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14 Basic Graphics Programming With The XCB Library
18 <li><a class="section" href="#intro">Introduction</a>
19 <li><a class="section" href="#Xmodel">The client and server model of the X window system</a>
20 <li><a class="section" href="#asynch">GUI programming: the asynchronous model</a>
21 <li><a class="section" href="#notions">Basic XCB notions</a>
23 <li><a class="subsection" href="#conn">The X Connection</a>
24 <li><a class="subsection" href="#requestsreplies">Requests and replies: the Xlib killers</a>
25 <li><a class="subsection" href="#gc">The Graphics Context</a>
27 <li>Memory allocation for XCB structures
28 <li><a class="subsection" href="#events">Events</a>
30 <li><a class="section" href="#use">Using XCB-based programs</a>
32 <li><a class="subsection" href="#inst">Installation of XCB</a>
33 <li><a class="subsection" href="#comp">Compiling XCB-based programs</a>
35 <li><a class="section" href="#openconn">Opening and closing the connection to an X server</a>
36 <li><a class="section" href="#screen">Checking basic information about a connection</a>
37 <li><a class="section" href="#helloworld">Creating a basic window - the "hello world" program</a>
38 <li><a class="section" href="#drawing">Drawing in a window</a>
40 <li><a class="subsection" href="#allocgc">Allocating a Graphics Context</a>
41 <li><a class="subsection" href="#changegc">Changing the attributes of a Graphics Context</a>
42 <li><a class="subsection" href="#drawingprim">Drawing primitives: point, line, box, circle,...</a>
44 <li><a class="section" href="#xevents">X Events</a>
46 <li><a class="subsection" href="#register">Registering for event types using event masks</a>
47 <li><a class="subsection" href="#loop">Receiving events: writing the events loop</a>
48 <li><a class="subsection" href="#expose">Expose events</a>
49 <li><a class="subsection" href="#userinput">Getting user input</a>
51 <li><a class="subsubsection" href="#mousepressrelease">Mouse button press and release events</a>
52 <li><a class="subsubsection" href="#mousemvnt">Mouse movement events</a>
53 <li><a class="subsubsection" href="#mouseenter">Mouse pointer enter and leave events</a>
54 <li><a class="subsubsection" href="#focus">The keyboard focus</a>
55 <li><a class="subsubsection" href="#keypress">Keyboard press and release events</a>
57 <li><a class="subsection" href="#eventex">X events: a complete example</a>
59 <li><a class="section" href="#font">Handling text and fonts</a>
61 <li><a class="subsection" href="#fontstruct">The Font structure</a>
63 <li>Assigning a Font to a Graphic Context
64 <li>Drawing text in a window
68 <li>Root, parent and child windows
69 <li>Events propagation
71 <li><a class="section" href="#wm">Interacting with the window manager</a>
73 <li><a class="subsection" href="#wmprop">Window properties</a>
74 <li><a class="subsection" href="#wmname">Setting the window name and icon name</a>
75 <li>Setting preferred window size(s)
76 <li>Setting miscellaneous window manager hints
77 <li>Setting an application's icon
78 <li>Obeying the delete-window protocol
80 <li><a class="section" href="#winop">Simple window operations</a>
82 <li><a class="subsection" href="#winmap">Mapping and unmapping a window</a>
83 <li><a class="subsection" href="#winconf">Configuring a window</a>
84 <li><a class="subsection" href="#winmove">Moving a window around the screen</a>
85 <li><a class="subsection" href="#winsize">Resizing a window</a>
86 <li><a class="subsection" href="#winstack">Changing windows stacking order: raise and lower</a>
87 <li>Iconifying and de-iconifying a window
88 <li><a class="subsection" href="#wingetinfo">Getting informations about a window</a>
90 <li><a class="section" href="#usecolor">Using colors to paint the rainbow</a>
92 <li><a class="subsection" href="#colormap">Color maps</a>
93 <li><a class="subsection" href="#colormapalloc">Allocating and freeing Color Maps</a>
94 <li><a class="subsection" href="#alloccolor">Allocating and freeing a color entry</a>
95 <li>Drawing with a color
97 <li><a class="section" href="#pixmaps">X Bitmaps and Pixmaps</a>
99 <li><a class="subsection" href="#pixmapswhat">What is a X Bitmap ? An X Pixmap ?</a>
100 <li>Loading a bitmap from a file
101 <li>Drawing a bitmap in a window
102 <li><a class="subsection" href="#pixmapscreate">Creating a pixmap</a>
103 <li><a class="subsection" href="#pixmapsdraw">Drawing a pixmap in a window</a>
104 <li><a class="subsection" href="#pixmapsfree">Freeing a pixmap</a>
106 <li><a class="subsection" href="#mousecursor">Messing with the mouse cursor</a>
108 <li><a class="subsection" href="#mousecursorcreate">Creating and destroying a mouse cursor</a>
109 <li><a class="subsection" href="#mousecursorset">Setting a window's mouse cursor</a>
110 <li><a class="subsection" href="#mousecursorexample">Complete example</a>
112 <li><a class="subsection" href="#translation">Translation of basic Xlib functions and macros</a>
114 <li><a class="subsection" href="#displaystructure">Members of the Display structure</a>
116 <li><a class="subsection" href="#ConnectionNumber">ConnectionNumber</a>
117 <li><a class="subsection" href="#DefaultScreen">DefaultScreen</a>
118 <li><a class="subsection" href="#QLength">QLength</a>
119 <li><a class="subsection" href="#ScreenCount">ScreenCount</a>
120 <li><a class="subsection" href="#ServerVendor">ServerVendor</a>
121 <li><a class="subsection" href="#ProtocolVersion">ProtocolVersion</a>
122 <li><a class="subsection" href="#ProtocolRevision">ProtocolRevision</a>
123 <li><a class="subsection" href="#VendorRelease">VendorRelease</a>
124 <li><a class="subsection" href="#DisplayString">DisplayString</a>
125 <li><a class="subsection" href="#BitmapUnit">BitmapUnit</a>
126 <li><a class="subsection" href="#BitmapBitOrder">BitmapBitOrder</a>
127 <li><a class="subsection" href="#BitmapPad">BitmapPad</a>
128 <li><a class="subsection" href="#ImageByteOrder">ImageByteOrder</a>
130 <li><a class="subsection" href="#screenofdisplay">ScreenOfDisplay related functions</a>
132 <li><a class="subsection" href="#ScreenOfDisplay">ScreenOfDisplay</a>
133 <li><a class="subsection" href="#DefaultScreenOfDisplay">DefaultScreenOfDisplay</a>
134 <li><a class="subsection" href="#RootWindow">RootWindow / RootWindowOfScreen</a>
135 <li><a class="subsection" href="#DefaultRootWindow">DefaultRootWindow</a>
136 <li><a class="subsection" href="#DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a>
137 <li><a class="subsection" href="#DefaultGC">DefaultGC / DefaultGCOfScreen</a>
138 <li><a class="subsection" href="#BlackPixel">BlackPixel / BlackPixelOfScreen</a>
139 <li><a class="subsection" href="#WhitePixel">WhitePixel / WhitePixelOfScreen</a>
140 <li><a class="subsection" href="#DisplayWidth">DisplayWidth / WidthOfScreen</a>
141 <li><a class="subsection" href="#DisplayHeight">DisplayHeight / HeightOfScreen</a>
142 <li><a class="subsection" href="#DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a>
143 <li><a class="subsection" href="#DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a>
144 <li><a class="subsection" href="#DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a>
145 <li><a class="subsection" href="#DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a>
146 <li><a class="subsection" href="#MinCmapsOfScreen">MinCmapsOfScreen</a>
147 <li><a class="subsection" href="#MaxCmapsOfScreen">MaxCmapsOfScreen</a>
148 <li><a class="subsection" href="#DoesSaveUnders">DoesSaveUnders</a>
149 <li><a class="subsection" href="#DoesBackingStore">DoesBackingStore</a>
150 <li><a class="subsection" href="#EventMaskOfScreen">EventMaskOfScreen</a>
152 <li><a class="subsection" href="#misc">Miscellaneaous macros</a>
154 <li><a class="subsection" href="#DisplayOfScreen">DisplayOfScreen</a>
155 <li><a class="subsection" href="#DisplayCells">DisplayCells / CellsOfScreen</a>
160 <div class="section">
162 <li class="title"><a name="intro">Introduction</a>
164 This tutorial is based on the
165 <a href="http://users.actcom.co.il/~choo/lupg/tutorials/xlib-programming/xlib-programming.html">Xlib Tutorial</a>
166 written by <a href="mailto:choor at atcom dot co dot il">Guy Keren</a>. The
167 author allowed me to take some parts of his text, mainly the text which
168 deals with the X Windows generality.
171 This tutorial is intended for people who want to start to program
172 with the <a href="http://xcb.freedesktop.org">XCB</a>
173 library. keep in mind that XCB, like the
174 <a href="http://tronche.com/gui/x/xlib/introduction">Xlib</a>
175 library, isn't what post programmers wanting to write X
176 applications are looking for. They should use a much higher
177 level GUI toolkit like Motif,
178 <a href="http://www.lesstif.org">LessTiff</a>,
179 <a href="http://www.gtk.org">GTK</a>,
180 <a href="http://www.trolltech.com">QT</a> or
181 <a href="http://www.enlightenment.org">EWL</a>, or use
182 <a href="http://cairographics.org">Cairo</a>.
184 we need to start somewhere. More than this, knowing how things
185 work down below is never a bad idea.
188 After reading this tutorial, one should be able to write very
189 simple graphical programs, but not programs with decent user
190 interfaces. For such programs, one of the previously mentioned
191 libraries should be used.
194 But what is XCB? Xlib has been
195 the standard C binding for the <a href="http://www.x.org">X
196 Window System</a> protocol for many years now. It is an
197 excellent piece of work, but there are applications for which it
198 is not ideal, for example:
201 <li><b>Small platforms</b>: Xlib is a large piece of code, and
202 it's difficult to make it smaller
203 <li><b>Latency hiding</b>: Xlib requests requiring a reply are
204 effectively synchronous: they block until the reply appears,
205 whether the result is needed immediately or not.
206 <li><b>Direct access to the protocol</b>: Xlib does quite a
207 bit of caching, layering, and similar optimizations. While this
208 is normally a feature, it makes it difficult to simply emit
209 specified X protocol requests and process specific
211 <li><b>Threaded applications</b>: While Xlib does attempt to
212 support multithreading, the API makes this difficult and
214 <li><b>New extensions</b>: The Xlib infrastructure provides
215 limited support for the new creation of X extension client side
219 For these reasons, among others, XCB, an X C binding, has been
220 designed to solve the above problems and thus provide a base for
223 <li>Toolkit implementation.
224 <li>Direct protocol-level programming.
225 <li>Lightweight emulation of commonly used portions of the
229 <li class="title"><a name="Xmodel">The client and server model of the X window system</a>
231 The X Window System was developed with one major goal:
232 flexibility. The idea was that the way things look is one thing,
233 but the way things work is another matter. Thus, the lower
234 levels provide the tools required to draw windows, handle user
235 input, allow drawing graphics using colors (or black and white
236 screens), etc. To this point, a decision was made to separate
237 the system into two parts. A client that decides what to do, and
238 a server that actually draws on the screen and reads user input
239 in order to send it to the client for processing.
242 This model is the complete opposite of what is used to when
243 dealing with clients and servers. In our case, the user sits
244 near the machine controlled by the server, while the client
245 might be running on a remote machine. The server controls the
246 screens, mouse and keyboard. A client may connect to the server,
247 request that it draws a window (or several windows), and ask the
248 server to send it any input the user sends to these
249 windows. Thus, several clients may connect to a single X server
250 (one might be running mail software, one running a WWW
251 browser, etc). When input is sent by the user to some window,
252 the server sends a message to the client controlling this window
253 for processing. The client decides what to do with this input,
254 and sends the server requests for drawing in the window.
257 The whole session is carried out using the X message
258 protocol. This protocol was originally carried over the TCP/IP
259 protocol suite, allowing the client to run on any machine
260 connected to the same network that the server is. Later on, the
261 X servers were extended to allow clients running on the local
262 machine with more optimized access to the server (note that an X
263 protocol message may be several hundreds of KB in size), such as
264 using shared memory, or using Unix domain sockets (a method for
265 creating a logical channel on a Unix system between two processes).
267 <li class="title"><a name="asynch">GUI programming: the asynchronous model</a>
269 Unlike conventional computer programs, that carry some serial
270 nature, a GUI program usually uses an asynchronous programming
271 model, also known as "event-driven programming". This means that
272 that program mostly sits idle, waiting for events sent by the X
273 server, and then acts upon these events. An event may say "The
274 user pressed the 1st button mouse in spot (x,y)", or "The window
275 you control needs to be redrawn". In order for the program to be
276 responsive to the user input, as well as to refresh requests, it
277 needs to handle each event in a rather short period of time
278 (e.g. less that 200 milliseconds, as a rule of thumb).
281 This also implies that the program may not perform operations
282 that might take a long time while handling an event (such as
283 opening a network connection to some remote server, or
284 connecting to a database server, or even performing a long file
285 copy operation). Instead, it needs to perform all these
286 operations in an asynchronous manner. This may be done by using
287 various asynchronous models to perform the longish operations,
288 or by performing them in a different process or thread.
291 So the way a GUI program looks is something like that:
294 <li>Perform initialization routines.
295 <li>Connect to the X server.
296 <li>Perform X-related initialization.
297 <li>While not finished:
299 <li>Receive the next event from the X server.
300 <li>Handle the event, possibly sending various drawing
301 requests to the X server.
302 <li>If the event was a quit message, exit the loop.
304 <li>Close down the connection to the X server.
305 <li>Perform cleanup operations.
308 <li class="title"><a name="notions">Basic XCB notions</a>
310 XCB has been created to eliminate the need for
311 programs to actually implement the X protocol layer. This
312 library gives a program a very low-level access to any X
313 server. Since the protocol is standardized, a client using any
314 implementation of XCB may talk with any X server (the same
315 occurs for Xlib, of course). We now give a brief description of
316 the basic XCB notions. They will be detailed later.
319 <li class="subtitle"><a name="conn">The X Connection</a>
321 The major notion of using XCB is the X Connection. This is a
322 structure representing the connection we have open with a
323 given X server. It hides a queue of messages coming from the
324 server, and a queue of pending requests that our client
325 intends to send to the server. In XCB, this structure is named
326 'xcb_connection_t'. It is analogous to the Xlib Display.
327 When we open a connection to an X server, the
328 library returns a pointer to such a structure. Later, we
329 supply this pointer to any XCB function that should send
330 messages to the X server or receive messages from this server.
332 <li class="subtitle"><a name="requestsreplies">Requests and
333 replies: the Xlib killers</a>
335 To ask for information from the X server, we have to make a request
336 and ask for a reply. With Xlib, these two tasks are
337 automatically done: Xlib locks the system, sends a request,
338 waits for a reply from the X server and unlocks. This is
339 annoying, especially if one makes a lot of requests to the X
340 server. Indeed, Xlib has to wait for the end of a reply
341 before asking for the next request (because of the locks that
342 Xlib sends). For example, here is a time-line of N=4
343 requests/replies with Xlib, with a round-trip latency
344 <b>T_round_trip</b> that is 5 times long as the time required
345 to write or read a request/reply (<b>T_write/T_read</b>):
348 W-----RW-----RW-----RW-----R
351 <li>W: Writing request
352 <li>-: Stalled, waiting for data
356 The total time is N * (T_write + T_round_trip + T_read).
359 With XCB, we can suppress most of the round-trips as the
360 requests and the replies are not locked. We usually send a
361 request, then XCB returns to us a <b>cookie</b>, which is an
362 identifier. Then, later, we ask for a reply using this
363 <b>cookie</b> and XCB returns a
364 pointer to that reply. Hence, with XCB, we can send a lot of
365 requests, and later in the program, ask for all the replies
366 when we need them. Here is the time-line for 4
367 requests/replies when we use this property of XCB:
373 The total time is N * T_write + max (0, T_round_trip - (N-1) *
374 T_write) + N * T_read. Which can be considerably faster than
375 all those Xlib round-trips.
378 Here is a program that computes the time to create 500 atoms
379 with Xlib and XCB. It shows the Xlib way, the bad XCB way
380 (which is similar to Xlib) and the good XCB way. On my
381 computer, XCB is 25 times faster than Xlib.
384 #include <stdlib.h>
385 #include <stdio.h>
386 #include <string.h>
387 #include <sys/time.h>
389 #include <xcb/xcb.h>
391 #include <X11/Xlib.h>
396 struct timeval timev;
398 gettimeofday(&timev, NULL);
400 return (double)timev.tv_sec + (((double)timev.tv_usec) / 1000000);
408 xcb_intern_atom_cookie_t *cs;
421 c = xcb_connect (NULL, NULL);
424 atoms = (xcb_atom_t *)malloc (count * sizeof (atoms));
425 names = (char **)malloc (count * sizeof (char *));
428 for (i = 0; i < count; ++i) {
431 sprintf (buf, "NAME%d", i);
432 names[i] = strdup (buf);
438 for (i = 0; i < count; ++i)
439 atoms[i] = xcb_intern_atom_reply (c,
448 printf ("bad use time : %f\n", diff);
453 cs = (xcb_intern_atom_cookie_t *) malloc (count * sizeof(xcb_intern_atom_cookie_t));
454 for(i = 0; i < count; ++i)
455 cs[i] = xcb_intern_atom (c, 0, strlen(names[i]), names[i]);
457 for(i = 0; i < count; ++i) {
458 xcb_intern_atom_reply_t *r;
460 r = xcb_intern_atom_reply(c, cs[i], 0);
467 printf ("good use time : %f\n", end - start);
468 printf ("ratio : %f\n", diff / (end - start));
472 for (i = 0; i < count; ++i)
480 disp = XOpenDisplay (getenv("DISPLAY"));
482 atoms_x = (Atom *)malloc (count * sizeof (atoms_x));
486 for (i = 0; i < count; ++i)
487 atoms_x[i] = XInternAtom(disp, names[i], 0);
490 diff_x = end - start;
491 printf ("Xlib use time : %f\n", diff_x);
492 printf ("ratio : %f\n", diff_x / diff);
497 XCloseDisplay (disp);
502 <li class="subtitle"><a name="gc">The Graphic Context</a>
504 When we perform various drawing operations (graphics, text,
505 etc), we may specify various options for controlling how the
506 data will be drawn (what foreground and background colors to
507 use, how line edges will be connected, what font to use when
508 drawing some text, etc). In order to avoid the need to supply
509 hundreds of parameters to each drawing function, a graphical
510 context structure is used. We set the various drawing options
511 in this structure, and then we pass a pointer to this
512 structure to any drawing routines. This is rather handy, as we
513 often need to perform several drawing requests with the same
514 options. Thus, we would initialize a graphical context, set
515 the desired options, and pass this structure to all drawing
519 Note that graphic contexts have no client-side structure in
520 XCB, they're just XIDs. Xlib has a client-side structure
521 because it caches the GC contents so it can avoid making
522 redundant requests, but of course XCB doesn't do that.
524 <li class="subtitle"><a name="events">Events</a>
526 A structure is used to pass events received from the X
527 server. XCB supports exactly the events specified in the
528 protocol (33 events). This structure contains the type
529 of event received (including a bit for whether it came
530 from the server or another client), as well as the data associated with the
531 event (e.g. position on the screen where the event was
532 generated, mouse button associated with the event, region of
533 the screen associated with a "redraw" event, etc). The way to
534 read the event's data depends on the event type.
538 <li class="title"><a name="use">Using XCB-based programs</a>
541 <li class="subtitle"><a name="inst">Installation of XCB</a>
543 <b>TODO:</b> These instructions are out of date.
544 Just reference the <a href="http://xcb.freedesktop.org/">main XCB page</a>
545 so we don't have to maintain these instructions in more than
549 To build XCB from source, you need to have installed at
554 <li><a href="http://www.gnu.org/software/automake/">automake 1.7</a>
555 <li><a href="http://www.gnu.org/software/autoconf/">autoconf 2.50</a>
556 <li><a href="http://www.check.org">check</a>
557 <li><a href="http://xmlsoft.org/XSLT/">xsltproc</a>
558 <li><a href="http://www.gnu.org/software/gperf/">gperf 3.0.1</a>
561 You have to checkout in the git repository the following modules:
569 Note that xcb-proto exists only to install header
570 files, so typing 'make' or 'make all' will produce the message
571 "Nothing to be done for 'all'". That's normal.
573 <li class="subtitle"><a name="comp">Compiling XCB-based programs</a>
575 Compiling XCB-based programs requires linking them with the XCB
576 library. This is easily done thanks to pkgconfig:
579 gcc -Wall prog.c -o prog `pkg-config --cflags --libs xcb`
582 <li class="title"><a name="openconn">Opening and closing the connection to an X server</a>
584 An X program first needs to open the connection to the X
585 server. There is a function that opens a connection. It requires
586 the display name, or NULL. In the latter case, the display name
587 will be the one in the environment variable DISPLAY.
590 <span class="type">xcb_connection_t</span> *xcb_connect (<span class="keyword">const</span> <span class="type">char</span> *displayname,
591 <span class="type">int</span> *screenp);
594 The second parameter returns the screen number used for the
595 connection. The returned structure describes an XCB connection
596 and is opaque. Here is how the connection can be opened:
599 #<span class="include">include</span> <span class="string"><xcb/xcb.h></span>
601 <span class="type">int</span>
602 <span class="function">main</span> ()
604 <span class="type">xcb_connection_t</span> *c;
606 /* Open the connection to the X server. Use the DISPLAY environment variable as the default display name */
607 c = xcb_connect (NULL, NULL);
609 <span class="keyword">return</span> 0;
613 To close a connection, it suffices to use:
616 <span class="type">void</span> xcb_disconnect (<span class="type">xcb_connection_t</span> *c);
639 <li>xcb_disconnect ()
644 <li class="title"><a name="screen">Checking basic information about a connection</a>
646 Once we have opened a connection to an X server, we should check some
647 basic information about it: what screens it has, what is the
648 size (width and height) of the screen, how many colors it
649 supports (black and white ? grey scale ?, 256 colors ? more ?),
650 and so on. We get such information from the xcb_screen_t
656 xcb_colormap_t default_colormap;
657 uint32_t white_pixel;
658 uint32_t black_pixel;
659 uint32_t current_input_masks;
660 uint16_t width_in_pixels;
661 uint16_t height_in_pixels;
662 uint16_t width_in_millimeters;
663 uint16_t height_in_millimeters;
664 uint16_t min_installed_maps;
665 uint16_t max_installed_maps;
666 xcb_visualid_t root_visual;
667 uint8_t backing_stores;
670 uint8_t allowed_depths_len;
674 We could retrieve the first screen of the connection by using the
678 xcb_screen_iterator_t xcb_setup_roots_iterator (xcb_setup_t *R);
681 Here is a small program that shows how to use this function:
684 #include <stdio.h>
686 #include <xcb/xcb.h>
692 xcb_screen_t *screen;
694 xcb_screen_iterator_t iter;
696 /* Open the connection to the X server. Use the DISPLAY environment variable */
697 c = xcb_connect (NULL, &screen_nbr);
699 /* Get the screen #screen_nbr */
700 iter = xcb_setup_roots_iterator (xcb_get_setup (c));
701 for (; iter.rem; --screen_nbr, xcb_screen_next (&iter))
702 if (screen_nbr == 0) {
708 printf ("Informations of screen %ld:\n", screen->root.xid);
709 printf (" width.........: %d\n", screen->width_in_pixels);
710 printf (" height........: %d\n", screen->height_in_pixels);
711 printf (" white pixel...: %ld\n", screen->white_pixel);
712 printf (" black pixel...: %ld\n", screen->black_pixel);
718 <li class="title"><a name="helloworld">Creating a basic window - the "hello world" program</a>
720 After we got some basic information about our screen, we can
721 create our first window. In the X Window System, a window is
722 characterized by an Id. So, in XCB, a window is of type:
730 We first ask for a new Id for our window, with this function:
733 xcb_window_t xcb_generate_id(xcb_connection_t *c);
736 Then, XCB supplies the following function to create new windows:
739 xcb_void_cookie_t xcb_create_window (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
740 uint8_t depth, /* Depth of the screen */
741 xcb_window_t wid, /* Id of the window */
742 xcb_window_t parent, /* Id of an existing window that should be the parent of the new window */
743 int16_t x, /* X position of the top-left corner of the window (in pixels) */
744 int16_t y, /* Y position of the top-left corner of the window (in pixels) */
745 uint16_t width, /* Width of the window (in pixels) */
746 uint16_t height, /* Height of the window (in pixels) */
747 uint16_t border_width, /* Width of the window's border (in pixels) */
749 xcb_visualid_t visual,
751 const uint32_t *value_list);
754 The fact that we created the window does not mean that it will
755 be drawn on screen. By default, newly created windows are not
756 mapped on the screen (they are invisible). In order to make our
757 window visible, we use the function <span class="code">xcb_map_window()</span>, whose
761 xcb_void_cookie_t xcb_map_window (xcb_connection_t *c,
762 xcb_window_t window);
765 Finally, here is a small program to create a window of size
766 150x150 pixels, positioned at the top-left corner of the screen:
769 #include <unistd.h> /* pause() */
771 #include <xcb/xcb.h>
777 xcb_screen_t *screen;
780 /* Open the connection to the X server */
781 c = xcb_connect (NULL, NULL);
783 /* Get the first screen */
784 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
786 /* Ask for our window's Id */
787 win = xcb_generate_id(c);
789 /* Create the window */
790 xcb_create_window (c, /* Connection */
791 XCB_COPY_FROM_PARENT, /* depth (same as root)*/
793 screen->root, /* parent window */
795 150, 150, /* width, height */
796 10, /* border_width */
797 XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
798 screen->root_visual, /* visual */
799 0, NULL); /* masks, not used yet */
801 /* Map the window on the screen */
802 xcb_map_window (c, win);
804 /* Make sure commands are sent before we pause, so window is shown */
807 pause (); /* hold client until Ctrl-C */
813 In this code, you see one more function - <span class="code">xcb_flush()</span>, not explained
814 yet. It is used to flush all the pending requests. More
815 precisely, there are 2 functions that do such things. The first
816 one is <span class="code">xcb_flush()</span>:
819 int xcb_flush (xcb_connection_t *c);
822 This function flushes all pending requests to the X server (much
823 like the <span class="code">fflush()</span> function is used to
824 flush standard output). The second function is
825 <span class="code">xcb_aux_sync()</span>:
828 int xcb_aux_sync (xcb_connection_t *c);
831 This functions also flushes all pending requests to the X
832 server, and then waits until the X server finishing processing
833 these requests. In a normal program, this will not be necessary
834 (we'll see why when we get to write a normal X program), but for
835 now, we put it there.
838 The window that is created by the above code has a non defined
839 background. This one can be set to a specific color,
840 thanks to the two last parameters of
841 <span class="code">xcb_create_window()</span>, which are not
842 described yet. See the subsections
843 <a href="#winconf">Configuring a window</a> or
844 <a href="#winconf">Registering for event types using event masks</a>
845 for examples on how to use these parameters. In addition, as no
846 events are handled, you have to make a Ctrl-C to interrupt the
850 <b>TODO</b>: one should tell what these functions return and
851 about the generic error
864 <li>xcb_generate_id ()
865 <li>xcb_create_window ()
870 <li class="title"><a name="drawing">Drawing in a window</a>
872 Drawing in a window can be done using various graphical
873 functions (drawing pixels, lines, rectangles, etc). In order to
874 draw in a window, we first need to define various general
875 drawing parameters (what line width to use, which color to draw
876 with, etc). This is done using a graphical context.
879 <li class="subtitle"><a name="allocgc">Allocating a Graphics Context</a>
881 As we said, a graphical context defines several attributes to
882 be used with the various drawing functions. For this, we
883 define a graphical context. We can use more than one graphical
884 context with a single window, in order to draw in multiple
885 styles (different colors, different line widths, etc). In XCB,
886 a Graphics Context is, as a window, characterized by an Id:
894 We first ask the X server to attribute an Id to our graphic
895 context with this function:
898 xcb_gcontext_t xcb_generate_id (xcb_connection_t *c);
901 Then, we set the attributes of the graphic context with this function:
904 xcb_void_cookie_t xcb_create_gc (xcb_connection_t *c,
906 xcb_drawable_t drawable,
908 const uint32_t *value_list);
911 We give now an example on how to allocate a graphic context
912 that specifies that each drawing function that uses it will
913 draw in foreground with a black color.
916 #include <xcb/xcb.h>
922 xcb_screen_t *screen;
924 xcb_gcontext_t black;
928 /* Open the connection to the X server and get the first screen */
929 c = xcb_connect (NULL, NULL);
930 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
932 /* Create a black graphic context for drawing in the foreground */
933 win = screen->root;
934 black = xcb_generate_id (c);
935 mask = XCB_GC_FOREGROUND;
936 value[0] = screen->black_pixel;
937 xcb_create_gc (c, black, win, mask, value);
943 Note should be taken regarding the role of "value_mask" and
944 "value_list" in the prototype of <span class="code">xcb_create_gc()</span>. Since a
945 graphic context has many attributes, and since we often just
946 want to define a few of them, we need to be able to tell the
947 <span class="code">xcb_create_gc()</span> which attributes we
948 want to set. This is what the "value_mask" parameter is
949 for. We then use the "value_list" parameter to specify actual
950 values for the attribute we defined in "value_mask". Thus, for
951 each constant used in "value_list", we will use the matching
952 constant in "value_mask". In this case, we define a graphic
953 context with one attribute: when drawing (a point, a line,
954 etc), the foreground color will be black. The rest of the
955 attributes of this graphic context will be set to their
959 See the next Subsection for more details.
972 <li>xcb_generate_id ()
978 <li class="subtitle"><a name="changegc">Changing the attributes of a Graphics Context</a>
980 Once we have allocated a Graphic Context, we may need to
981 change its attributes (for example, changing the foreground
982 color we use to draw a line, or changing the attributes of the
983 font we use to display strings. See Subsections Drawing with a
984 color and Assigning a Font to a Graphic Context). This is done
985 by using this function:
988 xcb_void_cookie_t xcb_change_gc (xcb_connection_t *c, /* The XCB Connection */
989 xcb_gcontext_t gc, /* The Graphic Context */
990 uint32_t value_mask, /* Components of the Graphic Context that have to be set */
991 const uint32_t *value_list); /* Value as specified by value_mask */
994 The <span class="code">value_mask</span> parameter could take
995 any combination of these masks from the xcb_gc_t enumeration:
999 <li>XCB_GC_PLANE_MASK
1000 <li>XCB_GC_FOREGROUND
1001 <li>XCB_GC_BACKGROUND
1002 <li>XCB_GC_LINE_WIDTH
1003 <li>XCB_GC_LINE_STYLE
1004 <li>XCB_GC_CAP_STYLE
1005 <li>XCB_GC_JOIN_STYLE
1006 <li>XCB_GC_FILL_STYLE
1007 <li>XCB_GC_FILL_RULE
1010 <li>XCB_GC_TILE_STIPPLE_ORIGIN_X
1011 <li>XCB_GC_TILE_STIPPLE_ORIGIN_Y
1013 <li>XCB_GC_SUBWINDOW_MODE
1014 <li>XCB_GC_GRAPHICS_EXPOSURES
1015 <li>XCB_GC_CLIP_ORIGIN_X
1016 <li>XCB_GC_CLIP_ORIGIN_Y
1017 <li>XCB_GC_CLIP_MASK
1018 <li>XCB_GC_DASH_OFFSET
1019 <li>XCB_GC_DASH_LIST
1023 It is possible to set several attributes at the same
1024 time (for example setting the attributes of a font and the
1025 color which will be used to display a string), by OR'ing these
1026 values in <span class="code">value_mask</span>. Then
1027 <span class="code">value_list</span> has to be an array which
1028 lists the value for the respective attributes. <b>These values
1029 must be in the same order as masks listed above.</b> See Subsection
1030 Drawing with a color to have an example.
1033 <b>TODO</b>: set the links of the 3 subsections, once they will
1037 <b>TODO</b>: give an example which sets several attributes.
1039 <li class="subtitle"><a name="drawingprim">Drawing primitives: point, line, box, circle,...</a>
1041 After we have created a Graphic Context, we can draw on a
1042 window using this Graphic Context, with a set of XCB
1043 functions, collectively called "drawing primitives". Let see
1047 To draw a point, or several points, we use
1050 xcb_void_cookie_t xcb_poly_point (xcb_connection_t *c, /* The connection to the X server */
1051 uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */
1052 xcb_drawable_t drawable, /* The drawable on which we want to draw the point(s) */
1053 xcb_gcontext_t gc, /* The Graphic Context we use to draw the point(s) */
1054 uint32_t points_len, /* The number of points */
1055 const xcb_point_t *points); /* An array of points */
1058 The <span class="code">coordinate_mode</span> parameter
1059 specifies the coordinate mode. Available values are
1062 <li><span class="code">XCB_COORD_MODE_ORIGIN</span>
1063 <li><span class="code">XCB_COORD_MODE_PREVIOUS</span>
1066 If XCB_COORD_MODE_PREVIOUS is used, then all points but the first one
1067 are relative to the immediately previous point.
1070 The <span class="code">xcb_point_t</span> type is just a
1071 structure with two fields (the coordinates of the point):
1080 You could see an example in xpoints.c. <b>TODO</b> Set the link.
1083 To draw a line, or a polygonal line, we use
1086 xcb_void_cookie_t xcb_poly_line (xcb_connection_t *c, /* The connection to the X server */
1087 uint8_t coordinate_mode, /* Coordinate mode, usually set to XCB_COORD_MODE_ORIGIN */
1088 xcb_drawable_t drawable, /* The drawable on which we want to draw the line(s) */
1089 xcb_gcontext_t gc, /* The Graphic Context we use to draw the line(s) */
1090 uint32_t points_len, /* The number of points in the polygonal line */
1091 const xcb_point_t *points); /* An array of points */
1094 This function will draw the line between the first and the
1095 second points, then the line between the second and the third
1099 To draw a segment, or several segments, we use
1102 xcb_void_cookie_t xcb_poly_segment (xcb_connection_t *c, /* The connection to the X server */
1103 xcb_drawable_t drawable, /* The drawable on which we want to draw the segment(s) */
1104 xcb_gcontext_t gc, /* The Graphic Context we use to draw the segment(s) */
1105 uint32_t segments_len, /* The number of segments */
1106 const xcb_segment_t *segments); /* An array of segments */
1109 The <span class="code">xcb_segment_t</span> type is just a
1110 structure with four fields (the coordinates of the two points
1111 that define the segment):
1122 To draw a rectangle, or several rectangles, we use
1125 xcb_void_cookie_t xcb_poly_rectangle (xcb_connection_t *c, /* The connection to the X server */
1126 xcb_drawable_t drawable, /* The drawable on which we want to draw the rectangle(s) */
1127 xcb_gcontext_t gc, /* The Graphic Context we use to draw the rectangle(s) */
1128 uint32_t rectangles_len, /* The number of rectangles */
1129 const xcb_rectangle_t *rectangles); /* An array of rectangles */
1132 The <span class="code">xcb_rectangle_t</span> type is just a
1133 structure with four fields (the coordinates of the top-left
1134 corner of the rectangle, and its width and height):
1144 <!-- There's no coordinate_mode. Is it normal? -->
1145 <!-- [iano] Yes, it's not in the protocol. -->
1147 To draw an elliptical arc, or several elliptical arcs, we use
1150 xcb_void_cookie_t xcb_poly_arc (xcb_connection_t *c, /* The connection to the X server */
1151 xcb_drawable_t drawable, /* The drawable on which we want to draw the arc(s) */
1152 xcb_gcontext_t gc, /* The Graphic Context we use to draw the arc(s) */
1153 uint32_t arcs_len, /* The number of arcs */
1154 const xcb_arc_t *arcs); /* An array of arcs */
1157 The <span class="code">xcb_arc_t</span> type is a structure with
1162 int16_t x; /* Top left x coordinate of the rectangle surrounding the ellipse */
1163 int16_t y; /* Top left y coordinate of the rectangle surrounding the ellipse */
1164 uint16_t width; /* Width of the rectangle surrounding the ellipse */
1165 uint16_t height; /* Height of the rectangle surrounding the ellipse */
1166 int16_t angle1; /* Angle at which the arc begins */
1167 int16_t angle2; /* Angle at which the arc ends */
1172 Note: the angles are expressed in units of 1/64 of a degree,
1173 so to have an angle of 90 degrees, starting at 0,
1174 <span class="code">angle1 = 0</span> and
1175 <span class="code">angle2 = 90 << 6</span>. Positive angles
1176 indicate counterclockwise motion, while negative angles
1177 indicate clockwise motion.
1180 <!-- I think that (x,y) should be the center of the
1181 ellipse, and (width, height) the radius. It's more logical. -->
1182 <!-- iano: Yes, and I bet some toolkits do that.
1183 But the protocol (and many other graphics APIs) define arcs
1184 by bounding rectangles. -->
1186 The corresponding function which fill inside the geometrical
1187 object are listed below, without further explanation, as they
1188 are used as the above functions.
1191 To Fill a polygon defined by the points given as arguments ,
1195 xcb_void_cookie_t xcb_fill_poly (xcb_connection_t *c,
1196 xcb_drawable_t drawable,
1199 uint8_t coordinate_mode,
1200 uint32_t points_len,
1201 const xcb_point_t *points);
1204 The <span class="code">shape</span> parameter specifies a
1205 shape that helps the server to improve performance. Available
1209 <li><span class="code">XCB_POLY_SHAPE_COMPLEX</span>
1210 <li><span class="code">XCB_POLY_SHAPE_NONCONVEX</span>
1211 <li><span class="code">XCB_POLY_SHAPE_CONVEX</span>
1214 To fill one or several rectangles, we use
1217 xcb_void_cookie_t xcb_poly_fill_rectangle (xcb_connection_t *c,
1218 xcb_drawable_t drawable,
1220 uint32_t rectangles_len,
1221 const xcb_rectangle_t *rectangles);
1224 To fill one or several arcs, we use
1227 xcb_void_cookie_t xcb_poly_fill_arc (xcb_connection_t *c,
1228 xcb_drawable_t drawable,
1231 const xcb_arc_t *arcs);
1234 <a name="points.c"></a>
1236 To illustrate these functions, here is an example that draws
1237 four points, a polygonal line, two segments, two rectangles
1238 and two arcs. Remark that we use events for the first time, as
1239 an introduction to the next section.
1242 <b>TODO:</b> Use screen->root_depth for depth parameter.
1245 #include <stdlib.h>
1246 #include <stdio.h>
1248 #include <xcb/xcb.h>
1253 xcb_connection_t *c;
1254 xcb_screen_t *screen;
1256 xcb_gcontext_t foreground;
1257 xcb_generic_event_t *e;
1261 /* geometric objects */
1262 xcb_point_t points[] = {
1268 xcb_point_t polyline[] = {
1270 { 5, 20}, /* rest of points are relative */
1274 xcb_segment_t segments[] = {
1276 {110, 25, 130, 60}};
1278 xcb_rectangle_t rectangles[] = {
1282 xcb_arc_t arcs[] = {
1283 {10, 100, 60, 40, 0, 90 << 6},
1284 {90, 100, 55, 40, 0, 270 << 6}};
1286 /* Open the connection to the X server */
1287 c = xcb_connect (NULL, NULL);
1289 /* Get the first screen */
1290 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
1292 /* Create black (foreground) graphic context */
1293 win = screen->root;
1295 foreground = xcb_generate_id (c);
1296 mask = XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES;
1297 values[0] = screen->black_pixel;
1299 xcb_create_gc (c, foreground, win, mask, values);
1301 /* Ask for our window's Id */
1302 win = xcb_generate_id(c);
1304 /* Create the window */
1305 mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
1306 values[0] = screen->white_pixel;
1307 values[1] = XCB_EVENT_MASK_EXPOSURE;
1308 xcb_create_window (c, /* Connection */
1309 XCB_COPY_FROM_PARENT, /* depth */
1310 win, /* window Id */
1311 screen->root, /* parent window */
1313 150, 150, /* width, height */
1314 10, /* border_width */
1315 XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
1316 screen->root_visual, /* visual */
1317 mask, values); /* masks */
1319 /* Map the window on the screen */
1320 xcb_map_window (c, win);
1323 /* We flush the request */
1326 while ((e = xcb_wait_for_event (c))) {
1327 switch (e->response_type & ~0x80) {
1329 /* We draw the points */
1330 xcb_poly_point (c, XCB_COORD_MODE_ORIGIN, win, foreground, 4, points);
1332 /* We draw the polygonal line */
1333 xcb_poly_line (c, XCB_COORD_MODE_PREVIOUS, win, foreground, 4, polyline);
1335 /* We draw the segements */
1336 xcb_poly_segment (c, win, foreground, 2, segments);
1338 /* We draw the rectangles */
1339 xcb_poly_rectangle (c, win, foreground, 2, rectangles);
1341 /* We draw the arcs */
1342 xcb_poly_arc (c, win, foreground, 2, arcs);
1344 /* We flush the request */
1350 /* Unknown event type, ignore it */
1354 /* Free the Generic Event */
1362 <li class="title"><a name="xevents">X Events</a>
1364 In an X program, everything is driven by events. Event painting
1365 on the screen is sometimes done as a response to an event (an
1366 <span class="code">Expose</span> event). If part of a program's
1367 window that was hidden, gets exposed (e.g. the window was raised
1368 above other widows), the X server will send an "expose" event to
1369 let the program know it should repaint that part of the
1370 window. User input (key presses, mouse movement, etc) is also
1371 received as a set of events.
1374 <li class="subtitle"><a name="register">Registering for event types using event masks</a>
1376 During the creation of a window, you should give it what kind
1377 of events it wishes to receive. Thus, you may register for
1378 various mouse (also called pointer) events, keyboard events,
1379 expose events, and so on. This is done for optimizing the
1380 server-to-client connection (i.e. why send a program (that
1381 might even be running at the other side of the globe) an event
1382 it is not interested in ?)
1385 In XCB, you use the "value_mask" and "value_list" data in the
1386 <span class="code">xcb_create_window()</span> function to
1387 register for events. Here is how we register for
1388 <span class="code">Expose</span> event when creating a window:
1391 mask = XCB_CW_EVENT_MASK;
1392 valwin[0] = XCB_EVENT_MASK_EXPOSURE;
1393 win = xcb_generate_id (c);
1394 xcb_create_window (c, depth, win, root->root,
1396 XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual,
1400 <span class="code">XCB_EVENT_MASK_EXPOSURE</span> is a constant defined
1401 in the xcb_event_mask_t enumeration in the "xproto.h" header file. If we wanted to register for several
1402 event types, we can logically "or" them, as follows:
1405 mask = XCB_CW_EVENT_MASK;
1406 valwin[0] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS;
1407 win = xcb_generate_id (c);
1408 xcb_create_window (c, depth, win, root->root,
1410 XCB_WINDOW_CLASS_INPUT_OUTPUT, root->root_visual,
1414 This registers for <span class="code">Expose</span> events as
1415 well as for mouse button presses inside the created
1416 window. You should note that a mask may represent several
1420 The values that a mask could take are given
1421 by the <span class="code">xcb_cw_t</span> enumeration:
1425 XCB_CW_BACK_PIXMAP = 1L<<0,
1426 XCB_CW_BACK_PIXEL = 1L<<1,
1427 XCB_CW_BORDER_PIXMAP = 1L<<2,
1428 XCB_CW_BORDER_PIXEL = 1L<<3,
1429 XCB_CW_BIT_GRAVITY = 1L<<4,
1430 XCB_CW_WIN_GRAVITY = 1L<<5,
1431 XCB_CW_BACKING_STORE = 1L<<6,
1432 XCB_CW_BACKING_PLANES = 1L<<7,
1433 XCB_CW_BACKING_PIXEL = 1L<<8,
1434 XCB_CW_OVERRIDE_REDIRECT = 1L<<9,
1435 XCB_CW_SAVE_UNDER = 1L<<10,
1436 XCB_CW_EVENT_MASK = 1L<<11,
1437 XCB_CW_DONT_PROPAGATE = 1L<<12,
1438 XCB_CW_COLORMAP = 1L<<13,
1439 XCB_CW_CURSOR = 1L<<14
1443 <p>Note: we must be careful when setting the values of the valwin
1444 parameter, as they have to follow the order the
1445 <span class="code">xcb_cw_t</span> enumeration. Here is an
1450 mask = XCB_CW_EVENT_MASK | XCB_CW_BACK_PIXMAP;
1451 valwin[0] = XCB_NONE; /* for XCB_CW_BACK_PIXMAP (whose value is 1) */
1452 valwin[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS; /* for XCB_CW_EVENT_MASK, whose value (2048) */
1453 /* is greater than the one of XCB_CW_BACK_PIXMAP */
1456 If the window has already been created, we can use the
1457 <span class="code">xcb_configure_window()</span> function to set
1458 the events that the window will receive. The subsection
1459 <a href="#winconf">Configuring a window</a> shows its
1460 prototype. As an example, here is a piece of code that
1461 configures the window to receive the
1462 <span class="code">Expose</span> and
1463 <span class="code">ButtonPress</span> events:
1466 const static uint32_t values[] = { XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS };
1468 /* The connection c and the window win are supposed to be defined */
1470 xcb_configure_window (c, win, XCB_CW_EVENT_MASK, values);
1474 Note: A common bug programmers do is adding code to handle new
1475 event types in their program, while forgetting to add the
1476 masks for these events in the creation of the window. Such a
1477 programmer then should sit down for hours debugging his
1478 program, wondering "Why doesn't my program notice that I
1479 released the button?", only to find that they registered for
1480 button press events but not for button release events.
1483 <li class="subtitle"><a name="loop">Receiving events: writing the events loop</a>
1485 After we have registered for the event types we are interested
1486 in, we need to enter a loop of receiving events and handling
1487 them. There are two ways to receive events: a blocking way and
1492 <span class="code">xcb_wait_for_event (xcb_connection_t *c)</span>
1493 is the blocking way. It waits (so blocks...) until an event is
1494 queued in the X server. Then it retrieves it into a newly
1495 allocated structure (it dequeues it from the queue) and returns
1496 it. This structure has to be freed. The function returns
1497 <span class="code">NULL</span> if an error occurs.
1501 <span class="code">xcb_poll_for_event (xcb_connection_t *c, int
1502 *error)</span> is the non-blocking way. It looks at the event
1503 queue and returns (and dequeues too) an existing event into
1504 a newly allocated structure. This structure has to be
1505 freed. It returns <span class="code">NULL</span> if there is
1506 no event. If an error occurs, the parameter <span
1507 class="code">error</span> will be filled with the error
1511 There are various ways to write such a loop. We present two
1512 ways to write such a loop, with the two functions above. The
1513 first one uses <span class="code">xcb_wait_for_event_t</span>, which
1514 is similar to an event Xlib loop using only <span
1515 class="code">XNextEvent</span>:
1518 xcb_generic_event_t *e;
1520 while ((e = xcb_wait_for_event (c))) {
1521 switch (e->response_type & ~0x80) {
1523 /* Handle the Expose event type */
1524 xcb_expose_event_t *ev = (xcb_expose_event_t *)e;
1530 case XCB_BUTTON_PRESS: {
1531 /* Handle the ButtonPress event type */
1532 xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e;
1539 /* Unknown event type, ignore it */
1543 /* Free the Generic Event */
1548 You will certainly want to use <span
1549 class="code">xcb_poll_for_event(xcb_connection_t *c, int
1550 *error)</span> if, in Xlib, you use <span
1551 class="code">XPending</span> or
1552 <span class="code">XCheckMaskEvent</span>:
1555 while (XPending (display)) {
1558 XNextEvent(d, &ev);
1560 /* Manage your event */
1564 Such a loop in XCB looks like:
1567 xcb_generic_event_t *ev;
1569 while ((ev = xcb_poll_for_event (conn, 0))) {
1570 /* Manage your event */
1574 The events are managed in the same way as with <span
1575 class="code">xcb_wait_for_event_t</span>.
1576 Obviously, we will need to give the user some way of
1577 terminating the program. This is usually done by handling a
1578 special "quit" event, as we will soon see.
1591 <li>xcb_wait_for_event ()
1597 <li>XCheckMaskEvent ()
1602 <li>xcb_poll_for_event ()
1607 <li class="subtitle"><a name="expose">Expose events</a>
1609 The <span class="code">Expose</span> event is one of the most
1610 basic (and most used) events an application may receive. It
1611 will be sent to us in one of several cases:
1614 <li>A window that covered part of our window has moved
1615 away, exposing part (or all) of our window.
1616 <li>Our window was raised above other windows.
1617 <li>Our window mapped for the first time.
1618 <li>Our window was de-iconified.
1621 You should note the implicit assumption hidden here: the
1622 contents of our window is lost when it is being obscured
1623 (covered) by either windows. One may wonder why the X server
1624 does not save this contents. The answer is: to save
1625 memory. After all, the number of windows on a display at a
1626 given time may be very large, and storing the contents of all
1627 of them might require a lot of memory. Actually, there is a
1628 way to tell the X server to store the contents of a window in
1629 special cases, as we will see later.
1632 When we get an <span class="code">Expose</span> event, we
1633 should take the event's data from the members of the following
1638 uint8_t response_type; /* The type of the event, here it is XCB_EXPOSE */
1641 xcb_window_t window; /* The Id of the window that receives the event (in case */
1642 /* our application registered for events on several windows */
1643 uint16_t x; /* The x coordinate of the top-left part of the window that needs to be redrawn */
1644 uint16_t y; /* The y coordinate of the top-left part of the window that needs to be redrawn */
1645 uint16_t width; /* The width of the part of the window that needs to be redrawn */
1646 uint16_t height; /* The height of the part of the window that needs to be redrawn */
1648 } xcb_expose_event_t;
1650 <li class="subtitle"><a name="userinput">Getting user input</a>
1652 User input traditionally comes from two sources: the mouse
1653 and the keyboard. Various event types exist to notify us of
1654 user input (a key being presses on the keyboard, a key being
1655 released on the keyboard, the mouse moving over our window,
1656 the mouse entering (or leaving) our window, and so on.
1659 <li class="subsubtitle"><a name="mousepressrelease">Mouse button press and release events</a>
1661 The first event type we will deal with is a mouse
1662 button-press (or button-release) event in our window. In
1663 order to register to such an event type, we should add one
1664 (or more) of the following masks when we create our window:
1667 <li><span class="code">XCB_EVENT_MASK_BUTTON_PRESS</span>: notify us
1668 of any button that was pressed in one of our windows.
1669 <li><span class="code">XCB_EVENT_MASK_BUTTON_RELEASE</span>: notify us
1670 of any button that was released in one of our windows.
1673 The structure to be checked for in our events loop is the
1674 same for these two events, and is the following:
1678 uint8_t response_type; /* The type of the event, here it is xcb_button_press_event_t or xcb_button_release_event_t */
1679 xcb_button_t detail;
1681 xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
1687 int16_t event_x; /* The x coordinate where the mouse has been pressed in the window */
1688 int16_t event_y; /* The y coordinate where the mouse has been pressed in the window */
1689 uint16_t state; /* A mask of the buttons (or keys) during the event */
1690 uint8_t same_screen;
1691 } xcb_button_press_event_t;
1693 typedef xcb_button_press_event_t xcb_button_release_event_t;
1696 The <span class="code">time</span> field may be used to calculate "double-click"
1697 situations by an application (e.g. if the mouse button was
1698 clicked two times in a duration shorter than a given amount
1699 of time, assume this was a double click).
1702 The <span class="code">state</span> field is a mask of the buttons held down during
1703 the event. It is a bitwise OR of any of the following (from the xcb_button_mask_t and
1704 xcb_mod_mask_t enumerations):
1707 <li><span class="code">XCB_BUTTON_MASK_1</span>
1708 <li><span class="code">XCB_BUTTON_MASK_2</span>
1709 <li><span class="code">XCB_BUTTON_MASK_3</span>
1710 <li><span class="code">XCB_BUTTON_MASK_4</span>
1711 <li><span class="code">XCB_BUTTON_MASK_5</span>
1712 <li><span class="code">XCB_MOD_MASK_SHIFT</span>
1713 <li><span class="code">XCB_MOD_MASK_LOCK</span>
1714 <li><span class="code">XCB_MOD_MASK_CONTROL</span>
1715 <li><span class="code">XCB_MOD_MASK_1</span>
1716 <li><span class="code">XCB_MOD_MASK_2</span>
1717 <li><span class="code">XCB_MOD_MASK_3</span>
1718 <li><span class="code">XCB_MOD_MASK_4</span>
1719 <li><span class="code">XCB_MOD_MASK_5</span>
1722 Their names are self explanatory, where the first 5 refer to
1723 the mouse buttons that are being pressed, while the rest
1724 refer to various "special keys" that are being pressed (Mod1
1725 is usually the 'Alt' key or the 'Meta' key).
1728 <b>TODO:</b> Problem: it seems that the state does not
1729 change when clicking with various buttons.
1731 <li class="subsubtitle"><a name="mousemvnt">Mouse movement events</a>
1733 Similar to mouse button press and release events, we also
1734 can be notified of various mouse movement events. These can
1735 be split into two families. One is of mouse pointer
1736 movement while no buttons are pressed, and the second is a
1737 mouse pointer motion while one (or more) of the buttons are
1738 pressed (this is sometimes called "a mouse drag operation",
1739 or just "dragging"). The following event masks may be added
1740 during the creation of our window:
1743 <li><span class="code">XCB_EVENT_MASK_POINTER_MOTION</span>: events of
1744 the pointer moving in one of the windows controlled by our
1745 application, while no mouse button is held pressed.
1746 <li><span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>: Events of
1747 the pointer moving while one or more of the mouse buttons
1749 <li><span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>: same as
1750 <span class="code">XCB_EVENT_MASK_BUTTON_MOTION</span>, but only when
1751 the 1st mouse button is held pressed.
1752 <li><span class="code">XCB_EVENT_MASK_BUTTON_2_MOTION</span>,
1753 <span class="code">XCB_EVENT_MASK_BUTTON_3_MOTION</span>,
1754 <span class="code">XCB_EVENT_MASK_BUTTON_4_MOTION</span>,
1755 <span class="code">XCB_EVENT_MASK_BUTTON_5_MOTION</span>: same as
1756 <span class="code">XCB_EVENT_MASK_BUTTON_1_MOTION</span>, but
1757 respectively for 2nd, 3rd, 4th and 5th mouse button.
1760 The structure to be checked for in our events loop is the
1761 same for these events, and is the following:
1765 uint8_t response_type; /* The type of the event */
1768 xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
1774 int16_t event_x; /* The x coordinate of the mouse when the event was generated */
1775 int16_t event_y; /* The y coordinate of the mouse when the event was generated */
1776 uint16_t state; /* A mask of the buttons (or keys) during the event */
1777 uint8_t same_screen;
1778 } xcb_motion_notify_event_t;
1780 <li class="subsubtitle"><a name="mouseenter">Mouse pointer enter and leave events</a>
1782 Another type of event that applications might be interested
1783 in, is a mouse pointer entering a window the program
1784 controls, or leaving such a window. Some programs use these
1785 events to show the user that the application is now in
1786 focus. In order to register for such an event type, we
1787 should add one (or more) of the following masks when we
1791 <li><span class="code">xcb_event_enter_window_t</span>: notify us
1792 when the mouse pointer enters any of our controlled
1794 <li><span class="code">xcb_event_leave_window_t</span>: notify us
1795 when the mouse pointer leaves any of our controlled
1799 The structure to be checked for in our events loop is the
1800 same for these two events, and is the following:
1804 uint8_t response_type; /* The type of the event */
1807 xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
1813 int16_t event_x; /* The x coordinate of the mouse when the event was generated */
1814 int16_t event_y; /* The y coordinate of the mouse when the event was generated */
1815 uint16_t state; /* A mask of the buttons (or keys) during the event */
1816 uint8_t mode; /* The number of mouse button that was clicked */
1817 uint8_t same_screen_focus;
1818 } xcb_enter_notify_event_t;
1820 typedef xcb_enter_notify_event_t xcb_leave_notify_event_t;
1822 <li class="subsubtitle"><a name="focus">The keyboard focus</a>
1824 There may be many windows on a screen, but only a single
1825 keyboard attached to them. How does the X server then know
1826 which window should be sent a given keyboard input ? This is
1827 done using the keyboard focus. Only a single window on the
1828 screen may have the keyboard focus at a given time. There
1829 is a XCB function that allows a program to set the keyboard
1830 focus to a given window. The user can usually set the
1831 keyboard focus using the window manager (often by clicking
1832 on the title bar of the desired window). Once our window
1833 has the keyboard focus, every key press or key release will
1834 cause an event to be sent to our program (if it regsitered
1835 for these event types...).
1837 <li class="subsubtitle"><a name="keypress">Keyboard press and release events</a>
1839 If a window controlled by our program currently holds the
1840 keyboard focus, it can receive key press and key release
1841 events. So, we should add one (or more) of the following
1842 masks when we create our window:
1845 <li><span class="code">XCB_EVENT_MASK_KEY_PRESS</span>: notify us when
1846 a key was pressed while any of our controlled windows had
1848 <li><span class="code">XCB_EVENT_MASK_KEY_RELEASE</span>: notify us
1849 when a key was released while any of our controlled
1850 windows had the keyboard focus.
1853 The structure to be checked for in our events loop is the
1854 same for these two events, and is the following:
1858 uint8_t response_type; /* The type of the event */
1859 xcb_keycode_t detail;
1861 xcb_timestamp_t time; /* Time, in milliseconds the event took place in */
1870 uint8_t same_screen;
1871 } xcb_key_press_event_t;
1873 typedef xcb_key_press_event_t xcb_key_release_event_t;
1876 The <span class="code">detail</span> field refers to the
1877 physical key on the keyboard.
1880 <b>TODO:</b> Talk about getting the ASCII code from the key code.
1883 <li class="subtitle"><a name="eventex">X events: a complete example</a>
1885 As an example for handling events, we show a program that
1886 creates a window, enters an events loop and checks for all the
1887 events described above, and writes on the terminal the relevant
1888 characteristics of the event. With this code, it should be
1889 easy to add drawing operations, like those which have been
1893 #include <stdlib.h>
1894 #include <stdio.h>
1896 #include <xcb/xcb.h>
1899 print_modifiers (uint32_t mask)
1901 const char **mod, *mods[] = {
1902 "Shift", "Lock", "Ctrl", "Alt",
1903 "Mod2", "Mod3", "Mod4", "Mod5",
1904 "Button1", "Button2", "Button3", "Button4", "Button5"
1906 printf ("Modifier mask: ");
1907 for (mod = mods ; mask; mask >>= 1, mod++)
1916 xcb_connection_t *c;
1917 xcb_screen_t *screen;
1919 xcb_generic_event_t *e;
1923 /* Open the connection to the X server */
1924 c = xcb_connect (NULL, NULL);
1926 /* Get the first screen */
1927 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
1929 /* Ask for our window's Id */
1930 win = xcb_generate_id (c);
1932 /* Create the window */
1933 mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
1934 values[0] = screen->white_pixel;
1935 values[1] = XCB_EVENT_MASK_EXPOSURE | XCB_EVENT_MASK_BUTTON_PRESS |
1936 XCB_EVENT_MASK_BUTTON_RELEASE | XCB_EVENT_MASK_POINTER_MOTION |
1937 XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW |
1938 XCB_EVENT_MASK_KEY_PRESS | XCB_EVENT_MASK_KEY_RELEASE;
1939 xcb_create_window (c, /* Connection */
1941 win, /* window Id */
1942 screen->root, /* parent window */
1944 150, 150, /* width, height */
1945 10, /* border_width */
1946 XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
1947 screen->root_visual, /* visual */
1948 mask, values); /* masks */
1950 /* Map the window on the screen */
1951 xcb_map_window (c, win);
1955 while ((e = xcb_wait_for_event (c))) {
1956 switch (e->response_type & ~0x80) {
1958 xcb_expose_event_t *ev = (xcb_expose_event_t *)e;
1960 printf ("Window %ld exposed. Region to be redrawn at location (%d,%d), with dimension (%d,%d)\n",
1961 ev->window.xid, ev->x, ev->y, ev->width, ev->height);
1964 case XCB_BUTTON_PRESS: {
1965 xcb_button_press_event_t *ev = (xcb_button_press_event_t *)e;
1966 print_modifiers(ev->state);
1968 switch (ev->detail.id) {
1970 printf ("Wheel Button up in window %ld, at coordinates (%d,%d)\n",
1971 ev->event.xid, ev->event_x, ev->event_y);
1974 printf ("Wheel Button down in window %ld, at coordinates (%d,%d)\n",
1975 ev->event.xid, ev->event_x, ev->event_y);
1978 printf ("Button %d pressed in window %ld, at coordinates (%d,%d)\n",
1979 ev->detail.id, ev->event.xid, ev->event_x, ev->event_y);
1983 case XCB_BUTTON_RELEASE: {
1984 xcb_button_release_event_t *ev = (xcb_button_release_event_t *)e;
1985 print_modifiers(ev->state);
1987 printf ("Button %d released in window %ld, at coordinates (%d,%d)\n",
1988 ev->detail.id, ev->event.xid, ev->event_x, ev->event_y);
1991 case XCB_MOTION_NOTIFY: {
1992 xcb_motion_notify_event_t *ev = (xcb_motion_notify_event_t *)e;
1994 printf ("Mouse moved in window %ld, at coordinates (%d,%d)\n",
1995 ev->event.xid, ev->event_x, ev->event_y);
1998 case XCB_ENTER_NOTIFY: {
1999 xcb_enter_notify_event_t *ev = (xcb_enter_notify_event_t *)e;
2001 printf ("Mouse entered window %ld, at coordinates (%d,%d)\n",
2002 ev->event.xid, ev->event_x, ev->event_y);
2005 case XCB_LEAVE_NOTIFY: {
2006 xcb_leave_notify_event_t *ev = (xcb_leave_notify_event_t *)e;
2008 printf ("Mouse left window %ld, at coordinates (%d,%d)\n",
2009 ev->event.xid, ev->event_x, ev->event_y);
2012 case XCB_KEY_PRESS: {
2013 xcb_key_press_event_t *ev = (xcb_key_press_event_t *)e;
2014 print_modifiers(ev->state);
2016 printf ("Key pressed in window %ld\n",
2020 case XCB_KEY_RELEASE: {
2021 xcb_key_release_event_t *ev = (xcb_key_release_event_t *)e;
2022 print_modifiers(ev->state);
2024 printf ("Key released in window %ld\n",
2029 /* Unknown event type, ignore it */
2030 printf("Unknown event: %d\n", e->response_type);
2033 /* Free the Generic Event */
2041 <li class="title"><a name="font">Handling text and fonts</a>
2043 Besides drawing graphics on a window, we often want to draw
2044 text. Text strings have two major properties: the characters to
2045 be drawn and the font with which they are drawn. In order to
2046 draw text, we need to first request the X server to load a
2047 font. We then assign a font to a Graphic Context, and finally, we
2048 draw the text in a window, using the Graphic Context.
2051 <li class="subtitle"><a name="fontstruct">The Font structure</a>
2053 In order to support flexible fonts, a font structure is
2054 defined. You know what ? It's an Id:
2062 It is used to contain information about a font, and is passed
2063 to several functions that handle fonts selection and text drawing.
2066 <b>TODO:</b> example for picking a font and displaying some text.
2067 Even better, also demonstrate translating keypresses to text.
2070 <li class="title"><a name="wm">Interacting with the window manager</a>
2072 After we have seen how to create windows and draw on them, we
2073 take one step back, and look at how our windows are interacting
2074 with their environment (the full screen and the other
2075 windows). First of all, our application needs to interact with
2076 the window manager. The window manager is responsible to
2077 decorating drawn windows (i.e. adding a frame, an iconify
2078 button, a system menu, a title bar, etc), as well as handling
2079 icons shown when windows are being iconified. It also handles
2080 ordering of windows on the screen, and other administrative
2081 tasks. We need to give it various hints as to how we want it to
2082 treat our application's windows.
2085 <li class="subtitle"><a name="wmprop">Window properties</a>
2087 Many of the parameters communicated to the window manager are
2088 passed using data called "properties". These properties are
2089 attached by the X server to different windows, and are stored
2090 in a format that makes it possible to read them from different
2091 machines that may use different architectures (remember that
2092 an X client program may run on a remote machine).
2095 The property and its type (a string, an integer, etc) are
2096 Id. Their type are <span class="code">xcb_atom_t</span>:
2104 To change the property of a window, we use the following
2108 xcb_void_cookie_t xcb_change_property (xcb_connection_t *c, /* Connection to the X server */
2109 uint8_t mode, /* Property mode */
2110 xcb_window_t window, /* Window */
2111 xcb_atom_t property, /* Property to change */
2112 xcb_atom_t type, /* Type of the property */
2113 uint8_t format, /* Format of the property (8, 16, 32) */
2114 uint32_t data_len, /* Length of the data parameter */
2115 const void *data); /* Data */
2118 The <span class="code">mode</span> parameter coud be one of
2119 the following values (defined in enumeration xcb_prop_mode_t in
2120 the xproto.h header file):
2123 <li>XCB_PROP_MODE_REPLACE
2124 <li>XCB_PROP_MODE_PREPEND
2125 <li>XCB_PROP_MODE_APPEND
2128 <li class="subtitle"><a name="wmname">Setting the window name and icon name</a>
2130 The first thing we want to do would be to set the name for our
2131 window. This is done using the
2132 <span class="code">xcb_change_property()</span> function. This
2133 name may be used by the window manager as the title of the
2134 window (in the title bar), in a task list, etc. The property
2135 atom to use to set the name of a window is
2136 <span class="code">WM_NAME</span> (and
2137 <span class="code">WM_ICON_NAME</span> for the iconified
2138 window) and its type is <span class="code">STRING</span>. Here
2139 is an example of utilization:
2142 #include <string.h>
2144 #include <xcb/xcb.h>
2145 #include <xcb/xcb_atom.h>
2150 xcb_connection_t *c;
2151 xcb_screen_t *screen;
2153 char *title = "Hello World !";
2154 char *title_icon = "Hello World ! (iconified)";
2158 /* Open the connection to the X server */
2159 c = xcb_connect (NULL, NULL);
2161 /* Get the first screen */
2162 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
2164 /* Ask for our window's Id */
2165 win = xcb_generate_id (c);
2167 /* Create the window */
2168 xcb_create_window (c, /* Connection */
2170 win, /* window Id */
2171 screen->root, /* parent window */
2173 250, 150, /* width, height */
2174 10, /* border_width */
2175 XCB_WINDOW_CLASS_INPUT_OUTPUT, /* class */
2176 screen->root_visual, /* visual */
2177 0, NULL); /* masks, not used */
2179 /* Set the title of the window */
2180 xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
2182 strlen (title), title);
2184 /* Set the title of the window icon */
2185 xcb_change_property (c, XCB_PROP_MODE_REPLACE, win,
2186 WM_ICON_NAME, STRING, 8,
2187 strlen(title_icon), title_icon);
2189 /* Map the window on the screen */
2190 xcb_map_window (c, win);
2200 <p>Note: the use of the atoms needs our program to be compiled
2201 and linked against xcb_atom, so that we have to use
2205 gcc prog.c -o prog `pkg-config --cflags --libs xcb_atom`
2209 for the program to compile fine.
2213 <li class="title"><a name="winop">Simple window operations</a>
2215 One more thing we can do to our window is manipulate them on the
2216 screen (resize them, move them, raise or lower them, iconify
2217 them, and so on). Some window operations functions are supplied
2218 by XCB for this purpose.
2221 <li class="subtitle"><a name="winmap">Mapping and un-mapping a window</a>
2223 The first pair of operations we can apply on a window is
2224 mapping it, or un-mapping it. Mapping a window causes the
2225 window to appear on the screen, as we have seen in our simple
2226 window program example. Un-mapping it causes it to be removed
2227 from the screen (although the window as a logical entity still
2228 exists). This gives the effect of making a window hidden
2229 (unmapped) and shown again (mapped). For example, if we have a
2230 dialog box window in our program, instead of creating it every
2231 time the user asks to open it, we can create the window once,
2232 in an un-mapped mode, and when the user asks to open it, we
2233 simply map the window on the screen. When the user clicked the
2234 'OK' or 'Cancel' button, we simply un-map the window. This is
2235 much faster than creating and destroying the window, however,
2236 the cost is wasted resources, both on the client side, and on
2240 To map a window, you use the following function:
2243 xcb_void_cookie_t xcb_map_window (xcb_connection_t *c,
2244 xcb_window_t window);
2247 To have a simple example, see the <a href="#helloworld">example</a>
2248 above. The mapping operation will cause an
2249 <span class="code">Expose</span> event to be sent to our
2250 application, unless the window is completely covered by other
2254 Un-mapping a window is also simple. You use the function
2257 xcb_void_cookie_t xcb_unmap_window (xcb_connection_t *c,
2258 xcb_window_t window);
2261 The utilization of this function is the same as
2262 <span class="code">xcb_map_window()</span>.
2264 <li class="subtitle"><a name="winconf">Configuring a window</a>
2266 As we have seen when we have created our first window, in the
2267 X Events subsection, we can set some attributes for the window
2268 (that is, the position, the size, the events the window will
2269 receive, etc). If we want to modify them, but the window is
2270 already created, we can change them by using the following
2274 xcb_void_cookie_t xcb_configure_window (xcb_connection_t *c, /* The connection to the X server*/
2275 xcb_window_t window, /* The window to configure */
2276 uint16_t value_mask, /* The mask */
2277 const uint32_t *value_list); /* The values to set */
2280 We set the <span class="code">value_mask</span> to one or
2281 several mask values that are in the xcb_config_window_t enumeration in the xproto.h header:
2284 <li><span class="code">XCB_CONFIG_WINDOW_X</span>: new x coordinate of the window's top left corner
2285 <li><span class="code">XCB_CONFIG_WINDOW_Y</span>: new y coordinate of the window's top left corner
2286 <li><span class="code">XCB_CONFIG_WINDOW_WIDTH</span>: new width of the window
2287 <li><span class="code">XCB_CONFIG_WINDOW_HEIGHT</span>: new height of the window
2288 <li><span class="code">XCB_CONFIG_WINDOW_BORDER_WIDTH</span>: new width of the border of the window
2289 <li><span class="code">XCB_CONFIG_WINDOW_SIBLING</span>
2290 <li><span class="code">XCB_CONFIG_WINDOW_STACK_MODE</span>: the new stacking order
2293 We then give to <span class="code">value_mask</span> the new
2294 value. We now describe how to use
2295 <span class="code">xcb_configure_window_t</span> in some useful
2298 <li class="subtitle"><a name="winmove">Moving a window around the screen</a>
2300 An operation we might want to do with windows is to move them
2301 to a different location. This can be done like this:
2304 const static uint32_t values[] = { 10, 20 };
2306 /* The connection c and the window win are supposed to be defined */
2308 /* Move the window to coordinates x = 10 and y = 20 */
2309 xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y, values);
2312 Note that when the window is moved, it might get partially
2313 exposed or partially hidden by other windows, and thus we
2314 might get <span class="code">Expose</span> events due to this
2317 <li class="subtitle"><a name="winsize">Resizing a window</a>
2319 Yet another operation we can do is to change the size of a
2320 window. This is done using the following code:
2323 const static uint32_t values[] = { 200, 300 };
2325 /* The connection c and the window win are supposed to be defined */
2327 /* Resize the window to width = 10 and height = 20 */
2328 xcb_configure_window (c, win, XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
2331 We can also combine the move and resize operations using one
2332 single call to <span class="code">xcb_configure_window_t</span>:
2335 const static uint32_t values[] = { 10, 20, 200, 300 };
2337 /* The connection c and the window win are supposed to be defined */
2339 /* Move the window to coordinates x = 10 and y = 20 */
2340 /* and resize the window to width = 10 and height = 20 */
2341 xcb_configure_window (c, win, XCB_CONFIG_WINDOW_X | XCB_CONFIG_WINDOW_Y | XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
2343 <li class="subtitle"><a name="winstack">Changing windows stacking order: raise and lower</a>
2345 Until now, we changed properties of a single window. We'll see
2346 that there are properties that relate to the window and other
2347 windows. One of them is the stacking order. That is, the order
2348 in which the windows are layered on top of each other. The
2349 front-most window is said to be on the top of the stack, while
2350 the back-most window is at the bottom of the stack. Here is
2351 how to manipulate our windows stack order:
2354 const static uint32_t values[] = { XCB_STACK_MODE_ABOVE };
2356 /* The connection c and the window win are supposed to be defined */
2358 /* Move the window on the top of the stack */
2359 xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values);
2362 const static uint32_t values[] = { XCB_STACK_MODE_BELOW };
2364 /* The connection c and the window win are supposed to be defined */
2366 /* Move the window on the bottom of the stack */
2367 xcb_configure_window (c, win, XCB_CONFIG_WINDOW_STACK_MODE, values);
2369 <li class="subtitle"><a name="wingetinfo">Getting information about a window</a>
2371 Just like we can set various attributes of our windows, we can
2372 also ask the X server supply the current values of these
2373 attributes. For example, we can check where a window is
2374 located on the screen, what is its current size, whether it is
2375 mapped or not, etc. The structure that contains some of this
2380 uint8_t response_type;
2381 uint8_t depth; /* depth of the window */
2384 xcb_window_t root; /* Id of the root window *>
2385 int16_t x; /* X coordinate of the window's location */
2386 int16_t y; /* Y coordinate of the window's location */
2387 uint16_t width; /* Width of the window */
2388 uint16_t height; /* Height of the window */
2389 uint16_t border_width; /* Width of the window's border */
2390 } xcb_get_geometry_reply_t;
2393 XCB fill this structure with two functions:
2396 xcb_get_geometry_cookie_t xcb_get_geometry (xcb_connection_t *c,
2397 xcb_drawable_t drawable);
2398 xcb_get_geometry_reply_t *xcb_get_geometry_reply (xcb_connection_t *c,
2399 xcb_get_geometry_cookie_t cookie,
2400 xcb_generic_error_t **e);
2403 You use them as follows:
2406 xcb_connection_t *c;
2408 xcb_get_geometry_reply_t *geom;
2410 /* You initialize c and win */
2412 geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL);
2414 /* Do something with the fields of geom */
2419 Remark that you have to free the structure, as
2420 <span class="code">xcb_get_geometry_reply_t</span> allocates a
2424 One problem is that the returned location of the window is
2425 relative to its parent window. This makes these coordinates
2426 rather useless for any window manipulation functions, like
2427 moving it on the screen. In order to overcome this problem, we
2428 need to take a two-step operation. First, we find out the Id
2429 of the parent window of our window. We then translate the
2430 above relative coordinates to the screen coordinates.
2433 To get the Id of the parent window, we need this structure:
2437 uint8_t response_type;
2442 xcb_window_t parent; /* Id of the parent window */
2443 uint16_t children_len;
2445 } xcb_query_tree_reply_t;
2448 To fill this structure, we use these two functions:
2451 xcb_query_tree_cookie_t xcb_query_tree (xcb_connection_t *c,
2452 xcb_window_t window);
2453 xcb_query_tree_reply_t *xcb_query_tree_reply (xcb_connection_t *c,
2454 xcb_query_tree_cookie_t cookie,
2455 xcb_generic_error_t **e);
2458 The translated coordinates will be found in this structure:
2462 uint8_t response_type;
2463 uint8_t same_screen;
2467 uint16_t dst_x; /* Translated x coordinate */
2468 uint16_t dst_y; /* Translated y coordinate */
2469 } xcb_translate_coordinates_reply_t;
2472 As usual, we need two functions to fill this structure:
2475 xcb_translate_coordinates_cookie_t xcb_translate_coordinates (xcb_connection_t *c,
2476 xcb_window_t src_window,
2477 xcb_window_t dst_window,
2480 xcb_translate_coordinates_reply_t *xcb_translate_coordinates_reply (xcb_connection_t *c,
2481 xcb_translate_coordinates_cookie_t cookie,
2482 xcb_generic_error_t **e);
2485 We use them as follows:
2488 xcb_connection_t *c;
2490 xcb_get_geometry_reply_t *geom;
2491 xcb_query_tree_reply_t *tree;
2492 xcb_translate_coordinates_reply_t *trans;
2494 /* You initialize c and win */
2496 geom = xcb_get_geometry_reply (c, xcb_get_geometry (c, win), NULL);
2500 tree = xcb_query_tree_reply (c, xcb_query_tree (c, win), NULL);
2504 trans = xcb_translate_coordinates_reply (c,
2505 xcb_translate_coordinates (c,
2508 geom->x, geom->y),
2513 /* the translated coordinates are in trans->dst_x and trans->dst_y */
2520 Of course, as for <span class="code">geom</span>,
2521 <span class="code">tree</span> and
2522 <span class="code">trans</span> have to be freed.
2525 The work is a bit hard, but XCB is a very low-level library.
2528 <b>TODO:</b> the utilization of these functions should be a
2529 prog, which displays the coordinates of the window.
2532 There is another structure that gives informations about our window:
2536 uint8_t response_type;
2537 uint8_t backing_store;
2540 xcb_visualid_t visual; /* Visual of the window */
2542 uint8_t bit_gravity;
2543 uint8_t win_gravity;
2544 uint32_t backing_planes;
2545 uint32_t backing_pixel;
2547 uint8_t map_is_installed;
2548 uint8_t map_state; /* Map state of the window */
2549 uint8_t override_redirect;
2550 xcb_colormap_t colormap; /* Colormap of the window */
2551 uint32_t all_event_masks;
2552 uint32_t your_event_mask;
2553 uint16_t do_not_propagate_mask;
2554 } xcb_get_window_attributes_reply_t;
2557 XCB supplies these two functions to fill it:
2560 xcb_get_window_attributes_cookie_t xcb_get_window_attributes (xcb_connection_t *c,
2561 xcb_window_t window);
2562 xcb_get_window_attributes_reply_t *xcb_get_window_attributes_reply (xcb_connection_t *c,
2563 xcb_get_window_attributes_cookie_t cookie,
2564 xcb_generic_error_t **e);
2567 You use them as follows:
2570 xcb_connection_t *c;
2572 xcb_get_window_attributes_reply_t *attr;
2574 /* You initialize c and win */
2576 attr = xcb_get_window_attributes_reply (c, xcb_get_window_attributes (c, win), NULL);
2581 /* Do something with the fields of attr */
2586 As for <span class="code">geom</span>,
2587 <span class="code">attr</span> has to be freed.
2590 <li class="title"><a name="usecolor">Using colors to paint the rainbow</a>
2592 Up until now, all our painting operation were done using black
2593 and white. We will (finally) see now how to draw using colors.
2596 <li class="subtitle"><a name="colormap">Color maps</a>
2598 In the beginning, there were not enough colors. Screen
2599 controllers could only support a limited number of colors
2600 simultaneously (initially 2, then 4, 16 and 256). Because of
2601 this, an application could not just ask to draw in a "light
2602 purple-red" color, and expect that color to be available. Each
2603 application allocated the colors it needed, and when all the
2604 color entries (4, 16, 256 colors) were in use, the next color
2605 allocation would fail.
2608 Thus, the notion of "a color map" was introduced. A color map
2609 is a table whose size is the same as the number of
2610 simultaneous colors a given screen controller. Each entry
2611 contained the RGB (Red, Green and Blue) values of a different
2612 color (all colors can be drawn using some combination of red,
2613 green and blue). When an application wants to draw on the
2614 screen, it does not specify which color to use. Rather, it
2615 specifies which color entry of some color map to be used
2616 during this drawing. Change the value in this color map entry
2617 and the drawing will use a different color.
2620 In order to be able to draw using colors that got something to
2621 do with what the programmer intended, color map allocation
2622 functions are supplied. You could ask to allocate entry for a
2623 color with a set of RGB values. If one already existed, you
2624 would get its index in the table. If none existed, and the
2625 table was not full, a new cell would be allocated to contain
2626 the given RGB values, and its index returned. If the table was
2627 full, the procedure would fail. You could then ask to get a
2628 color map entry with a color that is closest to the one you
2629 were asking for. This would mean that the actual drawing on
2630 the screen would be done using colors similar to what you
2631 wanted, but not the same.
2634 On today's more modern screens where one runs an X server with
2635 support for 16 million colors, this limitation looks a little
2636 silly, but remember that there are still older computers with
2637 older graphics cards out there. Using color map, support for
2638 these screen becomes transparent to you. On a display
2639 supporting 16 million colors, any color entry allocation
2640 request would succeed. On a display supporting a limited
2641 number of colors, some color allocation requests would return
2642 similar colors. It won't look as good, but your application
2645 <li class="subtitle"><a name="colormapalloc">Allocating and freeing Color Maps</a>
2647 When you draw using XCB, you can choose to use the standard
2648 color map of the screen your window is displayed on, or you
2649 can allocate a new color map and apply it to a window. In the
2650 latter case, each time the mouse moves onto your window, the
2651 screen color map will be replaced by your window's color map,
2652 and you'll see all the other windows on screen change their
2653 colors into something quite bizzare. In fact, this is the
2654 effect you get with X applications that use the "-install"
2655 command line option.
2658 In XCB, a color map is (as often in X) an Id:
2666 In order to access the screen's default color map, you just
2667 have to retrieve the <span class="code">default_colormap</span>
2668 field of the <span class="code">xcb_screen_t</span> structure
2670 <a href="#screen">Checking basic information about a connection</a>):
2673 #include <stdio.h>
2675 #include <xcb/xcb.h>
2680 xcb_connection_t *c;
2681 xcb_screen_t *screen;
2682 xcb_colormap_t colormap;
2684 /* Open the connection to the X server and get the first screen */
2685 c = xcb_connect (NULL, NULL);
2686 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
2688 colormap = screen->default_colormap;
2694 This will return the color map used by default on the first
2695 screen (again, remember that an X server may support several
2696 different screens, each of which might have its own resources).
2699 The other option, that of allocating a new colormap, works as
2700 follows. We first ask the X server to give an Id to our color
2701 map, with this function:
2704 xcb_colormap_t xcb_generate_id (xcb_connection_t *c);
2707 Then, we create the color map with
2710 xcb_void_cookie_t xcb_create_colormap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
2711 uint8_t alloc, /* Colormap entries to be allocated (AllocNone or AllocAll) */
2712 xcb_colormap_t mid, /* Id of the color map */
2713 xcb_window_t window, /* Window on whose screen the colormap will be created */
2714 xcb_visualid_t visual); /* Id of the visual supported by the screen */
2717 Here is an example of creation of a new color map:
2720 #include <xcb/xcb.h>
2725 xcb_connection_t *c;
2726 xcb_screen_t *screen;
2730 /* Open the connection to the X server and get the first screen */
2731 c = xcb_connect (NULL, NULL);
2732 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
2734 /* We create the window win here*/
2736 cmap = xcb_generate_id (c);
2737 xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual);
2743 Note that the window parameter is only used to allow the X
2744 server to create the color map for the given screen. We can
2745 then use this color map for any window drawn on the same screen.
2748 To free a color map, it suffices to use this function:
2751 xcb_void_cookie_t xcb_free_colormap (xcb_connection_t *c, /* The connection */
2752 xcb_colormap_t cmap); /* The color map */
2760 <li>XCreateColormap ()
2765 <li>xcb_generate_id ()
2766 <li>xcb_create_colormap ()
2771 <li>XFreeColormap ()
2776 <li>xcb_free_colormap ()
2781 <li class="subtitle"><a name="alloccolor">Allocating and freeing a color entry</a>
2783 Once we got access to some color map, we can start allocating
2784 colors. The informations related to a color are stored in the
2785 following structure:
2789 uint8_t response_type;
2793 uint16_t red; /* The red component */
2794 uint16_t green; /* The green component */
2795 uint16_t blue; /* The blue component */
2797 uint32_t pixel; /* The entry in the color map, supplied by the X server */
2798 } xcb_alloc_color_reply_t;
2801 XCB supplies these two functions to fill it:
2804 xcb_alloc_color_cookie_t xcb_alloc_color (xcb_connection_t *c,
2805 xcb_colormap_t cmap,
2809 xcb_alloc_color_reply_t *xcb_alloc_color_reply (xcb_connection_t *c,
2810 xcb_alloc_color_cookie_t cookie,
2811 xcb_generic_error_t **e);
2814 The fuction <span class="code">xcb_alloc_color()</span> takes the
2815 3 RGB components as parameters (red, green and blue). Here is an
2816 example of using these functions:
2819 #include <malloc.h>
2821 #include <xcb/xcb.h>
2826 xcb_connection_t *c;
2827 xcb_screen_t *screen;
2829 xcb_colormap_t cmap;
2830 xcb_alloc_color_reply_t *rep;
2832 /* Open the connection to the X server and get the first screen */
2833 c = xcb_connect (NULL, NULL);
2834 screen = xcb_setup_roots_iterator (xcb_get_setup (c)).data;
2836 /* We create the window win here*/
2838 cmap = xcb_generate_id (c);
2839 xcb_create_colormap (c, XCB_COLORMAP_ALLOC_NONE, cmap, win, screen->root_visual);
2841 rep = xcb_alloc_color_reply (c, xcb_alloc_color (c, cmap, 65535, 0, 0), NULL);
2846 /* Do something with r->pixel or the components */
2854 As <span class="code">xcb_alloc_color_reply()</span> allocates
2855 memory, you have to free <span class="code">rep</span>.
2858 <b>TODO</b>: Talk about freeing colors.
2861 <li class="title"><a name="pixmaps">X Bitmaps and Pixmaps</a>
2863 One thing many so-called "Multi-Media" applications need to do,
2864 is display images. In the X world, this is done using bitmaps
2865 and pixmaps. We have already seen some usage of them when
2866 setting an icon for our application. Lets study them further,
2867 and see how to draw these images inside a window, along side the
2868 simple graphics and text we have seen so far.
2871 One thing to note before delving further, is that XCB (nor Xlib)
2872 supplies no means of manipulating popular image formats, such as
2873 gif, png, jpeg or tiff. It is up to the programmer (or to higher
2874 level graphics libraries) to translate these image formats into
2875 formats that the X server is familiar with (x bitmaps and x
2879 <li class="subtitle"><a name="pixmapswhat">What is a X Bitmap? An X Pixmap?</a>
2881 An X bitmap is a two-color image stored in a format specific
2882 to the X window system. When stored in a file, the bitmap data
2883 looks like a C source file. It contains variables defining the
2884 width and the height of the bitmap, an array containing the
2885 bit values of the bitmap (the size of the array is
2886 (width+7)/8*height and the bit and byte order are LSB), and
2887 an optional hot-spot location (that will
2888 be explained later, when discussing mouse cursors).
2891 An X pixmap is a format used to stored images in the memory of
2892 an X server. This format can store both black and white images
2893 (such as x bitmaps) as well as color images. It is the only
2894 image format supported by the X protocol, and any image to be
2895 drawn on screen, should be first translated into this format.
2898 In actuality, an X pixmap can be thought of as a window that
2899 does not appear on the screen. Many graphics operations that
2900 work on windows, will also work on pixmaps. Indeed, the type
2901 of X pixmap in XCB is an Id like a window:
2909 In order to make the difference between a window and a pixmap,
2910 XCB introduces a drawable type, which is a <b>union</b>
2914 xcb_window_t window;
2915 xcb_pixmap_t pixmap;
2919 in order to avoid confusion between a window and a pixmap. The
2920 operations that will work the same on a window or a pixmap
2921 will require a <span class="code">xcb_drawable_t</span>
2925 Remark: In Xlib, there is no specific difference between a
2926 <span class="code">Drawable</span>, a
2927 <span class="code">Pixmap</span> or a
2928 <span class="code">Window</span>: all are 32 bit long
2929 integer. XCB wraps all these different IDs in structures to
2930 provide some measure of type-safety.
2933 <li class="subtitle"><a name="pixmapscreate">Creating a pixmap</a>
2935 Sometimes we want to create an un-initialized pixmap, so we
2936 can later draw into it. This is useful for image drawing
2937 programs (creating a new empty canvas will cause the creation
2938 of a new pixmap on which the drawing can be stored). It is
2939 also useful when reading various image formats: we load the
2940 image data into memory, create a pixmap on the server, and
2941 then draw the decoded image data onto that pixmap.
2944 To create a new pixmap, we first ask the X server to give an
2945 Id to our pixmap, with this function:
2948 xcb_pixmap_t xcb_generate_id (xcb_connection_t *c);
2951 Then, XCB supplies the following function to create new pixmaps:
2954 xcb_void_cookie_t xcb_create_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
2955 uint8_t depth, /* Depth of the screen */
2956 xcb_pixmap_t pid, /* Id of the pixmap */
2957 xcb_drawable_t drawable,
2958 uint16_t width, /* Width of the window (in pixels) */
2959 uint16_t height); /* Height of the window (in pixels) */
2962 <b>TODO</b>: Explain the drawable parameter, and give an
2963 example (like <a href="xpoints.c">xpoints.c</a>)
2965 <li class="subtitle"><a name="pixmapsdraw"></a>Drawing a pixmap in a window
2967 Once we got a handle to a pixmap, we can draw it on some
2968 window, using the following function:
2971 xcb_void_cookie_t xcb_copy_area (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
2972 xcb_drawable_t src_drawable, /* The Drawable we want to paste */
2973 xcb_drawable_t dst_drawable, /* The Drawable on which we copy the previous Drawable */
2974 xcb_gcontext_t gc, /* A Graphic Context */
2975 int16_t src_x, /* Top left x coordinate of the region we want to copy */
2976 int16_t src_y, /* Top left y coordinate of the region we want to copy */
2977 int16_t dst_x, /* Top left x coordinate of the region where we want to copy */
2978 int16_t dst_y, /* Top left y coordinate of the region where we want to copy */
2979 uint16_t width, /* Width of the region we want to copy */
2980 uint16_t height); /* Height of the region we want to copy */
2983 As you can see, we could copy the whole pixmap, as well as
2984 only a given rectangle of the pixmap. This is useful to
2985 optimize the drawing speed: we could copy only what we have
2986 modified in the pixmap.
2989 <b>One important note should be made</b>: it is possible to
2990 create pixmaps with different depths on the same screen. When
2991 we perform copy operations (a pixmap onto a window, etc), we
2992 should make sure that both source and target have the same
2993 depth. If they have a different depth, the operation would
2994 fail. The exception to this is if we copy a specific bit plane
2995 of the source pixmap using the
2996 <span class="code">xcb_copy_plane_t</span> function. In such an
2997 event, we can copy a specific plane to the target window (in
2998 actuality, setting a specific bit in the color of each pixel
2999 copied). This can be used to generate strange graphic effects
3000 in a window, but that is beyond the scope of this tutorial.
3002 <li class="subtitle"><a name="pixmapsfree"></a>Freeing a pixmap
3004 Finally, when we are done using a given pixmap, we should free
3005 it, in order to free resources of the X server. This is done
3006 using this function:
3009 xcb_void_cookie_t xcb_free_pixmap (xcb_connection_t *c, /* Pointer to the xcb_connection_t structure */
3010 xcb_pixmap_t pixmap); /* A given pixmap */
3013 Of course, after having freed it, we must not try accessing
3017 <b>TODO</b>: Give an example, or a link to xpoints.c
3020 <li class="title"><a name="mousecursor">Messing with the mouse cursor</a>
3022 It it possible to modify the shape of the mouse pointer (also
3023 called the X pointer) when in certain states, as we otfen see in
3024 programs. For example, a busy application would often display
3025 the sand clock over its main window, to give the user a visual
3026 hint that he should wait. Let's see how we can change the mouse
3027 cursor of our windows.
3030 <li class="subtitle"><a name="mousecursorcreate">Creating and destroying a mouse cursor</a>
3032 There are two methods for creating cursors. One of them is by
3033 using a set of predefined cursors, that are supplied by the X
3034 server, the other is by using a user-supplied bitmap.
3037 In the first method, we use a special font named "cursor", and
3038 the function <span class="code">xcb_create_glyph_cursor</span>:
3041 xcb_void_cookie_t xcb_create_glyph_cursor (xcb_connection_t *c,
3043 xcb_font_t source_font, /* font for the source glyph */
3044 xcb_font_t mask_font, /* font for the mask glyph or XCB_NONE */
3045 uint16_t source_char, /* character glyph for the source */
3046 uint16_t mask_char, /* character glyph for the mask */
3047 uint16_t fore_red, /* red value for the foreground of the source */
3048 uint16_t fore_green, /* green value for the foreground of the source */
3049 uint16_t fore_blue, /* blue value for the foreground of the source */
3050 uint16_t back_red, /* red value for the background of the source */
3051 uint16_t back_green, /* green value for the background of the source */
3052 uint16_t back_blue) /* blue value for the background of the source */
3055 <b>TODO</b>: Describe <span class="code">source_char</span>
3056 and <span class="code">mask_char</span>, for example by giving
3057 an example on how to get the values. There is a list there:
3058 <a href="http://tronche.com/gui/x/xlib/appendix/b/">X Font Cursors</a>
3061 So we first open that font (see <a href="#loadfont">Loading a Font</a>)
3062 and create the new cursor. As for every X ressource, we have to
3063 ask for an X id with <span class="code">xcb_generate_id</span>
3068 xcb_cursor_t cursor;
3070 /* The connection is set */
3072 font = xcb_generate_id (conn);
3073 xcb_open_font (conn, font, strlen ("cursor"), "cursor");
3075 cursor = xcb_generate_id (conn);
3076 xcb_create_glyph_cursor (conn, cursor, font, font,
3082 We have created the cursor "right hand" by specifying 58 to
3083 the <span class="code">source_fon</span>t argument and 58 + 1
3084 to the <span class="code">mask_font</span>.
3087 The cursor is destroyed by using the function
3090 xcb_void_cookie_t xcb_free_cursor (xcb_connection_t *c,
3091 xcb_cursor_t cursor);
3094 In the second method, we create a new cursor by using a pair
3095 of pixmaps, with depth of one (that is, two colors
3096 pixmaps). One pixmap defines the shape of the cursor, while
3097 the other works as a mask, specifying which pixels of the
3098 cursor will be actually drawn. The rest of the pixels will be
3102 <b>TODO</b>: give an example.
3104 <li class="subtitle"><a name="mousecursorset">Setting a window's mouse cursor</a>
3106 Once the cursor is created, we can modify the cursor of our
3107 window by using <span class="code">xcb_change_window_attributes</span>
3108 and using the <span class="code">XCB_CWCURSOR</span> attribute:
3112 uint32_t value_list;
3114 /* The connection and window are set */
3115 /* The cursor is already created */
3117 mask = XCB_CWCURSOR;
3118 value_list = cursor.xid;
3119 xcb_change_window_attributes (conn, window, mask, &value_list);
3122 Of course, the cursor and the font must be freed.
3124 <li class="subtitle"><a name="mousecursorexample">Complete example</a>
3126 The following example displays a window with a
3127 button. When entering the window, the window cursor is changed
3128 to an arrow. When clicking once on the button, the cursor is
3129 changed to a hand. When clicking again on the button, the
3130 cursor window gets back to the arrow. The Esc key exits the
3134 #include <stdlib.h>
3135 #include <stdio.h>
3136 #include <string.h>
3138 #include <xcb/xcb.h>
3145 static xcb_gc_t gc_font_get (xcb_connection_t *c,
3146 xcb_screen_t *screen,
3147 xcb_window_t window,
3148 const char *font_name);
3150 static void button_draw (xcb_connection_t *c,
3151 xcb_screen_t *screen,
3152 xcb_window_t window,
3157 static void text_draw (xcb_connection_t *c,
3158 xcb_screen_t *screen,
3159 xcb_window_t window,
3164 static void cursor_set (xcb_connection_t *c,
3165 xcb_screen_t *screen,
3166 xcb_window_t window,
3171 button_draw (xcb_connection_t *c,
3172 xcb_screen_t *screen,
3173 xcb_window_t window,
3178 xcb_point_t points[5];
3179 xcb_void_cookie_t cookie_gc;
3180 xcb_void_cookie_t cookie_line;
3181 xcb_void_cookie_t cookie_text;
3182 xcb_generic_error_t *error;
3189 length = strlen (label);
3192 gc = gc_font_get(c, screen, window, "7x13");
3194 width = 7 * length + 2 * (inset + 1);
3195 height = 13 + 2 * (inset + 1);
3198 points[1].x = x1 + width;
3200 points[2].x = x1 + width;
3201 points[2].y = y1 - height;
3203 points[3].y = y1 - height;
3206 cookie_line = xcb_poly_line_checked (c, XCB_COORD_MODE_ORIGIN,
3207 window, gc, 5, points);
3209 error = xcb_request_check (c, cookie_line);
3211 fprintf (stderr, "ERROR: can't draw lines : %d\n", error->error_code);
3216 cookie_text = xcb_image_text_8_checked (c, length, window, gc,
3218 y1 - inset - 1, label);
3219 error = xcb_request_check (c, cookie_text);
3221 fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
3226 cookie_gc = xcb_free_gc (c, gc);
3227 error = xcb_request_check (c, cookie_gc);
3229 fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
3236 text_draw (xcb_connection_t *c,
3237 xcb_screen_t *screen,
3238 xcb_window_t window,
3243 xcb_void_cookie_t cookie_gc;
3244 xcb_void_cookie_t cookie_text;
3245 xcb_generic_error_t *error;
3249 length = strlen (label);
3251 gc = gc_font_get(c, screen, window, "7x13");
3253 cookie_text = xcb_image_text_8_checked (c, length, window, gc,
3256 error = xcb_request_check (c, cookie_text);
3258 fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
3263 cookie_gc = xcb_free_gc (c, gc);
3264 error = xcb_request_check (c, cookie_gc);
3266 fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
3273 gc_font_get (xcb_connection_t *c,
3274 xcb_screen_t *screen,
3275 xcb_window_t window,
3276 const char *font_name)
3278 uint32_t value_list[3];
3279 xcb_void_cookie_t cookie_font;
3280 xcb_void_cookie_t cookie_gc;
3281 xcb_generic_error_t *error;
3286 font = xcb_generate_id (c);
3287 cookie_font = xcb_open_font_checked (c, font,
3291 error = xcb_request_check (c, cookie_font);
3293 fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
3298 gc = xcb_generate_id (c);
3299 mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
3300 value_list[0] = screen->black_pixel;
3301 value_list[1] = screen->white_pixel;
3302 value_list[2] = font;
3303 cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list);
3304 error = xcb_request_check (c, cookie_gc);
3306 fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
3311 cookie_font = xcb_close_font_checked (c, font);
3312 error = xcb_request_check (c, cookie_font);
3314 fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
3323 cursor_set (xcb_connection_t *c,
3324 xcb_screen_t *screen,
3325 xcb_window_t window,
3328 uint32_t values_list[3];
3329 xcb_void_cookie_t cookie_font;
3330 xcb_void_cookie_t cookie_gc;
3331 xcb_generic_error_t *error;
3333 xcb_cursor_t cursor;
3336 uint32_t value_list;
3338 font = xcb_generate_id (c);
3339 cookie_font = xcb_open_font_checked (c, font,
3342 error = xcb_request_check (c, cookie_font);
3344 fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
3349 cursor = xcb_generate_id (c);
3350 xcb_create_glyph_cursor (c, cursor, font, font,
3351 cursor_id, cursor_id + 1,
3355 gc = xcb_generate_id (c);
3356 mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
3357 values_list[0] = screen->black_pixel;
3358 values_list[1] = screen->white_pixel;
3359 values_list[2] = font;
3360 cookie_gc = xcb_create_gc_checked (c, gc, window, mask, values_list);
3361 error = xcb_request_check (c, cookie_gc);
3363 fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
3368 mask = XCB_CW_CURSOR;
3369 value_list = cursor;
3370 xcb_change_window_attributes (c, window, mask, &value_list);
3372 xcb_free_cursor (c, cursor);
3374 cookie_font = xcb_close_font_checked (c, font);
3375 error = xcb_request_check (c, cookie_font);
3377 fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
3385 xcb_screen_iterator_t screen_iter;
3386 xcb_connection_t *c;
3387 const xcb_setup_t *setup;
3388 xcb_screen_t *screen;
3389 xcb_generic_event_t *e;
3390 xcb_generic_error_t *error;
3391 xcb_void_cookie_t cookie_window;
3392 xcb_void_cookie_t cookie_map;
3393 xcb_window_t window;
3397 uint8_t is_hand = 0;
3399 /* getting the connection */
3400 c = xcb_connect (NULL, &screen_number);
3402 fprintf (stderr, "ERROR: can't connect to an X server\n");
3406 /* getting the current screen */
3407 setup = xcb_get_setup (c);
3410 screen_iter = xcb_setup_roots_iterator (setup);
3411 for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter))
3412 if (screen_number == 0)
3414 screen = screen_iter.data;
3418 fprintf (stderr, "ERROR: can't get the current screen\n");
3423 /* creating the window */
3424 window = xcb_generate_id (c);
3425 mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
3426 values[0] = screen->white_pixel;
3428 XCB_EVENT_MASK_KEY_RELEASE |
3429 XCB_EVENT_MASK_BUTTON_PRESS |
3430 XCB_EVENT_MASK_EXPOSURE |
3431 XCB_EVENT_MASK_POINTER_MOTION;
3432 cookie_window = xcb_create_window_checked (c,
3434 window, screen->root,
3435 20, 200, WIDTH, HEIGHT,
3436 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
3437 screen->root_visual,
3439 cookie_map = xcb_map_window_checked (c, window);
3441 /* error managing */
3442 error = xcb_request_check (c, cookie_window);
3444 fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code);
3448 error = xcb_request_check (c, cookie_map);
3450 fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code);
3455 cursor_set (c, screen, window, 68);
3460 e = xcb_poll_for_event(c);
3462 switch (e->response_type) {
3466 text = "click here to change cursor";
3467 button_draw (c, screen, window,
3468 (WIDTH - 7 * strlen(text)) / 2,
3469 (HEIGHT - 16) / 2, text);
3471 text = "Press ESC key to exit...";
3472 text_draw (c, screen, window, 10, HEIGHT - 10, text);
3475 case XCB_BUTTON_PRESS: {
3476 xcb_button_press_event_t *ev;
3479 ev = (xcb_button_press_event_t *)e;
3480 length = strlen ("click here to change cursor");
3482 if ((ev->event_x >= (WIDTH - 7 * length) / 2) &&
3483 (ev->event_x <= ((WIDTH - 7 * length) / 2 + 7 * length + 6)) &&
3484 (ev->event_y >= (HEIGHT - 16) / 2 - 19) &&
3485 (ev->event_y <= ((HEIGHT - 16) / 2)))
3486 is_hand = 1 - is_hand;
3488 is_hand ? cursor_set (c, screen, window, 58) : cursor_set (c, screen, window, 68);
3490 case XCB_KEY_RELEASE: {
3491 xcb_key_release_event_t *ev;
3493 ev = (xcb_key_release_event_t *)e;
3495 switch (ev->detail) {
3512 <li class="title"><a name="translation">Translation of basic Xlib functions and macros</a>
3514 The problem when you want to port an Xlib program to XCB is that
3515 you don't know if the Xlib function that you want to "translate"
3516 is a X Window one or an Xlib macro. In that section, we describe
3517 a way to translate the usual functions or macros that Xlib
3518 provides. It's usually just a member of a structure.
3521 <li class="subtitle"><a name="displaystructure">Members of the Display structure</a>
3523 In this section, we look at how to translate the macros that
3524 return some members of the <span class="code">Display</span>
3525 structure. They are obtained by using a function that requires a
3526 <span class="code">xcb_connection_t *</span> or a member of the
3527 <span class="code">xcb_setup_t</span> structure
3528 (via the function <span class="code">xcb_get_setup</span>), or
3529 a function that requires that structure.
3532 <li class="subtitle"><a name="ConnectionNumber">ConnectionNumber</a>
3534 This number is the file descriptor that connects the client
3535 to the server. You just have to use that function:
3538 int xcb_get_file_descriptor (xcb_connection_t *c);
3540 <li class="subtitle"><a name="DefaultScreen"></a>DefaultScreen
3542 That number is not stored by XCB. It is returned in the
3543 second parameter of the function <span class="code"><a href="#openconn">xcb_connect</a></span>.
3544 Hence, you have to store it yourself if you want to use
3545 it. Then, to get the <span class="code">xcb_screen_t</span>
3546 structure, you have to iterate on the screens.
3547 The equivalent function of the Xlib's
3548 <span class="code">ScreenOfDisplay</span> function can be
3549 found <a href="#ScreenOfDisplay">below</a>. This is also provided in the
3550 xcb_aux_t library as <span class="code">xcb_aux_get_screen()</span>. OK, here is the
3551 small piece of code to get that number:
3554 xcb_connection_t *c;
3555 int screen_default_nbr;
3557 /* you pass the name of the display you want to xcb_connect_t */
3559 c = xcb_connect (display_name, &screen_default_nbr);
3561 /* screen_default_nbr contains now the number of the default screen */
3563 <li class="subtitle"><a name="QLength"></a>QLength
3568 However, this points out a basic difference in philosophy between
3569 Xlib and XCB. Xlib has several functions for filtering and
3570 manipulating the incoming and outgoing X message queues. XCB
3571 wishes to hide this as much as possible from the user, which
3572 allows for more freedom in implementation strategies.
3574 <li class="subtitle"><a name="ScreenCount"></a>ScreenCount
3576 You get the count of screens with the functions
3577 <span class="code">xcb_get_setup</span>
3579 <span class="code">xcb_setup_roots_iterator</span>
3580 (if you need to iterate):
3583 xcb_connection_t *c;
3586 /* you init the connection */
3588 screen_count = xcb_setup_roots_iterator (xcb_get_setup (c)).rem;
3590 /* screen_count contains now the count of screens */
3593 If you don't want to iterate over the screens, a better way
3594 to get that number is to use
3595 <span class="code">xcb_setup_roots_length_t</span>:
3598 xcb_connection_t *c;
3601 /* you init the connection */
3603 screen_count = xcb_setup_roots_length (xcb_get_setup (c));
3605 /* screen_count contains now the count of screens */
3607 <li class="subtitle"><a name="ServerVendor"></a>ServerVendor
3609 You get the name of the vendor of the server hardware with
3610 the functions <span class="code">xcb_get_setup</span>
3613 class="code">xcb_setup_vendor</span>. Beware
3614 that, unlike Xlib, the string returned by XCB is not
3615 necessarily null-terminaled:
3618 xcb_connection_t *c;
3619 char *vendor = NULL;
3622 /* you init the connection */
3623 length = xcb_setup_vendor_length (xcb_get_setup (c));
3624 vendor = (char *)malloc (length + 1);
3626 memcpy (vendor, xcb_setup_vendor (xcb_get_setup (c)), length);
3627 vendor[length] = '\0';
3629 /* vendor contains now the name of the vendor. Must be freed when not used anymore */
3631 <li class="subtitle"><a name="ProtocolVersion"></a>ProtocolVersion
3633 You get the major version of the protocol in the
3634 <span class="code">xcb_setup_t</span>
3635 structure, with the function <span class="code">xcb_get_setup</span>:
3638 xcb_connection_t *c;
3639 uint16_t protocol_major_version;
3641 /* you init the connection */
3643 protocol_major_version = xcb_get_setup (c)->protocol_major_version;
3645 /* protocol_major_version contains now the major version of the protocol */
3647 <li class="subtitle"><a name="ProtocolRevision"></a>ProtocolRevision
3649 You get the minor version of the protocol in the
3650 <span class="code">xcb_setup_t</span>
3651 structure, with the function <span class="code">xcb_get_setup</span>:
3654 xcb_connection_t *c;
3655 uint16_t protocol_minor_version;
3657 /* you init the connection */
3659 protocol_minor_version = xcb_get_setup (c)->protocol_minor_version;
3661 /* protocol_minor_version contains now the minor version of the protocol */
3663 <li class="subtitle"><a name="VendorRelease"></a>VendorRelease
3665 You get the number of the release of the server hardware in the
3666 <span class="code">xcb_setup_t</span>
3667 structure, with the function <span class="code">xcb_get_setup</span>:
3670 xcb_connection_t *c;
3671 uint32_t release_number;
3673 /* you init the connection */
3675 release_number = xcb_get_setup (c)->release_number;
3677 /* release_number contains now the number of the release of the server hardware */
3679 <li class="subtitle"><a name="DisplayString"></a>DisplayString
3681 The name of the display is not stored in XCB. You have to
3682 store it by yourself.
3684 <li class="subtitle"><a name="BitmapUnit"></a>BitmapUnit
3686 You get the bitmap scanline unit in the
3687 <span class="code">xcb_setup_t</span>
3688 structure, with the function <span class="code">xcb_get_setup</span>:
3691 xcb_connection_t *c;
3692 uint8_t bitmap_format_scanline_unit;
3694 /* you init the connection */
3696 bitmap_format_scanline_unit = xcb_get_setup (c)->bitmap_format_scanline_unit;
3698 /* bitmap_format_scanline_unit contains now the bitmap scanline unit */
3700 <li class="subtitle"><a name="BitmapBitOrder"></a>BitmapBitOrder
3702 You get the bitmap bit order in the
3703 <span class="code">xcb_setup_t</span>
3704 structure, with the function <span class="code">xcb_get_setup</span>:
3707 xcb_connection_t *c;
3708 uint8_t bitmap_format_bit_order;
3710 /* you init the connection */
3712 bitmap_format_bit_order = xcb_get_setup (c)->bitmap_format_bit_order;
3714 /* bitmap_format_bit_order contains now the bitmap bit order */
3716 <li class="subtitle"><a name="BitmapPad"></a>BitmapPad
3718 You get the bitmap scanline pad in the
3719 <span class="code">xcb_setup_t</span>
3720 structure, with the function <span class="code">xcb_get_setup</span>:
3723 xcb_connection_t *c;
3724 uint8_t bitmap_format_scanline_pad;
3726 /* you init the connection */
3728 bitmap_format_scanline_pad = xcb_get_setup (c)->bitmap_format_scanline_pad;
3730 /* bitmap_format_scanline_pad contains now the bitmap scanline pad */
3732 <li class="subtitle"><a name="ImageByteOrder"></a>ImageByteOrder
3734 You get the image byte order in the
3735 <span class="code">xcb_setup_t</span>
3736 structure, with the function <span class="code">xcb_get_setup</span>:
3739 xcb_connection_t *c;
3740 uint8_t image_byte_order;
3742 /* you init the connection */
3744 image_byte_order = xcb_get_setup (c)->image_byte_order;
3746 /* image_byte_order contains now the image byte order */
3749 <li class="subtitle"><a name="screenofdisplay">ScreenOfDisplay related functions</a>
3751 in Xlib, <span class="code">ScreenOfDisplay</span> returns a
3752 <span class="code">Screen</span> structure that contains
3753 several characteristics of your screen. XCB has a similar
3754 structure (<span class="code">xcb_screen_t</span>),
3755 but the way to obtain it is a bit different. With
3756 Xlib, you just provide the number of the screen and you grab it
3757 from an array. With XCB, you iterate over all the screens to
3758 obtain the one you want. The complexity of this operation is
3759 O(n). So the best is to store this structure if you use
3760 it often. See <a href="#ScreenOfDisplay">screen_of_display</a> just below.
3763 Xlib provides generally two functions to obtain the characteristics
3764 related to the screen. One with the display and the number of
3765 the screen, which calls <span class="code">ScreenOfDisplay</span>,
3766 and the other that uses the <span class="code">Screen</span> structure.
3767 This might be a bit confusing. As mentioned above, with XCB, it
3768 is better to store the <span class="code">xcb_screen_t</span>
3769 structure. Then, you have to read the members of this
3770 structure. That's why the Xlib functions are put by pairs (or
3771 more) as, with XCB, you will use the same code.
3774 <li class="subtitle"><a name="ScreenOfDisplay">ScreenOfDisplay</a>
3776 This function returns the Xlib <span class="code">Screen</span>
3777 structure. With XCB, you iterate over all the screens and
3778 once you get the one you want, you return it:
3780 <pre class="code"><a name="ScreenOfDisplay"></a>
3781 xcb_screen_t *screen_of_display (xcb_connection_t *c,
3784 xcb_screen_iterator_t iter;
3786 iter = xcb_setup_roots_iterator (xcb_get_setup (c));
3787 for (; iter.rem; --screen, xcb_screen_next (&iter))
3795 As mentioned above, you might want to store the value
3796 returned by this function.
3799 All the functions below will use the result of that
3800 function, as they just grab a specific member of the
3801 <span class="code">xcb_screen_t</span> structure.
3803 <li class="subtitle"><a name="DefaultScreenOfDisplay"></a>DefaultScreenOfDisplay
3805 It is the default screen that you obtain when you connect to
3806 the X server. It suffices to call the <a href="#ScreenOfDisplay">screen_of_display</a>
3807 function above with the connection and the number of the
3811 xcb_connection_t *c;
3812 int screen_default_nbr;
3813 xcb_screen_t *default_screen; /* the returned default screen */
3815 /* you pass the name of the display you want to xcb_connect_t */
3817 c = xcb_connect (display_name, &screen_default_nbr);
3818 default_screen = screen_of_display (c, screen_default_nbr);
3820 /* default_screen contains now the default root window, or a NULL window if no screen is found */
3822 <li class="subtitle"><a name="RootWindow">RootWindow / RootWindowOfScreen</a>
3825 xcb_connection_t *c;
3826 xcb_screen_t *screen;
3828 xcb_window_t root_window = { 0 }; /* the returned window */
3830 /* you init the connection and screen_nbr */
3832 screen = screen_of_display (c, screen_nbr);
3834 root_window = screen->root;
3836 /* root_window contains now the root window, or a NULL window if no screen is found */
3838 <li class="subtitle"><a name="DefaultRootWindow">DefaultRootWindow</a>
3840 It is the root window of the default screen. So, you call
3841 <a name="ScreenOfDisplay">ScreenOfDisplay</a> with the
3842 default screen number and you get the
3843 <a href="#RootWindow">root window</a> as above:
3846 xcb_connection_t *c;
3847 xcb_screen_t *screen;
3848 int screen_default_nbr;
3849 xcb_window_t root_window = { 0 }; /* the returned root window */
3851 /* you pass the name of the display you want to xcb_connect_t */
3853 c = xcb_connect (display_name, &screen_default_nbr);
3854 screen = screen_of_display (c, screen_default_nbr);
3856 root_window = screen->root;
3858 /* root_window contains now the default root window, or a NULL window if no screen is found */
3860 <li class="subtitle"><a name="DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a>
3862 While a Visual is, in Xlib, a structure, in XCB, there are
3863 two types: <span class="code">xcb_visualid_t</span>, which is
3864 the Id of the visual, and <span class="code">xcb_visualtype_t</span>,
3865 which corresponds to the Xlib Visual. To get the Id of the
3866 visual of a screen, just get the
3867 <span class="code">root_visual</span>
3868 member of a <span class="code">xcb_screen_t</span>:
3871 xcb_connection_t *c;
3872 xcb_screen_t *screen;
3874 xcb_visualid_t root_visual = { 0 }; /* the returned visual Id */
3876 /* you init the connection and screen_nbr */
3878 screen = screen_of_display (c, screen_nbr);
3880 root_visual = screen->root_visual;
3882 /* root_visual contains now the value of the Id of the visual, or a NULL visual if no screen is found */
3885 To get the <span class="code">xcb_visualtype_t</span>
3886 structure, it's a bit less easy. You have to get the
3887 <span class="code">xcb_screen_t</span> structure that you want,
3888 get its <span class="code">root_visual</span> member,
3889 then iterate over the <span class="code">xcb_depth_t</span>s
3890 and the <span class="code">xcb_visualtype_t</span>s, and compare
3891 the <span class="code">xcb_visualid_t</span> of these <span class="code">xcb_visualtype_t</span>s:
3892 with <span class="code">root_visual</span>:
3895 xcb_connection_t *c;
3896 xcb_screen_t *screen;
3898 xcb_visualid_t root_visual = { 0 };
3899 xcb_visualtype_t *visual_type = NULL; /* the returned visual type */
3901 /* you init the connection and screen_nbr */
3903 screen = screen_of_display (c, screen_nbr);
3905 xcb_depth_iterator_t depth_iter;
3907 depth_iter = xcb_screen_allowed_depths_iterator (screen);
3908 for (; depth_iter.rem; xcb_depth_next (&depth_iter)) {
3909 xcb_visualtype_iterator_t visual_iter;
3911 visual_iter = xcb_depth_visuals_iterator (depth_iter.data);
3912 for (; visual_iter.rem; xcb_visualtype_next (&visual_iter)) {
3913 if (screen->root_visual.id == visual_iter.data->visual_id.id) {
3914 visual_type = visual_iter.data;
3921 /* visual_type contains now the visual structure, or a NULL visual structure if no screen is found */
3923 <li class="subtitle"><a name="DefaultGC">DefaultGC / DefaultGCOfScreen</a>
3925 This default Graphic Context is just a newly created Graphic
3926 Context, associated to the root window of a
3927 <span class="code">xcb_screen_t</span>,
3928 using the black white pixels of that screen:
3931 xcb_connection_t *c;
3932 xcb_screen_t *screen;
3934 xcb_gcontext_t gc = { 0 }; /* the returned default graphic context */
3936 /* you init the connection and screen_nbr */
3938 screen = screen_of_display (c, screen_nbr);
3940 xcb_drawable_t draw;
3944 gc = xcb_generate_id (c);
3945 draw = screen->root;
3946 mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND;
3947 values[0] = screen->black_pixel;
3948 values[1] = screen->white_pixel;
3949 xcb_create_gc (c, gc, draw, mask, values);
3952 /* gc contains now the default graphic context */
3954 <li class="subtitle"><a name="BlackPixel">BlackPixel / BlackPixelOfScreen</a>
3956 It is the Id of the black pixel, which is in the structure
3957 of an <span class="code">xcb_screen_t</span>.
3960 xcb_connection_t *c;
3961 xcb_screen_t *screen;
3963 uint32_t black_pixel = 0; /* the returned black pixel */
3965 /* you init the connection and screen_nbr */
3967 screen = screen_of_display (c, screen_nbr);
3969 black_pixel = screen->black_pixel;
3971 /* black_pixel contains now the value of the black pixel, or 0 if no screen is found */
3973 <li class="subtitle"><a name="WhitePixel">WhitePixel / WhitePixelOfScreen</a>
3975 It is the Id of the white pixel, which is in the structure
3976 of an <span class="code">xcb_screen_t</span>.
3979 xcb_connection_t *c;
3980 xcb_screen_t *screen;
3982 uint32_t white_pixel = 0; /* the returned white pixel */
3984 /* you init the connection and screen_nbr */
3986 screen = screen_of_display (c, screen_nbr);
3988 white_pixel = screen->white_pixel;
3990 /* white_pixel contains now the value of the white pixel, or 0 if no screen is found */
3992 <li class="subtitle"><a name="DisplayWidth">DisplayWidth / WidthOfScreen</a>
3994 It is the width in pixels of the screen that you want, and
3995 which is in the structure of the corresponding
3996 <span class="code">xcb_screen_t</span>.
3999 xcb_connection_t *c;
4000 xcb_screen_t *screen;
4002 uint32_t width_in_pixels = 0; /* the returned width in pixels */
4004 /* you init the connection and screen_nbr */
4006 screen = screen_of_display (c, screen_nbr);
4008 width_in_pixels = screen->width_in_pixels;
4010 /* width_in_pixels contains now the width in pixels, or 0 if no screen is found */
4012 <li class="subtitle"><a name="DisplayHeight">DisplayHeight / HeightOfScreen</a>
4014 It is the height in pixels of the screen that you want, and
4015 which is in the structure of the corresponding
4016 <span class="code">xcb_screen_t</span>.
4019 xcb_connection_t *c;
4020 xcb_screen_t *screen;
4022 uint32_t height_in_pixels = 0; /* the returned height in pixels */
4024 /* you init the connection and screen_nbr */
4026 screen = screen_of_display (c, screen_nbr);
4028 height_in_pixels = screen->height_in_pixels;
4030 /* height_in_pixels contains now the height in pixels, or 0 if no screen is found */
4032 <li class="subtitle"><a name="DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a>
4034 It is the width in millimeters of the screen that you want, and
4035 which is in the structure of the corresponding
4036 <span class="code">xcb_screen_t</span>.
4039 xcb_connection_t *c;
4040 xcb_screen_t *screen;
4042 uint32_t width_in_millimeters = 0; /* the returned width in millimeters */
4044 /* you init the connection and screen_nbr */
4046 screen = screen_of_display (c, screen_nbr);
4048 width_in_millimeters = screen->width_in_millimeters;
4050 /* width_in_millimeters contains now the width in millimeters, or 0 if no screen is found */
4052 <li class="subtitle"><a name="DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a>
4054 It is the height in millimeters of the screen that you want, and
4055 which is in the structure of the corresponding
4056 <span class="code">xcb_screen_t</span>.
4059 xcb_connection_t *c;
4060 xcb_screen_t *screen;
4062 uint32_t height_in_millimeters = 0; /* the returned height in millimeters */
4064 /* you init the connection and screen_nbr */
4066 screen = screen_of_display (c, screen_nbr);
4068 height_in_millimeters = screen->height_in_millimeters;
4070 /* height_in_millimeters contains now the height in millimeters, or 0 if no screen is found */
4072 <li class="subtitle"><a name="DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a>
4074 It is the depth (in bits) of the root window of the
4075 screen. You get it from the <span class="code">xcb_screen_t</span> structure.
4078 xcb_connection_t *c;
4079 xcb_screen_t *screen;
4081 uint8_t root_depth = 0; /* the returned depth of the root window */
4083 /* you init the connection and screen_nbr */
4085 screen = screen_of_display (c, screen_nbr);
4087 root_depth = screen->root_depth;
4089 /* root_depth contains now the depth of the root window, or 0 if no screen is found */
4091 <li class="subtitle"><a name="DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a>
4093 This is the default colormap of the screen (and not the
4094 (default) colormap of the default screen !). As usual, you
4095 get it from the <span class="code">xcb_screen_t</span> structure:
4098 xcb_connection_t *c;
4099 xcb_screen_t *screen;
4101 xcb_colormap_t default_colormap = { 0 }; /* the returned default colormap */
4103 /* you init the connection and screen_nbr */
4105 screen = screen_of_display (c, screen_nbr);
4107 default_colormap = screen->default_colormap;
4109 /* default_colormap contains now the default colormap, or a NULL colormap if no screen is found */
4111 <li class="subtitle"><a name="MinCmapsOfScreen"></a>MinCmapsOfScreen
4113 You get the minimum installed colormaps in the <span class="code">xcb_screen_t</span> structure:
4116 xcb_connection_t *c;
4117 xcb_screen_t *screen;
4119 uint16_t min_installed_maps = 0; /* the returned minimum installed colormaps */
4121 /* you init the connection and screen_nbr */
4123 screen = screen_of_display (c, screen_nbr);
4125 min_installed_maps = screen->min_installed_maps;
4127 /* min_installed_maps contains now the minimum installed colormaps, or 0 if no screen is found */
4129 <li class="subtitle"><a name="MaxCmapsOfScreen"></a>MaxCmapsOfScreen
4131 You get the maximum installed colormaps in the <span class="code">xcb_screen_t</span> structure:
4134 xcb_connection_t *c;
4135 xcb_screen_t *screen;
4137 uint16_t max_installed_maps = 0; /* the returned maximum installed colormaps */
4139 /* you init the connection and screen_nbr */
4141 screen = screen_of_display (c, screen_nbr);
4143 max_installed_maps = screen->max_installed_maps;
4145 /* max_installed_maps contains now the maximum installed colormaps, or 0 if no screen is found */
4147 <li class="subtitle"><a name="DoesSaveUnders"></a>DoesSaveUnders
4149 You know if <span class="code">save_unders</span> is set,
4150 by looking in the <span class="code">xcb_screen_t</span> structure:
4153 xcb_connection_t *c;
4154 xcb_screen_t *screen;
4156 uint8_t save_unders = 0; /* the returned value of save_unders */
4158 /* you init the connection and screen_nbr */
4160 screen = screen_of_display (c, screen_nbr);
4162 save_unders = screen->save_unders;
4164 /* save_unders contains now the value of save_unders, or FALSE if no screen is found */
4166 <li class="subtitle"><a name="DoesBackingStore"></a>DoesBackingStore
4168 You know the value of <span class="code">backing_stores</span>,
4169 by looking in the <span class="code">xcb_screen_t</span> structure:
4172 xcb_connection_t *c;
4173 xcb_screen_t *screen;
4175 uint8_t backing_stores = 0; /* the returned value of backing_stores */
4177 /* you init the connection and screen_nbr */
4179 screen = screen_of_display (c, screen_nbr);
4181 backing_stores = screen->backing_stores;
4183 /* backing_stores contains now the value of backing_stores, or FALSE if no screen is found */
4185 <li class="subtitle"><a name="EventMaskOfScreen"></a>EventMaskOfScreen
4187 To get the current input masks,
4188 you look in the <span class="code">xcb_screen_t</span> structure:
4191 xcb_connection_t *c;
4192 xcb_screen_t *screen;
4194 uint32_t current_input_masks = 0; /* the returned value of current input masks */
4196 /* you init the connection and screen_nbr */
4198 screen = screen_of_display (c, screen_nbr);
4200 current_input_masks = screen->current_input_masks;
4202 /* current_input_masks contains now the value of the current input masks, or FALSE if no screen is found */
4205 <li class="subtitle"><a name="misc">Miscellaneous macros</a>
4207 <li class="subtitle"><a name="DisplayOfScreen"></a>DisplayOfScreen
4209 in Xlib, the <span class="code">Screen</span> structure
4210 stores its associated <span class="code">Display</span>
4211 structure. This is not the case in the X Window protocol,
4212 hence, it's also not the case in XCB. So you have to store
4215 <li class="subtitle"><a name="DisplayCells"></a>DisplayCells / CellsOfScreen
4217 To get the colormap entries,
4218 you look in the <span class="code">xcb_visualtype_t</span>
4219 structure, that you grab like <a class="subsection" href="#DefaultVisual">here</a>:
4222 xcb_connection_t *c;
4223 xcb_visualtype_t *visual_type;
4224 uint16_t colormap_entries = 0; /* the returned value of the colormap entries */
4226 /* you init the connection and visual_type */
4229 colormap_entries = visual_type->colormap_entries;
4231 /* colormap_entries contains now the value of the colormap entries, or FALSE if no screen is found */
projects / free-sw / xcb / libxcb / blob