generates no further keyboard events
until the grabbing client issues a releasing XAllowEvents call or until the keyboard grab is
released. Actual keyboard changes are not lost while the keyboard is frozen; they are simply
queued in the server for later processing.
If pointer_mode is GrabModeAsync, pointer event processing is unaffected by activation of the
grab. If pointer_mode is GrabModeSync, the state of the pointer (as seen by client applications)
appears to freeze, and the X server generates no further pointer events until the grabbing client
issues a releasing XAllowEvents call or until the keyboard grab is released. Actual pointer
changes are not lost while the pointer is frozen; they are simply queued in the server for later pro-
cessing.
If the keyboard is actively grabbed by some other client, XGrabKeyboard fails and returns
AlreadyGrabbed. If grab_window is not viewable, it fails and returns GrabNotViewable. If
the keyboard is frozen by an active grab of another client, it fails and returns GrabFrozen. If the
specified time is earlier than the last-keyboard-grab time or later than the current X server time, it
fails and returns GrabInvalidTime. Otherwise, the last-keyboard-grab time is set to the speci-
fied time (CurrentTime is replaced by the current X server time).
XGrabKeyboard can generate BadValue and BadWindow errors.
To ungrab the keyboard, use XUngrabKeyboard.
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XUngrabKeyboard (display, time)
Display *display;
Time time;
display
Specifies the connection to the X server.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XUngrabKeyboard function releases the keyboard and any queued events if this client has
it actively grabbed from either XGrabKeyboard or XGrabKey. XUngrabKeyboard does not
release the keyboard and any queued events if the specified time is earlier than the last-keyboard-
grab time or is later than the current X server time. It also generates FocusIn and FocusOut
ev ents. The X server automatically performs an UngrabKeyboard request if the event window
for an active keyboard grab becomes not viewable.
To passively grab a single key of the keyboard, use XGrabKey.
XGrabKey (display, keycode, modifiers, grab_window, owner_events, pointer_mode,
keyboard_mode)
Display *display;
int keycode;
unsigned int modifiers;
Window grab_window;
Bool owner_events;
int pointer_mode, keyboard_mode;
display
Specifies the connection to the X server.
keycode
Specifies the KeyCode or AnyKey.
modifiers
Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive
OR of the valid keymask bits.
grab_window
Specifies the grab window.
owner_events
Specifies a Boolean value that indicates whether the keyboard events are to be re-
ported as usual.
pointer_mode
Specifies further processing of pointer events. You can pass GrabModeSync or
GrabModeAsync.
keyboard_mode Specifies further processing of keyboard events. You can pass GrabModeSync
or GrabModeAsync.
The XGrabKey function establishes a passive grab on the keyboard. In the future, the keyboard
is actively grabbed (as for XGrabKeyboard), the last-keyboard-grab time is set to the time at
which the key was pressed (as transmitted in the KeyPress ev ent), and the KeyPress ev ent is
reported if all of the following conditions are true:

The keyboard is not grabbed and the specified key (which can itself be a modifier key) is
logically pressed when the specified modifier keys are logically down, and no other modi-
fier keys are logically down.

Either the grab_window is an ancestor of (or is) the focus window, or the grab_window is a
descendant of the focus window and contains the pointer.

A passive grab on the same key combination does not exist on any ancestor of grab_win-
dow.
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The interpretation of the remaining arguments is as for XGrabKeyboard. The active grab is ter-
minated automatically when the logical state of the keyboard has the specified key released (inde-
pendent of the logical state of the modifier keys).
Note that the logical state of a device (as seen by client applications) may lag the physical state if
device event processing is frozen.
A modifiers argument of AnyModifier is equivalent to issuing the request for all possible modi-
fier combinations (including the combination of no modifiers). It is not required that all modifiers
specified have currently assigned KeyCodes. A keycode argument of AnyKey is equivalent to
issuing the request for all possible KeyCodes. Otherwise, the specified keycode must be in the
range specified by min_keycode and max_keycode in the connection setup, or a BadValue error
results.
If some other client has issued a XGrabKey with the same key combination on the same win-
dow, a BadAccess error results. When using AnyModifier or AnyKey, the request fails com-
pletely, and a BadAccess error results (no grabs are established) if there is a conflicting grab for
any combination.
XGrabKey can generate BadAccess, BadValue, and BadWindow errors.
To ungrab a key, use XUngrabKey.
XUngrabKey (display, keycode, modifiers, grab_window)
Display *display;
int keycode;
unsigned int modifiers;
Window grab_window;
display
Specifies the connection to the X server.
keycode
Specifies the KeyCode or AnyKey.
modifiers
Specifies the set of keymasks or AnyModifier. The mask is the bitwise inclusive
OR of the valid keymask bits.
grab_window
Specifies the grab window.
The XUngrabKey function releases the key combination on the specified window if it was
grabbed by this client. It has no effect on an active grab. A modifiers of AnyModifier is equiv-
alent to issuing the request for all possible modifier combinations (including the combination of
no modifiers). A keycode argument of AnyKey is equivalent to issuing the request for all possi-
ble key codes.
XUngrabKey can generate BadValue and BadWindow errors.
12.3. Resuming Event Processing
The previous sections discussed grab mechanisms with which processing of events by the server
can be temporarily suspended. This section describes the mechanism for resuming event process-
ing.
To allow further events to be processed when the device has been frozen, use XAllowEvents.
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XAllowEvents (display, event_mode, time)
Display *display;
int event_mode;
Time time;
display
Specifies the connection to the X server.
event_mode
Specifies the event mode.
You can pass
AsyncPointer,
SyncPointer,
AsyncKeyboard,
SyncKeyboard,
ReplayPointer,
ReplayKeyboard,
AsyncBoth, or SyncBoth.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XAllowEvents function releases some queued events if the client has caused a device to
freeze. It has no effect if the specified time is earlier than the last-grab time of the most recent
active grab for the client or if the specified time is later than the current X server time. Depending
on the event_mode argument, the following occurs:
AsyncPointer
If the pointer is frozen by the client, pointer event processing continues
as usual. If the pointer is frozen twice by the client on behalf of two sep-
arate grabs, AsyncPointer thaws for both. AsyncPointer has no effect
if the pointer is not frozen by the client, but the pointer need not be
grabbed by the client.
SyncPointer
If the pointer is frozen and actively grabbed by the client, pointer event
processing continues as usual until the next ButtonPress or ButtonRe-
lease
ev ent is reported to the client. At this time, the pointer again
appears to freeze. However, if the reported event causes the pointer grab
to be released, the pointer does not freeze. SyncPointer has no effect if
the pointer is not frozen by the client or if the pointer is not grabbed by
the client.
ReplayPointer
If the pointer is actively grabbed by the client and is frozen as the result
of an event having been sent to the client (either from the activation of an
XGrabButton or from a previous XAllowEvents with mode Sync-
Pointer but not from an XGrabPointer), the pointer grab is released
and that event is completely reprocessed. This time, however, the func-
tion ignores any passive grabs at or above (toward the root of) the
grab_window of the grab just released. The request has no effect if the
pointer is not grabbed by the client or if the pointer is not frozen as the
result of an event.
AsyncKeyboard
If the keyboard is frozen by the client, keyboard event processing contin-
ues as usual. If the keyboard is frozen twice by the client on behalf of
two separate grabs, AsyncKeyboard thaws for both. AsyncKeyboard
has no effect if the keyboard is not frozen by the client, but the keyboard
need not be grabbed by the client.
SyncKeyboard
If the keyboard is frozen and actively grabbed by the client, keyboard
ev ent processing continues as usual until the next KeyPress or KeyRe-
lease
ev ent is reported to the client. At this time, the keyboard again
appears to freeze. However, if the reported event causes the keyboard
grab to be released, the keyboard does not freeze. SyncKeyboard has
no effect if the keyboard is not frozen by the client or if the keyboard is
not grabbed by the client.
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ReplayKeyboard
If the keyboard is actively grabbed by the client and is frozen as the
result of an event having been sent to the client (either from the acti-
vation of an XGrabKey or from a previous XAllowEvents with mode
SyncKeyboard but not from an XGrabKeyboard), the keyboard grab
is released and that event is completely reprocessed. This time, however,
the function ignores any passive grabs at or above (toward the root of)
the grab_window of the grab just released. The request has no effect if
the keyboard is not grabbed by the client or if the keyboard is not frozen
as the result of an event.
SyncBoth
If both pointer and keyboard are frozen by the client, event processing
for both devices continues as usual until the next ButtonPress,
ButtonRelease, KeyPress, or KeyRelease ev ent is reported to the
client for a grabbed device (button event for the pointer, key event for the
keyboard), at which time the devices again appear to freeze. However, if
the reported event causes the grab to be released, then the devices do not
freeze (but if the other device is still grabbed, then a subsequent event for
it will still cause both devices to freeze). SyncBoth has no effect unless
both pointer and keyboard are frozen by the client. If the pointer or
keyboard is frozen twice by the client on behalf of two separate grabs,
SyncBoth thaws for both (but a subsequent freeze for SyncBoth will
only freeze each device once).
AsyncBoth
If the pointer and the keyboard are frozen by the client, event processing
for both devices continues as usual. If a device is frozen twice by the
client on behalf of two separate grabs, AsyncBoth thaws for both.
AsyncBoth has no effect unless both pointer and keyboard are frozen by
the client.
AsyncPointer, SyncPointer, and ReplayPointer have no effect on the processing of keyboard
ev ents. AsyncKeyboard, SyncKeyboard, and ReplayKeyboard have no effect on the process-
ing of pointer events. It is possible for both a pointer grab and a keyboard grab (by the same or
different clients) to be active simultaneously. If a device is frozen on behalf of either grab, no
ev ent processing is performed for the device. It is possible for a single device to be frozen
because of both grabs. In this case, the freeze must be released on behalf of both grabs before
ev ents can again be processed. If a device is frozen twice by a single client, then a single Allow-
Events
releases both.
XAllowEvents can generate a BadValue error.
12.4. Moving the Pointer
Although movement of the pointer normally should be left to the control of the end user, some-
times it is necessary to move the pointer to a new position under program control.
To move the pointer to an arbitrary point in a window, use XWarpPointer.
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XWarpPointer (display, src_w, dest_w, src_x, src_y, src_width, src_height, dest_x,
dest_y)
Display *display;
Window src_w, dest_w;
int src_x, src_y;
unsigned int src_width, src_height;
int dest_x, dest_y;
display
Specifies the connection to the X server.
src_w
Specifies the source window or None.
dest_w
Specifies the destination window or None.
src_x
src_y
src_width
src_height
Specify a rectangle in the source window.
dest_x
dest_y
Specify the x and y coordinates within the destination window.
If dest_w is None, XWarpPointer moves the pointer by the offsets (dest_x, dest_y) relative to
the current position of the pointer. If dest_w is a window, XWarpPointer moves the pointer to
the offsets (dest_x, dest_y) relative to the origin of dest_w. Howev er, if src_w is a window, the
move only takes place if the window src_w contains the pointer and if the specified rectangle of
src_w contains the pointer.
The src_x and src_y coordinates are relative to the origin of src_w. If src_height is zero, it is
replaced with the current height of src_w minus src_y. If src_width is zero, it is replaced with the
current width of src_w minus src_x.
There is seldom any reason for calling this function. The pointer should normally be left to the
user. If you do use this function, however, it generates events just as if the user had instanta-
neously moved the pointer from one position to another. Note that you cannot use XWarp-
Pointer
to move the pointer outside the confine_to window of an active pointer grab. An attempt
to do so will only move the pointer as far as the closest edge of the confine_to window.
XWarpPointer can generate a BadWindow error.
12.5. Controlling Input Focus
Xlib provides functions that you can use to set and get the input focus. The input focus is a
shared resource, and cooperation among clients is required for correct interaction. See the Inter-
Client Communication Conventions Manual
for input focus policy.
To set the input focus, use XSetInputFocus.
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XSetInputFocus (display, focus, re vert_to, time)
Display *display;
Window focus;
int re vert_to;
Time time;
display
Specifies the connection to the X server.
focus
Specifies the window, PointerRoot, or None.
re vert_to
Specifies where the input focus reverts to if the window becomes not viewable.
You can pass RevertToParent, RevertToPointerRoot, or RevertToNone.
time
Specifies the time. You can pass either a timestamp or CurrentTime.
The XSetInputFocus function changes the input focus and the last-focus-change time. It has no
effect if the specified time is earlier than the current last-focus-change time or is later than the
current X server time. Otherwise, the last-focus-change time is set to the specified time (Cur-
rentTime
is replaced by the current X server time). XSetInputFocus causes the X server to
generate FocusIn and FocusOut ev ents.
Depending on the focus argument, the following occurs:

If focus is None, all keyboard events are discarded until a new focus window is set, and the
revert_to argument is ignored.

If focus is a window, it becomes the keyboard's focus window. If a generated keyboard
ev ent would normally be reported to this window or one of its inferiors, the event is
reported as usual. Otherwise, the event is reported relative to the focus window.

If focus is PointerRoot, the focus window is dynamically taken to be the root window of
whatever screen the pointer is on at each keyboard event. In this case, the revert_to argu-
ment is ignored.
The specified focus window must be viewable at the time XSetInputFocus is called, or a Bad-
Match
error results. If the focus window later becomes not viewable, the X server evaluates the
revert_to argument to determine the new focus window as follows:

If rev ert_to is RevertToParent, the focus reverts to the parent (or the closest viewable
ancestor), and the new rev ert_to value is taken to be RevertToNone.

If rev ert_to is RevertToPointerRoot or RevertToNone, the focus reverts to PointerRoot
or None, respectively. When the focus reverts, the X server generates FocusIn and Focu-
sOut
ev ents, but the last-focus-change time is not affected.
XSetInputFocus can generate BadMatch, BadValue, and BadWindow errors.
To obtain the current input focus, use XGetInputFocus.
XGetInputFocus (display, focus_return, re vert_to_return)
Display *display;
Window *focus_return;
int *re vert_to_return;
display
Specifies the connection to the X server.
focus_return
Returns the focus window, PointerRoot, or None.
re vert_to_returnReturns the current focus state (RevertToParent, RevertToPointerRoot, or
RevertToNone).
The XGetInputFocus function returns the focus window and the current focus state.
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12.6. Manipulating the Keyboard and Pointer Settings
Xlib provides functions that you can use to change the keyboard control, obtain a list of the auto-
repeat keys, turn keyboard auto-repeat on or off, ring the bell, set or obtain the pointer button or
keyboard mapping, and obtain a bit vector for the keyboard.
This section discusses the user-preference options of bell, key click, pointer behavior, and so on.
The default values for many of these options are server dependent. Not all implementations will
actually be able to control all of these parameters.
The XChangeKeyboardControl function changes control of a keyboard and operates on a
XKeyboardControl structure:
/* Mask bits for ChangeKeyboardControl */
#define
KBKeyClickPercent
(1L<<0)
#define
KBBellPercent
(1L<<1)
#define
KBBellPitch
(1L<<2)
#define
KBBellDuration
(1L<<3)
#define
KBLed
(1L<<4)
#define
KBLedMode
(1L<<5)
#define
KBKey
(1L<<6)
#define
KBAutoRepeatMode
(1L<<7)
/* Values */
typedef struct {
int key_click_percent;
int bell_percent;
int bell_pitch;
int bell_duration;
int led;
int led_mode;
/* LedModeOn, LedModeOff */
int key;
int auto_repeat_mode;
/* AutoRepeatModeOff, AutoRepeatModeOn,
AutoRepeatModeDefault */
} XKe yboardControl;
The key_click_percent member sets the volume for key clicks between 0 (off) and 100 (loud)
inclusive, if possible. A setting of -1 restores the default. Other negative values generate a Bad-
Value
error.
The bell_percent sets the base volume for the bell between 0 (off) and 100 (loud) inclusive, if
possible. A setting of -1 restores the default. Other negative values generate a BadValue error.
The bell_pitch member sets the pitch (specified in Hz) of the bell, if possible. A setting of -1
restores the default. Other negative values generate a BadValue error. The bell_duration mem-
ber sets the duration of the bell specified in milliseconds, if possible. A setting of -1 restores the
default. Other negative values generate a BadValue error.
If both the led_mode and led members are specified, the state of that LED is changed, if possible.
The led_mode member can be set to LedModeOn or LedModeOff. If only led_mode is speci-
fied, the state of all LEDs are changed, if possible. At most 32 LEDs numbered from one are sup-
ported. No standard interpretation of LEDs is defined. If led is specified without led_mode, a
BadMatch error results.
If both the auto_repeat_mode and key members are specified, the auto_repeat_mode of that key is
changed (according to AutoRepeatModeOn, AutoRepeatModeOff, or
AutoRepeatModeDefault), if possible. If only auto_repeat_mode is specified, the global
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auto_repeat_mode for the entire keyboard is changed, if possible, and does not affect the per-key
settings. If a key is specified without an auto_repeat_mode, a BadMatch error results. Each key
has an individual mode of whether or not it should auto-repeat and a default setting for the mode.
In addition, there is a global mode of whether auto-repeat should be enabled or not and a default
setting for that mode. When global mode is AutoRepeatModeOn, keys should obey their indi-
vidual auto-repeat modes. When global mode is AutoRepeatModeOff, no keys should auto-
repeat. An auto-repeating key generates alternating KeyPress and KeyRelease ev ents. When a
key is used as a modifier, it is desirable for the key not to auto-repeat, regardless of its auto-repeat
setting.
A bell generator connected with the console but not directly on a keyboard is treated as if it were
part of the keyboard. The order in which controls are verified and altered is server-dependent. If
an error is generated, a subset of the controls may have been altered.
XChangeKeyboardControl (display, value_mask, values)
Display *display;
unsigned long value_mask;
XKeyboardControl *values;
display
Specifies the connection to the X server.
value_mask
Specifies which controls to change. This mask is the bitwise inclusive OR of the
valid control mask bits.
values
Specifies one value for each bit set to 1 in the mask.
The XChangeKeyboardControl function controls the keyboard characteristics defined by the
XKeyboardControl structure. The value_mask argument specifies which values are to be
changed.
XChangeKeyboardControl can generate BadMatch and BadValue errors.
To obtain the current control values for the keyboard, use XGetKeyboardControl.
XGetKeyboardControl (display, values_return)
Display *display;
XKeyboardState *values_return;
display
Specifies the connection to the X server.
values_return
Returns the current keyboard controls in the specified XKeyboardState struc-
ture.
The XGetKeyboardControl function returns the current control values for the keyboard to the
XKeyboardState structure.
typedef struct {
int key_click_percent;
int bell_percent;
unsigned int bell_pitch, bell_duration;
unsigned long led_mask;
int global_auto_repeat;
char auto_repeats[32];
} XKe yboardState;
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For the LEDs, the least significant bit of led_mask corresponds to LED one, and each bit set to 1
in led_mask indicates an LED that is lit. The global_auto_repeat member can be set to AutoRe-
peatModeOn
or AutoRepeatModeOff. The auto_repeats member is a bit vector. Each bit set
to 1 indicates that auto-repeat is enabled for the corresponding key. The vector is represented as
32 bytes. Byte N (from 0) contains the bits for keys 8N to 8N + 7 with the least significant bit in
the byte representing key 8N.
To turn on keyboard auto-repeat, use XAutoRepeatOn.
XAutoRepeatOn (display)
Display *display;
display
Specifies the connection to the X server.
The XAutoRepeatOn function turns on auto-repeat for the keyboard on the specified display.
To turn off keyboard auto-repeat, use XAutoRepeatOff.
XAutoRepeatOff(display)
Display *display;
display
Specifies the connection to the X server.
The XAutoRepeatOff function turns off auto-repeat for the keyboard on the specified display.
To ring the bell, use XBell.
XBell (display, percent)
Display *display;
int percent;
display
Specifies the connection to the X server.
percent
Specifies the volume for the bell, which can range from -100 to 100 inclusive.
The XBell function rings the bell on the keyboard on the specified display, if possible. The speci-
fied volume is relative to the base volume for the keyboard. If the value for the percent argument
is not in the range -100 to 100 inclusive, a BadValue error results. The volume at which the bell
rings when the percent argument is nonnegative is:
base - [(base * percent) / 100] + percent
The volume at which the bell rings when the percent argument is negative is:
base + [(base * percent) / 100]
To change the base volume of the bell, use XChangeKeyboardControl.
XBell can generate a BadValue error.
To obtain a bit vector that describes the state of the keyboard, use XQueryKeymap.
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XQueryKeymap (display, keys_return)
Display *display;
char keys_return[32] ;
display
Specifies the connection to the X server.
keys_return
Returns an array of bytes that identifies which keys are pressed down. Each bit
represents one key of the keyboard.
The XQueryKeymap function returns a bit vector for the logical state of the keyboard, where
each bit set to 1 indicates that the corresponding key is currently pressed down. The vector is rep-
resented as 32 bytes. Byte N (from 0) contains the bits for keys 8N to 8N + 7 with the least sig-
nificant bit in the byte representing key 8N.
Note that the logical state of a device (as seen by client applications) may lag the physical state if
device event processing is frozen.
To set the mapping of the pointer buttons, use XSetPointerMapping.
int XSetPointerMapping(display, map, nmap)
Display *display;
unsigned char map[] ;
int nmap;
display
Specifies the connection to the X server.
map
Specifies the mapping list.
nmap
Specifies the number of items in the mapping list.
The XSetPointerMapping function sets the mapping of the pointer. If it succeeds, the X server
generates a MappingNotify ev ent, and XSetPointerMapping returns MappingSuccess. Ele-
ment map[i] defines the logical button number for the physical button i+1. The length of the list
must be the same as XGetPointerMapping would return, or a BadValue error results. A zero
element disables a button, and elements are not restricted in value by the number of physical but-
tons. However, no two elements can have the same nonzero value, or a BadValue error results.
If any of the buttons to be altered are logically in the down state, XSetPointerMapping returns
MappingBusy, and the mapping is not changed.
XSetPointerMapping can generate a BadValue error.
To get the pointer mapping, use XGetPointerMapping.
int XGetPointerMapping(display, map_return, nmap)
Display *display;
unsigned char map_return[] ;
int nmap;
display
Specifies the connection to the X server.
map_return
Returns the mapping list.
nmap
Specifies the number of items in the mapping list.
The XGetPointerMapping function returns the current mapping of the pointer. Pointer buttons
are numbered starting from one. XGetPointerMapping returns the number of physical buttons
actually on the pointer. The nominal mapping for a pointer is map[i]=i+1. The nmap argument
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specifies the length of the array where the pointer mapping is returned, and only the first nmap
elements are returned in map_return.
To control the pointer's interactive feel, use XChangePointerControl.
XChangePointerControl (display, do_accel, do_threshold, accel_numerator,
accel_denominator, threshold)
Display *display;
Bool do_accel, do_threshold;
int accel_numerator, accel_denominator;
int threshold;
display
Specifies the connection to the X server.
do_accel
Specifies a Boolean value that controls whether the values for the accel_numera-
tor or accel_denominator are used.
do_threshold
Specifies a Boolean value that controls whether the value for the threshold is
used.
accel_numeratorSpecifies the numerator for the acceleration multiplier.
accel_denominator
Specifies the denominator for the acceleration multiplier.
threshold
Specifies the acceleration threshold.
The XChangePointerControl function defines how the pointing device moves. The accelera-
tion, expressed as a fraction, is a multiplier for movement. For example, specifying 3/1 means the
pointer moves three times as fast as normal. The fraction may be rounded arbitrarily by the X
server. Acceleration only takes effect if the pointer moves more than threshold pixels at once and
only applies to the amount beyond the value in the threshold argument. Setting a value to -1
restores the default. The values of the do_accel and do_threshold arguments must be True for
the pointer values to be set, or the parameters are unchanged. Negative values (other than -1)
generate a BadValue error, as does a zero value for the accel_denominator argument.
XChangePointerControl can generate a BadValue error.
To get the current pointer parameters, use XGetPointerControl.
XGetPointerControl (display, accel_numerator_return, accel_denominator_return,
threshold_return)
Display *display;
int *accel_numerator_return, *accel_denominator_return;
int *threshold_return;
display
Specifies the connection to the X server.
accel_numerator_return
Returns the numerator for the acceleration multiplier.
accel_denominator_return
Returns the denominator for the acceleration multiplier.
threshold_returnReturns the acceleration threshold.
The XGetPointerControl function returns the pointer's current acceleration multiplier and accel-
eration threshold.
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12.7. Manipulating the Keyboard Encoding
A KeyCode represents a physical (or logical) key. KeyCodes lie in the inclusive range [8,255]. A
Ke yCode value carries no intrinsic information, although server implementors may attempt to
encode geometry (for example, matrix) information in some fashion so that it can be interpreted
in a server-dependent fashion. The mapping between keys and KeyCodes cannot be changed.
A KeySym is an encoding of a symbol on the cap of a key. The set of defined KeySyms includes
the ISO Latin character sets (1-4), Katakana, Arabic, Cyrillic, Greek, Technical, Special, Publish-
ing, APL, Hebrew, Thai, Korean and a miscellany of keys found on keyboards (Return, Help, Tab,
and so on). To the extent possible, these sets are derived from international standards. In areas
where no standards exist, some of these sets are derived from Digital Equipment Corporation
standards. The list of defined symbols can be found in <X11/keysymdef.h>. Unfortunately,
some C preprocessors have limits on the number of defined symbols. If you must use KeySyms
not in the Latin 1-4, Greek, and miscellaneous classes, you may have to define a symbol for those
sets. Most applications usually only include <X11/keysym.h>, which defines symbols for ISO
Latin 1-4, Greek, and miscellaneous.
A list of KeySyms is associated with each KeyCode. The list is intended to convey the set of
symbols on the corresponding key. If the list (ignoring trailing NoSymbol entries) is a single
Ke ySym ``K'', then the list is treated as if it were the list ``K NoSymbol K NoSymbol''. If the list
(ignoring trailing NoSymbol entries) is a pair of KeySyms ``K1 K2'', then the list is treated as if
it were the list ``K1 K2 K1 K2''. If the list (ignoring trailing NoSymbol entries) is a triple of
Ke ySyms ``K1 K2 K3'', then the list is treated as if it were the list ``K1 K2 K3 NoSymbol''.
When an explicit ``void'' element is desired in the list, the value VoidSymbol can be used.
The first four elements of the list are split into two groups of KeySyms. Group 1 contains the first
and second KeySyms; Group 2 contains the third and fourth KeySyms. Within each group, if the
second element of the group is NoSymbol, then the group should be treated as if the second ele-
ment were the same as the first element, except when the first element is an alphabetic KeySym
``K'' for which both lowercase and uppercase forms are defined. In that case, the group should be
treated as if the first element were the lowercase form of ``K'' and the second element were the
uppercase form of ``K''.
The standard rules for obtaining a KeySym from a KeyPress ev ent make use of only the Group 1
and Group 2 KeySyms; no interpretation of other KeySyms in the list is given. Which group to
use is determined by the modifier state. Switching between groups is controlled by the KeySym
named MODE SWITCH, by attaching that KeySym to some KeyCode and attaching that
Ke yCode to any one of the modifiers Mod1 through Mod5. This modifier is called the group
modifier
. For any KeyCode, Group 1 is used when the group modifier is off, and Group 2 is used
when the group modifier is on.
The Lock modifier is interpreted as CapsLock when the KeySym named XK_Caps_Lock is
attached to some KeyCode and that KeyCode is attached to the Lock modifier. The Lock modi-
fier is interpreted as ShiftLock when the KeySym named XK_Shift_Lock is attached to some
Ke yCode and that KeyCode is attached to the Lock modifier. If the Lock modifier could be
interpreted as both CapsLock and ShiftLock, the CapsLock interpretation is used.
The operation of keypad keys is controlled by the KeySym named XK_Num_Lock, by attaching
that KeySym to some KeyCode and attaching that KeyCode to any one of the modifiers Mod1
through Mod5. This modifier is called the numlock modifier. The standard KeySyms with the
prefix ``XK_KP_'' in their name are called keypad KeySyms; these are KeySyms with numeric
value in the hexadecimal range 0xFF80 to 0xFFBD inclusive. In addition, vendor-specific
Ke ySyms in the hexadecimal range 0x11000000 to 0x1100FFFF are also keypad KeySyms.
Within a group, the choice of KeySym is determined by applying the first rule that is satisfied
from the following list:

The numlock modifier is on and the second KeySym is a keypad KeySym. In this case, if
the Shift modifier is on, or if the Lock modifier is on and is interpreted as ShiftLock, then
the first KeySym is used, otherwise the second KeySym is used.
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The Shift and Lock modifiers are both off. In this case, the first KeySym is used.

The Shift modifier is off, and the Lock modifier is on and is interpreted as CapsLock. In
this case, the first KeySym is used, but if that KeySym is lowercase alphabetic, then the cor-
responding uppercase KeySym is used instead.

The Shift modifier is on, and the Lock modifier is on and is interpreted as CapsLock. In
this case, the second KeySym is used, but if that KeySym is lowercase alphabetic, then the
corresponding uppercase KeySym is used instead.

The Shift modifier is on, or the Lock modifier is on and is interpreted as ShiftLock, or
both. In this case, the second KeySym is used.
No spatial geometry of the symbols on the key is defined by their order in the KeySym list,
although a geometry might be defined on a server-specific basis. The X server does not use the
mapping between KeyCodes and KeySyms. Rather, it merely stores it for reading and writing by
clients.
To obtain the legal KeyCodes for a display, use XDisplayKeycodes.
XDisplayKeycodes (display, min_keycodes_return, max_keycodes_return)
Display *display;
int *min_keycodes_return, *max_keycodes_return;
display
Specifies the connection to the X server.
min_keycodes_return
Returns the minimum number of KeyCodes.
max_keycodes_return
Returns the maximum number of KeyCodes.
The XDisplayKeycodes function returns the min-keycodes and max-keycodes supported by the
specified display. The minimum number of KeyCodes returned is never less than 8, and the maxi-
mum number of KeyCodes returned is never greater than 255. Not all KeyCodes in this range are
required to have corresponding keys.
To obtain the symbols for the specified KeyCodes, use XGetKeyboardMapping.
Ke ySym *XGetKeyboardMapping(display, first_keycode, keycode_count,
keysyms_per_keycode_return)
Display *display;
Ke yCode first_keycode;
int keycode_count;
int *keysyms_per_keycode_return;
display
Specifies the connection to the X server.
first_keycode
Specifies the first KeyCode that is to be returned.
keycode_count Specifies the number of KeyCodes that are to be returned.
keysyms_per_keycode_return
Returns the number of KeySyms per KeyCode.
The XGetKeyboardMapping function returns the symbols for the specified number of
Ke yCodes starting with first_keycode. The value specified in first_keycode must be greater than
or equal to min_keycode as returned by XDisplayKeycodes, or a BadValue error results. In
addition, the following expression must be less than or equal to max_keycode as returned by
XDisplayKeycodes:
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first_keycode + keycode_count - 1
If this is not the case, a BadValue error results. The number of elements in the KeySyms list is:
keycode_count * keysyms_per_keycode_return
Ke ySym number N, counting from zero, for KeyCode K has the following index in the list, count-
ing from zero:
(K - first_code) * keysyms_per_code_return + N
The X server arbitrarily chooses the keysyms_per_keycode_return value to be large enough to
report all requested symbols. A special KeySym value of NoSymbol is used to fill in unused ele-
ments for individual KeyCodes. To free the storage returned by XGetKeyboardMapping, use
XFree.
XGetKeyboardMapping can generate a BadValue error.
To change the keyboard mapping, use XChangeKeyboardMapping.
XChangeKeyboardMapping(display, first_keycode, keysyms_per_keycode, keysyms, num_codes)
Display *display;
int first_keycode;
int keysyms_per_keycode;
Ke ySym *keysyms;
int num_codes;
display
Specifies the connection to the X server.
first_keycode
Specifies the first KeyCode that is to be changed.
keysyms_per_keycode
Specifies the number of KeySyms per KeyCode.
keysyms
Specifies an array of KeySyms.
num_codes
Specifies the number of KeyCodes that are to be changed.
The XChangeKeyboardMapping function defines the symbols for the specified number of
Ke yCodes starting with first_keycode. The symbols for KeyCodes outside this range remain
unchanged. The number of elements in keysyms must be:
num_codes * keysyms_per_keycode
The specified first_keycode must be greater than or equal to min_keycode returned by
XDisplayKeycodes, or a BadValue error results. In addition, the following expression must be
less than or equal to max_keycode as returned by XDisplayKeycodes, or a BadValue error
results:
first_keycode + num_codes - 1
Ke ySym number N, counting from zero, for KeyCode K has the following index in keysyms,
counting from zero:
(K - first_keycode) * keysyms_per_keycode + N
The specified keysyms_per_keycode can be chosen arbitrarily by the client to be large enough to
hold all desired symbols. A special KeySym value of NoSymbol should be used to fill in unused
elements for individual KeyCodes. It is legal for NoSymbol to appear in nontrailing positions of
the effective list for a KeyCode. XChangeKeyboardMapping generates a MappingNotify
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ev ent.
There is no requirement that the X server interpret this mapping. It is merely stored for reading
and writing by clients.
XChangeKeyboardMapping can generate BadAlloc and BadValue errors.
The next six functions make use of the XModifierKeymap data structure, which contains:
typedef struct {
int max_keypermod; /* This server's max number of keys per modifier */
Ke yCode *modifiermap;
/* An 8 by max_keypermod array of the modifiers */
} XModifierKeymap;
To create an XModifierKeymap structure, use XNewModifiermap.
XModifierKeymap *XNewModifiermap(max_keys_per_mod)
int max_keys_per_mod;
max_keys_per_mod
Specifies the number of KeyCode entries preallocated to the modifiers in the
map.
The XNewModifiermap function returns a pointer to XModifierKeymap structure for later use.
To add a new entry to an XModifierKeymap structure, use XInsertModifiermapEntry.
XModifierKeymap *XInsertModifiermapEntry(modmap, keycode_entry, modifier)
XModifierKeymap *modmap;
Ke yCode keycode_entry;
int modifier;
modmap
Specifies the XModifierKeymap structure.
keycode_entry Specifies the KeyCode.
modifier
Specifies the modifier.
The XInsertModifiermapEntry function adds the specified KeyCode to the set that controls the
specified modifier and returns the resulting XModifierKeymap structure (expanded as needed).
To delete an entry from an XModifierKeymap structure, use XDeleteModifiermapEntry.
XModifierKeymap *XDeleteModifiermapEntry(modmap, keycode_entry, modifier)
XModifierKeymap *modmap;
Ke yCode keycode_entry;
int modifier;
modmap
Specifies the XModifierKeymap structure.
keycode_entry Specifies the KeyCode.
modifier
Specifies the modifier.
The XDeleteModifiermapEntry function deletes the specified KeyCode from the set that con-
trols the specified modifier and returns a pointer to the resulting XModifierKeymap structure.
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To destroy an XModifierKeymap structure, use XFreeModifiermap.
XFreeModifiermap(modmap)
XModifierKeymap *modmap;
modmap
Specifies the XModifierKeymap structure.
The XFreeModifiermap function frees the specified XModifierKeymap structure.
To set the KeyCodes to be used as modifiers, use XSetModifierMapping.
int XSetModifierMapping(display, modmap)
Display *display;
XModifierKeymap *modmap;
display
Specifies the connection to the X server.
modmap
Specifies the XModifierKeymap structure.
The XSetModifierMapping function specifies the KeyCodes of the keys (if any) that are to be
used as modifiers. If it succeeds, the X server generates a MappingNotify ev ent, and XSetMod-
ifierMapping
returns MappingSuccess. X permits at most 8 modifier keys. If more than 8 are
specified in the XModifierKeymap structure, a BadLength error results.
The modifiermap member of the XModifierKeymap structure contains 8 sets of max_keyper-
mod KeyCodes, one for each modifier in the order Shift, Lock, Control, Mod1, Mod2, Mod3,
Mod4, and Mod5. Only nonzero KeyCodes have meaning in each set, and zero KeyCodes are
ignored. In addition, all of the nonzero KeyCodes must be in the range specified by min_keycode
and max_keycode in the Display structure, or a BadValue error results.
An X server can impose restrictions on how modifiers can be changed, for example, if certain
keys do not generate up transitions in hardware, if auto-repeat cannot be disabled on certain keys,
or if multiple modifier keys are not supported. If some such restriction is violated, the status
reply is MappingFailed, and none of the modifiers are changed. If the new KeyCodes specified
for a modifier differ from those currently defined and any (current or new) keys for that modifier
are in the logically down state, XSetModifierMapping returns MappingBusy, and none of the
modifiers is changed.
XSetModifierMapping can generate BadAlloc and BadValue errors.
To obtain the KeyCodes used as modifiers, use XGetModifierMapping.
XModifierKeymap *XGetModifierMapping(display)
Display *display;
display
Specifies the connection to the X server.
The XGetModifierMapping function returns a pointer to a newly created XModifierKeymap
structure that contains the keys being used as modifiers. The structure should be freed after use
by calling XFreeModifiermap. If only zero values appear in the set for any modifier, that modi-
fier is disabled.
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Chapter 13
Locales and Internationalized Text Functions
An internationalized application is one that is adaptable to the requirements of different native
languages, local customs, and character string encodings. The process of adapting the operation
to a particular native language, local custom, or string encoding is called localization. A goal of
internationalization is to permit localization without program source modifications or recompila-
tion.
As one of the localization mechanisms, Xlib provides an X Input Method (XIM) functional inter-
face for internationalized text input and an X Output Method (XOM) functional interface for
internationalized text output.
Internationalization in X is based on the concept of a locale. A locale defines the localized
behavior of a program at run time. Locales affect Xlib in its:

Encoding and processing of input method text

Encoding of resource files and values

Encoding and imaging of text strings

Encoding and decoding for inter-client text communication
Characters from various languages are represented in a computer using an encoding. Different
languages have different encodings, and there are even different encodings for the same charac-
ters in the same language.
This chapter defines support for localized text imaging and text input and describes the locale
mechanism that controls all locale-dependent Xlib functions. Sets of functions are provided for
multibyte (char *) text as well as wide character (wchar_t) text in the form supported by the host
C language environment. The multibyte and wide character functions are equivalent except for
the form of the text argument.
The Xlib internationalization functions are not meant to provide support for multilingual applica-
tions (mixing multiple languages within a single piece of text), but they make it possible to imple-
ment applications that work in limited fashion with more than one language in independent con-
texts.
The remainder of this chapter discusses:

X locale management

Locale and modifier dependencies

Variable argument lists

Output methods

Input methods

String constants
13.1. X Locale Management
X supports one or more of the locales defined by the host environment. On implementations that
conform to the ANSI C library, the locale announcement method is setlocale. This function con-
figures the locale operation of both the host C library and Xlib. The operation of Xlib is governed
by the LC_CTYPE category; this is called the current locale. An implementation is permitted to
provide implementation-dependent mechanisms for announcing the locale in addition to
setlocale.
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On implementations that do not conform to the ANSI C library, the locale announcement method
is Xlib implementation-dependent.
The mechanism by which the semantic operation of Xlib is defined for a specific locale is imple-
mentation-dependent.
X is not required to support all the locales supported by the host. To determine if the current
locale is supported by X, use XSupportsLocale.
Bool XSupportsLocale( )
The XSupportsLocale function returns True if Xlib functions are capable of operating under the
current locale. If it returns False, Xlib locale-dependent functions for which the XLocaleNot-
Supported
return status is defined will return XLocaleNotSupported. Other Xlib locale-depen-
dent routines will operate in the ``C'' locale.
The client is responsible for selecting its locale and X modifiers. Clients should provide a means
for the user to override the clients' locale selection at client invocation. Most single-display X
clients operate in a single locale for both X and the host processing environment. They will con-
figure the locale by calling three functions: the host locale configuration function,
XSupportsLocale, and XSetLocaleModifiers.
The semantics of certain categories of X internationalization capabilities can be configured by
setting modifiers. Modifiers are named by implementation-dependent and locale-specific strings.
The only standard use for this capability at present is selecting one of several styles of keyboard
input method.
To configure Xlib locale modifiers for the current locale, use XSetLocaleModifiers.
char *XSetLocaleModifiers(modifier_list)
char *modifier_list;
modifier_list
Specifies the modifiers.
The XSetLocaleModifiers function sets the X modifiers for the current locale setting. The modi-
fier_list argument is a null-terminated string of the form ``{@category=value}'', that is, having
zero or more concatenated ``@category=value'' entries, where category is a category name and
value is the (possibly empty) setting for that category. The values are encoded in the current
locale. Category names are restricted to the POSIX Portable Filename Character Set.
The local host X locale modifiers announcer (on POSIX-compliant systems, the XMODIFIERS
environment variable) is appended to the modifier_list to provide default values on the local host.
If a given category appears more than once in the list, the first setting in the list is used. If a given
category is not included in the full modifier list, the category is set to an implementation-depen-
dent default for the current locale. An empty value for a category explicitly specifies the imple-
mentation-dependent default.
If the function is successful, it returns a pointer to a string. The contents of the string are such
that a subsequent call with that string (in the same locale) will restore the modifiers to the same
settings. If modifier_list is a NULL pointer, XSetLocaleModifiers also returns a pointer to such
a string, and the current locale modifiers are not changed.
If invalid values are given for one or more modifier categories supported by the locale, a NULL
pointer is returned, and none of the current modifiers are changed.
At program startup, the modifiers that are in effect are unspecified until the first successful call to
set them. Whenever the locale is changed, the modifiers that are in effect become unspecified
until the next successful call to set them. Clients should always call XSetLocaleModifiers with
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a non-NULL modifier_list after setting the locale before they call any locale-dependent Xlib rou-
tine.
The only standard modifier category currently defined is ``im'', which identifies the desired input
method. The values for input method are not standardized. A single locale may use multiple
input methods, switching input method under user control. The modifier may specify the initial
input method in effect or an ordered list of input methods. Multiple input methods may be speci-
fied in a single im value string in an implementation-dependent manner.
The returned modifiers string is owned by Xlib and should not be modified or freed by the client.
It may be freed by Xlib after the current locale or modifiers are changed. Until freed, it will not
be modified by Xlib.
The recommended procedure for clients initializing their locale and modifiers is to obtain locale
and modifier announcers separately from one of the following prioritized sources:

A command line option

A resource

The empty string ("")
The first of these that is defined should be used. Note that when a locale command line option or
locale resource is defined, the effect should be to set all categories to the specified locale, overrid-
ing any category-specific settings in the local host environment.
13.2. Locale and Modifier Dependencies
The internationalized Xlib functions operate in the current locale configured by the host environ-
ment and X locale modifiers set by XSetLocaleModifiers or in the locale and modifiers config-
ured at the time some object supplied to the function was created. For each locale-dependent
function, the following table describes the locale (and modifiers) dependency:
Locale from Affects the Function
In
Locale Query/Configuration:
setlocale
XSupportsLocale
Locale queried
XSetLocaleModifiers
Locale modified
Resources:
setlocale
XrmGetFileDatabase
Locale of XrmDatabase
XrmGetStringDatabase
XrmDatabase
XrmPutFileDatabase
Locale of XrmDatabase
XrmLocaleOfDatabase
Setting Standard Properties:
setlocale
XmbSetWMProperties
Encoding of supplied/returned
text (some WM_ property
text in environment locale)
setlocale
XmbTextPropertyToTextList
Encoding of supplied/returned
text
XwcTextPropertyToTextList
XmbTextListToTextProperty
XwcTextListToTextProperty

Te xt Input:
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Locale from Affects the Function
In
setlocale
XOpenIM
XIM input method selection
XRegisterIMInstantiateCallback
XIM selection
XUnregisterIMInstantiateCallback
XIM selection
XIM
XCreateIC
XIC input method configuration
XLocaleOfIM, and so on
Queried locale
XIC
XmbLookupString
Ke yboard layout
XwcLookupString
Encoding of returned text
Te xt Drawing:
setlocale
XOpenOM
XOM output method selection
XCreateFontSet
Charsets of fonts in XFontSet
XOM
XCreateOC
XOC output method configura-
tion
XLocaleOfOM, and so on
Queried locale
XFontSet
XmbDrawText,
Locale of supplied text
XwcDrawText, and so on
Locale of supplied text
XExtentsOfFontSet, and so on
Locale-dependent metrics
XmbTextExtents,
XwcTextExtents, and so on
Xlib Errors:
setlocale
XGetErrorDatabaseText
Locale of error message
XGetErrorText
Clients may assume that a locale-encoded text string returned by an X function can be passed to a
C library routine, or vice versa, if the locale is the same at the two calls.
All text strings processed by internationalized Xlib functions are assumed to begin in the initial
state of the encoding of the locale, if the encoding is state-dependent.
All Xlib functions behave as if they do not change the current locale or X modifier setting. (This
means that if they do change locale or call XSetLocaleModifiers with a non-NULL argument,
they must save and restore the current state on entry and exit.) Also, Xlib functions on implemen-
tations that conform to the ANSI C library do not alter the global state associated with the ANSI
C functions mblen, mbtowc, wctomb, and strtok.
13.3. Variable Argument Lists
Various functions in this chapter have arguments that conform to the ANSI C variable argument
list calling convention. Each function denoted with an argument of the form ``...'' takes a vari-
able-length list of name and value pairs, where each name is a string and each value is of type
XPointer. A name argument that is NULL identifies the end of the list.
A variable-length argument list may contain a nested list. If the name XNVaNestedList is speci-
fied in place of an argument name, then the following value is interpreted as an XVaNestedList
value that specifies a list of values logically inserted into the original list at the point of declara-
tion. A NULL identifies the end of a nested list.
To allocate a nested variable argument list dynamically, use XVaCreateNestedList.
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typedef void * XVaNestedList;
XVaNestedList XVaCreateNestedList (dummy, ...)
int dummy;
dummy
Specifies an unused argument (required by ANSI C).
... Specifies the variable length argument list.
The XVaCreateNestedList function allocates memory and copies its arguments into a single list
pointer, which may be used as a value for arguments requiring a list value. Any entries are copied
as specified. Data passed by reference is not copied; the caller must ensure data remains valid for
the lifetime of the nested list. The list should be freed using XFree when it is no longer needed.
13.4. Output Methods
This section provides discussions of the following X Output Method (XOM) topics:

Output method overview

Output method functions

Output method values

Output context functions

Output context values

Creating and freeing a font set

Obtaining font set metrics

Drawing text using font sets
13.4.1. Output Method Overview
Locale-dependent text may include one or more text components, each of which may require dif-
ferent fonts and character set encodings. In some languages, each component might have a differ-
ent drawing direction, and some components might contain context-dependent characters that
change shape based on relationships with neighboring characters.
When drawing such locale-dependent text, some locale-specific knowledge is required; for exam-
ple, what fonts are required to draw the text, how the text can be separated into components, and
which fonts are selected to draw each component. Further, when bidirectional text must be
drawn, the internal representation order of the text must be changed into the visual representation
order to be drawn.
An X Output Method provides a functional interface so that clients do not have to deal directly
with such locale-dependent details. Output methods provide the following capabilities:

Creating a set of fonts required to draw locale-dependent text.

Drawing locale-dependent text with a font set without the caller needing to be aware of
locale dependencies.

Obtaining the escapement and extents in pixels of locale-dependent text.

Determining if bidirectional or context-dependent drawing is required in a specific locale
with a specific font set.
Tw o different abstractions are used in the representation of the output method for clients.
The abstraction used to communicate with an output method is an opaque data structure repre-
sented by the XOM data type. The abstraction for representing the state of a particular output
thread is called an output context. The Xlib representation of an output context is an XOC,
which is compatible with XFontSet in terms of its functional interface, but is a broader, more
generalized abstraction.
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13.4.2. Output Method Functions
To open an output method, use XOpenOM.
XOM XOpenOM(display, db, res_name, res_class)
Display *display;
XrmDatabase db;
char *res_name;
char *res_class;
display
Specifies the connection to the X server.
db
Specifies a pointer to the resource database.
res_name
Specifies the full resource name of the application.
res_class
Specifies the full class name of the application.
The XOpenOM function opens an output method matching the current locale and modifiers
specification. The current locale and modifiers are bound to the output method when XOpenOM
is called. The locale associated with an output method cannot be changed.
The specific output method to which this call will be routed is identified on the basis of the cur-
rent locale and modifiers. XOpenOM will identify a default output method corresponding to the
current locale. That default can be modified using XSetLocaleModifiers to set the output
method modifier.
The db argument is the resource database to be used by the output method for looking up
resources that are private to the output method. It is not intended that this database be used to
look up values that can be set as OC values in an output context. If db is NULL, no database is
passed to the output method.
The res_name and res_class arguments specify the resource name and class of the application.
They are intended to be used as prefixes by the output method when looking up resources that are
common to all output contexts that may be created for this output method. The characters used
for resource names and classes must be in the X Portable Character Set. The resources looked up
are not fully specified if res_name or res_class is NULL.
The res_name and res_class arguments are not assumed to exist beyond the call to XOpenOM.
The specified resource database is assumed to exist for the lifetime of the output method.
XOpenOM returns NULL if no output method could be opened.
To close an output method, use XCloseOM.
Status XCloseOM(om)
XOM om;
om
Specifies the output method.
The XCloseOM function closes the specified output method.
To set output method attributes, use XSetOMValues.
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char * XSetOMValues (om, ...)
XOM om;
om
Specifies the output method.
... Specifies the variable-length argument list to set XOM values.
The XSetOMValues function presents a variable argument list programming interface for setting
properties or features of the specified output method. This function returns NULL if it succeeds;
otherwise, it returns the name of the first argument that could not be obtained.
No standard arguments are currently defined by Xlib.
To query an output method, use XGetOMValues.
char * XGetOMValues (om, ...)
XOM om;
om
Specifies the output method.
... Specifies the variable-length argument list to get XOM values.
The XGetOMValues function presents a variable argument list programming interface for query-
ing properties or features of the specified output method. This function returns NULL if it suc-
ceeds; otherwise, it returns the name of the first argument that could not be obtained.
To obtain the display associated with an output method, use XDisplayOfOM.
Display * XDisplayOfOM(om)
XOM om;
om
Specifies the output method.
The XDisplayOfOM function returns the display associated with the specified output method.
To get the locale associated with an output method, use XLocaleOfOM.
char * XLocaleOfOM(om)
XOM om;
om
Specifies the output method.
The XLocaleOfOM returns the locale associated with the specified output method.
13.4.3. X Output Method Values
The following table describes how XOM values are interpreted by an output method. The first
column lists the XOM values. The second column indicates how each of the XOM values are
treated by a particular output style.
The following key applies to this table.
Key
Explanation
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Key
Explanation
G
This value may be read using XGetOMValues.
XOM Value Key
XNRequiredCharSet
G
XNQueryOrientation
G
XNDirectionalDependentDrawing
G
XNContextualDrawing
G
13.4.3.1. Required Char Set
The XNRequiredCharSet argument returns the list of charsets that are required for loading the
fonts needed for the locale. The value of the argument is a pointer to a structure of type
XOMCharSetList.
The XOMCharSetList structure is defined as follows:
typedef struct {
int charset_count;
char **charset_list;
} XOMCharSetList;
The charset_list member is a list of one or more null-terminated charset names, and the
charset_count member is the number of charset names.
The required charset list is owned by Xlib and should not be modified or freed by the client. It
will be freed by a call to XCloseOM with the associated XOM. Until freed, its contents will not
be modified by Xlib.
13.4.3.2. Query Orientation
The XNQueryOrientation argument returns the global orientation of text when drawn. Other
than XOMOrientation_LTR_TTB, the set of orientations supported is locale-dependent. The
value of the argument is a pointer to a structure of type XOMOrientation. Clients are responsi-
ble for freeing the XOMOrientation structure by using XFree; this also frees the contents of the
structure.
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typedef struct {
int num_orientation;
XOrientation *orientation;
/* Input Text description */
} XOMOrientation;
typedef enum {
XOMOrientation_LTR_TTB,
XOMOrientation_RTL_TTB,
XOMOrientation_TTB_LTR,
XOMOrientation_TTB_RTL,
XOMOrientation_Context
} XOrientation;
The possible value for XOrientation may be:

XOMOrientation_LTR_TTB left-to-right, top-to-bottom global orientation

XOMOrientation_RTL_TTB right-to-left, top-to-bottom global orientation

XOMOrientation_TTB_LTR top-to-bottom, left-to-right global orientation

XOMOrientation_TTB_RTL top-to-bottom, right-to-left global orientation

XOMOrientation_Context contextual global orientation
13.4.3.3. Directional Dependent Drawing
The XNDirectionalDependentDrawing argument indicates whether the text rendering functions
implement implicit handling of directional text. If this value is True, the output method has
knowledge of directional dependencies and reorders text as necessary when rendering text. If this
value is False, the output method does not implement any directional text handling, and all char-
acter directions are assumed to be left-to-right.
Regardless of the rendering order of characters, the origins of all characters are on the primary
draw direction side of the drawing origin.
This OM value presents functionality identical to the XDirectionalDependentDrawing function.
13.4.3.4. Context Dependent Drawing
The XNContextualDrawing argument indicates whether the text rendering functions implement
implicit context-dependent drawing. If this value is True, the output method has knowledge of
context dependencies and performs character shape editing, combining glyphs to present a single
character as necessary. The actual shape editing is dependent on the locale implementation and
the font set used.
This OM value presents functionality identical to the XContextualDrawing function.
13.4.4. Output Context Functions
An output context is an abstraction that contains both the data required by an output method and
the information required to display that data. There can be multiple output contexts for one out-
put method. The programming interfaces for creating, reading, or modifying an output context
use a variable argument list. The name elements of the argument lists are referred to as XOC val-
ues. It is intended that output methods be controlled by these XOC values. As new XOC values
are created, they should be registered with the X Consortium. An XOC can be used anywhere an
XFontSet can be used, and vice versa; XFontSet is retained for compatibility with previous
releases. The concepts of output methods and output contexts include broader, more generalized
abstraction than font set, supporting complex and more intelligent text display, and dealing not
only with multiple fonts but also with context dependencies. However, XFontSet is widely used
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in several interfaces, so XOC is defined as an upward compatible type of XFontSet.
To create an output context, use XCreateOC.
XOC XCreateOC(om, ...)
XOM om;
om
Specifies the output method.
... Specifies the variable-length argument list to set XOC values.
The XCreateOC function creates an output context within the specified output method.
The base font names argument is mandatory at creation time, and the output context will not be
created unless it is provided. All other output context values can be set later.
XCreateOC returns NULL if no output context could be created. NULL can be returned for any
of the following reasons:

A required argument was not set.

A read-only argument was set.

An argument name is not recognized.

The output method encountered an output method implementation-dependent error.
XCreateOC can generate a BadAtom error.
To destroy an output context, use XDestroyOC.
void XDestroyOC (oc)
XOC oc;
oc
Specifies the output context.
The XDestroyOC function destroys the specified output context.
To get the output method associated with an output context, use XOMOfOC.
XOM XOMOfOC(oc)
XOC oc;
oc
Specifies the output context.
The XOMOfOC function returns the output method associated with the specified output context.
Xlib provides two functions for setting and reading output context values, respectively, XSetOC-
Values
and XGetOCValues. Both functions have a variable-length argument list. In that argu-
ment list, any XOC value's name must be denoted with a character string using the X Portable
Character Set.
To set XOC values, use XSetOCValues.
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char * XSetOCValues (oc, ...)
XOC oc;
oc
Specifies the output context.
... Specifies the variable-length argument list to set XOC values.
The XSetOCValues function returns NULL if no error occurred; otherwise, it returns the name
of the first argument that could not be set. An argument might not be set for any of the following
reasons:

The argument is read-only.

The argument name is not recognized.

An implementation-dependent error occurs.
Each value to be set must be an appropriate datum, matching the data type imposed by the seman-
tics of the argument.
XSetOCValues can generate a BadAtom error.
To obtain XOC values, use XGetOCValues.
char * XGetOCValues (oc, ...)
XOC oc;
oc
Specifies the output context.
... Specifies the variable-length argument list to get XOC values.
The XGetOCValues function returns NULL if no error occurred; otherwise, it returns the name
of the first argument that could not be obtained. An argument might not be obtained for any of
the following reasons:

The argument name is not recognized.

An implementation-dependent error occurs.
Each argument value following a name must point to a location where the value is to be stored.
13.4.5. Output Context Values
The following table describes how XOC values are interpreted by an output method. The first
column lists the XOC values. The second column indicates the alternative interfaces that function
identically and are provided for compatibility with previous releases. The third column indicates
how each of the XOC values is treated.
The following keys apply to this table.
Key
Explanation
C
This value must be set with XCreateOC.
D
This value may be set using XCreateOC. If it is not set,
a default is provided.
G
This value may be read using XGetOCValues.
S
This value must be set using XSetOCValues.
XOC Value Alternative Interface Key
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XOC Value Alternative Interface Key
BaseFontName
XCreateFontSet
C-G
MissingCharSet
XCreateFontSet
G
DefaultString
XCreateFontSet
G
Orientation
-
D-S-G
ResourceName
-
S-G
ResourceClass
-
S-G
FontInfo
XFontsOfFontSet
G
OMAutomatic
-
G
13.4.5.1. Base Font Name
The XNBaseFontName argument is a list of base font names that Xlib uses to load the fonts
needed for the locale. The base font names are a comma-separated list. The string is null-termi-
nated and is assumed to be in the Host Portable Character Encoding; otherwise, the result is
implementation-dependent. White space immediately on either side of a separating comma is
ignored.
Use of XLFD font names permits Xlib to obtain the fonts needed for a variety of locales from a
single locale-independent base font name. The single base font name should name a family of
fonts whose members are encoded in the various charsets needed by the locales of interest.
An XLFD base font name can explicitly name a charset needed for the locale. This allows the
user to specify an exact font for use with a charset required by a locale, fully controlling the font
selection.
If a base font name is not an XLFD name, Xlib will attempt to obtain an XLFD name from the
font properties for the font. If Xlib is successful, the XGetOCValues function will return this
XLFD name instead of the client-supplied name.
This argument must be set at creation time and cannot be changed. If no fonts exist for any of the
required charsets, or if the locale definition in Xlib requires that a font exist for a particular
charset and a font is not found for that charset, XCreateOC returns NULL.
When querying for the XNBaseFontName XOC value, XGetOCValues returns a null-termi-
nated string identifying the base font names that Xlib used to load the fonts needed for the locale.
This string is owned by Xlib and should not be modified or freed by the client. The string will be
freed by a call to XDestroyOC with the associated XOC. Until freed, the string contents will
not be modified by Xlib.
13.4.5.2. Missing CharSet
The XNMissingCharSet argument returns the list of required charsets that are missing from the
font set. The value of the argument is a pointer to a structure of type XOMCharSetList.
If fonts exist for all of the charsets required by the current locale, charset_list is set to NULL and
charset_count is set to zero. If no fonts exist for one or more of the required charsets, charset_list
is set to a list of one or more null-terminated charset names for which no fonts exist, and
charset_count is set to the number of missing charsets. The charsets are from the list of the
required charsets for the encoding of the locale and do not include any charsets to which Xlib
may be able to remap a required charset.
The missing charset list is owned by Xlib and should not be modified or freed by the client. It
will be freed by a call to XDestroyOC with the associated XOC. Until freed, its contents will
not be modified by Xlib.
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13.4.5.3. Default String
When a drawing or measuring function is called with an XOC that has missing charsets, some
characters in the locale will not be drawable. The XNDefaultString argument returns a pointer
to a string that represents the glyphs that are drawn with this XOC when the charsets of the avail-
able fonts do not include all glyphs required to draw a character. The string does not necessarily
consist of valid characters in the current locale and is not necessarily drawn with the fonts loaded
for the font set, but the client can draw or measure the default glyphs by including this string in a
string being drawn or measured with the XOC.
If the XNDefaultString argument returned the empty string (""), no glyphs are drawn and the
escapement is zero. The returned string is null-terminated. It is owned by Xlib and should not be
modified or freed by the client. It will be freed by a call to XDestroyOC with the associated
XOC. Until freed, its contents will not be modified by Xlib.
13.4.5.4. Orientation
The XNOrientation argument specifies the current orientation of text when drawn. The value of
this argument is one of the values returned by the XGetOMValues function with the XNQuery-
Orientation
argument specified in the XOrientation list. The value of the argument is of type
XOrientation. When XNOrientation is queried, the value specifies the current orientation.
When XNOrientation is set, a value is used to set the current orientation.
When XOMOrientation_Context is set, the text orientation of the text is determined according
to an implementation-defined method (for example, ISO 6429 control sequences), and the initial
text orientation for locale-dependent Xlib functions is assumed to be
XOMOrientation_LTR_TTB.
The XNOrientation value does not change the prime drawing direction for Xlib drawing func-
tions.
13.4.5.5. Resource Name and Class
The XNResourceName and XNResourceClass arguments are strings that specify the full name
and class used by the client to obtain resources for the display of the output context. These values
should be used as prefixes for name and class when looking up resources that may vary according
to the output context. If these values are not set, the resources will not be fully specified.
It is not intended that values that can be set as XOM values be set as resources.
When querying for the XNResourceName or XNResourceClass XOC value, XGetOCValues
returns a null-terminated string. This string is owned by Xlib and should not be modified or freed
by the client. The string will be freed by a call to XDestroyOC with the associated XOC or
when the associated value is changed via XSetOCValues. Until freed, the string contents will
not be modified by Xlib.
13.4.5.6. Font Info
The XNFontInfo argument specifies a list of one or more XFontStruct structures and font
names for the fonts used for drawing by the given output context. The value of the argument is a
pointer to a structure of type XOMFontInfo.
typedef struct {
int num_font;
XFontStruct **font_struct_list;
char **font_name_list;
} XOMFontInfo;
A list of pointers to the XFontStruct structures is returned to font_struct_list. A list of pointers
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to null-terminated, fully-specified font name strings in the locale of the output context is returned
to font_name_list. The font_name_list order corresponds to the font_struct_list order. The num-
ber of XFontStruct structures and font names is returned to num_font.
Because it is not guaranteed that a given character will be imaged using a single font glyph, there
is no provision for mapping a character or default string to the font properties, font ID, or direc-
tion hint for the font for the character. The client may access the XFontStruct list to obtain these
values for all the fonts currently in use.
Xlib does not guarantee that fonts are loaded from the server at the creation of an XOC. Xlib
may choose to cache font data, loading it only as needed to draw text or compute text dimensions.
Therefore, existence of the per_char metrics in the XFontStruct structures in the XFontStruct-
Set
is undefined. Also, note that all properties in the XFontStruct structures are in the STRING
encoding.
The client must not free the XOMFontInfo struct itself; it will be freed when the XOC is closed.
13.4.5.7. OM Automatic
The XNOMAutomatic argument returns whether the associated output context was created by
XCreateFontSet or not. Because the XFreeFontSet function not only destroys the output con-
text but also closes the implicit output method associated with it, XFreeFontSet should be used
with any output context created by XCreateFontSet. Howev er, it is possible that a client does
not know how the output context was created. Before a client destroys the output context, it can
query whether XNOMAutomatic is set to determine whether XFreeFontSet or XDestroyOC
should be used to destroy the output context.
13.4.6. Creating and Freeing a Font Set
Xlib international text drawing is done using a set of one or more fonts, as needed for the locale
of the text. Fonts are loaded according to a list of base font names supplied by the client and the
charsets required by the locale. The XFontSet is an opaque type representing the state of a par-
ticular output thread and is equivalent to the type XOC.
The XCreateFontSet function is a convenience function for creating an output context using
only default values. The returned XFontSet has an implicitly created XOM. This XOM has an
OM value XNOMAutomatic automatically set to True so that the output context self indicates
whether it was created by XCreateOC or XCreateFontSet.
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XFontSet XCreateFontSet (display, base_font_name_list, missing_charset_list_return,
missing_charset_count_return, def_string_return)
Display *display;
char *base_font_name_list;
char ***missing_charset_list_return;
int *missing_charset_count_return;
char **def_string_return;
display
Specifies the connection to the X server.
base_font_name_list
Specifies the base font names.
missing_charset_list_return
Returns the missing charsets.
missing_charset_count_return
Returns the number of missing charsets.
def_string_returnReturns the string drawn for missing charsets.
The XCreateFontSet function creates a font set for the specified display. The font set is bound
to the current locale when XCreateFontSet is called. The font set may be used in subsequent
calls to obtain font and character information and to image text in the locale of the font set.
The base_font_name_list argument is a list of base font names that Xlib uses to load the fonts
needed for the locale. The base font names are a comma-separated list. The string is null-termi-
nated and is assumed to be in the Host Portable Character Encoding; otherwise, the result is
implementation-dependent. White space immediately on either side of a separating comma is
ignored.
Use of XLFD font names permits Xlib to obtain the fonts needed for a variety of locales from a
single locale-independent base font name. The single base font name should name a family of
fonts whose members are encoded in the various charsets needed by the locales of interest.
An XLFD base font name can explicitly name a charset needed for the locale. This allows the
user to specify an exact font for use with a charset required by a locale, fully controlling the font
selection.
If a base font name is not an XLFD name, Xlib will attempt to obtain an XLFD name from the
font properties for the font. If this action is successful in obtaining an XLFD name, the XBase-
FontNameListOfFontSet
function will return this XLFD name instead of the client-supplied
name.
Xlib uses the following algorithm to select the fonts that will be used to display text with the
XFontSet.
For each font charset required by the locale, the base font name list is searched for the first
appearance of one of the following cases that names a set of fonts that exist at the server:

The first XLFD-conforming base font name that specifies the required charset or a superset
of the required charset in its CharSetRegistry and CharSetEncoding fields. The imple-
mentation may use a base font name whose specified charset is a superset of the required
charset, for example, an ISO8859-1 font for an ASCII charset.

The first set of one or more XLFD-conforming base font names that specify one or more
charsets that can be remapped to support the required charset. The Xlib implementation
may recognize various mappings from a required charset to one or more other charsets and
use the fonts for those charsets. For example, JIS Roman is ASCII with tilde and backslash
replaced by yen and overbar; Xlib may load an ISO8859-1 font to support this character set
if a JIS Roman font is not available.
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The first XLFD-conforming font name or the first non-XLFD font name for which an
XLFD font name can be obtained, combined with the required charset (replacing the
CharSetRegistry and CharSetEncoding fields in the XLFD font name). As in case 1,
the implementation may use a charset that is a superset of the required charset.

The first font name that can be mapped in some implementation-dependent manner to one
or more fonts that support imaging text in the charset.
For example, assume that a locale required the charsets:
ISO8859-1
JISX0208.1983
JISX0201.1976
GB2312-1980.0
The user could supply a base_font_name_list that explicitly specifies the charsets, ensuring that
specific fonts are used if they exist. For example:
"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240-JISX0208.1983-0,\
-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120-JISX0201.1976-0,\
-GB-Fixed-Medium-R-Normal--26-180-100-100-C-240-GB2312-1980.0,\
-Adobe-Courier-Bold-R-Normal--25-180-75-75-M-150-ISO8859-1"
Alternatively, the user could supply a base_font_name_list that omits the charsets, letting Xlib
select font charsets required for the locale. For example:
"-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-240,\
-JIS-Fixed-Medium-R-Normal--26-180-100-100-C-120,\
-GB-Fixed-Medium-R-Normal--26-180-100-100-C-240,\
-Adobe-Courier-Bold-R-Normal--25-180-100-100-M-150"
Alternatively, the user could simply supply a single base font name that allows Xlib to select from
all available fonts that meet certain minimum XLFD property requirements. For example:
"-*-*-*-R-Normal--*-180-100-100-*-*"
If XCreateFontSet is unable to create the font set, either because there is insufficient memory or
because the current locale is not supported, XCreateFontSet returns NULL, miss-
ing_charset_list_return is set to NULL, and missing_charset_count_return is set to zero. If fonts
exist for all of the charsets required by the current locale, XCreateFontSet returns a valid
XFontSet, missing_charset_list_return is set to NULL, and missing_charset_count_return is set
to zero.
If no font exists for one or more of the required charsets, XCreateFontSet sets miss-
ing_charset_list_return to a list of one or more null-terminated charset names for which no font
exists and sets missing_charset_count_return to the number of missing fonts. The charsets are
from the list of the required charsets for the encoding of the locale and do not include any
charsets to which Xlib may be able to remap a required charset.
If no font exists for any of the required charsets or if the locale definition in Xlib requires that a
font exist for a particular charset and a font is not found for that charset, XCreateFontSet returns
NULL. Otherwise, XCreateFontSet returns a valid XFontSet to font_set.
When an Xmb/wc drawing or measuring function is called with an XFontSet that has missing
charsets, some characters in the locale will not be drawable. If def_string_return is non-NULL,
XCreateFontSet returns a pointer to a string that represents the glyphs that are drawn with this
XFontSet when the charsets of the available fonts do not include all font glyphs required to draw
a codepoint. The string does not necessarily consist of valid characters in the current locale and is
not necessarily drawn with the fonts loaded for the font set, but the client can draw and measure
the default glyphs by including this string in a string being drawn or measured with the
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XFontSet.
If the string returned to def_string_return is the empty string (""), no glyphs are drawn, and the
escapement is zero. The returned string is null-terminated. It is owned by Xlib and should not be
modified or freed by the client. It will be freed by a call to XFreeFontSet with the associated
XFontSet. Until freed, its contents will not be modified by Xlib.
The client is responsible for constructing an error message from the missing charset and default
string information and may choose to continue operation in the case that some fonts did not exist.
The returned XFontSet and missing charset list should be freed with XFreeFontSet and
XFreeStringList, respectively. The client-supplied base_font_name_list may be freed by the
client after calling XCreateFontSet.
To obtain a list of XFontStruct structures and full font names given an XFontSet, use
XFontsOfFontSet.
int XFontsOfFontSet (font_set, font_struct_list_return, font_name_list_return)
XFontSet font_set;
XFontStruct ***font_struct_list_return;
char ***font_name_list_return;
font_set
Specifies the font set.
font_struct_list_return
Returns the list of font structs.
font_name_list_return
Returns the list of font names.
The XFontsOfFontSet function returns a list of one or more XFontStructs and font names for
the fonts used by the Xmb and Xwc layers for the given font set. A list of pointers to the
XFontStruct structures is returned to font_struct_list_return. A list of pointers to null-termi-
nated, fully specified font name strings in the locale of the font set is returned to
font_name_list_return. The font_name_list order corresponds to the font_struct_list order. The
number of XFontStruct structures and font names is returned as the value of the function.
Because it is not guaranteed that a given character will be imaged using a single font glyph, there
is no provision for mapping a character or default string to the font properties, font ID, or direc-
tion hint for the font for the character. The client may access the XFontStruct list to obtain these
values for all the fonts currently in use.
Xlib does not guarantee that fonts are loaded from the server at the creation of an XFontSet.
Xlib may choose to cache font data, loading it only as needed to draw text or compute text dimen-
sions. Therefore, existence of the per_char metrics in the XFontStruct structures in the
XFontStructSet is undefined. Also, note that all properties in the XFontStruct structures are in
the STRING encoding.
The XFontStruct and font name lists are owned by Xlib and should not be modified or freed by
the client. They will be freed by a call to XFreeFontSet with the associated XFontSet. Until
freed, their contents will not be modified by Xlib.
To obtain the base font name list and the selected font name list given an XFontSet, use
XBaseFontNameListOfFontSet.
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char *XBaseFontNameListOfFontSet (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XBaseFontNameListOfFontSet function returns the original base font name list supplied
by the client when the XFontSet was created. A null-terminated string containing a list of
comma-separated font names is returned as the value of the function. White space may appear
immediately on either side of separating commas.
If XCreateFontSet obtained an XLFD name from the font properties for the font specified by a
non-XLFD base name, the XBaseFontNameListOfFontSet function will return the XLFD name
instead of the non-XLFD base name.
The base font name list is owned by Xlib and should not be modified or freed by the client. It
will be freed by a call to XFreeFontSet with the associated XFontSet. Until freed, its contents
will not be modified by Xlib.
To obtain the locale name given an XFontSet, use XLocaleOfFontSet.
char *XLocaleOfFontSet (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XLocaleOfFontSet function returns the name of the locale bound to the specified
XFontSet, as a null-terminated string.
The returned locale name string is owned by Xlib and should not be modified or freed by the
client. It may be freed by a call to XFreeFontSet with the associated XFontSet. Until freed, it
will not be modified by Xlib.
The XFreeFontSet function is a convenience function for freeing an output context. XFree-
FontSet
also frees its associated XOM if the output context was created by XCreateFontSet.
void XFreeFontSet (display, font_set)
Display *display;
XFontSet font_set;
display
Specifies the connection to the X server.
font_set
Specifies the font set.
The XFreeFontSet function frees the specified font set. The associated base font name list, font
name list, XFontStruct list, and XFontSetExtents, if any, are freed.
13.4.7. Obtaining Font Set Metrics
Metrics for the internationalized text drawing functions are defined in terms of a primary draw
direction, which is the default direction in which the character origin advances for each succeed-
ing character in the string. The Xlib interface is currently defined to support only a left-to-right
primary draw direction. The drawing origin is the position passed to the drawing function when
the text is drawn. The baseline is a line drawn through the drawing origin parallel to the primary
draw direction. Character ink is the pixels painted in the foreground color and does not include
interline or intercharacter spacing or image text background pixels.
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The drawing functions are allowed to implement implicit text directionality control, reversing the
order in which characters are rendered along the primary draw direction in response to locale-spe-
cific lexical analysis of the string.
Regardless of the character rendering order, the origins of all characters are on the primary draw
direction side of the drawing origin. The screen location of a particular character image may be
determined with XmbTextPerCharExtents or XwcTextPerCharExtents.
The drawing functions are allowed to implement context-dependent rendering, where the glyphs
drawn for a string are not simply a concatenation of the glyphs that represent each individual
character. A string of two characters drawn with XmbDrawString may render differently than if
the two characters were drawn with separate calls to XmbDrawString. If the client appends or
inserts a character in a previously drawn string, the client may need to redraw some adjacent char-
acters to obtain proper rendering.
To find out about direction-dependent rendering, use XDirectionalDependentDrawing.
Bool XDirectionalDependentDrawing (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XDirectionalDependentDrawing function returns True if the drawing functions implement
implicit text directionality; otherwise, it returns False.
To find out about context-dependent rendering, use XContextualDrawing.
Bool XContextualDrawing (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XContextualDrawing function returns True if text drawn with the font set might include
context-dependent drawing; otherwise, it returns False.
To find out about context-dependent or direction-dependent rendering, use
XContextDependentDrawing.
Bool XContextDependentDrawing (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XContextDependentDrawing function returns True if the drawing functions implement
implicit text directionality or if text drawn with the font_set might include context-dependent
drawing; otherwise, it returns False.
The drawing functions do not interpret newline, tab, or other control characters. The behavior
when nonprinting characters other than space are drawn is implementation-dependent. It is the
client's responsibility to interpret control characters in a text stream.
The maximum character extents for the fonts that are used by the text drawing layers can be
accessed by the XFontSetExtents structure:
typedef struct {
XRectangle max_ink_extent; /* over all drawable characters */
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XRectangle max_logical_extent; /* over all drawable characters */
} XFontSetExtents;
The XRectangle structures used to return font set metrics are the usual Xlib screen-oriented rect-
angles with x, y giving the upper left corner, and width and height always positive.
The max_ink_extent member gives the maximum extent, over all drawable characters, of the rect-
angles that bound the character glyph image drawn in the foreground color, relative to a constant
origin. See XmbTextExtents and XwcTextExtents for detailed semantics.
The max_logical_extent member gives the maximum extent, over all drawable characters, of the
rectangles that specify minimum spacing to other graphical features, relative to a constant origin.
Other graphical features drawn by the client, for example, a border surrounding the text, should
not intersect this rectangle. The max_logical_extent member should be used to compute mini-
mum interline spacing and the minimum area that must be allowed in a text field to draw a giv en
number of arbitrary characters.
Due to context-dependent rendering, appending a given character to a string may change the
string's extent by an amount other than that character's individual extent.
The rectangles for a given character in a string can be obtained from XmbPerCharExtents or
XwcPerCharExtents.
To obtain the maximum extents structure given an XFontSet, use XExtentsOfFontSet.
XFontSetExtents *XExtentsOfFontSet (font_set)
XFontSet font_set;
font_set
Specifies the font set.
The XExtentsOfFontSet function returns an XFontSetExtents structure for the fonts used by
the Xmb and Xwc layers for the given font set.
The XFontSetExtents structure is owned by Xlib and should not be modified or freed by the
client. It will be freed by a call to XFreeFontSet with the associated XFontSet. Until freed, its
contents will not be modified by Xlib.
To obtain the escapement in pixels of the specified text as a value, use XmbTextEscapement or
XwcTextEscapement.
int XmbTextEscapement (font_set, string, num_bytes)
XFontSet font_set;
char *string;
int num_bytes;
int XwcTextEscapement (font_set, string, num_wchars)
XFontSet font_set;
wchar_t *string;
int num_wchars;
font_set
Specifies the font set.
string
Specifies the character string.
num_bytes
Specifies the number of bytes in the string argument.
num_wchars
Specifies the number of characters in the string argument.
The XmbTextEscapement and XwcTextEscapement functions return the escapement in pixels
of the specified string as a value, using the fonts loaded for the specified font set. The escapement
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is the distance in pixels in the primary draw direction from the drawing origin to the origin of the
next character to be drawn, assuming that the rendering of the next character is not dependent on
the supplied string.
Regardless of the character rendering order, the escapement is always positive.
To obtain the overall_ink_return and overall_logical_return arguments, the overall bounding box
of the string's image, and a logical bounding box, use XmbTextExtents
or XwcTextExtents.
int XmbTextExtents (font_set, string, num_bytes, overall_ink_return, overall_logical_return)
XFontSet font_set;
char *string;
int num_bytes;
XRectangle *overall_ink_return;
XRectangle *overall_logical_return;
int XwcTextExtents (font_set, string, num_wchars,
overall_ink_return, overall_logical_return)
XFontSet font_set;
wchar_t *string;
int num_wchars;
XRectangle *overall_ink_return;
XRectangle *overall_logical_return;
font_set
Specifies the font set.
string
Specifies the character string.
num_bytes
Specifies the number of bytes in the string argument.
num_wchars
Specifies the number of characters in the string argument.
overall_ink_return
Returns the overall ink dimensions.
overall_logical_return
Returns the overall logical dimensions.
The XmbTextExtents and XwcTextExtents functions set the components of the specified over-
all_ink_return and overall_logical_return arguments to the overall bounding box of the string's
image and a logical bounding box for spacing purposes, respectively. They return the value
returned by XmbTextEscapement or XwcTextEscapement. These metrics are relative to the
drawing origin of the string, using the fonts loaded for the specified font set.
If the overall_ink_return argument is non-NULL, it is set to the bounding box of the string's char-
acter ink. The overall_ink_return for a nondescending, horizontally drawn Latin character is con-
ventionally entirely above the baseline; that is, overall_ink_return.height <= -over-
all_ink_return.y. The overall_ink_return for a nonkerned character is entirely at, and to the right
of, the origin; that is, overall_ink_return.x >= 0. A character consisting of a single pixel at the
origin would set overall_ink_return fields y = 0, x = 0, width = 1, and height = 1.
If the overall_logical_return argument is non-NULL, it is set to the bounding box that provides
minimum spacing to other graphical features for the string. Other graphical features, for exam-
ple, a border surrounding the text, should not intersect this rectangle.
When the XFontSet has missing charsets, metrics for each unavailable character are taken from
the default string returned by XCreateFontSet so that the metrics represent the text as it will
actually be drawn. The behavior for an invalid codepoint is undefined.
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To determine the effective drawing origin for a character in a drawn string, the client should call
XmbTextPerCharExtents on the entire string, then on the character, and subtract the x values of
the returned rectangles for the character. This is useful to redraw portions of a line of text or to
justify words, but for context-dependent rendering, the client should not assume that it can redraw
the character by itself and get the same rendering.
To obtain per-character information for a text string, use XmbTextPerCharExtents or
XwcTextPerCharExtents.
Status XmbTextPerCharExtents (font_set, string, num_bytes, ink_array_return,
logical_array_return, array_size, num_chars_return, overall_ink_return, overall_logical_return)
XFontSet font_set;
char *string;
int num_bytes;
XRectangle *ink_array_return;
XRectangle *logical_array_return;
int array_size;
int *num_chars_return;
XRectangle *overall_ink_return;
XRectangle *overall_logical_return;
Status XwcTextPerCharExtents (font_set, string, num_wchars, ink_array_return,
logical_array_return, array_size, num_chars_return, overall_ink_return, overall_ink_return)
XFontSet font_set;
wchar_t *string;
int num_wchars;
XRectangle *ink_array_return;
XRectangle *logical_array_return;
int array_size;
int *num_chars_return;
XRectangle *overall_ink_return;
XRectangle *overall_logical_return;
font_set
Specifies the font set.
string
Specifies the character string.
num_bytes
Specifies the number of bytes in the string argument.
num_wchars
Specifies the number of characters in the string argument.
ink_array_returnReturns the ink dimensions for each character.
logical_array_return
Returns the logical dimensions for each character.
array_size
Specifies the size of ink_array_return and logical_array_return. The caller must
pass in arrays of this size.
num_chars_return
Returns the number of characters in the string argument.
overall_ink_return
Returns the overall ink extents of the entire string.
overall_logical_return
Returns the overall logical extents of the entire string.
The XmbTextPerCharExtents and XwcTextPerCharExtents functions return the text dimen-
sions of each character of the specified text, using the fonts loaded for the specified font set. Each
successive element of ink_array_return and logical_array_return is set to the successive
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character's drawn metrics, relative to the drawing origin of the string and one rectangle for each
character in the supplied text string. The number of elements of ink_array_return and logi-
cal_array_return that have been set is returned to num_chars_return.
Each element of ink_array_return is set to the bounding box of the corresponding character's
drawn foreground color. Each element of logical_array_return is set to the bounding box that
provides minimum spacing to other graphical features for the corresponding character. Other
graphical features should not intersect any of the logical_array_return rectangles.
Note that an XRectangle represents the effective drawing dimensions of the character, reg ardless
of the number of font glyphs that are used to draw the character or the direction in which the char-
acter is drawn. If multiple characters map to a single character glyph, the dimensions of all the
XRectangles of those characters are the same.
When the XFontSet has missing charsets, metrics for each unavailable character are taken from
the default string returned by XCreateFontSet so that the metrics represent the text as it will
actually be drawn. The behavior for an invalid codepoint is undefined.
If the array_size is too small for the number of characters in the supplied text, the functions return
zero and num_chars_return is set to the number of rectangles required. Otherwise, the functions
return a nonzero value.
If the overall_ink_return or overall_logical_return argument is non-NULL, XmbTextPer-
CharExtents
and XwcTextPerCharExtents return the maximum extent of the string's metrics
to overall_ink_return or overall_logical_return, as returned by XmbTextExtents or
XwcTextExtents.
13.4.8. Drawing Text Using Font Sets
The functions defined in this section draw text at a specified location in a drawable. They are
similar to the functions XDrawText, XDrawString, and XDrawImageString except that they
work with font sets instead of single fonts and interpret the text based on the locale of the font set
instead of treating the bytes of the string as direct font indexes. See section 8.6 for details of the
use of Graphics Contexts (GCs) and possible protocol errors. If a BadFont error is generated,
characters prior to the offending character may have been drawn.
The text is drawn using the fonts loaded for the specified font set; the font in the GC is ignored
and may be modified by the functions. No validation that all fonts conform to some width rule is
performed.
The text functions XmbDrawText and XwcDrawText use the following structures:
typedef struct {
char *chars;
/* pointer to string */
int nchars;
/* number of bytes */
int delta;
/* pixel delta between strings */
XFontSet font_set;
/* fonts, None means don't change */
} XmbTextItem;
typedef struct {
wchar_t *chars;
/* pointer to wide char string */
int nchars;
/* number of wide characters */
int delta;
/* pixel delta between strings */
XFontSet font_set;
/* fonts, None means don't change */
} XwcTextItem;
To draw text using multiple font sets in a given drawable, use XmbDrawText or XwcDrawText.
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void XmbDrawText(display, d, gc, x, y, items, nitems)
Display *display;
Drawable d;
GC gc;
int x, y;
XmbTextItem *items;
int nitems;
void XwcDrawText(display, d, gc, x, y, items, nitems)
Display *display;
Drawable d;
GC gc;
int x, y;
XwcTextItem *items;
int nitems;
display
Specifies the connection to the X server.
d
Specifies the drawable.
gc
Specifies the GC.
x
y
Specify the x and y coordinates.
items
Specifies an array of text items.
nitems
Specifies the number of text items in the array.
The XmbDrawText and XwcDrawText functions allow complex spacing and font set shifts
between text strings. Each text item is processed in turn, with the origin of a text element
advanced in the primary draw direction by the escapement of the previous text item. A text item
delta specifies an additional escapement of the text item drawing origin in the primary draw direc-
tion. A font_set member other than None in an item causes the font set to be used for this and
subsequent text items in the text_items list. Leading text items with a font_set member set to
None will not be drawn.
XmbDrawText and XwcDrawText do not perform any context-dependent rendering between
text segments. Clients may compute the drawing metrics by passing each text segment to Xmb-
TextExtents
and XwcTextExtents or XmbTextPerCharExtents and
XwcTextPerCharExtents. When the XFontSet has missing charsets, each unavailable charac-
ter is drawn with the default string returned by XCreateFontSet. The behavior for an invalid
codepoint is undefined.
To draw text using a single font set in a given drawable, use XmbDrawString or
XwcDrawString.
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void XmbDrawString (display, d, font_set, gc, x, y, string, num_bytes)
Display *display;
Drawable d;
XFontSet font_set;
GC gc;
int x, y;
char *string;
int num_bytes;
void XwcDrawString (display, d, font_set, gc, x, y, string, num_wchars)
Display *display;
Drawable d;
XFontSet font_set;
GC gc;
int x, y;
wchar_t *string;
int num_wchars;
display
Specifies the connection to the X server.
d
Specifies the drawable.
font_set
Specifies the font set.
gc
Specifies the GC.
x
y
Specify the x and y coordinates.
string
Specifies the character string.
num_bytes
Specifies the number of bytes in the string argument.
num_wchars
Specifies the number of characters in the string argument.
The XmbDrawString and XwcDrawString functions draw the specified text with the fore-
ground pixel. When the XFontSet has missing charsets, each unavailable character is drawn
with the default string returned by XCreateFontSet. The behavior for an invalid codepoint is
undefined.
To draw image text using a single font set in a given drawable, use XmbDrawImageString or
XwcDrawImageString.
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void XmbDrawImageString (display, d, font_set, gc, x, y, string, num_bytes)
Display *display;
Drawable d;
XFontSet font_set;
GC gc;
int x, y;
char *string;
int num_bytes;
void XwcDrawImageString (display, d, font_set, gc, x, y, string, num_wchars)
Display *display;
Drawable d;
XFontSet font_set;
GC gc;
int x, y;
wchar_t *string;
int num_wchars;
display
Specifies the connection to the X server.
d
Specifies the drawable.
font_set
Specifies the font set.
gc
Specifies the GC.
x
y
Specify the x and y coordinates.
string
Specifies the character string.
num_bytes
Specifies the number of bytes in the string argument.
num_wchars
Specifies the number of characters in the string argument.
The XmbDrawImageString and XwcDrawImageString functions fill a destination rectangle
with the background pixel defined in the GC and then paint the text with the foreground pixel.
The filled rectangle is the rectangle returned to overall_logical_return by XmbTextExtents or
XwcTextExtents for the same text and XFontSet.
When the XFontSet has missing charsets, each unavailable character is drawn with the default
string returned by XCreateFontSet. The behavior for an invalid codepoint is undefined.
13.5. Input Methods
This section provides discussions of the following X Input Method (XIM) topics:

Input method overview

Input method management

Input method functions

Input method values

Input context functions

Input context values

Input method callback semantics

Event filtering

Getting keyboard input

Input method conventions
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13.5.1. Input Method Overview
This section provides definitions for terms and concepts used for internationalized text input and a
brief overview of the intended use of the mechanisms provided by Xlib.
A large number of languages in the world use alphabets consisting of a small set of symbols (let-
ters) to form words. To enter text into a computer in an alphabetic language, a user usually has a
keyboard on which there exist key symbols corresponding to the alphabet. Sometimes, a few
characters of an alphabetic language are missing on the keyboard. Many computer users who
speak a Latin-alphabet-based language only have an English-based keyboard. They need to hit a
combination of keystrokes to enter a character that does not exist directly on the keyboard. A
number of algorithms have been developed for entering such characters. These are known as
European input methods, compose input methods, or dead-key input methods.
Japanese is an example of a language with a phonetic symbol set, where each symbol represents a
specific sound. There are two phonetic symbol sets in Japanese: Katakana and Hiragana. In gen-
eral, Katakana is used for words that are of foreign origin, and Hiragana is used for writing native
Japanese words. Collectively, the two systems are called Kana. Each set consists of 48 charac-
ters.
Korean also has a phonetic symbol set, called Hangul. Each of the 24 basic phonetic symbols (14
consonants and 10 vowels) represents a specific sound. A syllable is composed of two or three
parts: the initial consonants, the vowels, and the optional last consonants. With Hangul, syllables
can be treated as the basic units on which text processing is done. For example, a delete opera-
tion may work on a phonetic symbol or a syllable. Korean code sets include several thousands of
these syllables. A user types the phonetic symbols that make up the syllables of the words to be
entered. The display may change as each phonetic symbol is entered. For example, when the
second phonetic symbol of a syllable is entered, the first phonetic symbol may change its shape
and size. Likewise, when the third phonetic symbol is entered, the first two phonetic symbols
may change their shape and size.
Not all languages rely solely on alphabetic or phonetic systems. Some languages, including
Japanese and Korean, employ an ideographic writing system. In an ideographic system, rather
than taking a small set of symbols and combining them in different ways to create words, each
word consists of one unique symbol (or, occasionally, sev eral symbols). The number of symbols
can be very large: approximately 50,000 have been identified in Hanzi, the Chinese ideographic
system.
Tw o major aspects of ideographic systems impact their use with computers. First, the standard
computer character sets in Japan, China, and Korea include roughly 8,000 characters, while sets
in Taiwan have between 15,000 and 30,000 characters. This makes it necessary to use more than
one byte to represent a character. Second, it obviously is impractical to have a keyboard that
includes all of a given language's ideographic symbols. Therefore, a mechanism is required for
entering characters so that a keyboard with a reasonable number of keys can be used. Those input
methods are usually based on phonetics, but there also exist methods based on the graphical prop-
erties of characters.
In Japan, both Kana and the ideographic system Kanji are used. In Korea, Hangul and sometimes
the ideographic system Hanja are used. Now consider entering ideographs in Japan, Korea,
China, and Taiwan.
In Japan, either Kana or English characters are typed and then a region is selected (sometimes
automatically) for conversion to Kanji. Several Kanji characters may have the same phonetic rep-
resentation. If that is the case with the string entered, a menu of characters is presented and the
user must choose the appropriate one. If no choice is necessary or a preference has been estab-
lished, the input method does the substitution directly. When Latin characters are converted to
Kana or Kanji, it is called a romaji conversion.
In Korea, it is usually acceptable to keep Korean text in Hangul form, but some people may
choose to write Hanja-originated words in Hanja rather than in Hangul. To change Hangul to
Hanja, the user selects a region for conversion and then follows the same basic method as that
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described for Japanese.
Probably because there are well-accepted phonetic writing systems for Japanese and Korean,
computer input methods in these countries for entering ideographs are fairly standard. Ke yboard
keys have both English characters and phonetic symbols engraved on them, and the user can
switch between the two sets.
The situation is different for Chinese. While there is a phonetic system called Pinyin promoted
by authorities, there is no consensus for entering Chinese text. Some vendors use a phonetic
decomposition (Pinyin or another), others use ideographic decomposition of Chinese words, with
various implementations and keyboard layouts. There are about 16 known methods, none of
which is a clear standard.
Also, there are actually two ideographic sets used: Traditional Chinese (the original written Chi-
nese) and Simplified Chinese. Several years ago, the People's Republic of China launched a cam-
paign to simplify some ideographic characters and eliminate redundancies altogether. Under the
plan, characters would be streamlined every five years. Characters have been revised several
times now, resulting in the smaller, simpler set that makes up Simplified Chinese.
13.5.1.1. Input Method Architecture
As shown in the previous section, there are many different input methods in use today, each vary-
ing with language, culture, and history. A common feature of many input methods is that the user
may type multiple keystrokes to compose a single character (or set of characters). The process of
composing characters from keystrokes is called preediting. It may require complex algorithms
and large dictionaries involving substantial computer resources.
Input methods may require one or more areas in which to show the feedback of the actual
keystrokes, to propose disambiguation to the user, to list dictionaries, and so on. The input
method areas of concern are as follows:

The status area is a logical extension of the LEDs that exist on the physical keyboard. It is
a window that is intended to present the internal state of the input method that is critical to
the user. The status area may consist of text data and bitmaps or some combination.

The preedit area displays the intermediate text for those languages that are composing prior
to the client handling the data.

The auxiliary area is used for pop-up menus and customizing dialogs that may be required
for an input method. There may be multiple auxiliary areas for an input method. Auxiliary
areas are managed by the input method independent of the client. Auxiliary areas are
assumed to be separate dialogs, which are maintained by the input method.
There are various user interaction styles used for preediting. The ones supported by Xlib are as
follows:

For on-the-spot input methods, preediting data will be displayed directly in the application
window. Application data is moved to allow preedit data to appear at the point of insertion.

Over-the-spot preediting means that the data is displayed in a preedit window that is placed
over the point of insertion.

Off-the-spot preediting means that the preedit window is inside the application window but
not at the point of insertion. Often, this type of window is placed at the bottom of the
application window.

Root-window preediting refers to input methods that use a preedit window that is the child
of RootWindow.
It would require a lot of computing resources if portable applications had to include input meth-
ods for all the languages in the world. To avoid this, a goal of the Xlib design is to allow an
application to communicate with an input method placed in a separate process. Such a process is
called an input server. The server to which the application should connect is dependent on the
environment when the application is started up, that is, the user language and the actual encoding
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to be used for it. The input method connection is said to be locale-dependent. It is also user-
dependent. For a given language, the user can choose, to some extent, the user interface style of
input method (if choice is possible among several).
Using an input server implies communication overhead, but applications can be migrated without
relinking. Input methods can be implemented either as a stub communicating to an input server
or as a local library.
An input method may be based on a front-end or a back-end architecture. In a front-end architec-
ture, there are two separate connections to the X server: keystrokes go directly from the X server
to the input method on one connection and other events to the regular client connection. The
input method is then acting as a filter and sends composed strings to the client. A front-end archi-
tecture requires synchronization between the two connections to avoid lost key events or locking
issues.
In a back-end architecture, a single X server connection is used. A dispatching mechanism must
decide on this channel to delegate appropriate keystrokes to the input method. For instance, it
may retain a Help keystroke for its own purpose. In the case where the input method is a separate
process (that is, a server), there must be a special communication protocol between the back-end
client and the input server.
A front-end architecture introduces synchronization issues and a filtering mechanism for nonchar-
acter keystrokes (Function keys, Help, and so on). A back-end architecture sometimes implies
more communication overhead and more process switching. If all three processes (X server,
input server, client) are running on a single workstation, there are two process switches for each
keystroke in a back-end architecture, but there is only one in a front-end architecture.
The abstraction used by a client to communicate with an input method is an opaque data structure
represented by the XIM data type. This data structure is returned by the XOpenIM function,
which opens an input method on a given display. Subsequent operations on this data structure
encapsulate all communication between client and input method. There is no need for an X client
to use any networking library or natural language package to use an input method.
A single input server may be used for one or more languages, supporting one or more encoding
schemes. But the strings returned from an input method will always be encoded in the (single)
locale associated with the XIM object.
13.5.1.2. Input Contexts
Xlib provides the ability to manage a multi-threaded state for text input. A client may be using
multiple windows, each window with multiple text entry areas, and the user possibly switching
among them at any time. The abstraction for representing the state of a particular input thread is
called an input context. The Xlib representation of an input context is an XIC.
An input context is the abstraction retaining the state, properties, and semantics of communica-
tion between a client and an input method. An input context is a combination of an input method,
a locale specifying the encoding of the character strings to be returned, a client window, internal
state information, and various layout or appearance characteristics. The input context concept
somewhat matches for input the graphics context abstraction defined for graphics output.
One input context belongs to exactly one input method. Different input contexts may be associ-
ated with the same input method, possibly with the same client window. An XIC is created with
the XCreateIC function, providing an XIM argument and affiliating the input context to the
input method for its lifetime. When an input method is closed with XCloseIM, all of its affili-
ated input contexts should not be used any more (and should preferably be destroyed before clos-
ing the input method).
Considering the example of a client window with multiple text entry areas, the application pro-
grammer could, for example, choose to implement as follows:

As many input contexts are created as text entry areas, and the client will get the input
accumulated on each context each time it looks up in that context.
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A single context is created for a top-level window in the application. If such a window
contains several text entry areas, each time the user moves to another text entry area, the
client has to indicate changes in the context.
A range of choices can be made by application designers to use either a single or multiple input
contexts, according to the needs of their application.
13.5.1.3. Getting Keyboard Input
To obtain characters from an input method, a client must call the function XmbLookupString or
XwcLookupString with an input context created from that input method. Both a locale and dis-
play are bound to an input method when it is opened, and an input context inherits this locale and
display. Any strings returned by XmbLookupString or XwcLookupString will be encoded in
that locale.
13.5.1.4. Focus Management
For each text entry area in which the XmbLookupString or XwcLookupString functions are
used, there will be an associated input context.
When the application focus moves to a text entry area, the application must set the input context
focus to the input context associated with that area. The input context focus is set by calling
XSetICFocus with the appropriate input context.
Also, when the application focus moves out of a text entry area, the application should unset the
focus for the associated input context by calling XUnsetICFocus. As an optimization, if XSet-
ICFocus
is called successively on two different input contexts, setting the focus on the second
will automatically unset the focus on the first.
To set and unset the input context focus correctly, it is necessary to track application-level focus
changes. Such focus changes do not necessarily correspond to X server focus changes.
If a single input context is being used to do input for multiple text entry areas, it will also be nec-
essary to set the focus window of the input context whenever the focus window changes (see sec-
tion 13.5.6.3).
13.5.1.5. Geometry Management
In most input method architectures (on-the-spot being the notable exception), the input method
will perform the display of its own data. To provide better visual locality, it is often desirable to
have the input method areas embedded within a client. To do this, the client may need to allocate
space for an input method. Xlib provides support that allows the size and position of input
method areas to be provided by a client. The input method areas that are supported for geometry
management are the status area and the preedit area.
The fundamental concept on which geometry management for input method windows is based is
the proper division of responsibilities between the client (or toolkit) and the input method. The
division of responsibilities is as follows:

The client is responsible for the geometry of the input method window.

The input method is responsible for the contents of the input method window.
An input method is able to suggest a size to the client, but it cannot suggest a placement. Also the
input method can only suggest a size. It does not determine the size, and it must accept the size it
is given.
Before a client provides geometry management for an input method, it must determine if geome-
try management is needed. The input method indicates the need for geometry management by
setting XIMPreeditArea or XIMStatusArea in its XIMStyles value returned by
XGetIMValues. When a client has decided that it will provide geometry management for an
input method, it indicates that decision by setting the XNInputStyle value in the XIC.
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After a client has established with the input method that it will do geometry management, the
client must negotiate the geometry with the input method. The geometry is negotiated by the fol-
lowing steps:

The client suggests an area to the input method by setting the XNAreaNeeded value for
that area. If the client has no constraints for the input method, it either will not suggest an
area or will set the width and height to zero. Otherwise, it will set one of the values.

The client will get the XIC value XNAreaNeeded. The input method will return its sug-
gested size in this value. The input method should pay attention to any constraints sug-
gested by the client.

The client sets the XIC value XNArea to inform the input method of the geometry of its
window. The client should try to honor the geometry requested by the input method. The
input method must accept this geometry.
Clients doing geometry management must be aware that setting other XIC values may affect the
geometry desired by an input method. For example, XNFontSet and XNLineSpacing may
change the geometry desired by the input method.
The table of XIC values (see section 13.5.6) indicates the values that can cause the desired geom-
etry to change when they are set. It is the responsibility of the client to renegotiate the geometry
of the input method window when it is needed.
In addition, a geometry management callback is provided by which an input method can initiate a
geometry change.
13.5.1.6. Event Filtering
A filtering mechanism is provided to allow input methods to capture X events transparently to
clients. It is expected that toolkits (or clients) using XmbLookupString or XwcLookupString
will call this filter at some point in the event processing mechanism to make sure that events
needed by an input method can be filtered by that input method.
If there were no filter, a client could receive and discard events that are necessary for the proper
functioning of an input method. The following provides a few examples of such events:

Expose events on preedit window in local mode.

Events may be used by an input method to communicate with an input server. Such input
server protocol-related events have to be intercepted if one does not want to disturb client
code.

Key events can be sent to a filter before they are bound to translations such as those the X
Toolkit Intrinsics library provides.
Clients are expected to get the XIC value XNFilterEvents and augment the event mask for the
client window with that event mask. This mask may be zero.
13.5.1.7. Callbacks
When an on-the-spot input method is implemented, only the client can insert or delete preedit
data in place and possibly scroll existing text. This means that the echo of the keystrokes has to
be achieved by the client itself, tightly coupled with the input method logic.
When the user enters a keystroke, the client calls XmbLookupString or XwcLookupString. At
this point, in the on-the-spot case, the echo of the keystroke in the preedit has not yet been done.
Before returning to the client logic that handles the input characters, the look-up function must
call the echoing logic to insert the new keystroke. If the keystrokes entered so far make up a char-
acter, the keystrokes entered need to be deleted, and the composed character will be returned.
Hence, what happens is that, while being called by client code, the input method logic has to call
back to the client before it returns. The client code, that is, a callback procedure, is called from
the input method logic.
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There are a number of cases where the input method logic has to call back the client. Each of
those cases is associated with a well-defined callback action. It is possible for the client to spec-
ify, for each input context, what callback is to be called for each action.
There are also callbacks provided for feedback of status information and a callback to initiate a
geometry request for an input method.
13.5.1.8. Visible Position Feedback Masks
In the on-the-spot input style, there is a problem when attempting to draw preedit strings that are
longer than the available space. Once the display area is exceeded, it is not clear how best to dis-
play the preedit string. The visible position feedback masks of XIMText help resolve this prob-
lem by allowing the input method to specify hints that indicate the essential portions of the
preedit string. For example, such hints can help developers implement scrolling of a long preedit
string within a short preedit display area.
13.5.1.9. Preedit String Management
As highlighted before, the input method architecture provides preediting, which supports a type
of preprocessor input composition. In this case, composition consists of interpreting a sequence
of key events and returning a committed string via XmbLookupString or XwcLookupString.
This provides the basics for input methods.
In addition to preediting based on key events, a general framework is provided to give a client that
desires it more advanced preediting based on the text within the client. This framework is called
string conversion and is provided using XIC values. The fundamental concept of string conver-
sion is to allow the input method to manipulate the client's text independent of any user preedit-
ing operation.
The need for string conversion is based on language needs and input method capabilities. The
following are some examples of string conversion:

Transliteration conversion provides language-specific conversions within the input method.
In the case of Korean input, users wish to convert a Hangul string into a Hanja string while
in preediting, after preediting, or in other situations (for example, on a selected string). The
conversion is triggered when the user presses a Hangul-to-Hanja key sequence (which may
be input method specific). Sometimes the user may want to invoke the conversion after fin-
ishing preediting or on a user-selected string. Thus, the string to be converted is in an
application buffer, not in the preedit area of the input method. The string conversion ser-
vices allow the client to request this transliteration conversion from the input method.
There are many other transliteration conversions defined for various languages, for exam-
ple, Kana-to-Kanji conversion in Japanese.
The key to remember is that transliteration conversions are triggered at the request of the
user and returned to the client immediately without affecting the preedit area of the input
method.

Reconversion of a previously committed string or a selected string is supported by many
input methods as a convenience to the user. For example, a user tends to mistype the com-
mit key while preediting. In that case, some input methods provide a special key sequence
to request a ``reconvert'' operation on the committed string, similiar to the undo facility
provided by most text editors. Another example is where the user is proofreading a docu-
ment that has some misconversions from preediting and wants to correct the misconverted
text. Such reconversion is again triggered by the user invoking some special action, but
reconversions should not affect the state of the preedit area.

Context-sensitive conversion is required for some languages and input methods that need to
retrieve text that surrounds the current spot location (cursor position) of the client's buffer.
Such text is needed when the preediting operation depends on some surrounding characters
(usually preceding the spot location). For example, in Thai language input, certain
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character sequences may be invalid and the input method may want to check whether char-
acters constitute a valid word. Input methods that do such context-dependent checking
need to retrieve the characters surrounding the current cursor position to obtain complete
words.
Unlike other conversions, this conversion is not explicitly requested by the user. Input
methods that provide such context-sensitive conversion continuously need to request con-
text from the client, and any change in the context of the spot location may affect such con-
versions. The client's context would be needed if the user moves the cursor and starts edit-
ing again.
For this reason, an input method supporting this type of conversion should take notice of
when the client calls XmbResetIC or XwcResetIC, which is usually an indication of a
context change.
Context-sensitive conversions just need a copy of the client's text, while other conversions replace
the client's text with new text to achieve the reconversion or transliteration. Yet in all cases the
result of a conversion, either immediately or via preediting, is returned by the XmbLookup-
String
and XwcLookupString functions.
String conversion support is dependent on the availability of the XNStringConversion or
XNStringConversionCallback XIC values. Because the input method may not support string
conversions, clients have to query the availability of string conversion operations by checking the
supported XIC values list by calling XGetIMValues with the XNQueryICValuesList IM value.
The difference between these two values is whether the conversion is invoked by the client or the
input method. The XNStringConversion XIC value is used by clients to request a string conver-
sion from the input method. The client is responsible for determining which events are used to
trigger the string conversion and whether the string to be converted should be copied or deleted.
The type of conversion is determined by the input method; the client can only pass the string to be
converted. The client is guaranteed that no XNStringConversionCallback will be issued when
this value is set; thus, the client need only set one of these values.
The XNStringConversionCallback XIC value is used by the client to notify the input method
that it will accept requests from the input method for string conversion. If this value is set, it is
the input method's responsibility to determine which events are used to trigger the string conver-
sion. When such events occur, the input method issues a call to the client-supplied procedure to
retrieve the string to be converted. The client's callback procedure is notified whether to copy or
delete the string and is provided with hints as to the amount of text needed. The XIMStringCon-
versionCallbackStruct
specifies which text should be passed back to the input method.
Finally, the input method may call the client's XNStringConversionCallback procedure multi-
ple times if the string returned from the callback is not sufficient to perform a successful conver-
sion. The arguments to the client's procedure allow the input method to define a position (in
character units) relative to the client's cursor position and the size of the text needed. By varying
the position and size of the desired text in subsequent callbacks, the input method can retrieve
additional text.
13.5.2. Input Method Management
The interface to input methods might appear to be simply creating an input method (XOpenIM)
and freeing an input method (XCloseIM). However, input methods may require complex com-
munication with input method servers (IM servers), for example:

If the X server, IM server, and X clients are started asynchronously, some clients may
attempt to connect to the IM server before it is fully operational, and fail. Therefore, some
mechanism is needed to allow clients to detect when an IM server has started.
It is up to clients to decide what should be done when an IM server is not available (for example,
wait, or use some other IM server).
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Some input methods may allow the underlying IM server to be switched. Such customiza-
tion may be desired without restarting the entire client.
To support management of input methods in these cases, the following functions are provided:
XRegisterIMInstantiateCallback
This function allows clients to register a callback pro-
cedure to be called when Xlib detects that an IM
server is up and available.
XOpenIM
A client calls this function as a result of the callback
procedure being called.
XSetIMValue, XSetICValue
These functions use the XIM and XIC values,
XNDestroyCallback, to allow a client to register a
callback procedure to be called when Xlib detects
that an IM server that was associated with an opened
input method is no longer available.
In addition, this function can be used to switch IM
servers for those input methods that support such
functionality. The IM value for switching IM servers
is implementation-dependent; see the description
below about switching IM servers.
XUnregisterIMInstantiateCallback
This function removes a callback procedure regis-
tered by the client.
Input methods that support switching of IM servers may exhibit some side-effects:

The input method will ensure that any new IM server supports any of the input styles being
used by input contexts already associated with the input method. However, the list of sup-
ported input styles may be different.

Geometry management requests on previously created input contexts may be initiated by
the new IM server.
13.5.2.1. Hot Keys
Some clients need to guarantee which keys can be used to escape from the input method, regard-
less of the input method state; for example, the client-specific Help key or the keys to move the
input focus. The HotKey mechanism allows clients to specify a set of keys for this purpose.
However, the input method might not allow clients to specify hot keys. Therefore, clients have to
query support of hot keys by checking the supported XIC values list by calling XGetIMValues
with the XNQueryICValuesList IM value. When the hot keys specified conflict with the key
bindings of the input method, hot keys take precedence over the key bindings of the input method.
13.5.2.2. Preedit State Operation
An input method may have sev eral internal states, depending on its implementation and the
locale. However, one state that is independent of locale and implementation is whether the input
method is currently performing a preediting operation. Xlib provides the ability for an applica-
tion to manage the preedit state programmatically. Two methods are provided for retrieving the
preedit state of an input context. One method is to query the state by calling XGetICValues with
the XNPreeditState XIC value. Another method is to receive notification whenever the preedit
state is changed. To receive such notification, an application needs to register a callback by call-
ing XSetICValues with the XNPreeditStateNotifyCallback XIC value. In order to change the
preedit state programmatically, an application needs to call XSetICValues with XNPreedit-
State.

Av ailability of the preedit state is input method dependent. The input method may not provide
the ability to set the state or to retrieve the state programmatically. Therefore, clients have to
query availability of preedit state operations by checking the supported XIC values list by calling
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XGetIMValues with the XNQueryICValuesList IM value.
13.5.3. Input Method Functions
To open a connection, use XOpenIM.
XIM XOpenIM(display, db, res_name, res_class)
Display *display;
XrmDatabase db;
char *res_name;
char *res_class;
display
Specifies the connection to the X server.
db
Specifies a pointer to the resource database.
res_name
Specifies the full resource name of the application.
res_class
Specifies the full class name of the application.
The XOpenIM function opens an input method, matching the current locale and modifiers speci-
fication. Current locale and modifiers are bound to the input method at opening time. The locale
associated with an input method cannot be changed dynamically. This implies that the strings
returned by XmbLookupString or XwcLookupString, for any input context affiliated with a
given input method, will be encoded in the locale current at the time the input method is opened.
The specific input method to which this call will be routed is identified on the basis of the current
locale. XOpenIM will identify a default input method corresponding to the current locale. That
default can be modified using XSetLocaleModifiers for the input method modifier.
The db argument is the resource database to be used by the input method for looking up resources
that are private to the input method. It is not intended that this database be used to look up values
that can be set as IC values in an input context. If db is NULL, no database is passed to the input
method.
The res_name and res_class arguments specify the resource name and class of the application.
They are intended to be used as prefixes by the input method when looking up resources that are
common to all input contexts that may be created for this input method. The characters used for
resource names and classes must be in the X Portable Character Set. The resources looked up are
not fully specified if res_name or res_class is NULL.
The res_name and res_class arguments are not assumed to exist beyond the call to XOpenIM.
The specified resource database is assumed to exist for the lifetime of the input method.
XOpenIM returns NULL if no input method could be opened.
To close a connection, use XCloseIM.
Status XCloseIM(im)
XIM im;
im
Specifies the input method.
The XCloseIM function closes the specified input method.
To set input method attributes, use XSetIMValues.
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char * XSetIMValues (im, ...)
XIM im;
im
Specifies the input method.
... Specifies the variable-length argument list to set XIM values.
The XSetIMValues function presents a variable argument list programming interface for setting
attributes of the specified input method. It returns NULL if it succeeds; otherwise, it returns the
name of the first argument that could not be set. Xlib does not attempt to set arguments from the
supplied list that follow the failed argument; all arguments in the list preceding the failed argu-
ment have been set correctly.
To query an input method, use XGetIMValues.
char * XGetIMValues (im, ...)
XIM im;
im
Specifies the input method.
... Specifies the variable length argument list to get XIM values.
The XGetIMValues function presents a variable argument list programming interface for query-
ing properties or features of the specified input method. This function returns NULL if it suc-
ceeds; otherwise, it returns the name of the first argument that could not be obtained.
Each XIM value argument (following a name) must point to a location where the XIM value is to
be stored. That is, if the XIM value is of type T, the argument must be of type T*. If T itself is a
pointer type, then XGetIMValues allocates memory to store the actual data, and the client is
responsible for freeing this data by calling XFree with the returned pointer.
To obtain the display associated with an input method, use XDisplayOfIM.
Display * XDisplayOfIM(im)
XIM im;
im
Specifies the input method.
The XDisplayOfIM function returns the display associated with the specified input method.
To get the locale associated with an input method, use XLocaleOfIM.
char * XLocaleOfIM(im)
XIM im;
im
Specifies the input method.
The XLocaleOfIM function returns the locale associated with the specified input method.
To register an input method instantiate callback, use XRegisterIMInstantiateCallback.
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Bool XRegisterIMInstantiateCallback (display, db, res_name, res_class, callback, client_data)
Display *display;
XrmDatabase db;
char *res_name;
char *res_class;
XIMProc callback;
XPointer *client_data;
display
Specifies the connection to the X server.
db
Specifies a pointer to the resource database.
res_name
Specifies the full resource name of the application.
res_class
Specifies the full class name of the application.
callback
Specifies a pointer to the input method instantiate callback.
client_data
Specifies the additional client data.
The XRegisterIMInstantiateCallback function registers a callback to be invoked whenever a
new input method becomes available for the specified display that matches the current locale and
modifiers.
The function returns True
if it succeeds; otherwise, it returns False.
The generic prototype is as follows:
void IMInstantiateCallback(display, client_data, call_data)
Display *display;
XPointer client_data;
XPointer call_data;
display
Specifies the connection to the X server.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
To unregister an input method instantiation callback, use XUnregisterIMInstantiateCallback.
Bool XUnregisterIMInstantiateCallback (display, db, res_name, res_class, callback, client_data)
Display *display;
XrmDatabase db;
char *res_name;
char *res_class;
XIMProc callback;
XPointer *client_data;
display
Specifies the connection to the X server.
db
Specifies a pointer to the resource database.
res_name
Specifies the full resource name of the application.
res_class
Specifies the full class name of the application.
callback
Specifies a pointer to the input method instantiate callback.
client_data
Specifies the additional client data.
The XUnregisterIMInstantiateCallback function removes an input method instantiation
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callback previously registered. The function returns True if it succeeds; otherwise, it returns
False.
13.5.4. Input Method Values
The following table describes how XIM values are interpreted by an input method. The first col-
umn lists the XIM values. The second column indicates how each of the XIM values are treated
by that input style.
The following keys apply to this table.
Key
Explanation
D
This value may be set using XSetIMValues. If it is not set,
a default is provided.
S
This value may be set using XSetIMValues.
G
This value may be read using XGetIMValues.
XIM Value Key
XNQueryInputStyle
G
XNResourceName
D-S-G
XNResourceClass
D-S-G
XNDestroyCallback
D-S-G
XNQueryIMValuesList
G
XNQueryICValuesList
G
XNVisiblePosition
G
XNR6PreeditCallbackBehavior
D-S-G
XNR6PreeditCallbackBehavior is obsolete and its use is not recommended (see section
13.5.4.6).
13.5.4.1. Query Input Style
A client should always query the input method to determine which input styles are supported.
The client should then find an input style it is capable of supporting.
If the client cannot find an input style that it can support, it should negotiate with the user the con-
tinuation of the program (exit, choose another input method, and so on).
The argument value must be a pointer to a location where the returned value will be stored. The
returned value is a pointer to a structure of type XIMStyles. Clients are responsible for freeing
the XIMStyles structure. To do so, use XFree.
The XIMStyles structure is defined as follows:
typedef unsigned long XIMStyle;
#define
XIMPreeditArea
0x0001L
#define
XIMPreeditCallbacks
0x0002L
#define
XIMPreeditPosition
0x0004L
#define
XIMPreeditNothing
0x0008L
#define
XIMPreeditNone
0x0010L
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#define
XIMStatusArea
0x0100L
#define
XIMStatusCallbacks
0x0200L
#define
XIMStatusNothing
0x0400L
#define
XIMStatusNone
0x0800L
typedef struct {
unsigned short count_styles;
XIMStyle * supported_styles;
} XIMStyles;
An XIMStyles structure contains the number of input styles supported in its count_styles field.
This is also the size of the supported_styles array.
The supported styles is a list of bitmask combinations, which indicate the combination of styles
for each of the areas supported. These areas are described later. Each element in the list should
select one of the bitmask values for each area. The list describes the complete set of combina-
tions supported. Only these combinations are supported by the input method.
The preedit category defines what type of support is provided by the input method for preedit
information.
XIMPreeditArea
If chosen, the input method would require the client to provide some
area values for it to do its preediting. Refer to XIC values XNArea
and XNAreaNeeded.
XIMPreeditPosition
If chosen, the input method would require the client to provide posi-
tional values. Refer to XIC values XNSpotLocation and
XNFocusWindow.
XIMPreeditCallbacks
If chosen, the input method would require the client to define the set
of preedit callbacks. Refer to XIC values XNPreeditStartCallback,
XNPreeditDoneCallback, XNPreeditDrawCallback, and
XNPreeditCaretCallback.
XIMPreeditNothing
If chosen, the input method can function without any preedit values.
XIMPreeditNone
The input method does not provide any preedit feedback. Any
preedit value is ignored. This style is mutually exclusive with the
other preedit styles.
The status category defines what type of support is provided by the input method for status infor-
mation.
XIMStatusArea
The input method requires the client to provide some area values for
it to do its status feedback. See XNArea and XNAreaNeeded.
XIMStatusCallbacks
The input method requires the client to define the set of status call-
backs, XNStatusStartCallback, XNStatusDoneCallback, and
XNStatusDrawCallback.
XIMStatusNothing
The input method can function without any status values.
XIMStatusNone
The input method does not provide any status feedback. If chosen,
any status value is ignored. This style is mutually exclusive with the
other status styles.
13.5.4.2. Resource Name and Class
The XNResourceName and XNResourceClass arguments are strings that specify the full name
and class used by the input method. These values should be used as prefixes for the name and
class when looking up resources that may vary according to the input method. If these values are
not set, the resources will not be fully specified.
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It is not intended that values that can be set as XIM values be set as resources.
13.5.4.3. Destroy Callback
The XNDestroyCallback argument is a pointer to a structure of type XIMCallback. XNDe-
stroyCallback
is triggered when an input method stops its service for any reason. After the call-
back is invoked, the input method is closed and the associated input context(s) are destroyed by
Xlib. Therefore, the client should not call XCloseIM or XDestroyIC.
The generic prototype of this callback function is as follows:
void DestroyCallback (im, client_data, call_data)
XIM im;
XPointer client_data;
XPointer call_data;
im
Specifies the input method.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
A DestroyCallback is always called with a NULL call_data argument.
13.5.4.4. Query IM/IC Values List
XNQueryIMValuesList and XNQueryICValuesList are used to query about XIM and XIC val-
ues supported by the input method.
The argument value must be a pointer to a location where the returned value will be stored. The
returned value is a pointer to a structure of type XIMValuesList. Clients are responsible for
freeing the XIMValuesList structure. To do so, use XFree.
The XIMValuesList structure is defined as follows:
typedef struct {
unsigned short count_values;
char **supported_values;
} XIMValuesList;
13.5.4.5. Visible Position
The XNVisiblePosition argument indicates whether the visible position masks of XIMFeed-
back
in XIMText are available.
The argument value must be a pointer to a location where the returned value will be stored. The
returned value is of type Bool. If the returned value is True, the input method uses the visible
position masks of XIMFeedback in XIMText; otherwise, the input method does not use the
masks.
Because this XIM value is optional, a client should call XGetIMValues with argument
XNQueryIMValues before using this argument. If the XNVisiblePosition does not exist in the
IM values list returned from XNQueryIMValues, the visible position masks of XIMFeedback
in XIMText are not used to indicate the visible position.
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13.5.4.6. Preedit Callback Behavior
The XNR6PreeditCallbackBehavior argument originally included in the X11R6 specification
has been deprecated.
The XNR6PreeditCallbackBehavior argument indicates whether the behavior of preedit call-
backs regarding XIMPreeditDrawCallbackStruct values follows Release 5 or Release 6 seman-
tics.
The value is of type Bool. When querying for XNR6PreeditCallbackBehavior, if the returned
value is True, the input method uses the Release 6 behavior; otherwise, it uses the Release 5
behavior. The default value is False. In order to use Release 6 semantics, the value of
XNR6PreeditCallbackBehavior must be set to True.
Because this XIM value is optional, a client should call XGetIMValues with argument
XNQueryIMValues before using this argument. If the XNR6PreeditCallbackBehavior does
not exist in the IM values list returned from XNQueryIMValues, the PreeditCallback behavior is
Release 5 semantics.
13.5.5. Input Context Functions
An input context is an abstraction that is used to contain both the data required (if any) by an
input method and the information required to display that data. There may be multiple input con-
texts for one input method. The programming interfaces for creating, reading, or modifying an
input context use a variable argument list. The name elements of the argument lists are referred
to as XIC values. It is intended that input methods be controlled by these XIC values. As new
XIC values are created, they should be registered with the X Consortium.
To create an input context, use XCreateIC.
XIC XCreateIC(im, ...)
XIM im;
im
Specifies the input method.
... Specifies the variable length argument list to set XIC values.
The XCreateIC function creates a context within the specified input method.
Some of the arguments are mandatory at creation time, and the input context will not be created if
those arguments are not provided. The mandatory arguments are the input style and the set of text
callbacks (if the input style selected requires callbacks). All other input context values can be set
later.
XCreateIC returns a NULL value if no input context could be created. A NULL value could be
returned for any of the following reasons:

A required argument was not set.

A read-only argument was set (for example, XNFilterEvents).

The argument name is not recognized.

The input method encountered an input method implementation-dependent error.
XCreateIC can generate BadAtom, BadColor, BadPixmap, and BadWindow errors.
To destroy an input context, use XDestroyIC.
During formulation of the X11R6 specification, the behavior of the R6 PreeditDrawCallbacks was going to differ significantly from
that of the R5 callbacks.
Late changes to the specification converged the R5 and R6 behaviors, eliminating the need for
XNR6PreeditCallbackBehavior. Unfortunately, this argument was not removed from the R6 specification before it was published.
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void XDestroyIC (ic)
XIC ic;
ic
Specifies the input context.
XDestroyIC destroys the specified input context.
To communicate to and synchronize with input method for any changes in keyboard focus from
the client side, use XSetICFocus and XUnsetICFocus.
void XSetICFocus (ic)
XIC ic;
ic
Specifies the input context.
The XSetICFocus function allows a client to notify an input method that the focus window
attached to the specified input context has received keyboard focus. The input method should
take action to provide appropriate feedback. Complete feedback specification is a matter of user
interface policy.
Calling XSetICFocus does not affect the focus window value.
void XUnsetICFocus (ic)
XIC ic;
ic
Specifies the input context.
The XUnsetICFocus function allows a client to notify an input method that the specified input
context has lost the keyboard focus and that no more input is expected on the focus window
attached to that input context. The input method should take action to provide appropriate feed-
back. Complete feedback specification is a matter of user interface policy.
Calling XUnsetICFocus does not affect the focus window value; the client may still receive
ev ents from the input method that are directed to the focus window.
To reset the state of an input context to its initial state, use XmbResetIC or XwcResetIC.
char * XmbResetIC(ic)
XIC ic;
wchar_t * XwcResetIC(ic)
XIC ic;
ic
Specifies the input context.
When XNResetState is set to XIMInitialState, XmbResetIC and XwcResetIC reset an input
context to its initial state; when XNResetState is set to XIMPreserveState, the current input
context state is preserved. In both cases, any input pending on that context is deleted. The input
method is required to clear the preedit area, if any, and update the status accordingly. Calling
XmbResetIC or XwcResetIC does not change the focus.
The return value of XmbResetIC is its current preedit string as a multibyte string. If there is any
preedit text drawn or visible to the user, then these procedures must return a non-NULL string. If
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there is no visible preedit text, then it is input method implementation-dependent whether these
procedures return a non-NULL string or NULL.
The client should free the returned string by calling XFree.
To get the input method associated with an input context, use XIMOfIC.
XIM XIMOfIC(ic)
XIC ic;
ic
Specifies the input context.
The XIMOfIC function returns the input method associated with the specified input context.
Xlib provides two functions for setting and reading XIC values, respectively, XSetICValues and
XGetICValues. Both functions have a variable-length argument list. In that argument list, any
XIC value's name must be denoted with a character string using the X Portable Character Set.
To set XIC values, use XSetICValues.
char * XSetICValues (ic, ...)
XIC ic;
ic
Specifies the input context.
... Specifies the variable length argument list to set XIC values.
The XSetICValues function returns NULL if no error occurred; otherwise, it returns the name of
the first argument that could not be set. An argument might not be set for any of the following
reasons:

The argument is read-only (for example, XNFilterEvents).

The argument name is not recognized.

An implementation-dependent error occurs.
Each value to be set must be an appropriate datum, matching the data type imposed by the seman-
tics of the argument.
XSetICValues can generate BadAtom, BadColor, BadCursor, BadPixmap, and BadWin-
dow errors.
To obtain XIC values, use XGetICValues.
char * XGetICValues (ic, ...)
XIC ic;
ic
Specifies the input context.
... Specifies the variable length argument list to get XIC values.
The XGetICValues function returns NULL if no error occurred; otherwise, it returns the name of
the first argument that could not be obtained. An argument could not be obtained for any of the
following reasons:

The argument name is not recognized.

The input method encountered an implementation-dependent error.
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Each IC attribute value argument (following a name) must point to a location where the IC value
is to be stored. That is, if the IC value is of type T, the argument must be of type T*. If T itself is
a pointer type, then XGetICValues allocates memory to store the actual data, and the client is
responsible for freeing this data by calling XFree with the returned pointer. The exception to this
rule is for an IC value of type XVaNestedList (for preedit and status attributes). In this case, the
argument must also be of type XVaNestedList. Then, the rule of changing type T to T* and free-
ing the allocated data applies to each element of the nested list.
13.5.6. Input Context Values
The following tables describe how XIC values are interpreted by an input method depending on
the input style chosen by the user.
The first column lists the XIC values. The second column indicates which values are involved in
affecting, negotiating, and setting the geometry of the input method windows. The subentries
under the third column indicate the different input styles that are supported. Each of these
columns indicates how each of the XIC values are treated by that input style.
The following keys apply to these tables.
Key
Explanation
C
This value must be set with XCreateIC.
D
This value may be set using XCreateIC. If it is not set, a default is pro-
vided.
G
This value may be read using XGetICValues.
GN
This value may cause geometry negotiation when its value is set by means of
XCreateIC or XSetICValues.
GR
This value will be the response of the input method when any GN value is
changed.
GS
This value will cause the geometry of the input method window to be set.
O
This value must be set once and only once. It need not be set at create time.
S
This value may be set with XSetICValues.
Ignored
This value is ignored by the input method for the given input style.
Input Style
XIC Value Geometry
Preedit Preedit Preedit Preedit Preedit
Management Callback
Position Area Nothing
None
Input Style
C-G C-G
C-G C-G C-G
Client Window
O-G O-G
O-G O-G
Ignored
Focus Window
GN
D-S-G D-S-G
D-S-G D-S-G
Ignored
Resource Name
Ignored D-S-G
D-S-G D-S-G
Ignored
Resource Class
Ignored D-S-G
D-S-G D-S-G
Ignored
Geometry Callback
Ignored Ignored
D-S-G Ignored
Ignored
Filter Events G
G
G
G
Ignored
Destroy Callback D-S-G
D-S-G D-S-G
D-S-G D-S-G
String Conversion Callback
S-G S-G
S-G S-G S-G
String Conversion D-S-G
D-S-G D-S-G
D-S-G D-S-G
Reset State
D-S-G D-S-G
D-S-G D-S-G
Ignored
HotKey S-G S-G
S-G S-G
Ignored
HotKeyState D-S-G
D-S-G D-S-G
D-S-G Ignored
Preedit
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Input Style
XIC Value Geometry
Preedit Preedit Preedit Preedit Preedit
Management Callback
Position Area Nothing
None
Area GS
Ignored D-S-G
D-S-G Ignored
Ignored
Area Needed
GN-GR Ignored
Ignored S-G
Ignored Ignored
Spot Location
Ignored D-S-G
Ignored Ignored Ignored
Colormap Ignored
D-S-G D-S-G
D-S-G Ignored
Foreground Ignored
D-S-G D-S-G
D-S-G Ignored
Background Ignored
D-S-G D-S-G
D-S-G Ignored
Background Pixmap
Ignored D-S-G
D-S-G D-S-G
Ignored
Font Set
GN Ignored
D-S-G D-S-G
D-S-G Ignored
Line Spacing
GN Ignored
D-S-G D-S-G
D-S-G Ignored
Cursor Ignored
D-S-G D-S-G
D-S-G Ignored
Preedit State
D-S-G D-S-G
D-S-G D-S-G
Ignored
Preedit State Notify Callback
S-G S-G
S-G S-G
Ignored
Preedit Callbacks
C-S-G Ignored
Ignored Ignored Ignored
Input Style
XIC Value Geometry
Status Status
Status Status
Management Callback
Area Nothing
None
Input Style
C-G C-G
C-G C-G
Client Window
O-G O-G
O-G Ignored
Focus Window
GN
D-S-G D-S-G
D-S-G Ignored
Resource Name
Ignored D-S-G
D-S-G Ignored
Resource Class
Ignored D-S-G
D-S-G Ignored
Geometry Callback
Ignored D-S-G
Ignored Ignored
Filter Events G
G
G
G
Status
Area GS
Ignored D-S-G
Ignored Ignored
Area Needed
GN-GR Ignored
S-G Ignored
Ignored
Colormap Ignored
D-S-G D-S-G
Ignored
Foreground Ignored
D-S-G D-S-G
Ignored
Background Ignored
D-S-G D-S-G
Ignored
Background Pixmap
Ignored D-S-G
D-S-G Ignored
Font Set
GN Ignored
D-S-G D-S-G
Ignored
Line Spacing
GN Ignored
D-S-G D-S-G
Ignored
Cursor Ignored
D-S-G D-S-G
Ignored
Status Callbacks
C-S-G Ignored
Ignored Ignored
13.5.6.1. Input Style
The XNInputStyle argument specifies the input style to be used. The value of this argument
must be one of the values returned by the XGetIMValues function with the XNQueryInput-
Style
argument specified in the supported_styles list.
Note that this argument must be set at creation time and cannot be changed.
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13.5.6.2. Client Window
The XNClientWindow argument specifies to the input method the client window in which the
input method can display data or create subwindows. Geometry values for input method areas are
given with respect to the client window. Dynamic change of client window is not supported.
This argument may be set only once and should be set before any input is done using this input
context. If it is not set, the input method may not operate correctly.
If an attempt is made to set this value a second time with XSetICValues, the string XNClien-
tWindow
will be returned by XSetICValues, and the client window will not be changed.
If the client window is not a valid window ID on the display attached to the input method, a Bad-
Window
error can be generated when this value is used by the input method.
13.5.6.3. Focus Window
The XNFocusWindow argument specifies the focus window. The primary purpose of the
XNFocusWindow is to identify the window that will receive the key event when input is com-
posed. In addition, the input method may possibly affect the focus window as follows:

Select events on it

Send events to it

Modify its properties

Grab the keyboard within that window
The associated value must be of type Window. If the focus window is not a valid window ID on
the display attached to the input method, a BadWindow error can be generated when this value is
used by the input method.
When this XIC value is left unspecified, the input method will use the client window as the
default focus window.
13.5.6.4. Resource Name and Class
The XNResourceName and XNResourceClass arguments are strings that specify the full name
and class used by the client to obtain resources for the client window. These values should be
used as prefixes for name and class when looking up resources that may vary according to the
input context. If these values are not set, the resources will not be fully specified.
It is not intended that values that can be set as XIC values be set as resources.
13.5.6.5. Geometry Callback
The XNGeometryCallback argument is a structure of type XIMCallback (see section
13.5.6.13.12).
The XNGeometryCallback argument specifies the geometry callback that a client can set. This
callback is not required for correct operation of either an input method or a client. It can be set
for a client whose user interface policy permits an input method to request the dynamic change of
that input method's window. An input method that does dynamic change will need to filter any
ev ents that it uses to initiate the change.
13.5.6.6. Filter Events
The XNFilterEvents argument returns the event mask that an input method needs to have
selected for. The client is expected to augment its own event mask for the client window with this
one.
This argument is read-only, is set by the input method at create time, and is never changed.
The type of this argument is unsigned long. Setting this value will cause an error.
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13.5.6.7. Destroy Callback
The XNDestroyCallback argument is a pointer to a structure of type XIMCallback (see section
13.5.6.13.12). This callback is triggered when the input method stops its service for any reason;
for example, when a connection to an IM server is broken. After the destroy callback is called,
the input context is destroyed and the input method is closed. Therefore, the client should not call
XDestroyIC and XCloseIM.
13.5.6.8. String Conversion Callback
The XNStringConversionCallback argument is a structure of type XIMCallback (see section
13.5.6.13.12).
The XNStringConversionCallback argument specifies a string conversion callback. This call-
back is not required for correct operation of either the input method or the client. It can be set by
a client to support string conversions that may be requested by the input method. An input
method that does string conversions will filter any events that it uses to initiate the conversion.
Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this argument.
13.5.6.9. String Conversion
The XNStringConversion argument is a structure of type XIMStringConversionText.
The XNStringConversion argument specifies the string to be converted by an input method.
This argument is not required for correct operation of either the input method or the client.
String conversion facilitates the manipulation of text independent of preediting. It is essential for
some input methods and clients to manipulate text by performing context-sensitive conversion,
reconversion, or transliteration conversion on it.
Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this argument.
The XIMStringConversionText structure is defined as follows:
typedef struct _XIMStringConversionText {
unsigned short length;
XIMStringConversionFeedback *feedback;
Bool encoding_is_wchar;
union {
char *mbs;
wchar_t *wcs;
} string;
} XIMStringConversionText;
typedef unsigned long XIMStringConversionFeedback;
The feedback member is reserved for future use. The text to be converted is defined by the string
and length members. The length is indicated in characters. To prevent the library from freeing
memory pointed to by an uninitialized pointer, the client should set the feedback element to
NULL.
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13.5.6.10. Reset State
The XNResetState argument specifies the state the input context will return to after calling
XmbResetIC or XwcResetIC.
The XIC state may be set to its initial state, as specified by the XNPreeditState value when
XCreateIC was called, or it may be set to preserve the current state.
The valid masks for XIMResetState are as follows:
typedef unsigned long XIMResetState;
#define
XIMInitialState
(1L)
#define
XIMPreserveState
(1L<<1)
If XIMInitialState is set, then XmbResetIC and XwcResetIC will return to the initial
XNPreeditState state of the XIC.
If XIMPreserveState is set, then XmbResetIC and XwcResetIC will preserve the current state
of the XIC.
If XNResetState is left unspecified, the default is XIMInitialState.
XIMResetState values other than those specified above will default to XIMInitialState.
Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this argument.
13.5.6.11. Hot Keys
The XNHotKey argument specifies the hot key list to the XIC. The hot key list is a pointer to the
structure of type XIMHotKeyTriggers, which specifies the key events that must be received
without any interruption of the input method. For the hot key list set with this argument to be uti-
lized, the client must also set XNHotKeyState to XIMHotKeyStateON.
Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this functionality.
The value of the argument is a pointer to a structure of type XIMHotKeyTriggers.
If an event for a key in the hot key list is found, then the process will receive the event and it will
be processed inside the client.
typedef struct {
Ke ySym keysym;
unsigned int modifier;
unsigned int modifier_mask;
} XIMHotKeyTrigger;
typedef struct {
int num_hot_key;
XIMHotKeyTrigger *key;
} XIMHotKeyTriggers;
The combination of modifier and modifier_mask are used to represent one of three states for each
modifier: either the modifier must be on, or the modifier must be off, or the modifier is a ``don't
care'' - it may be on or off. When a modifier_mask bit is set to 0, the state of the associated
modifier is ignored when evaluating whether the key is hot or not.
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Modifier Bit
Mask Bit
Meaning
0
1
The modifier must be off.
1
1
The modifier must be on.
n/a
0
Do not care if the modifier is on or off.
13.5.6.12. Hot Key State
The XNHotKeyState argument specifies the hot key state of the input method. This is usually
used to switch the input method between hot key operation and normal input processing.
The value of the argument is a pointer to a structure of type XIMHotKeyState .
typedef unsigned long XIMHotKeyState;
#define
XIMHotKeyStateON
(0x0001L)
#define
XIMHotKeyStateOFF
(0x0002L)
If not specified, the default is XIMHotKeyStateOFF.
13.5.6.13. Preedit and Status Attributes
The XNPreeditAttributes and XNStatusAttributes arguments specify to an input method the
attributes to be used for the preedit and status areas, if any. Those attributes are passed to XSet-
ICValues
or XGetICValues as a nested variable-length list. The names to be used in these lists
are described in the following sections.
13.5.6.13.1. Area
The value of the XNArea argument must be a pointer to a structure of type XRectangle. The
interpretation of the XNArea argument is dependent on the input method style that has been set.
If the input method style is XIMPreeditPosition, XNArea specifies the clipping region within
which preediting will take place. If the focus window has been set, the coordinates are assumed
to be relative to the focus window. Otherwise, the coordinates are assumed to be relative to the
client window. If neither has been set, the results are undefined.
If XNArea is not specified, is set to NULL, or is invalid, the input method will default the clip-
ping region to the geometry of the XNFocusWindow. If the area specified is NULL or invalid,
the results are undefined.
If the input style is XIMPreeditArea or XIMStatusArea, XNArea specifies the geometry pro-
vided by the client to the input method. The input method may use this area to display its data,
either preedit or status depending on the area designated. The input method may create a window
as a child of the client window with dimensions that fit the XNArea. The coordinates are relative
to the client window. If the client window has not been set yet, the input method should save
these values and apply them when the client window is set. If XNArea is not specified, is set to
NULL, or is invalid, the results are undefined.
13.5.6.13.2. Area Needed
When set, the XNAreaNeeded argument specifies the geometry suggested by the client for this
area (preedit or status). The value associated with the argument must be a pointer to a structure of
type XRectangle. Note that the x, y values are not used and that nonzero values for width or
height are the constraints that the client wishes the input method to respect.
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When read, the XNAreaNeeded argument specifies the preferred geometry desired by the input
method for the area.
This argument is only valid if the input style is XIMPreeditArea or XIMStatusArea. It is used
for geometry negotiation between the client and the input method and has no other effect on the
input method (see section 13.5.1.5).
13.5.6.13.3. Spot Location
The XNSpotLocation argument specifies to the input method the coordinates of the spot to be
used by an input method executing with XNInputStyle set to XIMPreeditPosition. When spec-
ified to any input method other than XIMPreeditPosition, this XIC value is ignored.
The x coordinate specifies the position where the next character would be inserted. The y coordi-
nate is the position of the baseline used by the current text line in the focus window. The x and y
coordinates are relative to the focus window, if it has been set; otherwise, they are relative to the
client window. If neither the focus window nor the client window has been set, the results are
undefined.
The value of the argument is a pointer to a structure of type XPoint.
13.5.6.13.4. Colormap
Tw o different arguments can be used to indicate what colormap the input method should use to
allocate colors, a colormap ID, or a standard colormap name.
The XNColormap argument is used to specify a colormap ID. The argument value is of type
Colormap. An inv alid argument may generate a BadColor error when it is used by the input
method.
The XNStdColormap argument is used to indicate the name of the standard colormap in which
the input method should allocate colors. The argument value is an Atom that should be a valid
atom for calling XGetRGBColormaps. An inv alid argument may generate a BadAtom error
when it is used by the input method.
If the colormap is left unspecified, the client window colormap becomes the default.
13.5.6.13.5. Foreground and Background
The XNForeground and XNBackground arguments specify the foreground and background
pixel, respectively. The argument value is of type unsigned long. It must be a valid pixel in the
input method colormap.
If these values are left unspecified, the default is determined by the input method.
13.5.6.13.6. Background Pixmap
The XNBackgroundPixmap argument specifies a background pixmap to be used as the back-
ground of the window. The value must be of type Pixmap. An inv alid argument may generate a
BadPixmap error when it is used by the input method.
If this value is left unspecified, the default is determined by the input method.
13.5.6.13.7. Font Set
The XNFontSet argument specifies to the input method what font set is to be used. The argu-
ment value is of type XFontSet.
If this value is left unspecified, the default is determined by the input method.
13.5.6.13.8. Line Spacing
The XNLineSpace argument specifies to the input method what line spacing is to be used in the
preedit window if more than one line is to be used. This argument is of type int.
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If this value is left unspecified, the default is determined by the input method.
13.5.6.13.9. Cursor
The XNCursor argument specifies to the input method what cursor is to be used in the specified
window. This argument is of type Cursor.
An invalid argument may generate a BadCursor error when it is used by the input method. If
this value is left unspecified, the default is determined by the input method.
13.5.6.13.10. Preedit State
The XNPreeditState argument specifies the state of input preediting for the input method. Input
preediting can be on or off.
The valid mask names for XNPreeditState are as follows:
typedef unsigned long XIMPreeditState;
#define
XIMPreeditUnknown
0L
#define
XIMPreeditEnable
1L
#define
XIMPreeditDisable
(1L<<1)
If a value of XIMPreeditEnable is set, then input preediting is turned on by the input method.
If a value of XIMPreeditDisable is set, then input preediting is turned off by the input method.
If XNPreeditState is left unspecified, then the state will be implementation-dependent.
When XNResetState is set to XIMInitialState, the XNPreeditState value specified at the cre-
ation time will be reflected as the initial state for XmbResetIC and XwcResetIC.
Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this argument.
13.5.6.13.11. Preedit State Notify Callback
The preedit state notify callback is triggered by the input method when the preediting state has
changed. The value of the XNPreeditStateNotifyCallback argument is a pointer to a structure
of type XIMCallback. The generic prototype is as follows:
void PreeditStateNotifyCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XIMPreeditStateNotifyCallbackStruct *call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Specifies the current preedit state.
The XIMPreeditStateNotifyCallbackStruct structure is defined as follows:
typedef struct _XIMPreeditStateNotifyCallbackStruct {
XIMPreeditState state;
} XIMPreeditStateNotifyCallbackStruct;
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Because this XIC value is optional, a client should call XGetIMValues with argument
XNQueryICValuesList before using this argument.
13.5.6.13.12. Preedit and Status Callbacks
A client that wants to support the input style XIMPreeditCallbacks must provide a set of preedit
callbacks to the input method. The set of preedit callbacks is as follows:
XNPreeditStartCallback
This is called when the input method starts preedit.
XNPreeditDoneCallback
This is called when the input method stops preedit.
XNPreeditDrawCallback
This is called when a number of preedit keystrokes should be
echoed.
XNPreeditCaretCallback
This is called to move the text insertion point within the preedit
string.
A client that wants to support the input style XIMStatusCallbacks must provide a set of status
callbacks to the input method. The set of status callbacks is as follows:
XNStatusStartCallback
This is called when the input method initializes the status area.
XNStatusDoneCallback
This is called when the input method no longer needs the status
area.
XNStatusDrawCallback
This is called when updating of the status area is required.
The value of any status or preedit argument is a pointer to a structure of type XIMCallback.
typedef void (*XIMProc)();
typedef struct {
XPointer client_data;
XIMProc callback;
} XIMCallback;
Each callback has some particular semantics and will carry the data that expresses the environ-
ment necessary to the client into a specific data structure. This paragraph only describes the argu-
ments to be used to set the callback.
Setting any of these values while doing preedit may cause unexpected results.
13.5.7. Input Method Callback Semantics
XIM callbacks are procedures defined by clients or text drawing packages that are to be called
from the input method when selected events occur. Most clients will use a text editing package or
a toolkit and, hence, will not need to define such callbacks. This section defines the callback
semantics, when they are triggered, and what their arguments are. This information is mostly
useful for X toolkit implementors.
Callbacks are mostly provided so that clients (or text editing packages) can implement on-the-
spot preediting in their own window. In that case, the input method needs to communicate and
synchronize with the client. The input method needs to communicate changes in the preedit win-
dow when it is under control of the client. Those callbacks allow the client to initialize the
preedit area, display a new preedit string, move the text insertion point during preedit, terminate
preedit, or update the status area.
All callback procedures follow the generic prototype:
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void CallbackPrototype(ic, client_data, call_data)
XIC ic;
XPointer client_data;
SomeType call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Specifies data specific to the callback.
The call_data argument is a structure that expresses the arguments needed to achieve the seman-
tics; that is, it is a specific data structure appropriate to the callback. In cases where no data is
needed in the callback, this call_data argument is NULL. The client_data argument is a closure
that has been initially specified by the client when specifying the callback and passed back. It
may serve, for example, to inherit application context in the callback.
The following paragraphs describe the programming semantics and specific data structure associ-
ated with the different reasons.
13.5.7.1. Geometry Callback
The geometry callback is triggered by the input method to indicate that it wants the client to
negotiate geometry. The generic prototype is as follows:
void GeometryCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
The callback is called with a NULL call_data argument.
13.5.7.2. Destroy Callback
The destroy callback is triggered by the input method when it stops service for any reason. After
the callback is invoked, the input context will be freed by Xlib. The generic prototype is as fol-
lows:
void DestroyCallback (ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
The callback is called with a NULL call_data argument.
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13.5.7.3. String Conversion Callback
The string conversion callback is triggered by the input method to request the client to return the
string to be converted. The returned string may be either a multibyte or wide character string,
with an encoding matching the locale bound to the input context. The callback prototype is as
follows:
void StringConversionCallback (ic, client_data, call_data)
XIC ic;
XPointer client_data;
XIMStringConversionCallbackStruct *call_data;
ic
Specifies the input method.
client_data
Specifies the additional client data.
call_data
Specifies the amount of the string to be converted.
The callback is passed an XIMStringConversionCallbackStruct structure in the call_data argu-
ment. The text member is an XIMStringConversionText structure (see section 13.5.6.9) to be
filled in by the client and describes the text to be sent to the input method. The data pointed to by
the string and feedback elements of the XIMStringConversionText structure will be freed using
XFree by the input method after the callback returns. So the client should not point to internal
buffers that are critical to the client. Similarly, because the feedback element is currently reserved
for future use, the client should set feedback to NULL to prevent the library from freeing memory
at some random location due to an uninitialized pointer.
The XIMStringConversionCallbackStruct structure is defined as follows:
typedef struct _XIMStringConversionCallbackStruct {
XIMStringConversionPosition position;
XIMCaretDirection direction;
short factor;
XIMStringConversionOperation operation;
XIMStringConversionText *text;
} XIMStringConversionCallbackStruct;
typedef short XIMStringConversionPosition;
typedef unsigned short XIMStringConversionOperation;
#define
XIMStringConversionSubstitution
(0x0001)
#define
XIMStringConversionRetrieval
(0x0002)
XIMStringConversionPosition specifies the starting position of the string to be returned in the
XIMStringConversionText structure. The value identifies a position, in units of characters, rel-
ative to the client's cursor position in the client's buffer.
The ending position of the text buffer is determined by the direction and factor members. Specifi-
cally, it is the character position relative to the starting point as defined by the
XIMCaretDirection. The factor member of XIMStringConversionCallbackStruct specifies
the number of XIMCaretDirection positions to be applied. For example, if the direction speci-
fies XIMLineEnd and factor is 1, then all characters from the starting position to the end of the
current display line are returned. If the direction specifies XIMForwardChar or
XIMBackwardChar, then the factor specifies a relative position, indicated in characters, from
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the starting position.
XIMStringConversionOperation specifies whether the string to be converted should be deleted
(substitution) or copied (retrieval) from the client's buffer. When the XIMStringConversionOp-
eration
is XIMStringConversionSubstitution, the client must delete the string to be converted
from its own buffer. When the XIMStringConversionOperation is
XIMStringConversionRetrieval, the client must not delete the string to be converted from its
buffer. The substitute operation is typically used for reconversion and transliteration conversion,
while the retrieval operation is typically used for context-sensitive conversion.
13.5.7.4. Preedit State Callbacks
When the input method turns preediting on or off, a PreeditStartCallback or PreeditDoneCall-
back
callback is triggered to let the toolkit do the setup or the cleanup for the preedit region.
int PreeditStartCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
When preedit starts on the specified input context, the callback is called with a NULL call_data
argument. PreeditStartCallback will return the maximum size of the preedit string. A positive
number indicates the maximum number of bytes allowed in the preedit string, and a value of -1
indicates there is no limit.
void PreeditDoneCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
When preedit stops on the specified input context, the callback is called with a NULL call_data
argument. The client can release the data allocated by PreeditStartCallback.
PreeditStartCallback should initialize appropriate data needed for displaying preedit informa-
tion and for handling further PreeditDrawCallback calls. Once PreeditStartCallback is
called, it will not be called again before PreeditDoneCallback has been called.
13.5.7.5. Preedit Draw Callback
This callback is triggered to draw and insert, delete or replace, preedit text in the preedit region.
The preedit text may include unconverted input text such as Japanese Kana, converted text such
as Japanese Kanji characters, or characters of both kinds. That string is either a multibyte or wide
character string, whose encoding matches the locale bound to the input context. The callback
prototype is as follows:
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void PreeditDrawCallback (ic, client_data, call_data)
XIC ic;
XPointer client_data;
XIMPreeditDrawCallbackStruct *call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Specifies the preedit drawing information.
The callback is passed an XIMPreeditDrawCallbackStruct structure in the call_data argument.
The text member of this structure contains the text to be drawn. After the string has been drawn,
the caret should be moved to the specified location.
The XIMPreeditDrawCallbackStruct structure is defined as follows:
typedef struct _XIMPreeditDrawCallbackStruct {
int caret;
/* Cursor offset within preedit string */
int chg_first;
/* Starting change position */
int chg_length;
/* Length of the change in character count */
XIMText *text;
} XIMPreeditDrawCallbackStruct;
The client must keep updating a buffer of the preedit text and the callback arguments referring to
indexes in that buffer. The call_data fields have specific meanings according to the operation, as
follows:

To indicate text deletion, the call_data member specifies a NULL text field. The text to be
deleted is then the current text in the buffer from position chg_first (starting at zero) on a
character length of chg_length.

When text is non-NULL, it indicates insertion or replacement of text in the buffer.
The chg_length member identifies the number of characters in the current preedit buffer
that are affected by this call. A positive chg_length indicates that chg_length number of
characters, starting at chg_first, must be deleted or must be replaced by text, whose length
is specified in the XIMText structure.
A chg_length value of zero indicates that text must be inserted right at the position speci-
fied by chg_first. A value of zero for chg_first specifies the first character in the buffer.
chg_length and chg_first combine to identify the modification required to the preedit
buffer; beginning at chg_first, replace chg_length number of characters with the text in the
supplied XIMText structure. For example, suppose the preedit buffer contains the string
"ABCDE".
Text: A B C D E
^ ^ ^ ^ ^ ^
CharPos: 0 1 2 3 4 5
The CharPos in the diagram shows the location of the character position relative to the
character.
If the value of chg_first is 1 and the value of chg_length is 3, this says to replace 3 charac-
ters beginning at character position 1 with the string in the XIMText structure. Hence,
BCD would be replaced by the value in the structure.
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Though chg_length and chg_first are both signed integers they will never hav e a neg ative
value.

The caret member identifies the character position before which the cursor should be placed
- after modification to the preedit buffer has been completed. For example, if caret is zero,
the cursor is at the beginning of the buffer. If the caret is one, the cursor is between the first
and second character.
typedef struct _XIMText {
unsigned short length;
XIMFeedback * feedback;
Bool encoding_is_wchar;
union {
char * multi_byte;
wchar_t * wide_char;
} string;
} XIMText;
The text string passed is actually a structure specifying as follows:

The length member is the text length in characters.

The encoding_is_wchar member is a value that indicates if the text string is encoded in
wide character or multibyte format. The text string may be passed either as multibyte or as
wide character; the input method controls in which form data is passed. The client's call-
back routine must be able to handle data passed in either form.

The string member is the text string.

The feedback member indicates rendering type for each character in the string member. If
string is NULL (indicating that only highlighting of the existing preedit buffer should be
updated), feedback points to length highlight elements that should be applied to the existing
preedit buffer, beginning at chg_first.
The feedback member expresses the types of rendering feedback the callback should apply when
drawing text. Rendering of the text to be drawn is specified either in generic ways (for example,
primary, secondary) or in specific ways (reverse, underline). When generic indications are given,
the client is free to choose the rendering style. It is necessary, howev er, that primary and sec-
ondary be mapped to two distinct rendering styles.
If an input method wants to control display of the preedit string, an input method can indicate the
visibility hints using feedbacks in a specific way. The XIMVisibleToForward,
XIMVisibleToBackward, and XIMVisibleCenter masks are exclusively used for these visibil-
ity hints. The XIMVisibleToForward mask indicates that the preedit text is preferably displayed
in the primary draw direction from the caret position in the preedit area forward. The XIMVisi-
bleToBackward
mask indicates that the preedit text is preferably displayed from the caret posi-
tion in the preedit area backward, relative to the primary draw direction. The XIMVisibleCenter
mask indicates that the preedit text is preferably displayed with the caret position in the preedit
area centered.
The insertion point of the preedit string could exist outside of the visible area when visibility hints
are used. Only one of the masks is valid for the entire preedit string, and only one character can
hold one of these feedbacks for a given input context at one time. This feedback may be OR'ed
together with another highlight (such as XIMReverse). Only the most recently set feedback is
valid, and any previous feedback is automatically canceled. This is a hint to the client, and the
client is free to choose how to display the preedit string.
The feedback member also specifies how rendering of the text argument should be performed. If
the feedback is NULL, the callback should apply the same feedback as is used for the
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surrounding characters in the preedit buffer; if chg_first is at a highlight boundary, the client can
choose which of the two highlights to use. If feedback is not NULL, feedback specifies an array
defining the rendering for each character of the string, and the length of the array is thus length.
If an input method wants to indicate that it is only updating the feedback of the preedit text with-
out changing the content of it, the XIMText structure will contain a NULL value for the string
field, the number of characters affected (relative to chg_first) will be in the length field, and the
feedback field will point to an array of XIMFeedback.
Each element in the feedback array is a bitmask represented by a value of type XIMFeedback.
The valid mask names are as follows:
typedef unsigned long XIMFeedback;
#define
XIMReverse
1L
#define
XIMUnderline
(1L<<1)
#define
XIMHighlight
(1L<<2)
#define
XIMPrimary
(1L<<5)
#define
XIMSecondary
(1L<<6)
#define
XIMTertiary
(1L<<7)
#define
XIMVisibleToForward
(1L<<8)
#define
XIMVisibleToBackward
(1L<<9)
#define
XIMVisibleCenter
(1L<<10)
Characters drawn with the XIMReverse highlight should be drawn by swapping the foreground
and background colors used to draw normal, unhighlighted characters. Characters drawn with the
XIMUnderline highlight should be underlined. Characters drawn with the XIMHighlight,
XIMPrimary, XIMSecondary, and XIMTertiary highlights should be drawn in some unique
manner that must be different from XIMReverse and XIMUnderline.
13.5.7.6. Preedit Caret Callback
An input method may have its own navigation keys to allow the user to move the text insertion
point in the preedit area (for example, to move backward or forward). Consequently, input
method needs to indicate to the client that it should move the text insertion point. It then calls the
PreeditCaretCallback.
void PreeditCaretCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XIMPreeditCaretCallbackStruct *call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Specifies the preedit caret information.
The input method will trigger PreeditCaretCallback to move the text insertion point during
preedit. The call_data argument contains a pointer to an XIMPreeditCaretCallbackStruct
structure, which indicates where the caret should be moved. The callback must move the
The values for XIMPrimary, XIMSecondary, and XIMTertiary were incorrectly defined in the R5 specification. The X Consor-
tium's X11R5 implementation correctly implemented the values for these highlights. The value of these highlights has been corrected in this
specification to agree with the values in the Consortium's X11R5 and X11R6 implementations.
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insertion point to its new location and return, in field position, the new offset value from the initial
position.
The XIMPreeditCaretCallbackStruct structure is defined as follows:
typedef struct _XIMPreeditCaretCallbackStruct {
int position;
/* Caret offset within preedit string */
XIMCaretDirection direction;
/* Caret moves direction */
XIMCaretStyle style;
/* Feedback of the caret */
} XIMPreeditCaretCallbackStruct;
The XIMCaretStyle structure is defined as follows:
typedef enum {
XIMIsInvisible, /* Disable caret feedback */
XIMIsPrimary,
/* UI defined caret feedback */
XIMIsSecondary,
/* UI defined caret feedback */
} XIMCaretStyle;
The XIMCaretDirection structure is defined as follows:
typedef enum {
XIMForwardChar, XIMBackwardChar,
XIMForwardWord, XIMBackwardWord,
XIMCaretUp, XIMCaretDown,
XIMNextLine, XIMPreviousLine,
XIMLineStart, XIMLineEnd,
XIMAbsolutePosition,
XIMDontChange,
} XIMCaretDirection;
These values are defined as follows:
XIMForwardChar
Move the caret forward one character position.
XIMBackwardChar
Move the caret backward one character position.
XIMForwardWord
Move the caret forward one word.
XIMBackwardWord
Move the caret backward one word.
XIMCaretUp
Move the caret up one line keeping the current horizontal offset.
XIMCaretDown
Move the caret down one line keeping the current horizontal offset.
XIMPreviousLine
Move the caret to the beginning of the previous line.
XIMNextLine
Move the caret to the beginning of the next line.
XIMLineStart
Move the caret to the beginning of the current display line that con-
tains the caret.
XIMLineEnd
Move the caret to the end of the current display line that contains the
caret.
XIMAbsolutePosition
The callback must move to the location specified by the position field
of the callback data, indicated in characters, starting from the begin-
ning of the preedit text. Hence, a value of zero means move back to
the beginning of the preedit text.
XIMDontChange
The caret position does not change.
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13.5.7.7. Status Callbacks
An input method may communicate changes in the status of an input context (for example, cre-
ated, destroyed, or focus changes) with three status callbacks: StatusStartCallback, Status-
DoneCallback, and StatusDrawCallback.
When the input context is created or gains focus, the input method calls the StatusStartCallback
callback.
void StatusStartCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
The callback should initialize appropriate data for displaying status and for responding to Status-
DrawCallback calls. Once StatusStartCallback is called, it will not be called again before Status-
DoneCallback has been called.
When an input context is destroyed or when it loses focus, the input method calls Status-
DoneCallback.
void StatusDoneCallback(ic, client_data, call_data)
XIC ic;
XPointer client_data;
XPointer call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Not used for this callback and always passed as NULL.
The callback may release any data allocated on StatusStart.
When an input context status has to be updated, the input method calls StatusDrawCallback.
void StatusDrawCallback (ic, client_data, call_data)
XIC ic;
XPointer client_data;
XIMStatusDrawCallbackStruct *call_data;
ic
Specifies the input context.
client_data
Specifies the additional client data.
call_data
Specifies the status drawing information.
The callback should update the status area by either drawing a string or imaging a bitmap in the
status area.
The XIMStatusDataType and XIMStatusDrawCallbackStruct structures are defined as fol-
lows:
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typedef enum {
XIMTextType,
XIMBitmapType,
} XIMStatusDataType;
typedef struct _XIMStatusDrawCallbackStruct {
XIMStatusDataType type;
union {
XIMText *text;
Pixmap bitmap;
} data;
} XIMStatusDrawCallbackStruct;
The feedback styles XIMVisibleToForward, XIMVisibleToBackward, and XIMVisibleTo-
Center
are not relevant and will not appear in the XIMFeedback element of the XIMText struc-
ture.
13.5.8. Event Filtering
Xlib provides the ability for an input method to register a filter internal to Xlib. This filter is
called by a client (or toolkit) by calling XFilterEvent after calling XNextEvent. Any client that
uses the XIM interface should call XFilterEvent to allow input methods to process their events
without knowledge of the client's dispatching mechanism. A client's user interface policy may
determine the priority of event filters with respect to other event-handling mechanisms (for exam-
ple, modal grabs).
Clients may not know how many filters there are, if any, and what they do. They may only know
if an event has been filtered on return of XFilterEvent. Clients should discard filtered events.
To filter an event, use XFilterEvent.
Bool XFilterEvent (event, w)
XEvent *event;
Window w;
event
Specifies the event to filter.
w
Specifies the window for which the filter is to be applied.
If the window argument is None, XFilterEvent applies the filter to the window specified in the
XEvent structure. The window argument is provided so that layers above Xlib that do event redi-
rection can indicate to which window an event has been redirected.
If XFilterEvent returns True, then some input method has filtered the event, and the client
should discard the event. If XFilterEvent returns False, then the client should continue process-
ing the event.
If a grab has occurred in the client and XFilterEvent returns True, the client should ungrab the
keyboard.
13.5.9. Getting Keyboard Input
To get composed input from an input method, use XmbLookupString or XwcLookupString.
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int XmbLookupString(ic, event, buffer_return, bytes_buffer, keysym_return, status_return)
XIC ic;
XKeyPressedEvent *event;
char *buffer_return;
int bytes_buffer;
Ke ySym *keysym_return;
Status *status_return;
int XwcLookupString(ic, event, buffer_return, bytes_buffer, keysym_return, status_return)
XIC ic;
XKeyPressedEvent *event;
wchar_t *buffer_return;
int wchars_buffer;
Ke ySym *keysym_return;
Status *status_return;
ic
Specifies the input context.
event
Specifies the key event to be used.
buffer_return
Returns a multibyte string or wide character string (if any) from the input
method.
bytes_buffer
wchars_buffer Specifies space available in the return buffer.
keysym_return Returns the KeySym computed from the event if this argument is not NULL.
status_return
Returns a value indicating what kind of data is returned.
The XmbLookupString and XwcLookupString functions return the string from the input
method specified in the buffer_return argument. If no string is returned, the buffer_return argu-
ment is unchanged.
The KeySym into which the KeyCode from the event was mapped is returned in the
keysym_return argument if it is non-NULL and the status_return argument indicates that a
Ke ySym was returned. If both a string and a KeySym are returned, the KeySym value does not
necessarily correspond to the string returned.
XmbLookupString returns the length of the string in bytes, and XwcLookupString returns the
length of the string in characters. Both XmbLookupString and XwcLookupString return text
in the encoding of the locale bound to the input method of the specified input context.
Each string returned by XmbLookupString and XwcLookupString begins in the initial state of
the encoding of the locale (if the encoding of the locale is state-dependent).
Note
To insure proper input processing, it is essential that the client pass only KeyPress
ev ents to XmbLookupString and XwcLookupString. Their behavior when a
client passes a KeyRelease ev ent is undefined.
Clients should check the status_return argument before using the other returned values. These
two functions both return a value to status_return that indicates what has been returned in the
other arguments. The possible values returned are:
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XBufferOverflow
The input string to be returned is too large for the supplied
buffer_return. The required size (XmbLookupString in bytes;
XwcLookupString in characters) is returned as the value of the func-
tion, and the contents of buffer_return and keysym_return are not
modified. The client should recall the function with the same event
and a buffer of adequate size to obtain the string.
XLookupNone
No consistent input has been composed so far. The contents of
buffer_return and keysym_return are not modified, and the function
returns zero.
XLookupChars
Some input characters have been composed. They are placed in the
buffer_return argument, and the string length is returned as the value
of the function. The string is encoded in the locale bound to the input
context. The content of the keysym_return argument is not modified.
XLookupKeySym
A KeySym has been returned instead of a string and is returned in
keysym_return. The content of the buffer_return argument is not
modified, and the function returns zero.
XLookupBoth
Both a KeySym and a string are returned; XLookupChars and
XLookupKeySym occur simultaneously.
It does not make any difference if the input context passed as an argument to XmbLookupString
and XwcLookupString is the one currently in possession of the focus or not. Input may have
been composed within an input context before it lost the focus, and that input may be returned on
subsequent calls to XmbLookupString or XwcLookupString ev en though it does not have any
more keyboard focus.
13.5.10. Input Method Conventions
The input method architecture is transparent to the client. However, clients should respect a num-
ber of conventions in order to work properly. Clients must also be aware of possible effects of
synchronization between input method and library in the case of a remote input server.
13.5.10.1. Client Conventions
A well-behaved client (or toolkit) should first query the input method style. If the client cannot
satisfy the requirements of the supported styles (in terms of geometry management or callbacks),
it should negotiate with the user continuation of the program or raise an exception or error of
some sort.
13.5.10.2. Synchronization Conventions
A KeyPress ev ent with a KeyCode of zero is used exclusively as a signal that an input method
has composed input that can be returned by XmbLookupString or XwcLookupString. No
other use is made of a KeyPress ev ent with KeyCode of zero.
Such an event may be generated by either a front-end or a back-end input method in an imple-
mentation-dependent manner. Some possible ways to generate this event include:

A synthetic event sent by an input method server

An artificial event created by a input method filter and pushed onto a client's event queue

A KeyPress ev ent whose KeyCode value is modified by an input method filter
When callback support is specified by the client, input methods will not take action unless they
explicitly called back the client and obtained no response (the callback is not specified or returned
invalid data).
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13.6. String Constants
The following symbols for string constants are defined in <X11/Xlib.h>. Although they are
shown here with particular macro definitions, they may be implemented as macros, as global
symbols, or as a mixture of the two. The string pointer value itself is not significant; clients must
not assume that inequality of two values implies inequality of the actual string data.
#define
XNVaNestedList
"XNVaNestedList"
#define
XNSeparatorofNestedList
"separatorofNestedList"
#define
XNQueryInputStyle
"queryInputStyle"
#define
XNClientWindow
"clientWindow"
#define
XNInputStyle
"inputStyle"
#define
XNFocusWindow
"focusWindow"
#define
XNResourceName
"resourceName"
#define
XNResourceClass
"resourceClass"
#define
XNGeometryCallback
"geometryCallback"
#define
XNDestroyCallback
"destroyCallback"
#define
XNFilterEvents
"filterEvents"
#define
XNPreeditStartCallback
"preeditStartCallback"
#define
XNPreeditDoneCallback
"preeditDoneCallback"
#define
XNPreeditDrawCallback
"preeditDrawCallback"
#define
XNPreeditCaretCallback
"preeditCaretCallback"
#define
XNPreeditStateNotifyCallback
"preeditStateNotifyCallback"
#define
XNPreeditAttributes
"preeditAttributes"
#define
XNStatusStartCallback
"statusStartCallback"
#define
XNStatusDoneCallback
"statusDoneCallback"
#define
XNStatusDrawCallback
"statusDrawCallback"
#define
XNStatusAttributes
"statusAttributes"
#define
XNArea
"area"
#define
XNAreaNeeded
"areaNeeded"
#define
XNSpotLocation
"spotLocation"
#define
XNColormap
"colorMap"
#define
XNStdColormap
"stdColorMap"
#define
XNForeground
"foreground"
#define
XNBackground
"background"
#define
XNBackgroundPixmap
"backgroundPixmap"
#define
XNFontSet
"fontSet"
#define
XNLineSpace
"lineSpace"
#define
XNCursor
"cursor"
#define
XNQueryIMValuesList
"queryIMValuesList"
#define
XNQueryICValuesList
"queryICValuesList"
#define
XNStringConversionCallback
"stringConversionCallback"
#define
XNStringConversion
"stringConversion"
#define
XNResetState
"resetState"
#define
XNHotKey
"hotkey"
#define
XNHotKeyState
"hotkeyState"
#define
XNPreeditState
"preeditState"
#define
XNVisiblePosition
"visiblePosition"
#define
XNR6PreeditCallbackBehavior
"r6PreeditCallback"
#define
XNRequiredCharSet
"requiredCharSet"
#define
XNQueryOrientation
"queryOrientation"
#define
XNDirectionalDependentDrawing
"directionalDependentDrawing"
#define
XNContextualDrawing
"contextualDrawing"
#define
XNBaseFontName
"baseFontName"
#define
XNMissingCharSet
"missingCharSet"
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#define
XNDefaultString
"defaultString"
#define
XNOrientation
"orientation"
#define
XNFontInfo
"fontInfo"
#define
XNOMAutomatic
"omAutomatic"
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Chapter 14
Inter-Client Communication Functions
The Inter-Client Communication Conventions Manual, hereafter referred to as the ICCCM,
details the X Consortium approved conventions that govern inter-client communications. These
conventions ensure peer-to-peer client cooperation in the use of selections, cut buffers, and shared
resources as well as client cooperation with window and session managers. For further informa-
tion, see the Inter-Client Communication Conventions Manual.
Xlib provides a number of standard properties and programming interfaces that are ICCCM com-
pliant. The predefined atoms for some of these properties are defined in the <X11/Xatom.h>
header file, where to avoid name conflicts with user symbols their #define name has an XA_ pre-
fix. For further information about atoms and properties, see section 4.3.
Xlib's selection and cut buffer mechanisms provide the primary programming interfaces by which
peer client applications communicate with each other (see sections 4.5 and 16.6). The functions
discussed in this chapter provide the primary programming interfaces by which client applications
communicate with their window and session managers as well as share standard colormaps.
The standard properties that are of special interest for communicating with window and session
managers are:
Name Type Format Description
WM_CLASS
STRING
8
Set by application programs to allow
window and session managers to
obtain the application's resources
from the resource database.
WM_CLIENT_MACHINE
TEXT
The string name of the machine on
which the client application is run-
ning.
WM_COLORMAP_WINDOWS
WINDOW
32
The list of window IDs that may
need a different colormap from that
of their top-level window.
WM_COMMAND
TEXT
The command and arguments, null-
separated, used to invoke the appli-
cation.
WM_HINTS
WM_HINTS
32
Additional hints set by the client for
use by the window manager. The C
type of this property is XWMHints.
WM_ICON_NAME
TEXT
The name to be used in an icon.
WM_ICON_SIZE
WM_ICON_SIZE
32
The window manager may set this
property on the root window to
specify the icon sizes it supports.
The C type of this property is
XIconSize.
WM_NAME
TEXT
The name of the application.
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Name Type Format Description
WM_NORMAL_HINTS
WM_SIZE_HINTS
32
Size hints for a window in its
normal state. The C type of this
property is XSizeHints.
WM_PROT OCOLS
AT OM
32
List of atoms that identify the com-
munications protocols between the
client and window manager in
which the client is willing to partici-
pate.
WM_STATE
WM_STATE
32
Intended for communication
between window and session man-
agers only.
WM_TRANSIENT_FOR
WINDOW
32
Set by application programs to indi-
cate to the window manager that a
transient top-level window, such as a
dialog box.
The remainder of this chapter discusses:

Client to window manager communication

Client to session manager communication

Standard colormaps
14.1. Client to Window Manager Communication
This section discusses how to:

Manipulate top-level windows

Convert string lists

Set and read text properties

Set and read the WM_NAME property

Set and read the WM_ICON_NAME property

Set and read the WM_HINTS property

Set and read the WM_NORMAL_HINTS property

Set and read the WM_CLASS property

Set and read the WM_TRANSIENT_FOR property

Set and read the WM_PROT OCOLS property

Set and read the WM_COLORMAP_WINDOWS property

Set and read the WM_ICON_SIZE property

Use window manager convenience functions
14.1.1. Manipulating Top-Level Windows
Xlib provides functions that you can use to change the visibility or size of top-level windows (that
is, those that were created as children of the root window). Note that the subwindows that you
create are ignored by window managers. Therefore, you should use the basic window functions
described in chapter 3 to manipulate your application's subwindows.
To request that a top-level window be iconified, use XIconifyWindow.
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Status XIconifyWindow(display, w, screen_number)
Display *display;
Window w;
int screen_number;
display
Specifies the connection to the X server.
w
Specifies the window.
screen_number Specifies the appropriate screen number on the host server.
The XIconifyWindow function sends a WM_CHANGE_STATE ClientMessage ev ent with a
format of 32 and a first data element of IconicState (as described in section 4.1.4 of the Inter-
Client Communication Conventions Manual
) and a window of w to the root window of the speci-
fied screen with an event mask set to SubstructureNotifyMask| SubstructureRedirectMask.
Window managers may elect to receive this message and if the window is in its normal state, may
treat it as a request to change the window's state from normal to iconic. If the
WM_CHANGE_STATE property cannot be interned, XIconifyWindow does not send a message
and returns a zero status. It returns a nonzero status if the client message is sent successfully; oth-
erwise, it returns a zero status.
To request that a top-level window be withdrawn, use XWithdrawWindow.
Status XWithdrawWindow(display, w, screen_number)
Display *display;
Window w;
int screen_number;
display
Specifies the connection to the X server.
w
Specifies the window.
screen_number Specifies the appropriate screen number on the host server.
The XWithdrawWindow function unmaps the specified window and sends a synthetic Unmap-
Notify
ev ent to the root window of the specified screen. Window managers may elect to receive
this message and may treat it as a request to change the window's state to withdrawn. When a
window is in the withdrawn state, neither its normal nor its iconic representations is visible. It
returns a nonzero status if the UnmapNotify ev ent is successfully sent; otherwise, it returns a
zero status.
XWithdrawWindow can generate a BadWindow error.
To request that a top-level window be reconfigured, use XReconfigureWMWindow.
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Status XReconfigureWMWindow(display, w, screen_number, value_mask, values)
Display *display;
Window w;
int screen_number;
unsigned int value_mask;
XWindowChanges *values;
display
Specifies the connection to the X server.
w
Specifies the window.
screen_number Specifies the appropriate screen number on the host server.
value_mask
Specifies which values are to be set using information in the values structure.
This mask is the bitwise inclusive OR of the valid configure window values bits.
values
Specifies the XWindowChanges structure.
The XReconfigureWMWindow function issues a ConfigureWindow request on the specified
top-level window. If the stacking mode is changed and the request fails with a BadMatch error,
the error is trapped by Xlib and a synthetic ConfigureRequestEvent containing the same config-
uration parameters is sent to the root of the specified window. Window managers may elect to
receive this event and treat it as a request to reconfigure the indicated window. It returns a
nonzero status if the request or event is successfully sent; otherwise, it returns a zero status.
XReconfigureWMWindow can generate BadValue and BadWindow errors.
14.1.2. Converting String Lists
Many of the text properties allow a variety of types and formats. Because the data stored in these
properties are not simple null-terminated strings, an XTextProperty structure is used to describe
the encoding, type, and length of the text as well as its value. The XTextProperty structure con-
tains:
typedef struct {
unsigned char *value; /* property data */
Atom encoding;
/* type of property */
int format;
/* 8, 16, or 32 */
unsigned long nitems;
/* number of items in value */
} XTe xtProperty;
Xlib provides functions to convert localized text to or from encodings that support the inter-client
communication conventions for text. In addition, functions are provided for converting between
lists of pointers to character strings and text properties in the STRING encoding.
The functions for localized text return a signed integer error status that encodes Success as zero,
specific error conditions as negative numbers, and partial conversion as a count of unconvertible
characters.
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#define
XNoMemory
-1
#define
XLocaleNotSupported
-2
#define
XConverterNotFound
-3
typedef enum {
XStringStyle, /* STRING */
XCompoundTextStyle, /* COMPOUND_TEXT */
XTextStyle, /* text in owner's encoding (current locale) */
XStdICCTextStyle /* STRING, else COMPOUND_TEXT */
} XICCEncodingStyle;
To convert a list of text strings to an XTextProperty structure, use XmbTextListToTextProp-
erty
or XwcTextListToTextProperty.
int XmbTextListToTextProperty (display, list, count, style, text_prop_return)
Display *display;
char **list;
int count;
XICCEncodingStyle style;
XTextProperty *text_prop_return;
int XwcTextListToTextProperty (display, list, count, style, text_prop_return)
Display *display;
wchar_t **list;
int count;
XICCEncodingStyle style;
XTextProperty *text_prop_return;
display
Specifies the connection to the X server.
list
Specifies a list of null-terminated character strings.
count
Specifies the number of strings specified.
style
Specifies the manner in which the property is encoded.
text_prop_returnReturns the XTextProperty structure.
The XmbTextListToTextProperty and XwcTextListToTextProperty functions set the specified
XTextProperty value to a set of null-separated elements representing the concatenation of the
specified list of null-terminated text strings. A final terminating null is stored at the end of the
value field of text_prop_return but is not included in the nitems member.
The functions set the encoding field of text_prop_return to an Atom for the specified display
naming the encoding determined by the specified style and convert the specified text list to this
encoding for storage in the text_prop_return value field. If the style XStringStyle or XCom-
poundTextStyle
is specified, this encoding is ``STRING'' or ``COMPOUND_TEXT'', respec-
tively. If the style XTextStyle is specified, this encoding is the encoding of the current locale. If
the style XStdICCTextStyle is specified, this encoding is ``STRING'' if the text is fully convert-
ible to STRING, else ``COMPOUND_TEXT''.
If insufficient memory is available for the new value string, the functions return XNoMemory. If
the current locale is not supported, the functions return XLocaleNotSupported. In both of these
error cases, the functions do not set text_prop_return.
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To determine if the functions are guaranteed not to return XLocaleNotSupported, use
XSupportsLocale.
If the supplied text is not fully convertible to the specified encoding, the functions return the num-
ber of unconvertible characters. Each unconvertible character is converted to an implementation-
defined and encoding-specific default string. Otherwise, the functions return Success. Note that
full convertibility to all styles except XStringStyle is guaranteed.
To free the storage for the value field, use XFree.
To obtain a list of text strings from an XTextProperty structure, use XmbTextPropertyTo-
TextList
or XwcTextPropertyToTextList.
int XmbTextPropertyToTextList (display, text_prop, list_return, count_return)
Display *display;
XTextProperty *text_prop;
char ***list_return;
int *count_return;
int XwcTextPropertyToTextList (display, text_prop, list_return, count_return)
Display *display;
XTextProperty *text_prop;
wchar_t ***list_return;
int *count_return;
display
Specifies the connection to the X server.
text_prop
Specifies the XTextProperty structure to be used.
list_return
Returns a list of null-terminated character strings.
count_return
Returns the number of strings.
The XmbTextPropertyToTextList and XwcTextPropertyToTextList functions return a list of
text strings in the current locale representing the null-separated elements of the specified
XTextProperty structure. The data in text_prop must be format 8.
Multiple elements of the property (for example, the strings in a disjoint text selection) are sepa-
rated by a null byte. The contents of the property are not required to be null-terminated; any ter-
minating null should not be included in text_prop.nitems.
If insufficient memory is available for the list and its elements, XmbTextPropertyToTextList
and XwcTextPropertyToTextList return XNoMemory. If the current locale is not supported,
the functions return XLocaleNotSupported. Otherwise, if the encoding field of text_prop is not
convertible to the encoding of the current locale, the functions return XConverterNotFound.
For supported locales, existence of a converter from COMPOUND_TEXT, STRING or the
encoding of the current locale is guaranteed if XSupportsLocale returns True for the current
locale (but the actual text may contain unconvertible characters). Conversion of other encodings
is implementation-dependent. In all of these error cases, the functions do not set any return val-
ues.
Otherwise, XmbTextPropertyToTextList and XwcTextPropertyToTextList return the list of
null-terminated text strings to list_return and the number of text strings to count_return.
If the value field of text_prop is not fully convertible to the encoding of the current locale, the
functions return the number of unconvertible characters. Each unconvertible character is con-
verted to a string in the current locale that is specific to the current locale. To obtain the value of
this string, use XDefaultString. Otherwise, XmbTextPropertyToTextList and XwcTextProp-
ertyToTextList
return Success.
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To free the storage for the list and its contents returned by XmbTextPropertyToTextList, use
XFreeStringList. To free the storage for the list and its contents returned by
XwcTextPropertyToTextList, use XwcFreeStringList.
To free the in-memory data associated with the specified wide character string list, use
XwcFreeStringList.
void XwcFreeStringList(list)
wchar_t **list;
list
Specifies the list of strings to be freed.
The XwcFreeStringList function frees memory allocated by XwcTextPropertyToTextList.
To obtain the default string for text conversion in the current locale, use XDefaultString.
char *XDefaultString ( )
The XDefaultString function returns the default string used by Xlib for text conversion (for
example, in XmbTextPropertyToTextList). The default string is the string in the current locale
that is output when an unconvertible character is found during text conversion. If the string
returned by XDefaultString is the empty string (""), no character is output in the converted text.
XDefaultString does not return NULL.
The string returned by XDefaultString is independent of the default string for text drawing; see
XCreateFontSet to obtain the default string for an XFontSet.
The behavior when an invalid codepoint is supplied to any Xlib function is undefined.
The returned string is null-terminated. It is owned by Xlib and should not be modified or freed by
the client. It may be freed after the current locale is changed. Until freed, it will not be modified
by Xlib.
To set the specified list of strings in the STRING encoding to a XTextProperty structure, use
XStringListToTextProperty.
Status XStringListToTextProperty (list, count, text_prop_return)
char **list;
int count;
XTextProperty *text_prop_return;
list
Specifies a list of null-terminated character strings.
count
Specifies the number of strings.
text_prop_returnReturns the XTextProperty structure.
The XStringListToTextProperty function sets the specified XTextProperty to be of type
STRING (format 8) with a value representing the concatenation of the specified list of null-sepa-
rated character strings. An extra null byte (which is not included in the nitems member) is stored
at the end of the value field of text_prop_return. The strings are assumed (without verification) to
be in the STRING encoding. If insufficient memory is available for the new value string,
XStringListToTextProperty does not set any fields in the XTextProperty structure and returns
a zero status. Otherwise, it returns a nonzero status. To free the storage for the value field, use
XFree.
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To obtain a list of strings from a specified XTextProperty structure in the STRING encoding,
use XTextPropertyToStringList.
Status XTextPropertyToStringList (text_prop, list_return, count_return)
XTextProperty *text_prop;
char ***list_return;
int *count_return;
text_prop
Specifies the XTextProperty structure to be used.
list_return
Returns a list of null-terminated character strings.
count_return
Returns the number of strings.
The XTextPropertyToStringList function returns a list of strings representing the null-separated
elements of the specified XTextProperty structure. The data in text_prop must be of type
STRING and format 8. Multiple elements of the property (for example, the strings in a disjoint
text selection) are separated by NULL (encoding 0). The contents of the property are not null-ter-
minated. If insufficient memory is available for the list and its elements, XTextProperty-
ToStringList
sets no return values and returns a zero status. Otherwise, it returns a nonzero sta-
tus. To free the storage for the list and its contents, use XFreeStringList.
To free the in-memory data associated with the specified string list, use XFreeStringList.
void XFreeStringList(list)
char **list;
list
Specifies the list of strings to be freed.
The XFreeStringList function releases memory allocated by XmbTextPropertyToTextList and
XTextPropertyToStringList and the missing charset list allocated by XCreateFontSet.
14.1.3. Setting and Reading Text Properties
Xlib provides two functions that you can use to set and read the text properties for a given win-
dow. You can use these functions to set and read those properties of type TEXT (WM_NAME,
WM_ICON_NAME, WM_COMMAND, and WM_CLIENT_MACHINE). In addition, Xlib pro-
vides separate convenience functions that you can use to set each of these properties. For further
information about these convenience functions, see sections 14.1.4, 14.1.5, 14.2.1, and 14.2.2,
respectively.
To set one of a window's text properties, use XSetTextProperty.
void XSetTextProperty (display, w, text_prop, property)
Display *display;
Window w;
XTextProperty *text_prop;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop
Specifies the XTextProperty structure to be used.
property
Specifies the property name.
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The XSetTextProperty function replaces the existing specified property for the named window
with the data, type, format, and number of items determined by the value field, the encoding field,
the format field, and the nitems field, respectively, of the specified XTextProperty structure. If
the property does not already exist, XSetTextProperty sets it for the specified window.
XSetTextProperty can generate BadAlloc, BadAtom, BadValue, and BadWindow errors.
To read one of a window's text properties, use XGetTextProperty.
Status XGetTextProperty (display, w, text_prop_return, property)
Display *display;
Window w;
XTextProperty *text_prop_return;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop_returnReturns the XTextProperty structure.
property
Specifies the property name.
The XGetTextProperty function reads the specified property from the window and stores the
data in the returned XTextProperty structure. It stores the data in the value field, the type of the
data in the encoding field, the format of the data in the format field, and the number of items of
data in the nitems field. An extra byte containing null (which is not included in the nitems mem-
ber) is stored at the end of the value field of text_prop_return. The particular interpretation of the
property's encoding and data as text is left to the calling application. If the specified property
does not exist on the window, XGetTextProperty sets the value field to NULL, the encoding
field to None, the format field to zero, and the nitems field to zero.
If it was able to read and store the data in the XTextProperty structure, XGetTextProperty
returns a nonzero status; otherwise, it returns a zero status.
XGetTextProperty can generate BadAtom and BadWindow errors.
14.1.4. Setting and Reading the WM_NAME Property
Xlib provides convenience functions that you can use to set and read the WM_NAME property
for a given window.
To set a window's WM_NAME property with the supplied convenience function, use
XSetWMName.
void XSetWMName(display, w, text_prop)
Display *display;
Window w;
XTextProperty *text_prop;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop
Specifies the XTextProperty structure to be used.
The XSetWMName convenience function calls XSetTextProperty to set the WM_NAME prop-
erty.
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To read a window's WM_NAME property with the supplied convenience function, use
XGetWMName.
Status XGetWMName(display, w, text_prop_return)
Display *display;
Window w;
XTextProperty *text_prop_return;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop_returnReturns the XTextProperty structure.
The XGetWMName convenience function calls XGetTextProperty to obtain the WM_NAME
property. It returns a nonzero status on success; otherwise, it returns a zero status.
The following two functions have been superseded by XSetWMName and XGetWMName,
respectively. You can use these additional convenience functions for window names that are
encoded as STRING properties.
To assign a name to a window, use XStoreName.
XStoreName (display, w, window_name)
Display *display;
Window w;
char *window_name;
display
Specifies the connection to the X server.
w
Specifies the window.
window_name Specifies the window name, which should be a null-terminated string.
The XStoreName function assigns the name passed to window_name to the specified window.
A window manager can display the window name in some prominent place, such as the title bar,
to allow users to identify windows easily. Some window managers may display a window's name
in the window's icon, although they are encouraged to use the window's icon name if one is pro-
vided by the application. If the string is not in the Host Portable Character Encoding, the result is
implementation-dependent.
XStoreName can generate BadAlloc and BadWindow errors.
To get the name of a window, use XFetchName.
Status XFetchName(display, w, window_name_return)
Display *display;
Window w;
char **window_name_return;
display
Specifies the connection to the X server.
w
Specifies the window.
window_name_return
Returns the window name, which is a null-terminated string.
The XFetchName function returns the name of the specified window. If it succeeds, it returns a
nonzero status; otherwise, no name has been set for the window, and it returns zero. If the
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WM_NAME property has not been set for this window, XFetchName sets window_name_return
to NULL. If the data returned by the server is in the Latin Portable Character Encoding, then the
returned string is in the Host Portable Character Encoding. Otherwise, the result is implementa-
tion-dependent. When finished with it, a client must free the window name string using XFree.
XFetchName can generate a BadWindow error.
14.1.5. Setting and Reading the WM_ICON_NAME Property
Xlib provides convenience functions that you can use to set and read the WM_ICON_NAME
property for a given window.
To set a window's WM_ICON_NAME property, use XSetWMIconName.
void XSetWMIconName(display, w, text_prop)
Display *display;
Window w;
XTextProperty *text_prop;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop
Specifies the XTextProperty structure to be used.
The XSetWMIconName convenience function calls XSetTextProperty to set the
WM_ICON_NAME property.
To read a window's WM_ICON_NAME property, use XGetWMIconName.
Status XGetWMIconName(display, w, text_prop_return)
Display *display;
Window w;
XTextProperty *text_prop_return;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop_returnReturns the XTextProperty structure.
The XGetWMIconName convenience function calls XGetTextProperty to obtain the
WM_ICON_NAME property. It returns a nonzero status on success; otherwise, it returns a zero
status.
The next two functions have been superseded by XSetWMIconName and XGetWMIconName,
respectively. You can use these additional convenience functions for window names that are
encoded as STRING properties.
To set the name to be displayed in a window's icon, use XSetIconName.
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XSetIconName (display, w, icon_name)
Display *display;
Window w;
char *icon_name;
display
Specifies the connection to the X server.
w
Specifies the window.
icon_name
Specifies the icon name, which should be a null-terminated string.
If the string is not in the Host Portable Character Encoding, the result is implementation-depen-
dent. XSetIconName can generate BadAlloc and BadWindow errors.
To get the name a window wants displayed in its icon, use XGetIconName.
Status XGetIconName(display, w, icon_name_return)
Display *display;
Window w;
char **icon_name_return;
display
Specifies the connection to the X server.
w
Specifies the window.
icon_name_return
Returns the window's icon name, which is a null-terminated string.
The XGetIconName function returns the name to be displayed in the specified window's icon. If
it succeeds, it returns a nonzero status; otherwise, if no icon name has been set for the window, it
returns zero. If you never assigned a name to the window, XGetIconName sets
icon_name_return to NULL. If the data returned by the server is in the Latin Portable Character
Encoding, then the returned string is in the Host Portable Character Encoding. Otherwise, the
result is implementation-dependent. When finished with it, a client must free the icon name
string using XFree.
XGetIconName can generate a BadWindow error.
14.1.6. Setting and Reading the WM_HINTS Property
Xlib provides functions that you can use to set and read the WM_HINTS property for a given
window. These functions use the flags and the XWMHints structure, as defined in the
<X11/Xutil.h> header file.
To allocate an XWMHints structure, use XAllocWMHints.
XWMHints *XAllocWMHints( )
The XAllocWMHints function allocates and returns a pointer to an XWMHints structure. Note
that all fields in the XWMHints structure are initially set to zero. If insufficient memory is avail-
able, XAllocWMHints returns NULL. To free the memory allocated to this structure, use
XFree.
The XWMHints structure contains:
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/* Window manager hints mask bits */
#define
InputHint
(1L << 0)
#define
StateHint
(1L << 1)
#define
IconPixmapHint
(1L << 2)
#define
IconWindowHint
(1L << 3)
#define
IconPositionHint
(1L << 4)
#define
IconMaskHint
(1L << 5)
#define
WindowGroupHint
(1L << 6)
#define
UrgencyHint
(1L << 8)
#define
AllHints
(InputHint|StateHint|IconPixmapHint|
IconWindowHint|IconPositionHint|
IconMaskHint|WindowGroupHint)
/* Values */
typedef struct {
long flags;
/* marks which fields in this structure are defined */
Bool input;
/* does this application rely on the window manager to
get keyboard input? */
int initial_state;
/* see below */
Pixmap icon_pixmap;
/* pixmap to be used as icon */
Window icon_window; /* window to be used as icon */
int icon_x, icon_y;
/* initial position of icon */
Pixmap icon_mask;
/* pixmap to be used as mask for icon_pixmap */
XID window_group; /* id of related window group */
/* this structure may be extended in the future */
} XWMHints;
The input member is used to communicate to the window manager the input focus model used by
the application. Applications that expect input but never explicitly set focus to any of their sub-
windows (that is, use the push model of focus management), such as X Version 10 style applica-
tions that use real-estate driven focus, should set this member to True. Similarly, applications
that set input focus to their subwindows only when it is given to their top-level window by a win-
dow manager should also set this member to True. Applications that manage their own input
focus by explicitly setting focus to one of their subwindows whenever they want keyboard input
(that is, use the pull model of focus management) should set this member to False. Applications
that never expect any keyboard input also should set this member to False.
Pull model window managers should make it possible for push model applications to get input by
setting input focus to the top-level windows of applications whose input member is True. Push
model window managers should make sure that pull model applications do not break them by
resetting input focus to PointerRoot when it is appropriate (for example, whenever an applica-
tion whose input member is False sets input focus to one of its subwindows).
The definitions for the initial_state flag are:
#define
WithdrawnState
0
#define
NormalState
1
/* most applications start this way */
#define
IconicState
3
/* application wants to start as an icon */
The icon_mask specifies which pixels of the icon_pixmap should be used as the icon. This allows
for nonrectangular icons. Both icon_pixmap and icon_mask must be bitmaps. The icon_window
lets an application provide a window for use as an icon for window managers that support such
use. The window_group lets you specify that this window belongs to a group of other windows.
For example, if a single application manipulates multiple top-level windows, this allows you to
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provide enough information that a window manager can iconify all of the windows rather than
just the one window.
The UrgencyHint flag, if set in the flags field, indicates that the client deems the window con-
tents to be urgent, requiring the timely response of the user. The window manager will make
some effort to draw the user's attention to this window while this flag is set. The client must pro-
vide some means by which the user can cause the urgency flag to be cleared (either mitigating the
condition that made the window urgent or merely shutting off the alarm) or the window to be
withdrawn.
To set a window's WM_HINTS property, use XSetWMHints.
XSetWMHints (display, w, wmhints)
Display *display;
Window w;
XWMHints *wmhints;
display
Specifies the connection to the X server.
w
Specifies the window.
wmhints
Specifies the XWMHints structure to be used.
The XSetWMHints function sets the window manager hints that include icon information and
location, the initial state of the window, and whether the application relies on the window man-
ager to get keyboard input.
XSetWMHints can generate BadAlloc and BadWindow errors.
To read a window's WM_HINTS property, use XGetWMHints.
XWMHints *XGetWMHints(display, w)
Display *display;
Window w;
display
Specifies the connection to the X server.
w
Specifies the window.
The XGetWMHints function reads the window manager hints and returns NULL if no
WM_HINTS property was set on the window or returns a pointer to an XWMHints structure if it
succeeds. When finished with the data, free the space used for it by calling XFree.
XGetWMHints can generate a BadWindow error.
14.1.7. Setting and Reading the WM_NORMAL_HINTS Property
Xlib provides functions that you can use to set or read the WM_NORMAL_HINTS property for a
given window. The functions use the flags and the XSizeHints structure, as defined in the
<X11/Xutil.h> header file.
The size of the XSizeHints structure may grow in future releases, as new components are added
to support new ICCCM features. Passing statically allocated instances of this structure into Xlib
may result in memory corruption when running against a future release of the library. As such, it
is recommended that only dynamically allocated instances of the structure be used.
To allocate an XSizeHints structure, use XAllocSizeHints.
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XSizeHints *XAllocSizeHints( )
The XAllocSizeHints function allocates and returns a pointer to an XSizeHints structure. Note
that all fields in the XSizeHints structure are initially set to zero. If insufficient memory is avail-
able, XAllocSizeHints returns NULL. To free the memory allocated to this structure, use
XFree.
The XSizeHints structure contains:
/* Size hints mask bits */
#define
USPosition
(1L << 0)
/* user specified x, y */
#define
USSize
(1L << 1)
/* user specified width, height */
#define
PPosition
(1L << 2)
/* program specified position */
#define
PSize
(1L << 3)
/* program specified size */
#define
PMinSize
(1L << 4)
/* program specified minimum size */
#define
PMaxSize
(1L << 5)
/* program specified maximum size */
#define
PResizeInc
(1L << 6)
/* program specified resize increments */
#define
PAspect
(1L << 7)
/* program specified min and max aspect ratios */
#define
PBaseSize
(1L << 8)
#define
PWinGravity
(1L << 9)
#define
PAllHints
(PPosition|PSize|
PMinSize|PMaxSize|
PResizeInc|PAspect)
/* Values */
typedef struct {
long flags;
/* marks which fields in this structure are defined */
int x, y;
/* Obsolete */
int width, height;
/* Obsolete */
int min_width, min_height;
int max_width, max_height;
int width_inc, height_inc;
struct {
int x;
/* numerator */
int y;
/* denominator */
} min_aspect, max_aspect;
int base_width, base_height;
int win_gravity;
/* this structure may be extended in the future */
} XSizeHints;
The x, y, width, and height members are now obsolete and are left solely for compatibility rea-
sons. The min_width and min_height members specify the minimum window size that still
allows the application to be useful. The max_width and max_height members specify the maxi-
mum window size. The width_inc and height_inc members define an arithmetic progression of
sizes (minimum to maximum) into which the window prefers to be resized. The min_aspect and
max_aspect members are expressed as ratios of x and y, and they allow an application to specify
the range of aspect ratios it prefers. The base_width and base_height members define the desired
size of the window. The window manager will interpret the position of the window and its border
width to position the point of the outer rectangle of the overall window specified by the win_grav-
ity member. The outer rectangle of the window includes any borders or decorations supplied by
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the window manager. In other words, if the window manager decides to place the window where
the client asked, the position on the parent window's border named by the win_gravity will be
placed where the client window would have been placed in the absence of a window manager.
Note that use of the PAllHints macro is highly discouraged.
To set a window's WM_NORMAL_HINTS property, use XSetWMNormalHints.
void XSetWMNormalHints(display, w, hints)
Display *display;
Window w;
XSizeHints *hints;
display
Specifies the connection to the X server.
w
Specifies the window.
hints
Specifies the size hints for the window in its normal state.
The XSetWMNormalHints function replaces the size hints for the WM_NORMAL_HINTS
property on the specified window. If the property does not already exist, XSetWMNormalHints
sets the size hints for the WM_NORMAL_HINTS property on the specified window. The prop-
erty is stored with a type of WM_SIZE_HINTS and a format of 32.
XSetWMNormalHints can generate BadAlloc and BadWindow errors.
To read a window's WM_NORMAL_HINTS property, use XGetWMNormalHints.
Status XGetWMNormalHints(display, w, hints_return, supplied_return)
Display *display;
Window w;
XSizeHints *hints_return;
long *supplied_return;
display
Specifies the connection to the X server.
w
Specifies the window.
hints_return
Returns the size hints for the window in its normal state.
supplied_return Returns the hints that were supplied by the user.
The XGetWMNormalHints function returns the size hints stored in the
WM_NORMAL_HINTS property on the specified window. If the property is of type
WM_SIZE_HINTS, is of format 32, and is long enough to contain either an old (pre-ICCCM) or
new size hints structure, XGetWMNormalHints sets the various fields of the XSizeHints struc-
ture, sets the supplied_return argument to the list of fields that were supplied by the user (whether
or not they contained defined values), and returns a nonzero status. Otherwise, it returns a zero
status.
If XGetWMNormalHints returns successfully and a pre-ICCCM size hints property is read, the
supplied_return argument will contain the following bits:
(USPosition|USSize|PPosition|PSize|PMinSize|
PMaxSize|PResizeInc|PAspect)
If the property is large enough to contain the base size and window gravity fields as well, the sup-
plied_return argument will also contain the following bits:
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PBaseSize|PWinGravity
XGetWMNormalHints can generate a BadWindow error.
To set a window's WM_SIZE_HINTS property, use XSetWMSizeHints.
void XSetWMSizeHints(display, w, hints, property)
Display *display;
Window w;
XSizeHints *hints;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
hints
Specifies the XSizeHints structure to be used.
property
Specifies the property name.
The XSetWMSizeHints function replaces the size hints for the specified property on the named
window. If the specified property does not already exist, XSetWMSizeHints sets the size hints
for the specified property on the named window. The property is stored with a type of
WM_SIZE_HINTS and a format of 32. To set a window's normal size hints, you can use the
XSetWMNormalHints function.
XSetWMSizeHints can generate BadAlloc, BadAtom, and BadWindow errors.
To read a window's WM_SIZE_HINTS property, use XGetWMSizeHints.
Status XGetWMSizeHints(display, w, hints_return, supplied_return, property)
Display *display;
Window w;
XSizeHints *hints_return;
long *supplied_return;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
hints_return
Returns the XSizeHints structure.
supplied_return Returns the hints that were supplied by the user.
property
Specifies the property name.
The XGetWMSizeHints function returns the size hints stored in the specified property on the
named window. If the property is of type WM_SIZE_HINTS, is of format 32, and is long enough
to contain either an old (pre-ICCCM) or new size hints structure, XGetWMSizeHints sets the
various fields of the XSizeHints structure, sets the supplied_return argument to the list of fields
that were supplied by the user (whether or not they contained defined values), and returns a
nonzero status. Otherwise, it returns a zero status. To get a window's normal size hints, you can
use the XGetWMNormalHints function.
If XGetWMSizeHints returns successfully and a pre-ICCCM size hints property is read, the sup-
plied_return argument will contain the following bits:
(USPosition|USSize|PPosition|PSize|PMinSize|
PMaxSize|PResizeInc|PAspect)
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If the property is large enough to contain the base size and window gravity fields as well, the sup-
plied_return argument will also contain the following bits:
PBaseSize|PWinGravity
XGetWMSizeHints can generate BadAtom and BadWindow errors.
14.1.8. Setting and Reading the WM_CLASS Property
Xlib provides functions that you can use to set and get the WM_CLASS property for a given win-
dow. These functions use the XClassHint structure, which is defined in the <X11/Xutil.h>
header file.
To allocate an XClassHint structure, use XAllocClassHint.
XClassHint *XAllocClassHint( )
The XAllocClassHint function allocates and returns a pointer to an XClassHint structure. Note
that the pointer fields in the XClassHint structure are initially set to NULL. If insufficient mem-
ory is available, XAllocClassHint returns NULL. To free the memory allocated to this structure,
use XFree.
The XClassHint contains:
typedef struct {
char *res_name;
char *res_class;
} XClassHint;
The res_name member contains the application name, and the res_class member contains the
application class. Note that the name set in this property may differ from the name set as
WM_NAME. That is, WM_NAME specifies what should be displayed in the title bar and, there-
fore, can contain temporal information (for example, the name of a file currently in an editor's
buffer). On the other hand, the name specified as part of WM_CLASS is the formal name of the
application that should be used when retrieving the application's resources from the resource
database.
To set a window's WM_CLASS property, use XSetClassHint.
XSetClassHint (display, w, class_hints)
Display *display;
Window w;
XClassHint *class_hints;
display
Specifies the connection to the X server.
w
Specifies the window.
class_hints
Specifies the XClassHint structure that is to be used.
The XSetClassHint function sets the class hint for the specified window. If the strings are not in
the Host Portable Character Encoding, the result is implementation-dependent.
XSetClassHint can generate BadAlloc and BadWindow errors.
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To read a window's WM_CLASS property, use XGetClassHint.
Status XGetClassHint(display, w, class_hints_return)
Display *display;
Window w;
XClassHint *class_hints_return;
display
Specifies the connection to the X server.
w
Specifies the window.
class_hints_return
Returns the XClassHint structure.
The XGetClassHint function returns the class hint of the specified window to the members of
the supplied structure. If the data returned by the server is in the Latin Portable Character Encod-
ing, then the returned strings are in the Host Portable Character Encoding. Otherwise, the result
is implementation-dependent. It returns a nonzero status on success; otherwise, it returns a zero
status. To free res_name and res_class when finished with the strings, use XFree on each indi-
vidually.
XGetClassHint can generate a BadWindow error.
14.1.9. Setting and Reading the WM_TRANSIENT_FOR Property
Xlib provides functions that you can use to set and read the WM_TRANSIENT_FOR property
for a given window.
To set a window's WM_TRANSIENT_FOR property, use XSetTransientForHint.
XSetTransientForHint (display, w, prop_window)
Display *display;
Window w;
Window prop_window;
display
Specifies the connection to the X server.
w
Specifies the window.
prop_window
Specifies the window that the WM_TRANSIENT_FOR property is to be set to.
The XSetTransientForHint function sets the WM_TRANSIENT_FOR property of the specified
window to the specified prop_window.
XSetTransientForHint can generate BadAlloc and BadWindow errors.
To read a window's WM_TRANSIENT_FOR property, use XGetTransientForHint.
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Status XGetTransientForHint (display, w, prop_window_return)
Display *display;
Window w;
Window *prop_window_return;
display
Specifies the connection to the X server.
w
Specifies the window.
prop_window_return
Returns the WM_TRANSIENT_FOR property of the specified window.
The XGetTransientForHint function returns the WM_TRANSIENT_FOR property for the
specified window. It returns a nonzero status on success; otherwise, it returns a zero status.
XGetTransientForHint can generate a BadWindow error.
14.1.10. Setting and Reading the WM_PROT OCOLS Property
Xlib provides functions that you can use to set and read the WM_PROT OCOLS property for a
given window.
To set a window's WM_PROT OCOLS property, use XSetWMProtocols.
Status XSetWMProtocols(display, w, protocols, count)
Display *display;
Window w;
Atom *protocols;
int count;
display
Specifies the connection to the X server.
w
Specifies the window.
protocols
Specifies the list of protocols.
count
Specifies the number of protocols in the list.
The XSetWMProtocols function replaces the WM_PROT OCOLS property on the specified win-
dow with the list of atoms specified by the protocols argument. If the property does not already
exist, XSetWMProtocols sets the WM_PROT OCOLS property on the specified window to the
list of atoms specified by the protocols argument. The property is stored with a type of ATOM
and a format of 32. If it cannot intern the WM_PROT OCOLS atom, XSetWMProtocols returns
a zero status. Otherwise, it returns a nonzero status.
XSetWMProtocols can generate BadAlloc and BadWindow errors.
To read a window's WM_PROT OCOLS property, use XGetWMProtocols.
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Status XGetWMProtocols(display, w, protocols_return, count_return)
Display *display;
Window w;
Atom **protocols_return;
int *count_return;
display
Specifies the connection to the X server.
w
Specifies the window.
protocols_returnReturns the list of protocols.
count_return
Returns the number of protocols in the list.
The XGetWMProtocols function returns the list of atoms stored in the WM_PROT OCOLS
property on the specified window. These atoms describe window manager protocols in which the
owner of this window is willing to participate. If the property exists, is of type ATOM, is of for-
mat 32, and the atom WM_PROT OCOLS can be interned, XGetWMProtocols sets the proto-
cols_return argument to a list of atoms, sets the count_return argument to the number of elements
in the list, and returns a nonzero status. Otherwise, it sets neither of the return arguments and
returns a zero status. To release the list of atoms, use XFree.
XGetWMProtocols can generate a BadWindow error.
14.1.11. Setting and Reading the WM_COLORMAP_WINDOWS Property
Xlib provides functions that you can use to set and read the WM_COLORMAP_WINDOWS
property for a given window.
To set a window's WM_COLORMAP_WINDOWS property, use XSetWMColormapWindows.
Status XSetWMColormapWindows (display, w, colormap_windows, count)
Display *display;
Window w;
Window *colormap_windows;
int count;
display
Specifies the connection to the X server.
w
Specifies the window.
colormap_windows
Specifies the list of windows.
count
Specifies the number of windows in the list.
The XSetWMColormapWindows function replaces the WM_COLORMAP_WINDOWS prop-
erty on the specified window with the list of windows specified by the colormap_windows argu-
ment. If the property does not already exist, XSetWMColormapWindows sets the WM_COL-
ORMAP_WINDOWS property on the specified window to the list of windows specified by the
colormap_windows argument. The property is stored with a type of WINDOW and a format of
32. If it cannot intern the WM_COLORMAP_WINDOWS atom, XSetWMColormapWindows
returns a zero status. Otherwise, it returns a nonzero status.
XSetWMColormapWindows can generate BadAlloc and BadWindow errors.
To read a window's WM_COLORMAP_WINDOWS property, use
XGetWMColormapWindows.
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Status XGetWMColormapWindows (display, w, colormap_windows_return, count_return)
Display *display;
Window w;
Window **colormap_windows_return;
int *count_return;
display
Specifies the connection to the X server.
w
Specifies the window.
colormap_windows_return
Returns the list of windows.
count_return
Returns the number of windows in the list.
The XGetWMColormapWindows function returns the list of window identifiers stored in the
WM_COLORMAP_WINDOWS property on the specified window. These identifiers indicate the
colormaps that the window manager may need to install for this window. If the property exists, is
of type WINDOW, is of format 32, and the atom WM_COLORMAP_WINDOWS can be
interned, XGetWMColormapWindows sets the windows_return argument to a list of window
identifiers, sets the count_return argument to the number of elements in the list, and returns a
nonzero status. Otherwise, it sets neither of the return arguments and returns a zero status. To
release the list of window identifiers, use XFree.
XGetWMColormapWindows can generate a BadWindow error.
14.1.12. Setting and Reading the WM_ICON_SIZE Property
Xlib provides functions that you can use to set and read the WM_ICON_SIZE property for a
given window. These functions use the XIconSize structure, which is defined in the
<X11/Xutil.h> header file.
To allocate an XIconSize structure, use XAllocIconSize.
XIconSize *XAllocIconSize( )
The XAllocIconSize function allocates and returns a pointer to an XIconSize structure. Note
that all fields in the XIconSize structure are initially set to zero. If insufficient memory is avail-
able, XAllocIconSize returns NULL. To free the memory allocated to this structure, use XFree.
The XIconSize structure contains:
typedef struct {
int min_width, min_height;
int max_width, max_height;
int width_inc, height_inc;
} XIconSize;
The width_inc and height_inc members define an arithmetic progression of sizes (minimum to
maximum) that represent the supported icon sizes.
To set a window's WM_ICON_SIZE property, use XSetIconSizes.
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XSetIconSizes (display, w, size_list, count)
Display *display;
Window w;
XIconSize *size_list;
int count;
display
Specifies the connection to the X server.
w
Specifies the window.
size_list
Specifies the size list.
count
Specifies the number of items in the size list.
The XSetIconSizes function is used only by window managers to set the supported icon sizes.
XSetIconSizes can generate BadAlloc and BadWindow errors.
To read a window's WM_ICON_SIZE property, use XGetIconSizes.
Status XGetIconSizes(display, w, size_list_return, count_return)
Display *display;
Window w;
XIconSize **size_list_return;
int *count_return;
display
Specifies the connection to the X server.
w
Specifies the window.
size_list_return Returns the size list.
count_return
Returns the number of items in the size list.
The XGetIconSizes function returns zero if a window manager has not set icon sizes; otherwise,
it returns nonzero. XGetIconSizes should be called by an application that wants to find out what
icon sizes would be most appreciated by the window manager under which the application is run-
ning. The application should then use XSetWMHints to supply the window manager with an
icon pixmap or window in one of the supported sizes. To free the data allocated in
size_list_return, use XFree.
XGetIconSizes can generate a BadWindow error.
14.1.13. Using Window Manager Convenience Functions
The XmbSetWMProperties function stores the standard set of window manager properties, with
text properties in standard encodings for internationalized text communication. The standard
window manager properties for a given window are WM_NAME, WM_ICON_NAME,
WM_HINTS, WM_NORMAL_HINTS, WM_CLASS, WM_COMMAND,
WM_CLIENT_MACHINE, and WM_LOCALE_NAME.
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void XmbSetWMProperties(display, w, window_name, icon_name, argv, argc,
normal_hints, wm_hints, class_hints)
Display *display;
Window w;
char *window_name;
char *icon_name;
char *argv[];
int argc;
XSizeHints *normal_hints;
XWMHints *wm_hints;
XClassHint *class_hints;
display
Specifies the connection to the X server.
w
Specifies the window.
window_name Specifies the window name, which should be a null-terminated string.
icon_name
Specifies the icon name, which should be a null-terminated string.
argv
Specifies the application's argument list.
argc
Specifies the number of arguments.
hints
Specifies the size hints for the window in its normal state.
wm_hints
Specifies the XWMHints structure to be used.
class_hints
Specifies the XClassHint structure to be used.
The XmbSetWMProperties convenience function provides a simple programming interface for
setting those essential window properties that are used for communicating with other clients (par-
ticularly window and session managers).
If the window_name argument is non-NULL, XmbSetWMProperties sets the WM_NAME
property. If the icon_name argument is non-NULL, XmbSetWMProperties sets the
WM_ICON_NAME property. The window_name and icon_name arguments are null-terminated
strings in the encoding of the current locale. If the arguments can be fully converted to the
STRING encoding, the properties are created with type ``STRING''; otherwise, the arguments are
converted to Compound Text, and the properties are created with type ``COMPOUND_TEXT''.
If the normal_hints argument is non-NULL, XmbSetWMProperties calls
XSetWMNormalHints, which sets the WM_NORMAL_HINTS property (see section 14.1.7).
If the wm_hints argument is non-NULL, XmbSetWMProperties calls XSetWMHints, which
sets the WM_HINTS property (see section 14.1.6).
If the argv argument is non-NULL, XmbSetWMProperties sets the WM_COMMAND property
from argv and argc. An argc of zero indicates a zero-length command.
The hostname of the machine is stored using XSetWMClientMachine (see section 14.2.2).
If the class_hints argument is non-NULL, XmbSetWMProperties sets the WM_CLASS prop-
erty. If the res_name member in the XClassHint structure is set to the NULL pointer and the
RESOURCE_NAME environment variable is set, the value of the environment variable is substi-
tuted for res_name. If the res_name member is NULL, the environment variable is not set, and
argv and argv[0] are set, then the value of argv[0], stripped of any directory prefixes, is substi-
tuted for res_name.
It is assumed that the supplied class_hints.res_name and argv, the RESOURCE_NAME environ-
ment variable, and the hostname of the machine are in the encoding of the locale announced for
the LC_CTYPE category (on POSIX-compliant systems, the LC_CTYPE, else LANG environ-
ment variable). The corresponding WM_CLASS, WM_COMMAND, and
WM_CLIENT_MACHINE properties are typed according to the local host locale announcer. No
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encoding conversion is performed prior to storage in the properties.
For clients that need to process the property text in a locale, XmbSetWMProperties sets the
WM_LOCALE_NAME property to be the name of the current locale. The name is assumed to be
in the Host Portable Character Encoding and is converted to STRING for storage in the property.
XmbSetWMProperties can generate BadAlloc and BadWindow errors.
To set a window's standard window manager properties with strings in client-specified encodings,
use XSetWMProperties. The standard window manager properties for a given window are
WM_NAME, WM_ICON_NAME, WM_HINTS, WM_NORMAL_HINTS, WM_CLASS,
WM_COMMAND, and WM_CLIENT_MACHINE.
void XSetWMProperties(display, w, window_name, icon_name, argv, argc, normal_hints, wm_hints, class_hints)
Display *display;
Window w;
XTextProperty *window_name;
XTextProperty *icon_name;
char **argv;
int argc;
XSizeHints *normal_hints;
XWMHints *wm_hints;
XClassHint *class_hints;
display
Specifies the connection to the X server.
w
Specifies the window.
window_name Specifies the window name, which should be a null-terminated string.
icon_name
Specifies the icon name, which should be a null-terminated string.
argv
Specifies the application's argument list.
argc
Specifies the number of arguments.
normal_hints
Specifies the size hints for the window in its normal state.
wm_hints
Specifies the XWMHints structure to be used.
class_hints
Specifies the XClassHint structure to be used.
The XSetWMProperties convenience function provides a single programming interface for set-
ting those essential window properties that are used for communicating with other clients (partic-
ularly window and session managers).
If the window_name argument is non-NULL, XSetWMProperties calls XSetWMName, which,
in turn, sets the WM_NAME property (see section 14.1.4). If the icon_name argument is non-
NULL, XSetWMProperties calls XSetWMIconName, which sets the WM_ICON_NAME
property (see section 14.1.5). If the argv argument is non-NULL, XSetWMProperties calls
XSetCommand, which sets the WM_COMMAND property (see section 14.2.1). Note that an
argc of zero is allowed to indicate a zero-length command. Note also that the hostname of this
machine is stored using XSetWMClientMachine (see section 14.2.2).
If the normal_hints argument is non-NULL, XSetWMProperties calls XSetWMNormalHints,
which sets the WM_NORMAL_HINTS property (see section 14.1.7). If the wm_hints argument
is non-NULL, XSetWMProperties calls XSetWMHints, which sets the WM_HINTS property
(see section 14.1.6).
If the class_hints argument is non-NULL, XSetWMProperties calls XSetClassHint, which sets
the WM_CLASS property (see section 14.1.8). If the res_name member in the XClassHint
structure is set to the NULL pointer and the RESOURCE_NAME environment variable is set,
then the value of the environment variable is substituted for res_name. If the res_name member is
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NULL, the environment variable is not set, and argv and argv[0] are set, then the value of argv[0],
stripped of any directory prefixes, is substituted for res_name.
XSetWMProperties can generate BadAlloc and BadWindow errors.
14.2. Client to Session Manager Communication
This section discusses how to:

Set and read the WM_COMMAND property

Set and read the WM_CLIENT_MACHINE property
14.2.1. Setting and Reading the WM_COMMAND Property
Xlib provides functions that you can use to set and read the WM_COMMAND property for a
given window.
To set a window's WM_COMMAND property, use XSetCommand.
XSetCommand (display, w, argv, argc)
Display *display;
Window w;
char **argv;
int argc;
display
Specifies the connection to the X server.
w
Specifies the window.
argv
Specifies the application's argument list.
argc
Specifies the number of arguments.
The XSetCommand function sets the command and arguments used to invoke the application.
(Typically, argv is the argv array of your main program.) If the strings are not in the Host
Portable Character Encoding, the result is implementation-dependent.
XSetCommand can generate BadAlloc and BadWindow errors.
To read a window's WM_COMMAND property, use XGetCommand.
Status XGetCommand(display, w, argv_return, argc_return)
Display *display;
Window w;
char ***argv_return;
int *argc_return;
display
Specifies the connection to the X server.
w
Specifies the window.
argv_return
Returns the application's argument list.
argc_return
Returns the number of arguments returned.
The XGetCommand function reads the WM_COMMAND property from the specified window
and returns a string list. If the WM_COMMAND property exists, it is of type STRING and for-
mat 8. If sufficient memory can be allocated to contain the string list, XGetCommand fills in
the argv_return and argc_return arguments and returns a nonzero status. Otherwise, it returns a
zero status. If the data returned by the server is in the Latin Portable Character Encoding, then
the returned strings are in the Host Portable Character Encoding. Otherwise, the result is
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implementation-dependent. To free the memory allocated to the string list, use XFreeStringList.
14.2.2. Setting and Reading the WM_CLIENT_MACHINE Property
Xlib provides functions that you can use to set and read the WM_CLIENT_MACHINE property
for a given window.
To set a window's WM_CLIENT_MACHINE property, use XSetWMClientMachine.
void XSetWMClientMachine(display, w, text_prop)
Display *display;
Window w;
XTextProperty *text_prop;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop
Specifies the XTextProperty structure to be used.
The XSetWMClientMachine convenience function calls XSetTextProperty to set the
WM_CLIENT_MACHINE property.
To read a window's WM_CLIENT_MACHINE property, use XGetWMClientMachine.
Status XGetWMClientMachine(display, w, text_prop_return)
Display *display;
Window w;
XTextProperty *text_prop_return;
display
Specifies the connection to the X server.
w
Specifies the window.
text_prop_returnReturns the XTextProperty structure.
The XGetWMClientMachine convenience function performs an XGetTextProperty on the
WM_CLIENT_MACHINE property. It returns a nonzero status on success; otherwise, it returns
a zero status.
14.3. Standard Colormaps
Applications with color palettes, smooth-shaded drawings, or digitized images demand large
numbers of colors. In addition, these applications often require an efficient mapping from color
triples to pixel values that display the appropriate colors.
As an example, consider a three-dimensional display program that wants to draw a smoothly
shaded sphere. At each pixel in the image of the sphere, the program computes the intensity and
color of light reflected back to the viewer. The result of each computation is a triple of red, green,
and blue (RGB) coefficients in the range 0.0 to 1.0. To draw the sphere, the program needs a col-
ormap that provides a large range of uniformly distributed colors. The colormap should be
arranged so that the program can convert its RGB triples into pixel values very quickly, because
drawing the entire sphere requires many such conversions.
On many current workstations, the display is limited to 256 or fewer colors. Applications must
allocate colors carefully, not only to make sure they cover the entire range they need but also to
make use of as many of the available colors as possible. On a typical X display, many applica-
tions are active at once. Most workstations have only one hardware look-up table for colors, so
only one application colormap can be installed at a given time. The application using the
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installed colormap is displayed correctly, and the other applications go technicolor and are dis-
played with false colors.
As another example, consider a user who is running an image processing program to display
earth-resources data. The image processing program needs a colormap set up with 8 reds, 8
greens, and 4 blues, for a total of 256 colors. Because some colors are already in use in the
default colormap, the image processing program allocates and installs a new colormap.
The user decides to alter some of the colors in the image by invoking a color palette program to
mix and choose colors. The color palette program also needs a colormap with eight reds, eight
greens, and four blues, so just like the image processing program, it must allocate and install a
new colormap.
Because only one colormap can be installed at a time, the color palette may be displayed incor-
rectly whenever the image processing program is active. Conversely, whenever the palette pro-
gram is active, the image may be displayed incorrectly. The user can never match or compare
colors in the palette and image. Contention for colormap resources can be reduced if applications
with similar color needs share colormaps.
The image processing program and the color palette program could share the same colormap if
there existed a convention that described how the colormap was set up. Whenever either program
was active, both would be displayed correctly.
The standard colormap properties define a set of commonly used colormaps. Applications that
share these colormaps and conventions display true colors more often and provide a better inter-
face to the user.
Standard colormaps allow applications to share commonly used color resources. This allows
many applications to be displayed in true colors simultaneously, even when each application
needs an entirely filled colormap.
Several standard colormaps are described in this section. Usually, a window manager creates
these colormaps. Applications should use the standard colormaps if they already exist.
To allocate an XStandardColormap structure, use XAllocStandardColormap.
XStandardColormap *XAllocStandardColormap( )
The XAllocStandardColormap function allocates and returns a pointer to an XStandardCol-
ormap
structure. Note that all fields in the XStandardColormap structure are initially set to
zero. If insufficient memory is available, XAllocStandardColormap returns NULL. To free the
memory allocated to this structure, use XFree.
The XStandardColormap structure contains:
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/* Hints */
#define
ReleaseByFreeingColormap
( (XID) 1L)
/* Values */
typedef struct {
Colormap colormap;
unsigned long red_max;
unsigned long red_mult;
unsigned long green_max;
unsigned long green_mult;
unsigned long blue_max;
unsigned long blue_mult;
unsigned long base_pixel;
VisualID visualid;
XID killid;
} XStandardColormap;
The colormap member is the colormap created by the XCreateColormap function. The
red_max, green_max, and blue_max members give the maximum red, green, and blue values,
respectively. Each color coefficient ranges from zero to its max, inclusive. For example, a com-
mon colormap allocation is 3/3/2 (3 planes for red, 3 planes for green, and 2 planes for blue).
This colormap would have red_max = 7, green_max = 7, and blue_max = 3. An alternate alloca-
tion that uses only 216 colors is red_max = 5, green_max = 5, and blue_max = 5.
The red_mult, green_mult, and blue_mult members give the scale factors used to compose a full
pixel value. (See the discussion of the base_pixel members for further information.) For a 3/3/2
allocation, red_mult might be 32, green_mult might be 4, and blue_mult might be 1. For a 6-col-
ors-each allocation, red_mult might be 36, green_mult might be 6, and blue_mult might be 1.
The base_pixel member gives the base pixel value used to compose a full pixel value. Usually,
the base_pixel is obtained from a call to the XAllocColorPlanes function. Given integer red,
green, and blue coefficients in their appropriate ranges, one then can compute a corresponding
pixel value by using the following expression:
(r * red_mult + g * green_mult + b * blue_mult + base_pixel) & 0xFFFFFFFF
For GrayScale colormaps, only the colormap, red_max, red_mult, and base_pixel members are
defined. The other members are ignored. To compute a GrayScale pixel value, use the follow-
ing expression:
(gray * red_mult + base_pixel) & 0xFFFFFFFF
Negative multipliers can be represented by converting the 2's complement representation of the
multiplier into an unsigned long and storing the result in the appropriate _mult field. The step of
masking by 0xFFFFFFFF effectively converts the resulting positive multiplier into a negative one.
The masking step will take place automatically on many machine architectures, depending on the
size of the integer type used to do the computation.
The visualid member gives the ID number of the visual from which the colormap was created.
The killid member gives a resource ID that indicates whether the cells held by this standard col-
ormap are to be released by freeing the colormap ID or by calling the XKillClient function on
the indicated resource. (Note that this method is necessary for allocating out of an existing col-
ormap.)
The properties containing the XStandardColormap information have the type
RGB_COLOR_MAP.
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The remainder of this section discusses standard colormap properties and atoms as well as how to
manipulate standard colormaps.
14.3.1. Standard Colormap Properties and Atoms
Several standard colormaps are available. Each standard colormap is defined by a property, and
each such property is identified by an atom. The following list names the atoms and describes the
colormap associated with each one. The <X11/Xatom.h> header file contains the definitions for
each of the following atoms, which are prefixed with XA_.
RGB_DEFAULT_MAP
This atom names a property. The value of the property is an array of XStandardCol-
ormap
structures. Each entry in the array describes an RGB subset of the default color
map for the Visual specified by visual_id.
Some applications only need a few RGB colors and may be able to allocate them from the
system default colormap. This is the ideal situation because the fewer colormaps that are
active in the system the more applications are displayed with correct colors at all times.
A typical allocation for the RGB_DEFAULT_MAP on 8-plane displays is 6 reds, 6 greens,
and 6 blues. This gives 216 uniformly distributed colors (6 intensities of 36 different hues)
and still leaves 40 elements of a 256-element colormap available for special-purpose colors
for text, borders, and so on.
RGB_BEST_MAP
This atom names a property. The value of the property is an XStandardColormap.
The property defines the best RGB colormap available on the screen. (Of course, this is a
subjective evaluation.) Many image processing and three-dimensional applications need to
use all available colormap cells and to distribute as many perceptually distinct colors as
possible over those cells. This implies that there may be more green values available than
red, as well as more green or red than blue.
For an 8-plane PseudoColor visual, RGB_BEST_MAP is likely to be a 3/3/2 allocation.
For a 24-plane DirectColor visual, RGB_BEST_MAP is normally an 8/8/8 allocation.
RGB_RED_MAP
RGB_GREEN_MAP
RGB_BLUE_MAP
These atoms name properties. The value of each property is an XStandardColormap.
The properties define all-red, all-green, and all-blue colormaps, respectively. These maps
are used by applications that want to make color-separated images. For example, a user
might generate a full-color image on an 8-plane display both by rendering an image three
times (once with high color resolution in red, once with green, and once with blue) and by
multiply exposing a single frame in a camera.
RGB_GRAY_MAP
This atom names a property. The value of the property is an XStandardColormap.
The property describes the best GrayScale colormap available on the screen. As previ-
ously mentioned, only the colormap, red_max, red_mult, and base_pixel members of the
XStandardColormap structure are used for GrayScale colormaps.
14.3.2. Setting and Obtaining Standard Colormaps
Xlib provides functions that you can use to set and obtain an XStandardColormap structure.
To set an XStandardColormap structure, use XSetRGBColormaps.
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void XSetRGBColormaps(display, w, std_colormap, count, property)
Display *display;
Window w;
XStandardColormap *std_colormap;
int count;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
std_colormap
Specifies the XStandardColormap structure to be used.
count
Specifies the number of colormaps.
property
Specifies the property name.
The XSetRGBColormaps function replaces the RGB colormap definition in the specified prop-
erty on the named window. If the property does not already exist, XSetRGBColormaps sets the
RGB colormap definition in the specified property on the named window. The property is stored
with a type of RGB_COLOR_MAP and a format of 32. Note that it is the caller's responsibility
to honor the ICCCM restriction that only RGB_DEFAULT_MAP contain more than one defini-
tion.
The XSetRGBColormaps function usually is only used by window or session managers. To cre-
ate a standard colormap, follow this procedure:
1. Open a new connection to the same server.
2. Grab the server.
3. See if the property is on the property list of the root window for the screen.
4. If the desired property is not present:

Create a colormap (unless you are using the default colormap of the screen).

Determine the color characteristics of the visual.

Allocate cells in the colormap (or create it with AllocAll).

Call XStoreColors to store appropriate color values in the colormap.

Fill in the descriptive members in the XStandardColormap structure.

Attach the property to the root window.

Use XSetCloseDownMode to make the resource permanent.
5. Ungrab the server.
XSetRGBColormaps can generate BadAlloc, BadAtom, and BadWindow errors.
To obtain the XStandardColormap structure associated with the specified property, use
XGetRGBColormaps.
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Status XGetRGBColormaps(display, w, std_colormap_return, count_return, property)
Display *display;
Window w;
XStandardColormap **std_colormap_return;
int *count_return;
Atom property;
display
Specifies the connection to the X server.
w
Specifies the window.
std_colormap_return
Returns the XStandardColormap structure.
count_return
Returns the number of colormaps.
property
Specifies the property name.
The XGetRGBColormaps function returns the RGB colormap definitions stored in the specified
property on the named window. If the property exists, is of type RGB_COLOR_MAP, is of for-
mat 32, and is long enough to contain a colormap definition, XGetRGBColormaps allocates and
fills in space for the returned colormaps and returns a nonzero status. If the visualid is not pre-
sent, XGetRGBColormaps assumes the default visual for the screen on which the window is
located; if the killid is not present, None is assumed, which indicates that the resources cannot be
released. Otherwise, none of the fields are set, and XGetRGBColormaps returns a zero status.
Note that it is the caller's responsibility to honor the ICCCM restriction that only
RGB_DEFAULT_MAP contain more than one definition.
XGetRGBColormaps can generate BadAtom and BadWindow errors.
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Chapter 15
Resource Manager Functions
A program often needs a variety of options in the X environment (for example, fonts, colors,
icons, and cursors). Specifying all of these options on the command line is awkward because
users may want to customize many aspects of the program and need a convenient way to establish
these customizations as the default settings. The resource manager is provided for this purpose.
Resource specifications are usually stored in human-readable files and in server properties.
The resource manager is a database manager with a twist. In most database systems, you perform
a query using an imprecise specification, and you get back a set of records. The resource man-
ager, howev er, allows you to specify a large set of values with an imprecise specification, to query
the database with a precise specification, and to get back only a single value. This should be used
by applications that need to know what the user prefers for colors, fonts, and other resources. It is
this use as a database for dealing with X resources that inspired the name ``Resource Manager,''
although the resource manager can be and is used in other ways.
For example, a user of your application may want to specify that all windows should have a blue
background but that all mail-reading windows should have a red background. With well-engi-
neered and coordinated applications, a user can define this information using only two lines of
specifications.
As an example of how the resource manager works, consider a mail-reading application called
xmh. Assume that it is designed so that it uses a complex window hierarchy all the way down to
individual command buttons, which may be actual small subwindows in some toolkits. These are
often called objects or widgets. In such toolkit systems, each user interface object can be com-
posed of other objects and can be assigned a name and a class. Fully qualified names or classes
can have arbitrary numbers of component names, but a fully qualified name always has the same
number of component names as a fully qualified class. This generally reflects the structure of the
application as composed of these objects, starting with the application itself.
For example, the xmh mail program has a name ``xmh'' and is one of a class of ``Mail'' pro-
grams. By convention, the first character of class components is capitalized, and the first letter of
name components is in lowercase. Each name and class finally has an attribute (for example,
``foreground'' or ``font''). If each window is properly assigned a name and class, it is easy for the
user to specify attributes of any portion of the application.
At the top level, the application might consist of a paned window (that is, a window divided into
several sections) named ``toc''. One pane of the paned window is a button box window named
``buttons'' and is filled with command buttons. One of these command buttons is used to incorpo-
rate new mail and has the name ``incorporate''. This window has a fully qualified name,
``xmh.toc.buttons.incorporate'', and a fully qualified class, ``Xmh.Paned.Box.Command''. Its
fully qualified name is the name of its parent, ``xmh.toc.buttons'', followed by its name, ``incor-
porate''. Its class is the class of its parent, ``Xmh.Paned.Box'', followed by its particular class,
``Command''. The fully qualified name of a resource is the attribute's name appended to the
object's fully qualified name, and the fully qualified class is its class appended to the object's
class.
The incorporate button might need the following resources: Title string, Font, Foreground color
for its inactive state, Background color for its inactive state, Foreground color for its active state,
and Background color for its active state. Each resource is considered to be an attribute of the
button and, as such, has a name and a class. For example, the foreground color for the button in
its active state might be named ``activeForeground'', and its class might be ``Foreground''.
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When an application looks up a resource (for example, a color), it passes the complete name and
complete class of the resource to a look-up routine. The resource manager compares this com-
plete specification against the incomplete specifications of entries in the resource database, finds
the best match, and returns the corresponding value for that entry.
The definitions for the resource manager are contained in <X11/Xresource.h>.
15.1. Resource File Syntax
The syntax of a resource file is a sequence of resource lines terminated by newline characters or
the end of the file. The syntax of an individual resource line is:
ResourceLine =
Comment | IncludeFile | ResourceSpec | <empty line>
Comment =
"!" {<any character except null or newline>}
IncludeFile =
"#" WhiteSpace "include" WhiteSpace FileName WhiteSpace
FileName =
<valid filename for operating system>
ResourceSpec =
WhiteSpace ResourceName WhiteSpace ":" WhiteSpace Value
ResourceName =
[Binding] {Component Binding} ComponentName
Binding =
"." | "*"
WhiteSpace =
{<space> | <horizontal tab>}
Component =
"?" | ComponentName
ComponentName =
NameChar {NameChar}
NameChar =
"a"-"z" | "A"-"Z" | "0"-"9" | "_" | "-"
Value =
{<any character except null or unescaped newline>}
Elements separated by vertical bar (|) are alternatives. Curly braces ({...}) indicate zero or more
repetitions of the enclosed elements. Square brackets ([...]) indicate that the enclosed element is
optional. Quotes ("...") are used around literal characters.
IncludeFile lines are interpreted by replacing the line with the contents of the specified file. The
word ``include'' must be in lowercase. The file name is interpreted relative to the directory of the
file in which the line occurs (for example, if the file name contains no directory or contains a rela-
tive directory specification).
If a ResourceName contains a contiguous sequence of two or more Binding characters, the
sequence will be replaced with a single ``.'' character if the sequence contains only ``.'' characters;
otherwise, the sequence will be replaced with a single ``*'' character.
A resource database never contains more than one entry for a given ResourceName. If a resource
file contains multiple lines with the same ResourceName, the last line in the file is used.
Any white space characters before or after the name or colon in a ResourceSpec are ignored. To
allow a Value to begin with white space, the two-character sequence ``\space'' (backslash fol-
lowed by space) is recognized and replaced by a space character, and the two-character sequence
`` \tab'' (backslash followed by horizontal tab) is recognized and replaced by a horizontal tab
character. To allow a Value to contain embedded newline characters, the two-character sequence
`` \ n'' is recognized and replaced by a newline character. To allow a Value to be broken across
multiple lines in a text file, the two-character sequence ``\newline'' (backslash followed by new-
line) is recognized and removed from the value. To allow a Value to contain arbitrary character
codes, the four-character sequence ``\nnn'', where each n is a digit character in the range of
``0''-``7'', is recognized and replaced with a single byte that contains the octal value specified by
the sequence. Finally, the two-character sequence ``\\'' is recognized and replaced with a single
backslash.
As an example of these sequences, the following resource line contains a value consisting of four
characters: a backslash, a null, a ``z'', and a newline:
magic.values: \\\000 \
z\ n
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15.2. Resource Manager Matching Rules
The algorithm for determining which resource database entry matches a given query is the heart
of the resource manager. All queries must fully specify the name and class of the desired
resource (use of the characters ``*'' and ``?'' is not permitted). The library supports up to 100
components in a full name or class. Resources are stored in the database with only partially spec-
ified names and classes, using pattern matching constructs. An asterisk (*) is a loose binding and
is used to represent any number of intervening components, including none. A period (.) is a tight
binding and is used to separate immediately adjacent components. A question mark (?) is used to
match any single component name or class. A database entry cannot end in a loose binding; the
final component (which cannot be the character ``?'') must be specified. The lookup algorithm
searches the database for the entry that most closely matches (is most specific for) the full name
and class being queried. When more than one database entry matches the full name and class,
precedence rules are used to select just one.
The full name and class are scanned from left to right (from highest level in the hierarchy to low-
est), one component at a time. At each level, the corresponding component and/or binding of
each matching entry is determined, and these matching components and bindings are compared
according to precedence rules. Each of the rules is applied at each level before moving to the
next level, until a rule selects a single entry over all others. The rules, in order of precedence, are:
1. An entry that contains a matching component (whether name, class, or the character ``?'')
takes precedence over entries that elide the level (that is, entries that match the level in a
loose binding).
2. An entry with a matching name takes precedence over both entries with a matching class
and entries that match using the character ``?''. An entry with a matching class takes prece-
dence over entries that match using the character ``?''.
3. An entry preceded by a tight binding takes precedence over entries preceded by a loose
binding.
To illustrate these rules, consider the following resource database entries:
xmh*Paned*activeForeground: red
(entry A)
*incorporate.Foreground: blue
(entry B)
xmh.toc*Command*activeForeground: green
(entry C)
xmh.toc*?.Foreground: white
(entry D)
xmh.toc*Command.activeForeground: black
(entry E)
Consider a query for the resource:
xmh.toc.messagefunctions.incorporate.activeForeground (name)
Xmh.Paned.Box.Command.Foreground
(class)
At the first level (xmh, Xmh), rule 1 eliminates entry B. At the second level (toc, Paned), rule 2
eliminates entry A. At the third level (messagefunctions, Box), no entries are eliminated. At the
fourth level (incorporate, Command), rule 2 eliminates entry D. At the fifth level (activeFore-
ground, Foreground), rule 3 eliminates entry C.
15.3. Quarks
Most uses of the resource manager involve defining names, classes, and representation types as
string constants. However, always referring to strings in the resource manager can be slow,
because it is so heavily used in some toolkits. To solve this problem, a shorthand for a string is
used in place of the string in many of the resource manager functions. Simple comparisons can
be performed rather than string comparisons. The shorthand name for a string is called a quark
and is the type XrmQuark. On some occasions, you may want to allocate a quark that has no
string equivalent.
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A quark is to a string what an atom is to a string in the server, but its use is entirely local to your
application.
To allocate a new quark, use XrmUniqueQuark.
XrmQuark XrmUniqueQuark( )
The XrmUniqueQuark function allocates a quark that is guaranteed not to represent any string
that is known to the resource manager.
Each name, class, and representation type is typedef'd as an XrmQuark.
typedef int XrmQuark, *XrmQuarkList;
typedef XrmQuark XrmName;
typedef XrmQuark XrmClass;
typedef XrmQuark XrmRepresentation;
#define NULLQUARK ((XrmQuark) 0)
Lists are represented as null-terminated arrays of quarks. The size of the array must be large
enough for the number of components used.
typedef XrmQuarkList XrmNameList;
typedef XrmQuarkList XrmClassList;
To convert a string to a quark, use XrmStringToQuark or XrmPermStringToQuark.
#define XrmStringToName(string) XrmStringToQuark(string)
#define XrmStringToClass(string) XrmStringToQuark(string)
#define XrmStringToRepresentation(string) XrmStringToQuark(string)
XrmQuark XrmStringToQuark (string)
char *string;
XrmQuark XrmPermStringToQuark (string)
char *string;
string
Specifies the string for which a quark is to be allocated.
These functions can be used to convert from string to quark representation. If the string is not in
the Host Portable Character Encoding, the conversion is implementation-dependent. The string
argument to XrmStringToQuark need not be permanently allocated storage. XrmPermString-
ToQuark
is just like XrmStringToQuark, except that Xlib is permitted to assume the string
argument is permanently allocated, and, hence, that it can be used as the value to be returned by
XrmQuarkToString.
For any giv en quark, if XrmStringToQuark returns a non-NULL value, all future calls will
return the same value (identical address).
To convert a quark to a string, use XrmQuarkToString.
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#define XrmNameToString(name) XrmQuarkToString(name)
#define XrmClassToString(class) XrmQuarkToString(class)
#define XrmRepresentationToString(type) XrmQuarkToString(type)
char *XrmQuarkToString (quark)
XrmQuark quark;
quark
Specifies the quark for which the equivalent string is desired.
These functions can be used to convert from quark representation to string. The string pointed to
by the return value must not be modified or freed. The returned string is byte-for-byte equal to
the original string passed to one of the string-to-quark routines. If no string exists for that quark,
XrmQuarkToString returns NULL. For any giv en quark, if XrmQuarkToString returns a
non-NULL value, all future calls will return the same value (identical address).
To convert a string with one or more components to a quark list, use XrmStringToQuarkList.
#define XrmStringToNameList(str, name) XrmStringToQuarkList((str), (name))
#define XrmStringToClassList(str, class) XrmStringToQuarkList((str), (class))
void XrmStringToQuarkList (string, quarks_return)
char *string;
XrmQuarkList quarks_return;
string
Specifies the string for which a quark list is to be allocated.
quarks_return Returns the list of quarks.
The XrmStringToQuarkList function converts the null-terminated string (generally a fully qual-
ified name) to a list of quarks. Note that the string must be in the valid ResourceName format
(see section 15.1). If the string is not in the Host Portable Character Encoding, the conversion is
implementation-dependent.
A binding list is a list of type XrmBindingList and indicates if components of name or class lists
are bound tightly or loosely (that is, if wildcarding of intermediate components is specified).
typedef enum {XrmBindTightly, XrmBindLoosely} XrmBinding, *XrmBindingList;
XrmBindTightly indicates that a period separates the components, and XrmBindLoosely indi-
cates that an asterisk separates the components.
To convert a string with one or more components to a binding list and a quark list, use
XrmStringToBindingQuarkList.
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XrmStringToBindingQuarkList (string, bindings_return, quarks_return)
char *string;
XrmBindingList bindings_return;
XrmQuarkList quarks_return;
string
Specifies the string for which a quark list is to be allocated.
bindings_return Returns the binding list. The caller must allocate sufficient space for the binding
list before calling XrmStringToBindingQuarkList.
quarks_return Returns the list of quarks. The caller must allocate sufficient space for the quarks
list before calling XrmStringToBindingQuarkList.
Component names in the list are separated by a period or an asterisk character. The string must
be in the format of a valid ResourceName (see section 15.1). If the string does not start with a
period or an asterisk, a tight binding is assumed. For example, the string ``*a.b*c'' becomes:
quarks: a
b
c
bindings: loose
tight loose
15.4. Creating and Storing Databases
A resource database is an opaque type, XrmDatabase. Each database value is stored in an Xrm-
Value
structure. This structure consists of a size, an address, and a representation type. The size
is specified in bytes. The representation type is a way for you to store data tagged by some appli-
cation-defined type (for example, the strings ``font'' or ``color''). It has nothing to do with the C
data type or with its class. The XrmValue structure is defined as:
typedef struct {
unsigned int size;
XPointer addr;
} XrmValue, *XrmValuePtr;
To initialize the resource manager, use XrmInitialize.
void XrmInitialize( );
To retrieve a database from disk, use XrmGetFileDatabase.
XrmDatabase XrmGetFileDatabase(filename)
char *filename;
filename
Specifies the resource database file name.
The XrmGetFileDatabase function opens the specified file, creates a new resource database, and
loads it with the specifications read in from the specified file. The specified file should contain a
sequence of entries in valid ResourceLine format (see section 15.1); the database that results from
reading a file with incorrect syntax is implementation-dependent. The file is parsed in the current
locale, and the database is created in the current locale. If it cannot open the specified file,
XrmGetFileDatabase returns NULL.
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To store a copy of a database to disk, use XrmPutFileDatabase.
void XrmPutFileDatabase(database, stored_db)
XrmDatabase database;
char *stored_db;
database
Specifies the database that is to be used.
stored_db
Specifies the file name for the stored database.
The XrmPutFileDatabase function stores a copy of the specified database in the specified file.
Te xt is written to the file as a sequence of entries in valid ResourceLine format (see section 15.1).
The file is written in the locale of the database. Entries containing resource names that are not in
the Host Portable Character Encoding or containing values that are not in the encoding of the
database locale, are written in an implementation-dependent manner. The order in which entries
are written is implementation-dependent. Entries with representation types other than ``String''
are ignored.
To obtain a pointer to the screen-independent resources of a display, use
XResourceManagerString.
char *XResourceManagerString(display)
Display *display;
display
Specifies the connection to the X server.
The XResourceManagerString function returns the RESOURCE_MANAGER property from
the server's root window of screen zero, which was returned when the connection was opened
using XOpenDisplay. The property is converted from type STRING to the current locale. The
conversion is identical to that produced by XmbTextPropertyToTextList for a single element
STRING property. The returned string is owned by Xlib and should not be freed by the client.
The property value must be in a format that is acceptable to XrmGetStringDatabase. If no
property exists, NULL is returned.
To obtain a pointer to the screen-specific resources of a screen, use XScreenResourceString.
char *XScreenResourceString(screen)
Screen *screen;
screen
Specifies the screen.
The XScreenResourceString function returns the SCREEN_RESOURCES property from the
root window of the specified screen. The property is converted from type STRING to the current
locale. The conversion is identical to that produced by XmbTextPropertyToTextList for a sin-
gle element STRING property. The property value must be in a format that is acceptable to
XrmGetStringDatabase. If no property exists, NULL is returned. The caller is responsible for
freeing the returned string by using XFree.
To create a database from a string, use XrmGetStringDatabase.
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XrmDatabase XrmGetStringDatabase(data)
char *data;
data
Specifies the database contents using a string.
The XrmGetStringDatabase function creates a new database and stores the resources specified
in the specified null-terminated string. XrmGetStringDatabase is similar to XrmGetFile-
Database
except that it reads the information out of a string instead of out of a file. The string
should contain a sequence of entries in valid ResourceLine format (see section 15.1) terminated
by a null character; the database that results from using a string with incorrect syntax is imple-
mentation-dependent. The string is parsed in the current locale, and the database is created in the
current locale.
To obtain the locale name of a database, use XrmLocaleOfDatabase.
char *XrmLocaleOfDatabase(database)
XrmDatabase database;
database
Specifies the resource database.
The XrmLocaleOfDatabase function returns the name of the locale bound to the specified
database, as a null-terminated string. The returned locale name string is owned by Xlib and
should not be modified or freed by the client. Xlib is not permitted to free the string until the
database is destroyed. Until the string is freed, it will not be modified by Xlib.
To destroy a resource database and free its allocated memory, use XrmDestroyDatabase.
void XrmDestroyDatabase (database)
XrmDatabase database;
database
Specifies the resource database.
If database is NULL, XrmDestroyDatabase returns immediately.
To associate a resource database with a display, use XrmSetDatabase.
void XrmSetDatabase(display, database)
Display *display;
XrmDatabase database;
display
Specifies the connection to the X server.
database
Specifies the resource database.
The XrmSetDatabase function associates the specified resource database (or NULL) with the
specified display. The database previously associated with the display (if any) is not destroyed.
A client or toolkit may find this function convenient for retaining a database once it is con-
structed.
To get the resource database associated with a display, use XrmGetDatabase.
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XrmDatabase XrmGetDatabase(display)
Display *display;
display
Specifies the connection to the X server.
The XrmGetDatabase function returns the database associated with the specified display. It
returns NULL if a database has not yet been set.
15.5. Merging Resource Databases
To merge the contents of a resource file into a database, use XrmCombineFileDatabase.
Status XrmCombineFileDatabase(filename, target_db, override)
char *filename;
XrmDatabase *target_db;
Bool override;
filename
Specifies the resource database file name.
target_db
Specifies the resource database into which the source database is to be merged.
override
Specifies whether source entries override target ones.
The XrmCombineFileDatabase function merges the contents of a resource file into a database.
If the same specifier is used for an entry in both the file and the database, the entry in the file will
replace the entry in the database if override is True; otherwise, the entry in the file is discarded.
The file is parsed in the current locale. If the file cannot be read, a zero status is returned; other-
wise, a nonzero status is returned. If target_db contains NULL, XrmCombineFileDatabase cre-
ates and returns a new database to it. Otherwise, the database pointed to by target_db is not
destroyed by the merge. The database entries are merged without changing values or types,
regardless of the locale of the database. The locale of the target database is not modified.
To merge the contents of one database into another database, use XrmCombineDatabase.
void XrmCombineDatabase(source_db, target_db, override)
XrmDatabase source_db, *target_db;
Bool override;
source_db
Specifies the resource database that is to be merged into the target database.
target_db
Specifies the resource database into which the source database is to be merged.
override
Specifies whether source entries override target ones.
The XrmCombineDatabase function merges the contents of one database into another. If the
same specifier is used for an entry in both databases, the entry in the source_db will replace the
entry in the target_db if override is True; otherwise, the entry in source_db is discarded. If tar-
get_db contains NULL, XrmCombineDatabase simply stores source_db in it. Otherwise,
source_db is destroyed by the merge, but the database pointed to by target_db is not destroyed.
The database entries are merged without changing values or types, regardless of the locales of the
databases. The locale of the target database is not modified.
To merge the contents of one database into another database with override semantics, use
XrmMergeDatabases.
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void XrmMergeDatabases(source_db, target_db)
XrmDatabase source_db, *target_db;
source_db
Specifies the resource database that is to be merged into the target database.
target_db
Specifies the resource database into which the source database is to be merged.
Calling the XrmMergeDatabases function is equivalent to calling the XrmCombineDatabase
function with an override argument of True.
15.6. Looking Up Resources
To retrieve a resource from a resource database, use XrmGetResource, XrmQGetResource, or
XrmQGetSearchResource.
Bool XrmGetResource(database, str_name, str_class, str_type_return, value_return)
XrmDatabase database;
char *str_name;
char *str_class;
char **str_type_return;
XrmValue *value_return;
database
Specifies the database that is to be used.
str_name
Specifies the fully qualified name of the value being retrieved (as a string).
str_class
Specifies the fully qualified class of the value being retrieved (as a string).
str_type_return Returns the representation type of the destination (as a string).
value_return
Returns the value in the database.
Bool XrmQGetResource(database, quark_name, quark_class, quark_type_return, value_return)
XrmDatabase database;
XrmNameList quark_name;
XrmClassList quark_class;
XrmRepresentation *quark_type_return;
XrmValue *value_return;
database
Specifies the database that is to be used.
quark_name
Specifies the fully qualified name of the value being retrieved (as a quark).
quark_class
Specifies the fully qualified class of the value being retrieved (as a quark).
quark_type_return
Returns the representation type of the destination (as a quark).
value_return
Returns the value in the database.
The XrmGetResource and XrmQGetResource functions retrieve a resource from the specified
database. Both take a fully qualified name/class pair, a destination resource representation, and
the address of a value (size/address pair). The value and returned type point into database mem-
ory; therefore, you must not modify the data.
The database only frees or overwrites entries on XrmPutResource, XrmQPutResource, or
XrmMergeDatabases. A client that is not storing new values into the database or is not merging
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the database should be safe using the address passed back at any time until it exits. If a resource
was found, both XrmGetResource and XrmQGetResource return True; otherwise, they return
False.
Most applications and toolkits do not make random probes into a resource database to fetch
resources. The X toolkit access pattern for a resource database is quite stylized. A series of from
1 to 20 probes is made with only the last name/class differing in each probe. The XrmGetRe-
source
function is at worst a 2n algorithm, where n is the length of the name/class list. This can
be improved upon by the application programmer by prefetching a list of database levels that
might match the first part of a name/class list.
To obtain a list of database levels, use XrmQGetSearchList.
typedef XrmHashTable *XrmSearchList;
Bool XrmQGetSearchList(database, names, classes, list_return, list_length)
XrmDatabase database;
XrmNameList names;
XrmClassList classes;
XrmSearchList list_return;
int list_length;
database
Specifies the database that is to be used.
names
Specifies a list of resource names.
classes
Specifies a list of resource classes.
list_return
Returns a search list for further use. The caller must allocate sufficient space for
the list before calling XrmQGetSearchList.
list_length
Specifies the number of entries (not the byte size) allocated for list_return.
The XrmQGetSearchList function takes a list of names and classes and returns a list of database
levels where a match might occur. The returned list is in best-to-worst order and uses the same
algorithm as XrmGetResource for determining precedence. If list_return was large enough for
the search list, XrmQGetSearchList returns True; otherwise, it returns False.
The size of the search list that the caller must allocate is dependent upon the number of levels and
wildcards in the resource specifiers that are stored in the database. The worst case length is 3n,
where n is the number of name or class components in names or classes.
When using XrmQGetSearchList followed by multiple probes for resources with a common
name and class prefix, only the common prefix should be specified in the name and class list to
XrmQGetSearchList.
To search resource database levels for a given resource, use XrmQGetSearchResource.
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Bool XrmQGetSearchResource(list, name, class, type_return, value_return)
XrmSearchList list;
XrmName name;
XrmClass class;
XrmRepresentation *type_return;
XrmValue *value_return;
list
Specifies the search list returned by XrmQGetSearchList.
name
Specifies the resource name.
class
Specifies the resource class.
type_return
Returns data representation type.
value_return
Returns the value in the database.
The XrmQGetSearchResource function searches the specified database levels for the resource
that is fully identified by the specified name and class. The search stops with the first match.
XrmQGetSearchResource returns True if the resource was found; otherwise, it returns False.
A call to XrmQGetSearchList with a name and class list containing all but the last component
of a resource name followed by a call to XrmQGetSearchResource with the last component
name and class returns the same database entry as XrmGetResource and XrmQGetResource
with the fully qualified name and class.
15.7. Storing into a Resource Database
To store resources into the database, use XrmPutResource or XrmQPutResource. Both func-
tions take a partial resource specification, a representation type, and a value. This value is copied
into the specified database.
void XrmPutResource(database, specifier, type, value)
XrmDatabase *database;
char *specifier;
char *type;
XrmValue *value;
database
Specifies the resource database.
specifier
Specifies a complete or partial specification of the resource.
type
Specifies the type of the resource.
value
Specifies the value of the resource, which is specified as a string.
If database contains NULL, XrmPutResource creates a new database and returns a pointer to it.
XrmPutResource is a convenience function that calls XrmStringToBindingQuarkList fol-
lowed by:
XrmQPutResource(database, bindings, quarks, XrmStringToQuark(type), value)
If the specifier and type are not in the Host Portable Character Encoding, the result is implemen-
tation-dependent. The value is stored in the database without modification.
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void XrmQPutResource(database, bindings, quarks, type, value)
XrmDatabase *database;
XrmBindingList bindings;
XrmQuarkList quarks;
XrmRepresentation type;
XrmValue *value;
database
Specifies the resource database.
bindings
Specifies a list of bindings.
quarks
Specifies the complete or partial name or the class list of the resource.
type
Specifies the type of the resource.
value
Specifies the value of the resource, which is specified as a string.
If database contains NULL, XrmQPutResource creates a new database and returns a pointer to
it. If a resource entry with the identical bindings and quarks already exists in the database, the
previous type and value are replaced by the new specified type and value. The value is stored in
the database without modification.
To add a resource that is specified as a string, use XrmPutStringResource.
void XrmPutStringResource(database, specifier, value)
XrmDatabase *database;
char *specifier;
char *value;
database
Specifies the resource database.
specifier
Specifies a complete or partial specification of the resource.
value
Specifies the value of the resource, which is specified as a string.
If database contains NULL, XrmPutStringResource creates a new database and returns a
pointer to it. XrmPutStringResource adds a resource with the specified value to the specified
database. XrmPutStringResource is a convenience function that first calls XrmStringToBind-
ingQuarkList
on the specifier and then calls XrmQPutResource, using a ``String'' representa-
tion type. If the specifier is not in the Host Portable Character Encoding, the result is implemen-
tation-dependent. The value is stored in the database without modification.
To add a string resource using quarks as a specification, use XrmQPutStringResource.
void XrmQPutStringResource(database, bindings, quarks, value)
XrmDatabase *database;
XrmBindingList bindings;
XrmQuarkList quarks;
char *value;
database
Specifies the resource database.
bindings
Specifies a list of bindings.
quarks
Specifies the complete or partial name or the class list of the resource.
value
Specifies the value of the resource, which is specified as a string.
If database contains NULL, XrmQPutStringResource creates a new database and returns a
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pointer to it. XrmQPutStringResource is a convenience routine that constructs an XrmValue
for the value string (by calling strlen to compute the size) and then calls XrmQPutResource,
using a ``String'' representation type. The value is stored in the database without modification.
To add a single resource entry that is specified as a string that contains both a name and a value,
use XrmPutLineResource.
void XrmPutLineResource(database, line)
XrmDatabase *database;
char *line;
database
Specifies the resource database.
line
Specifies the resource name and value pair as a single string.
If database contains NULL, XrmPutLineResource creates a new database and returns a pointer
to it. XrmPutLineResource adds a single resource entry to the specified database. The line
should be in valid ResourceLine format (see section 15.1) terminated by a newline or null charac-
ter; the database that results from using a string with incorrect syntax is implementation-depen-
dent. The string is parsed in the locale of the database. If the ResourceName is not in the Host
Portable Character Encoding, the result is implementation-dependent. Note that comment lines
are not stored.
15.8. Enumerating Database Entries
To enumerate the entries of a database, use XrmEnumerateDatabase.
#define
XrmEnumAllLevels
0
#define
XrmEnumOneLevel
1
Bool XrmEnumerateDatabase(database, name_prefix, class_prefix, mode, proc, arg)
XrmDatabase database;
XrmNameList name_prefix;
XrmClassList class_prefix;
int mode;
Bool (*proc)();
XPointer arg;
database
Specifies the resource database.
name_prefix
Specifies the resource name prefix.
class_prefix
Specifies the resource class prefix.
mode
Specifies the number of levels to enumerate.
proc
Specifies the procedure that is to be called for each matching entry.
arg
Specifies the user-supplied argument that will be passed to the procedure.
The XrmEnumerateDatabase function calls the specified procedure for each resource in the
database that would match some completion of the given name/class resource prefix. The order
in which resources are found is implementation-dependent. If mode is XrmEnumOneLevel, a
resource must match the given name/class prefix with just a single name and class appended. If
mode is XrmEnumAllLevels, the resource must match the given name/class prefix with one or
more names and classes appended. If the procedure returns True, the enumeration terminates
and the function returns True. If the procedure always returns False, all matching resources are
enumerated and the function returns False.
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The procedure is called with the following arguments:
(*proc)(database, bindings, quarks, type, value, arg)
XrmDatabase *database;
XrmBindingList bindings;
XrmQuarkList quarks;
XrmRepresentation *type;
XrmValue *value;
XPointer arg;
The bindings and quarks lists are terminated by NULLQUARK. Note that pointers to the
database and type are passed, but these values should not be modified.
The procedure must not modify the database. If Xlib has been initialized for threads, the proce-
dure is called with the database locked and the result of a call by the procedure to any Xlib func-
tion using the same database is not defined.
15.9. Parsing Command Line Options
The XrmParseCommand function can be used to parse the command line arguments to a pro-
gram and modify a resource database with selected entries from the command line.
typedef enum {
XrmoptionNoArg, /* Value is specified in XrmOptionDescRec.value */
XrmoptionIsArg, /* Value is the option string itself */
XrmoptionStickyArg, /* Value is characters immediately following option */
XrmoptionSepArg, /* Value is next argument in argv */
XrmoptionResArg, /* Resource and value in next argument in argv */
XrmoptionSkipArg, /* Ignore this option and the next argument in argv */
XrmoptionSkipLine, /* Ignore this option and the rest of argv */
XrmoptionSkipNArgs /* Ignore this option and the next
XrmOptionDescRec.value arguments in argv */
} XrmOptionKind;
Note that XrmoptionSkipArg is equivalent to XrmoptionSkipNArgs with the XrmOptionDe-
scRec.value
field containing the value one. Note also that the value zero for XrmoptionSkip-
NArgs
indicates that only the option itself is to be skipped.
typedef struct {
char *option;
/* Option specification string in argv */
char *specifier;
/* Binding and resource name (sans application name)
*/
XrmOptionKind argKind; /* Which style of option it is
*/
XPointer value; /* Value to provide if XrmoptionNoArg or
XrmoptionSkipNArgs */
} XrmOptionDescRec, *XrmOptionDescList;
To load a resource database from a C command line, use XrmParseCommand.
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void XrmParseCommand (database, table, table_count, name, argc_in_out, argv_in_out)
XrmDatabase *database;
XrmOptionDescList table;
int table_count;
char *name;
int *argc_in_out;
char **argv_in_out;
database
Specifies the resource database.
table
Specifies the table of command line arguments to be parsed.
table_count
Specifies the number of entries in the table.
name
Specifies the application name.
argc_in_out
Specifies the number of arguments and returns the number of remaining argu-
ments.
argv_in_out
Specifies the command line arguments and returns the remaining arguments.
The XrmParseCommand function parses an (argc, argv) pair according to the specified option
table, loads recognized options into the specified database with type ``String,'' and modifies the
(argc, argv) pair to remove all recognized options. If database contains NULL, XrmParseCom-
mand
creates a new database and returns a pointer to it. Otherwise, entries are added to the
database specified. If a database is created, it is created in the current locale.
The specified table is used to parse the command line. Recognized options in the table are
removed from argv, and entries are added to the specified resource database in the order they
occur in argv. The table entries contain information on the option string, the option name, the
style of option, and a value to provide if the option kind is XrmoptionNoArg. The option names
are compared byte-for-byte to arguments in argv, independent of any locale. The resource values
given in the table are stored in the resource database without modification. All resource database
entries are created using a ``String'' representation type. The argc argument specifies the number
of arguments in argv and is set on return to the remaining number of arguments that were not
parsed. The name argument should be the name of your application for use in building the
database entry. The name argument is prefixed to the resourceName in the option table before
storing a database entry. The name argument is treated as a single component, even if it has
embedded periods. No separating (binding) character is inserted, so the table must contain either
a period (.) or an asterisk (*) as the first character in each resourceName entry. To specify a more
completely qualified resource name, the resourceName entry can contain multiple components. If
the name argument and the resourceNames are not in the Host Portable Character Encoding, the
result is implementation-dependent.
The following provides a sample option table:
static XrmOptionDescRec opTable[] = {
{"-background", "*background",
XrmoptionSepArg, (XPointer) NULL},
{"-bd", "*borderColor",
XrmoptionSepArg, (XPointer) NULL},
{"-bg", "*background",
XrmoptionSepArg, (XPointer) NULL},
{"-borderwidth", "*TopLevelShell.borderWidth", XrmoptionSepArg, (XPointer) NULL},
{"-bordercolor", "*borderColor",
XrmoptionSepArg, (XPointer) NULL},
{"-bw", "*TopLevelShell.borderWidth", XrmoptionSepArg, (XPointer) NULL},
{"-display", ".display",
XrmoptionSepArg, (XPointer) NULL},
{"-fg", "*foreground", XrmoptionSepArg, (XPointer) NULL},
{"-fn", "*font",
XrmoptionSepArg, (XPointer) NULL},
{"-font", "*font",
XrmoptionSepArg, (XPointer) NULL},
{"-foreground", "*foreground", XrmoptionSepArg, (XPointer) NULL},
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{"-geometry", ".TopLevelShell.geometry", XrmoptionSepArg, (XPointer) NULL},
{"-iconic", ".TopLevelShell.iconic", XrmoptionNoArg, (XPointer) "on"},
{"-name", ".name",
XrmoptionSepArg, (XPointer) NULL},
{"-reverse", "*reverseVideo", XrmoptionNoArg, (XPointer) "on"},
{"-rv", "*reverseVideo", XrmoptionNoArg, (XPointer) "on"},
{"-synchronous", "*synchronous",
XrmoptionNoArg, (XPointer) "on"},
{"-title", ".TopLevelShell.title", XrmoptionSepArg, (XPointer) NULL},
{"-xrm", NULL,
XrmoptionResArg, (XPointer) NULL},
};
In this table, if the -background (or -bg) option is used to set background colors, the stored
resource specifier matches all resources of attribute background. If the -borderwidth option is
used, the stored resource specifier applies only to border width attributes of class TopLevelShell
(that is, outer-most windows, including pop-up windows). If the -title option is used to set a win-
dow name, only the topmost application windows receive the resource.
When parsing the command line, any unique unambiguous abbreviation for an option name in the
table is considered a match for the option. Note that uppercase and lowercase matter.
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Chapter 16
Application Utility Functions
Once you have initialized the X system, you can use the Xlib utility functions to:

Use keyboard utility functions

Use Latin-1 keyboard event functions

Allocate permanent storage

Parse the window geometry

Manipulate regions

Use cut buffers

Determine the appropriate visual type

Manipulate images

Manipulate bitmaps

Use the context manager
As a group, the functions discussed in this chapter provide the functionality that is frequently
needed and that spans toolkits. Many of these functions do not generate actual protocol requests
to the server.
16.1. Using Keyboard Utility Functions
This section discusses mapping between KeyCodes and KeySyms, classifying KeySyms, and
mapping between KeySyms and string names. The first three functions in this section operate on
a cached copy of the server keyboard mapping. The first four KeySyms for each KeyCode are
modified according to the rules given in section 12.7.