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authorJosh Triplett <josh@freedesktop.org>2006-02-18 16:49:41 -0800
committerJosh Triplett <josh@josh-mobile.localdomain>2006-02-18 16:49:41 -0800
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+<!DOCTYPE html public "-//W3C//DTD HTML 4.01 Transitional//EN"
+"http://www.w3.org/TR/html4/loose.dtd">
+
+<html>
+
+<head>
+ <title>Basic Graphics Programming With The XCB Library</title>
+ <link href="xcb.css" rel="stylesheet" type="text/css" />
+</head>
+
+<body>
+ <div class="title">
+ Basic Graphics Programming With The XCB Library
+ </div>
+ <div class="toc">
+ <ol>
+ <li><a class="section" href="#intro">Introduction</a></li>
+ <li><a class="section" href="#Xmodel">The client and server model of the X window system</a></li>
+ <li><a class="section" href="#asynch">GUI programming: the asynchronous model</a></li>
+ <li><a class="section" href="#notions">Basic XCB notions</a></li>
+ <ol>
+ <li><a class="subsection" href="#conn">The X Connection</a></li>
+ <li><a class="subsection" href="#requestsreplies">Requests and replies: the Xlib killers</a></li>
+ <li><a class="subsection" href="#gc">The Graphics Context</a></li>
+ <li>Object handles</li>
+ <li>Memory allocation for XCB structures</li>
+ <li><a class="subsection" href="#events">Events</a></li>
+ </ol>
+ <li><a class="section" href="#use">Using XCB-based programs</a></li>
+ <ol>
+ <li><a class="subsection" href="#inst">Installation of XCB</a></li>
+ <li><a class="subsection" href="#comp">Compiling XCB-based programs</a></li>
+ </ol>
+ <li><a class="section" href="#openconn">Opening and closing the connection to an X server</a></li>
+ <li><a class="section" href="#screen">Checking basic information about a connection</a></li>
+ <li><a class="section" href="#helloworld">Creating a basic window - the "hello world" program</a></li>
+ <li><a class="section" href="#drawing">Drawing in a window</a></li>
+ <ol>
+ <li><a class="subsection" href="#allocgc">Allocating a Graphics Context</a></li>
+ <li><a class="subsection" href="#changegc">Changing the attributes of a Graphics Context</a></li>
+ <li><a class="subsection" href="#drawingprim">Drawing primitives: point, line, box, circle,...</a></li>
+ </ol>
+ <li><a class="section" href="#xevents">X Events</a></li>
+ <ol>
+ <li><a class="subsection" href="#register">Registering for event types using event masks</a></li>
+ <li><a class="subsection" href="#loop">Receiving events: writing the events loop</a></li>
+ <li><a class="subsection" href="#expose">Expose events</a></li>
+ <li><a class="subsection" href="#userinput">Getting user input</a></li>
+ <ol>
+ <li><a class="subsubsection" href="#mousepressrelease">Mouse button press and release events</a></li>
+ <li><a class="subsubsection" href="#mousemvnt">Mouse movement events</a></li>
+ <li><a class="subsubsection" href="#mouseenter">Mouse pointer enter and leave events</a></li>
+ <li><a class="subsubsection" href="#focus">The keyboard focus</a></li>
+ <li><a class="subsubsection" href="#keypress">Keyboard press and release events</a></li>
+ </ol>
+ <li><a class="subsection" href="#eventex">X events: a complete example</a></li>
+ </ol>
+ <li><a class="section" href="#font">Handling text and fonts</a></li>
+ <ol>
+ <li><a class="subsection" href="#fontstruct">The Font structure</a></li>
+ <li>Loading a Font</li>
+ <li>Assigning a Font to a Graphic Context</li>
+ <li>Drawing text in a window</li>
+ </ol>
+ <li>Windows hierarchy</li>
+ <ol>
+ <li>Root, parent and child windows</li>
+ <li>Events propagation</li>
+ </ol>
+ <li><a class="section" href="#wm">Interacting with the window manager</a></li>
+ <ol>
+ <li><a class="subsection" href="#wmprop">Window properties</a></li>
+ <li><a class="subsection" href="#wmname">Setting the window name and icon name</a></li>
+ <li>Setting preferred window size(s)</li>
+ <li>Setting miscellaneous window manager hints</li>
+ <li>Setting an application's icon</li>
+ </ol>
+ <li><a class="section" href="#winop">Simple window operations</a></li>
+ <ol>
+ <li><a class="subsection" href="#winmap">Mapping and un-mapping a window</a></li>
+ <li><a class="subsection" href="#winconf">Configuring a window</a></li>
+ <li><a class="subsection" href="#winmove">Moving a window around the screen</a></li>
+ <li><a class="subsection" href="#winsize">Resizing a window</a></li>
+ <li><a class="subsection" href="#winstack">Changing windows stacking order: raise and lower</a></li>
+ <li>Iconifying and de-iconifying a window</li>
+ <li><a class="subsection" href="#wingetinfo">Getting informations about a window</a></li>
+ </ol>
+ <li><a class="section" href="#usecolor">Using colors to paint the rainbow</a></li>
+ <ol>
+ <li><a class="subsection" href="#colormap">Color maps</a></li>
+ <li><a class="subsection" href="#colormapalloc">Allocating and freeing Color Maps</a></li>
+ <li><a class="subsection" href="#alloccolor">Allocating and freeing a color entry</a></li>
+ <li>Drawing with a color</li>
+ </ol>
+ <li><a class="section" href="#pixmaps">X Bitmaps and Pixmaps</a></li>
+ <ol>
+ <li><a class="subsection" href="#pixmapswhat">What is a X Bitmap ? An X Pixmap ?</a></li>
+ <li>Loading a bitmap from a file</li>
+ <li>Drawing a bitmap in a window</li>
+ <li><a class="subsection" href="#pixmapscreate">Creating a pixmap</a></li>
+ <li><a class="subsection" href="#pixmapsdraw">Drawing a pixmap in a window</a></li>
+ <li><a class="subsection" href="#pixmapsfree">Freeing a pixmap</a></li>
+ </ol>
+ <li>Messing with the mouse cursor</li>
+ <ol>
+ <li>Creating and destroying a mouse cursor</li>
+ <li>Setting a window's mouse cursor</li>
+ </ol>
+ <li><a class="subsection" href="#translation">Translation of basic Xlib functions and macros</a></li>
+ <ol>
+ <li><a class="subsection" href="#displaystructure">Members of the Display structure</a></li>
+ <ol>
+ <li><a class="subsection" href="#ConnectionNumber">ConnectionNumber</a></li>
+ <li><a class="subsection" href="#DefaultScreen">DefaultScreen</a></li>
+ <li><a class="subsection" href="#QLength">QLength</a></li>
+ <li><a class="subsection" href="#ScreenCount">ScreenCount</a></li>
+ <li><a class="subsection" href="#ServerVendor">ServerVendor</a></li>
+ <li><a class="subsection" href="#ProtocolVersion">ProtocolVersion</a></li>
+ <li><a class="subsection" href="#ProtocolRevision">ProtocolRevision</a></li>
+ <li><a class="subsection" href="#VendorRelease">VendorRelease</a></li>
+ <li><a class="subsection" href="#DisplayString">DisplayString</a></li>
+ <li><a class="subsection" href="#BitmapUnit">BitmapUnit</a></li>
+ <li><a class="subsection" href="#BitmapBitOrder">BitmapBitOrder</a></li>
+ <li><a class="subsection" href="#BitmapPad">BitmapPad</a></li>
+ <li><a class="subsection" href="#ImageByteOrder">ImageByteOrder</a></li>
+ </ol>
+ <li><a class="subsection" href="#screenofdisplay">ScreenOfDisplay related functions</a></li>
+ <ol>
+ <li><a class="subsection" href="#ScreenOfDisplay">ScreenOfDisplay</a></li>
+ <li><a class="subsection" href="#DefaultScreenOfDisplay">DefaultScreenOfDisplay</a></li>
+ <li><a class="subsection" href="#RootWindow">RootWindow / RootWindowOfScreen</a></li>
+ <li><a class="subsection" href="#DefaultRootWindow">DefaultRootWindow</a></li>
+ <li><a class="subsection" href="#DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a></li>
+ <li><a class="subsection" href="#DefaultGC">DefaultGC / DefaultGCOfScreen</a></li>
+ <li><a class="subsection" href="#BlackPixel">BlackPixel / BlackPixelOfScreen</a></li>
+ <li><a class="subsection" href="#WhitePixel">WhitePixel / WhitePixelOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayWidth">DisplayWidth / WidthOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayHeight">DisplayHeight / HeightOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a></li>
+ <li><a class="subsection" href="#DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a></li>
+ <li><a class="subsection" href="#MinCmapsOfScreen">MinCmapsOfScreen</a></li>
+ <li><a class="subsection" href="#MaxCmapsOfScreen">MaxCmapsOfScreen</a></li>
+ <li><a class="subsection" href="#DoesSaveUnders">DoesSaveUnders</a></li>
+ <li><a class="subsection" href="#DoesBackingStore">DoesBackingStore</a></li>
+ <li><a class="subsection" href="#EventMaskOfScreen">EventMaskOfScreen</a></li>
+ </ol>
+ <li><a class="subsection" href="#misc">Miscellaneaous macros</a></li>
+ <ol>
+ <li><a class="subsection" href="#DisplayOfScreen">DisplayOfScreen</a></li>
+ <li><a class="subsection" href="#DisplayCells">DisplayCells / CellsOfScreen</a></li>
+ </ol>
+ </ol>
+ </ol>
+ </div>
+ <div class="section">
+ <ol>
+ <li class="title"><a name="intro">Introduction</a></li>
+ <p>
+ This tutorial is based on the
+ <a href="http://users.actcom.co.il/~choo/lupg/tutorials/xlib-programming/xlib-programming.html">Xlib Tutorial</a>
+ written by <a href="mailto:choor@atcom.co.il">Guy Keren</a>. The
+ author allowed me to take some parts of his text, mainly the text which
+ deals with the X Windows generality.
+ </p>
+ <p>
+ This tutorial is intended to people who want to start to program
+ with the <a href="http://xcb.freedesktop.org">XCB</a>
+ library. As for the <a href="http://tronche.com/gui/x/xlib/introduction">Xlib</a>
+ library, it is useless and a real X
+ programmer should use a much higher level of abstraction, such
+ as using Motif,
+ <a href="http://www.lesstif.org">LessTiff</a>,
+ <a href="http://www.gtk.org">GTK</a>,
+ <a href="http://www.trolltech.com">QT</a> or
+ <a href="http://www.enlightenment.org">EWL</a>. However,
+ we need to start somewhere. More than this, knowing how things
+ work down below is never a bad idea.
+ </p>
+ <p>
+ After reading this tutorial, one should be able to write very
+ simple graphical programs, but not programs with a descent user
+ interface. For such programs, one of the previously mentioned
+ library should be used.
+ </p>
+ <p>
+ But what is XCB ? Xlib has been
+ the standard C binding for the <a href="http://www.xfree86.org">X
+ Window System</a> protocol for many years now. It is an
+ excellent piece of work, but there are applications for which it
+ is not ideal, for example
+ <ul>
+ <li><b>Small platforms</b>: Xlib is a large piece of code, and
+ it's difficult to make it smaller</li>
+ <li><b>Latency hiding</b>: Xlib requests requiring a reply are
+ effectively synchronous: they block until the reply appears,
+ whether the result is needed immediately or not.</li>
+ <li><b>Direct access to the protocol</b>: Xlib does quite a
+ bit of caching, layering, and similar optimizations. While this
+ is normally a feature, it makes it difficult to simply emit
+ specified X protocol requests and process specific
+ responses.</li>
+ <li><b>Threaded applications</b>: While Xlib does attempt to
+ support multithreading, the API makes this difficult and
+ error-prone.</li>
+ <li><b>New extensions</b>: The Xlib infrastructure provides
+ limited support for the new creation of X extension client side
+ code.</li>
+ </ul>
+ </p>
+ <p>
+ For these reasons, among others, XCB, an X C binding, has been
+ designed to solve the above problems and thus provide a base for
+ <ul>
+ <li>Toolkit implementation.</li>
+ <li>Direct protocol-level programming.</li>
+ <li>Lightweight emulation of commonly used portions of the
+ Xlib API (in progress)</li>
+ </ul>
+ </p>
+ <p></p>
+ <li class="title"><a name="Xmodel">The client and server model of the X window system</a></li>
+ <p>
+ The X Window System was developed with one major goal:
+ flexibility. The idea was that the way things look is one thing,
+ but the way things work is another matter. Thus, the lower
+ levels provide the tools required to draw windows, handle user
+ input, allow drawing graphics using colors (or black and white
+ screens), etc. To this point, a decision was made to separate
+ the system into two parts. A client that decides what to do, and
+ a server that actually draws on the screen and reads user input
+ in order to send it to the client for processing.
+ </p>
+ <p>
+ This model is the complete opposite of what is used to when
+ dealing with clients and servers. In our case, the user seats
+ near the machine controlled by the server, while the client
+ might be running on a remote machine. The server controls the
+ screens, mouse and keyboard. A client may connect to the server,
+ request that it draws a window (or several windows), and ask the
+ server to send it any input the user sends to these
+ windows. Thus, several clients may connect to a single X server
+ (one might be running an mail software, one running a WWW
+ browser, etc). When input is sent by the user to some window,
+ the server sends a message to the client controlling this window
+ for processing. The client decides what to do with this input,
+ and sends the server requests for drawing in the window.
+ </p>
+ <p>
+ The whole session is carried out using the X message
+ protocol. This protocol was originally carried over the TCP/IP
+ protocol suite, allowing the client to run on any machine
+ connected to the same network that the server is. Later on, the
+ X servers were extended to allow clients running on the local
+ machine with more optimized access to the server (note that an X
+ protocol message may be several hundreds of KB in size), such as
+ using shred memory, or using Unix domain sockets (a method for
+ creating a logical channel on a Unix system between two processors).
+ </p>
+ <li class="title"><a name="asynch">GUI programming: the asynchronous model</a></li>
+ <p>
+ Unlike conventional computer programs, that carry some serial
+ nature, a GUI program usually uses an asynchronous programming
+ model, also known as "event-driven programming". This means that
+ that program mostly sits idle, waiting for events sent by the X
+ server, and then acts upon these events. An event may say "The
+ user pressed the 1st button mouse in spot (x,y)", or "The window
+ you control needs to be redrawn". In order for the program to e
+ responsive to the user input, as well as to refresh requests, it
+ needs to handle each event in a rather short period of time
+ (e.g. less that 200 milliseconds, as a rule of thumb).
+ </p>
+ <p>
+ This also implies that the program may not perform operations
+ that might take a long time while handling an event (such as
+ opening a network connection to some remote server, or
+ connecting to a database server, or even performing a long file
+ copy operation). Instead, it needs to perform all these
+ operations in an asynchronous manner. This may be done by using
+ various asynchronous models to perform the longish operations,
+ or by performing them in a different process or thread.
+ </p>
+ <p>
+ So the way a GUI program looks is something like that:
+ <ol>
+ <li>Perform initialization routines.</li>
+ <li>Connect to the X server.</li>
+ <li>Perform X-related initialization.</li>
+ <li>While not finished:</li>
+ <ol>
+ <li>Receive the next event from the X server.</li>
+ <li>Handle the event, possibly sending various drawing
+ requests to the X server.</li>
+ <li>If the event was a quit message, exit the loop.</li>
+ </ol>
+ <li>Close down the connection to the X server. </li>
+ <li>Perform cleanup operations.</li>
+ </ol>
+ </p>
+ <p></p>
+ <li class="title"><a name="notions">Basic XCB notions</a></li>
+ <p>
+ XCB has been created to eliminate the needs of
+ programs to actually implement the X protocol layer. This
+ library gives a program a very low-level access to any X
+ server. Since the protocol is standardized, a client using any
+ implementation of XCB may talk with any X server (the same
+ occurs for Xlib, of course). We now give a brief description of
+ the basic XCB notions. They will be detailed later.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="conn">The X Connection</a></li>
+ <p>
+ The major notion of using XCB is the X Connection. This is a
+ structure representing the connection we have open with a
+ given X server. It hides a queue of messages coming from the
+ server, and a queue of pending requests that our client
+ intends to send to the server. In XCB, this structure is named
+ 'XCBConnection'. When we open a connection to an X server, the
+ library returns a pointer to such a structure. Later, we
+ supply this pointer to any XCB function that should send
+ messages to the X server or receive messages from this server.
+ </p>
+ <li class="subtitle"><a name="requestsreplies">Requests and
+ replies: the Xlib killers</a></li>
+ <p>
+ To ask informations to the X server, we have to make a request
+ and ask for a reply. With Xlib, these two tasks are
+ automatically done: Xlib locks the system, sends a request,
+ waits for a reply from the X server and unlocks. This is
+ annoying, especially if one makes a lot of requests to the X
+ server. Indeed, Xlib has to wait for the end of a reply
+ before asking for the next request (because of the locks that
+ Xlib sends). For example, here is a time-line of N=4
+ requests/replies with Xlib, with a round-trip latency
+ <b>T_round_trip</b> that is 5 times long as the time required
+ to write or read a request/reply (<b>T_write/T_read</b>):
+ </p>
+ <pre class="text">
+ W-----RW-----RW-----RW-----R
+</pre>
+ <ul>
+ <li>W: Writing request</li>
+ <li>-: Stalled, waiting for data</li>
+ <li>R: Reading reply</li>
+ </ul>
+ <p>
+ The total time is N * (T_write + T_round_trip + T_read).
+ </p>
+ <p>
+ With XCB, we can suppress most of the round-trips as the
+ requests and the replies are not locked. We usually send a
+ request, then XCB returns to us a <b>cookie</b>, which is an
+ identifier. Then, later, we ask for a reply using this
+ <b>cookie</b> and XCB returns a
+ pointer to that reply. Hence, with XCB, we can send a lot of
+ requests, and later in the program, ask for all the replies
+ when we need them. Here is the time-line for 4
+ requests/replies when we use this property of XCB:
+ </p>
+ <pre class="text">
+ WWWW--RRRR
+</pre>
+ <p>
+ The total time is N * T_write + max (0, T_round_trip - (N-1) *
+ T_write) + N * T_read. Which can be considerably faster than
+ all those Xlib round-trips.
+ </p>
+ <p>
+ Here is a program that computes the time to create 500 atoms
+ with Xlib and XCB. It shows the Xlib way, the bad XCB way
+ (which is similar to Xlib) and the good XCB way. On my
+ computer, XCB is 25 times faster than Xlib.
+ </p>
+ <pre class="code">
+#include &lt;stdlib.h&gt;
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+#include &lt;sys/time.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+#include &lt;X11/Xlib.h&gt;
+
+double
+get_time(void)
+{
+ struct timeval timev;
+
+ gettimeofday(&timev, NULL);
+
+ return (double)timev.tv_sec + (((double)timev.tv_usec) / 1000000);
+}
+
+int
+main ()
+{
+ XCBConnection *c;
+ XCBATOM *atoms;
+ XCBInternAtomCookie *cs;
+ char **names;
+ int count;
+ int i;
+ double start;
+ double end;
+ double diff;
+
+ /* Xlib */
+ Display *disp;
+ Atom *atoms_x;
+ double diff_x;
+
+ c = XCBConnectBasic ();
+
+ count = 500;
+ atoms = (XCBATOM *)malloc (count * sizeof (atoms));
+ names = (char **)malloc (count * sizeof (char *));
+
+ /* init names */
+ for (i = 0; i &lt; count; ++i)
+ {
+ char buf[100];
+
+ sprintf (buf, "NAME%d", i);
+ names[i] = strdup (buf);
+ }
+
+ /* bad use */
+ start = get_time ();
+
+ for (i = 0; i &lt; count; ++i)
+ atoms[i] = XCBInternAtomReply (c,
+ XCBInternAtom (c,
+ 0,
+ strlen(names[i]),
+ names[i]),
+ NULL)->atom;
+
+ end = get_time ();
+ diff = end - start;
+ printf ("bad use time : %f\n", diff);
+
+ /* good use */
+ start = get_time ();
+
+ cs = (XCBInternAtomCookie *) malloc (count * sizeof(XCBInternAtomCookie));
+ for(i = 0; i &lt; count; ++i)
+ cs[i] = XCBInternAtom (c, 0, strlen(names[i]), names[i]);
+
+ for(i = 0; i &lt; count; ++i)
+ {
+ XCBInternAtomRep *r;
+
+ r = XCBInternAtomReply(c, cs[i], 0);
+ if(r)
+ atoms[i] = r->atom;
+ free(r);
+ }
+
+ end = get_time ();
+ printf ("good use time : %f\n", end - start);
+ printf ("ratio : %f\n", diff / (end - start));
+ diff = end - start;
+
+ /* free var */
+ for (i = 0; i &lt; count; ++i)
+ {
+ free (names[i]);
+ }
+ free (atoms);
+ free (cs);
+
+ XCBDisconnect (c);
+
+ /* Xlib */
+ disp = XOpenDisplay (getenv("DISPLAY"));
+
+ atoms_x = (Atom *)malloc (count * sizeof (atoms_x));
+
+ start = get_time ();
+
+ for (i = 0; i &lt; count; ++i)
+ atoms_x[i] = XInternAtom(disp, names[i], 0);
+
+ end = get_time ();
+ diff_x = end - start;
+ printf ("Xlib use time : %f\n", diff_x);
+ printf ("ratio : %f\n", diff_x / diff);
+
+ free (atoms_x);
+ free (names);
+
+ XCloseDisplay (disp);
+
+ return 1;
+}
+</pre>
+ <li class="subtitle"><a name="gc">The Graphic Context</a></li>
+ <p>
+ When we perform various drawing operations (graphics, text,
+ etc), we may specify various options for controlling how the
+ data will be drawn (what foreground and background colors to
+ use, how line edges will be connected, what font to use when
+ drawing some text, etc). In order to avoid the need to supply
+ hundreds of parameters to each drawing function, a graphical
+ context structure is used. We set the various drawing options
+ in this structure, and then, we pass a pointer to this
+ structure to any drawing routines. This is rather handy, as we
+ often need to perform several drawing requests with the same
+ options. Thus, we would initialize a graphical context, set
+ the desired options, and pass this structure to all drawing
+ functions.
+ </p>
+ <p>
+ Note that graphic contexts have no client-side structure in
+ XCB, they're just XIDs. Xlib has a client-side structure
+ because it caches the GC contents so it can avoid making
+ redundant requests, but of course XCB doesn't do that.
+ </p>
+ <li class="subtitle"><a name="events">Events</a></li>
+ <p>
+ A structure is used to pass events received from the X
+ server. XCB supports exactly the events specified in the
+ protocol (33 events). This structure contains the type
+ of event received, as well as the data associated with the
+ event (e.g. position on the screen where the event was
+ generated, mouse button associated with the event, region of
+ the screen associated with a "redraw" event, etc). The way to
+ read the event's data epends on the event type.
+ </p>
+ </ol>
+ <p></p>
+ <li class="title"><a name="use">Using XCB-based programs</a></li>
+ <p></p>
+ <ol>
+ <li class="subtitle"><a name="inst">Installation of XCB</a></li>
+ <p>
+ To build XCB from source, you need to have installed at
+ least:
+ </p>
+ <ul>
+ <li>pkgconfig 0.15.0</li>
+ <li>automake 1.7</li>
+ <li>autoconf 2.50</li>
+ <li><a href="http://www.check.org">check</a></li>
+ <li><a href="http://xmlsoft.org/XSLT/">xsltproc</a></li>
+ </ul>
+ <p>
+ You have to checkout in CVS the following modules:
+ </p>
+ <ul>
+ <li>Xproto from xlibs</li>
+ <li>Xau from xlibs</li>
+ <li>xcb-proto</li>
+ <li>xcb</li>
+ </ul>
+ <p>
+ Note that Xproto and xcb-proto exist only to install header
+ files, so typing 'make' or 'make all' will produce the message
+ "Nothing to be done for 'all'". That's normal.
+ </p>
+ <li class="subtitle"><a name="comp">Compiling XCB-based programs</a></li>
+ <p>
+ Compiling XCB-based programs requires linking them with the XCB
+ library. This is easily done thanks to pkgconfig:
+ </p>
+ <pre class="text">
+gcc -Wall prog.c -o prog `pkg-config --cflags --libs xcb`
+</pre>
+ </ol>
+ <li class="title"><a name="openconn">Opening and closing the connection to an X server</a></li>
+ <p>
+ An X program first needs to open the connection to the X
+ server. There is a function that opens a connection. It requires
+ the display name, or NULL. In the latter case, the display name
+ will be the one in the environment variable DISPLAY.
+ </p>
+ <pre class="code">
+XCBConnection *XCBConnect (const char *displayname,
+ int *screenp);
+</pre>
+ <p>
+ The second parameter returns the screen number used for the
+ connection. The returned structure describes an XCB connection
+ and is opaque. Here is how the connection can be opened:
+ </p>
+ <pre class="code">
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+
+ /* Open the connection to the X server. use the DISPLAY environment variable as the default display name */
+ c = XCBConnect (NULL, NULL);
+
+ return 1;
+}
+</pre>
+ <p>
+ To close a connection, it suffices to use:
+ </p>
+ <pre class="code">
+void XCBDisconnect (XCBConnection *c);
+</pre>
+ <div class="comp">
+ <div class="title">
+ Comparison Xlib/XCB
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XOpenDisplay ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBConnect ()</li>
+ </ul>
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XCloseDisplay ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBDisconnect ()</li>
+ </ul>
+ </div>
+ </div>
+ <p>
+ </p>
+ <li class="title"><a name="screen">Checking basic information about a connection</a></li>
+ <p>
+ Once we opened a connection to an X server, we should check some
+ basic informations about it: what screens it has, what is the
+ size (width and height) of the screen, how many colors it
+ supports (black and white ? grey scale ?, 256 colors ? more ?),
+ and so on. We get such informations from the XCBSCREEN
+ structure:
+ </p>
+ <pre class="code">
+typedef struct {
+ XCBWINDOW root;
+ XCBCOLORMAP default_colormap;
+ CARD32 white_pixel;
+ CARD32 black_pixel;
+ CARD32 current_input_masks;
+ CARD16 width_in_pixels;
+ CARD16 height_in_pixels;
+ CARD16 width_in_millimeters;
+ CARD16 height_in_millimeters;
+ CARD16 min_installed_maps;
+ CARD16 max_installed_maps;
+ XCBVISUALID root_visual;
+ BYTE backing_stores;
+ BOOL save_unders;
+ CARD8 root_depth;
+ CARD8 allowed_depths_len;
+} XCBSCREEN;
+</pre>
+ <p>
+ We could retrieve the first screen of the connection by using the
+ following function:
+ </p>
+ <pre class="code">
+XCBSCREENIter XCBConnSetupSuccessRepRootsIter (XCBConnSetupSuccessRep *R);
+</pre>
+ <p>
+ Here is a small program that shows how to use this function:
+ </p>
+ <pre class="code">
+#include &lt;stdio.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ int screen_nbr;
+ XCBSCREENIter iter;
+
+ /* Open the connection to the X server. Use the DISPLAY environment variable */
+ c = XCBConnect (NULL, &screen_nbr);
+
+ /* Get the screen #screen_nbr */
+ iter = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c));
+ for (; iter.rem; --screen_nbr, XCBSCREENNext (&iter))
+ if (screen_nbr == 0)
+ {
+ screen = iter.data;
+ break;
+ }
+
+ printf ("\n");
+ printf ("Informations of screen %ld:\n", screen-&gt;root.xid);
+ printf (" width.........: %d\n", screen-&gt;width_in_pixels);
+ printf (" height........: %d\n", screen-&gt;height_in_pixels);
+ printf (" white pixel...: %ld\n", screen-&gt;white_pixel);
+ printf (" black pixel...: %ld\n", screen-&gt;black_pixel);
+ printf ("\n");
+
+ return 1;
+}
+</pre>
+ <li class="title"><a name="helloworld">Creating a basic window - the "hello world" program</a></li>
+ <p>
+ After we got some basic informations about our screen, we can
+ create our first window. In the X Window System, a window is
+ characterized by an Id. So, in XCB, a window is of type:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBWINDOW;
+</pre>
+ <p>
+ We first ask for a new Id for our window, with this function:
+ </p>
+ <pre class="code">
+XCBWINDOW XCBWINDOWNew(XCBConnection *c);
+</pre>
+ <p>
+ Then, XCB supplies the following function to create new windows:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBCreateWindow (XCBConnection *c, /* Pointer to the XCBConnection structure */
+ CARD8 depth, /* Depth of the screen */
+ XCBWINDOW wid, /* Id of the window */
+ XCBWINDOW parent, /* Id of an existing window that should be the parent of the new window */
+ INT16 x, /* X position of the top-left corner of the window (in pixels) */
+ INT16 y, /* Y position of the top-left corner of the window (in pixels) */
+ CARD16 width, /* Width of the window (in pixels) */
+ CARD16 height, /* Height of the window (in pixels) */
+ CARD16 border_width, /* Width of the window's border (in pixels) */
+ CARD16 _class,
+ XCBVISUALID visual,
+ CARD32 value_mask,
+ const CARD32 *value_list);
+</pre>
+ <p>
+ The fact that we created the window does not mean that it will
+ be drawn on screen. By default, newly created windows are not
+ mapped on the screen (they are invisible). In order to make our
+ window visible, we use the function <span class="code">XCBMapWindow()</span>, whose
+ prototype is
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBMapWindow (XCBConnection *c, XCBWINDOW window);
+</pre>
+ <p>
+ Finally, here is a small program to create a window of size
+ 150x150 pixels, positioned at the top-left corner of the screen:
+ </p>
+ <pre class="code">
+#include &lt;unistd.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBDRAWABLE win;
+
+ /* Open the connection to the X server */
+ c = XCBConnect (NULL, NULL);
+
+ /* Get the first screen */
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* Ask for our window's Id */
+ win.window = XCBWINDOWNew(c);
+
+ /* Create the window */
+ XCBCreateWindow (c, /* Connection */
+ 0, /* depth */
+ win.window, /* window Id */
+ screen-&gt;root, /* parent window */
+ 0, 0, /* x, y */
+ 150, 150, /* width, height */
+ 10, /* border_width */
+ InputOutput, /* class */
+ screen-&gt;root_visual, /* visual */
+ 0, NULL); /* masks, not used yet */
+
+ /* Map the window on the screen */
+ XCBMapWindow (c, win.window);
+
+ XCBSync (c, 0);
+
+ pause ();
+
+ return 1;
+}
+</pre>
+ <p>
+ In this code, you see one more function - <span class="code">XCBSync()</span>, not explained
+ yet. It is used to flush all the pending requests. More
+ precisely, there are 2 functions that do such things. The first
+ one is <span class="code">XCBFlush()</span>:
+ </p>
+ <pre class="code">
+int XCBFlush (XCBConnection *c);
+</pre>
+ <p>
+ This function flushes all pending requests to the X server (much
+ like the <span class="code">fflush()</span> function is used to
+ flush standard output). The second function is
+ <span class="code">XCBSync()</span>:
+ </p>
+ <pre class="code">
+int XCBSync(XCBConnection *c, XCBGenericError **e);
+</pre>
+ <p>
+ This functions also flushes all pending requests to the X
+ server, and then waits until the X server finishing processing
+ these requests. In a normal program, this will not be necessary
+ (we'll see why when we get to write a normal X program), but for
+ now, we put it there.
+ </p>
+ <p>
+ The window that is created by the above code has a default
+ background (gray). This one can be set to a specific color,
+ thanks to the two last parameters of
+ <span class="code">XCBCreateWindow()</span>, which are not
+ described yet. See the subsections
+ <a href="#winconf">Configuring a window</a> or
+ <a href="#winconf">Registering for event types using event masks</a>
+ for exemples on how to use these parameters. In addition, as no
+ events are handled, you have to make a Ctrl-C to interrupt the
+ program.
+ </p>
+ <p>
+ <b>TODO</b>: one should tell what these functions return and
+ about the generic error
+ </p>
+ <div class="comp">
+ <div class="title">
+ Comparison Xlib/XCB
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XCreateWindow ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBWINDOWNew ()</li>
+ <li>XCBCreateWindow ()</li>
+ </ul>
+ </div>
+ </div>
+ <p></p>
+ <li class="title"><a name="drawing">Drawing in a window</a></li>
+ <p>
+ Drawing in a window can be done using various graphical
+ functions (drawing pixels, lines, rectangles, etc). In order to
+ draw in a window, we first need to define various general
+ drawing parameters (what line width to use, which color to draw
+ with, etc). This is done using a graphical context.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="allocgc">Allocating a Graphics Context</a></li>
+ <p>
+ As we said, a graphical context defines several attributes to
+ be used with the various drawing functions. For this, we
+ define a graphical context. We can use more than one graphical
+ context with a single window, in order to draw in multiple
+ styles (different colors, different line widths, etc). In XCB,
+ a Graphics Context is, as a window, characterized by an Id:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBGCONTEXT;
+</pre>
+ <p>
+ We first ask the X server to attribute an Id to our graphic
+ context with this function:
+ </p>
+ <pre class="code">
+XCBGCONTEXT XCBGCONTEXTNew (XCBConnection *c);
+</pre>
+ <p>
+ Then, we set the attributes of the graphic context with this function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBCreateGC (XCBConnection *c,
+ XCBGCONTEXT cid,
+ XCBDRAWABLE drawable,
+ CARD32 value_mask,
+ const CARD32 *value_list);
+</pre>
+ <p>
+ We give now an example on how to allocate a graphic context
+ that specifies that each drawing functions that use it will
+ draw in foreground with a black color.
+ </p>
+ <pre class="code">
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBDRAWABLE win;
+ XCBGCONTEXT black;
+ CARD32 mask;
+ CARD32 value[1];
+
+ /* Open the connection to the X server and get the first screen */
+ c = XCBConnect (NULL, NULL);
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* Create a black graphic context for drawing in the foreground */
+ win.window = screen-&gt;root;
+ black = XCBGCONTEXTNew (c);
+ mask = GCForeground;
+ value[0] = screen-&gt;black_pixel;
+ XCBCreateGC (c, black, win, mask, value);
+
+ return 1;
+}
+</pre>
+ <p>
+ Note should be taken regarding the role of "value_mask" and
+ "value_list" in the prototype of <span class="code">XCBCreateGC()</span>. Since a
+ graphic context has many attributes, and since we often just
+ want to define a few of them, we need to be able to tell the
+ <span class="code">XCBCreateGC()</span> which attributes we
+ want to set. This is what the "value_mask" parameter is
+ for. We then use the "value_list" parameter to specify actual
+ values for the attribute we defined in "value_mask". Thus, for
+ each constant used in "value_list", we will use the matching
+ constant in "value_mask". In this case, we define a graphic
+ context with one attribute: when drawing (a point, a line,
+ etc), the foreground color will be black. The rest of the
+ attributes of this graphic context will be set to their
+ default values.
+ </p>
+ <p>
+ See the next Subsection for more details.
+ </p>
+ <div class="comp">
+ <div class="title">
+ Comparison Xlib/XCB
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XCreateGC ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBGCONTEXTNew ()</li>
+ <li>XCBCreateGC ()</li>
+ </ul>
+ </div>
+ </div>
+ <p></p>
+ <li class="subtitle"><a name="changegc">Changing the attributes of a Graphics Context</a></li>
+ <p>
+ Once we have allocated a Graphic Context, we may need to
+ change its attributes (for example, changing the foreground
+ color we use to draw a line, or changing the attributes of the
+ font we use to display strings. See Subsections Drawing with a
+ color and Assigning a Font to a Graphic Context). This is done
+ by using this function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBChangeGC (XCBConnection *c, /* The XCB Connection */
+ XCBGCONTEXT gc, /* The Graphic Context */
+ CARD32 value_mask, /* Components of the Graphic Context that have to be set */
+ const CARD32 *value_list); /* Value as specified by value_mask */
+</pre>
+ <p>
+ The <span class="code">value_mask</span> parameter could take
+ these values:
+ </p>
+ <ul>
+ <li>GCFunction</li>
+ <li>GCPlaneMask</li>
+ <li>GCForeground</li>
+ <li>GCBackground</li>
+ <li>GCLineWidth</li>
+ <li>GCLineStyle</li>
+ <li>GCCapStyle</li>
+ <li>GCJoinStyle</li>
+ <li>GCFillStyle</li>
+ <li>GCFillRule</li>
+ <li>GCTile</li>
+ <li>GCStipple</li>
+ <li>GCTileStipXOrigin</li>
+ <li>GCTileStipYOrigin</li>
+ <li>GCFont</li>
+ <li>GCSubwindowMode</li>
+ <li>GCGraphicsExposures</li>
+ <li>GCClipXOrigin</li>
+ <li>GCClipYOrigin</li>
+ <li>GCClipMask</li>
+ <li>GCDashOffset</li>
+ <li>GCDashList</li>
+ <li>GCArcMode</li>
+ </ul>
+ <p>
+ It is possible to set several attributes at the same
+ time (for example setting the attributes of a font and the
+ color which will be used to display a string), by OR'ing these
+ values in <span class="code">value_mask</span>. Then
+ <span class="code">value_list</span> has to be an array which
+ lists the value for the respective attributes. See Subsection
+ Drawing with a color to have an example.
+ </p>
+ <p>
+ <b>TODO</b>: set the links of the 3 subsections, once they will
+ be written :)
+ </p>
+ <p>
+ <b>TODO</b>: give an example which sets several attributes.
+ </p>
+ <li class="subtitle"><a name="drawingprim">Drawing primitives: point, line, box, circle,...</a></li>
+ <p>
+ After we have created a Graphic Context, we can draw on a
+ window using this Graphic Context, with a set of XCB
+ functions, collectively called "drawing primitive". Let see
+ how they are used.
+ </p>
+ <p>
+ To draw a point, or several points, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyPoint (XCBConnection *c, /* The connection to the X server */
+ BYTE coordinate_mode, /* Coordinate mode, usually set to CoordModeOrigin */
+ XCBDRAWABLE drawable, /* The drawable on which we want to draw the point(s) */
+ XCBGCONTEXT gc, /* The Graphic Context we use to draw the point(s) */
+ CARD32 points_len, /* The number of points */
+ const XCBPOINT *points); /* An array of points */
+</pre>
+ <p>
+ The <span class="code">coordinate_mode</span> parameter
+ specifies the coordinate mode. Available values are
+ </p>
+ <ul>
+ <li><span class="code">CoordModeOrigin</span></li>
+ <li><span class="code">CoordModePrevious</span></li>
+ </ul>
+ <p>
+ The <span class="code">XCBPOINT</span> type is just a
+ structure with two fields (the coordinates of the point):
+ </p>
+ <pre class="code">
+typedef struct {
+ INT16 x;
+ INT16 y;
+} XCBPOINT;
+</pre>
+ <p>
+ You could see an example in xpoints.c. <b>TODO</b> Set the link.
+ </p>
+ <p>
+ To draw a line, or a polygonal line, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyLine (XCBConnection *c, /* The connection to the X server */
+ BYTE coordinate_mode, /* Coordinate mode, usually set to CoordModeOrigin */
+ XCBDRAWABLE drawable, /* The drawable on which we want to draw the line(s) */
+ XCBGCONTEXT gc, /* The Graphic Context we use to draw the line(s) */
+ CARD32 points_len, /* The number of points in the polygonal line */
+ const XCBPOINT *points); /* An array of points */
+</pre>
+ <p>
+ This function will draw the line between the first and the
+ second points, then the line between the second and the third
+ points, and so on.
+ </p>
+ <p>
+ To draw a segment, or several segments, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolySegment (XCBConnection *c, /* The connection to the X server */
+ XCBDRAWABLE drawable, /* The drawable on which we want to draw the segment(s) */
+ XCBGCONTEXT gc, /* The Graphic Context we use to draw the segment(s) */
+ CARD32 segments_len, /* The number of segments */
+ const XCBSEGMENT *segments); /* An array of segments */
+</pre>
+ <p>
+ The <span class="code">XCBSEGMENT</span> type is just a
+ structure with four fields (the coordinates of the two points
+ that define the segment):
+ </p>
+ <pre class="code">
+typedef struct {
+ INT16 x1;
+ INT16 y1;
+ INT16 x2;
+ INT16 y2;
+} XCBSEGMENT;
+</pre>
+ <p>
+ To draw a rectangle, or several rectangles, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyRectangle (XCBConnection *c, /* The connection to the X server */
+ XCBDRAWABLE drawable, /* The drawable on which we want to draw the rectangle(s) */
+ XCBGCONTEXT gc, /* The Graphic Context we use to draw the rectangle(s) */
+ CARD32 rectangles_len, /* The number of rectangles */
+ const XCBRECTANGLE *rectangles); /* An array of rectangles */
+</pre>
+ <p>
+ The <span class="code">XCBRECTANGLE</span> type is just a
+ structure with four fields (the coordinates of the top-left
+ corner of the rectangle, and its width and height):
+ </p>
+ <pre class="code">
+typedef struct {
+ INT16 x;
+ INT16 y;
+ CARD16 width;
+ CARD16 height;
+} XCBRECTANGLE;
+</pre>
+ <p>
+ <b>TODO</b>: there's no coordinate_mode. Is it normal ?
+ </p>
+ <p>
+ To draw an elliptical arc, or several elliptical arcs, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyArc (XCBConnection *c, /* The connection to the X server */
+ XCBDRAWABLE drawable, /* The drawable on which we want to draw the arc(s) */
+ XCBGCONTEXT gc, /* The Graphic Context we use to draw the arc(s) */
+ CARD32 arcs_len, /* The number of arcs */
+ const XCBARC *arcs); /* An array of arcs */
+</pre>
+ <p>
+ The <span class="code">XCBARC</span> type is a structure with
+ six fields:
+ </p>
+ <pre class="code">
+typedef struct {
+ INT16 x; /* Top left x coordinate of the rectangle surrounding the ellipse */
+ INT16 y; /* Top left y coordinate of the rectangle surrounding the ellipse */
+ CARD16 width; /* Width of the rectangle surrounding the ellipse */
+ CARD16 height; /* Height of the rectangle surrounding the ellipse */
+ INT16 angle1; /* Angle at which the arc begins */
+ INT16 angle2; /* Angle at which the arc ends */
+} XCBARC;
+</pre>
+ <div class="emph">
+ <p>
+ Note: the angles are expressed in units of 1/64 of a degree,
+ so to have an angle of 90 degrees, starting at 0,
+ <span class="code">angle1 = 0</span> and
+ <span class="code">angle2 = 90 &lt;&lt; 6</span>. Positive angles
+ indicate counterclockwise motion, while negative angles
+ indicate clockwise motion.
+ </p>
+ </div>
+ <p>
+ <b>TODO</b>: there's no coordinate_mode. Is it normal ?
+ </p>
+ <p>
+ <b>TODO</b>: I think that (x,y) should be the center of the
+ ellipse, and (width, height) the radius. It's more logical.
+ </p>
+ <p>
+ The corresponding function which fill inside the geometrical
+ object are listed below, without further explanation, as they
+ are used as the above functions.
+ </p>
+ <p>
+ To Fill a polygon defined by the points given as arguments ,
+ we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBFillPoly (XCBConnection *c,
+ XCBDRAWABLE drawable,
+ XCBGCONTEXT gc,
+ CARD8 shape,
+ CARD8 coordinate_mode,
+ CARD32 points_len,
+ const XCBPOINT *points);
+</pre>
+ <p>
+ The <span class="code">shape</span> parameter specifies a
+ shape that helps the server to improve performance. Available
+ values are
+ </p>
+ <ul>
+ <li><span class="code">Complex</span></li>
+ <li><span class="code">Convex</span></li>
+ <li><span class="code">Nonconvex</span></li>
+ </ul>
+ <p>
+ To fill one or several rectangles, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyFillRectangle (XCBConnection *c,
+ XCBDRAWABLE drawable,
+ XCBGCONTEXT gc,
+ CARD32 rectangles_len,
+ const XCBRECTANGLE *rectangles);
+</pre>
+ <p>
+ To fill one or several arcs, we use
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBPolyFillArc (XCBConnection *c,
+ XCBDRAWABLE drawable,
+ XCBGCONTEXT gc,
+ CARD32 arcs_len,
+ const XCBARC *arcs);
+</pre>
+ <p></p>
+ <p>
+ To illustrate these functions, here is an example that draws
+ four points, a polygonal line, two segments, two rectangles
+ and two arcs. Remark that we use events for the first time, as
+ an introduction to the next section.
+ </p>
+ <pre class="code">
+#include &lt;stdlib.h&gt;
+#include &lt;stdio.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+/* Get the depth of the screen. Needed in order to draw something */
+int
+get_depth(XCBConnection *c,
+ XCBSCREEN *root)
+{
+ XCBDRAWABLE drawable;
+ XCBGetGeometryRep *geom;
+ int depth;
+
+ drawable.window = root-&gt;root;
+ geom = XCBGetGeometryReply (c, XCBGetGeometry(c, drawable), 0);
+
+ if(!geom)
+ {
+ perror ("GetGeometry(root) failed");
+ exit (0);
+ }
+
+ depth = geom-&gt;depth;
+ free (geom);
+
+ return depth;
+}
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBDRAWABLE win;
+ XCBGCONTEXT foreground;
+ XCBGenericEvent *e;
+ CARD32 mask = 0;
+ CARD32 values[2];
+
+ /* geometric objects */
+ XCBPOINT points[] = {
+ {10, 10},
+ {10, 20},
+ {20, 10},
+ {20, 20}};
+
+ XCBPOINT polyline[] = {
+ {50, 10},
+ {55, 30},
+ {80, 10},
+ {90, 20}};
+
+ XCBSEGMENT segments[] = {
+ {100, 10, 140, 30},
+ {110, 25, 130, 60}};
+
+ XCBRECTANGLE rectangles[] = {
+ { 10, 50, 40, 20},
+ { 80, 50, 10, 40}};
+
+ XCBARC arcs[] = {
+ {10, 100, 60, 40, 0, 90 << 6},
+ {90, 100, 55, 40, 0, 270 << 6}};
+
+ /* Open the connection to the X server */
+ c = XCBConnect (NULL, NULL);
+
+ /* Get the first screen */
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* Create black (foregroung) graphic context */
+ win.window = screen-&gt;root;
+
+ foreground = XCBGCONTEXTNew (c);
+ mask = GCForeground | GCGraphicsExposures;
+ values[0] = screen-&gt;black_pixel;
+ values[1] = 0;
+ XCBCreateGC (c, foreground, win, mask, values);
+
+ /* Ask for our window's Id */
+ win.window = XCBWINDOWNew(c);
+
+ /* Create the window */
+ mask = XCBCWBackPixel | XCBCWEventMask;
+ values[0] = screen-&gt;white_pixel;
+ values[1] = ExposureMask;
+ XCBCreateWindow (c, /* Connection */
+ 0, /* depth */
+ win.window, /* window Id */
+ screen-&gt;root, /* parent window */
+ 0, 0, /* x, y */
+ 150, 150, /* width, height */
+ 10, /* border_width */
+ InputOutput, /* class */
+ screen-&gt;root_visual, /* visual */
+ mask, values); /* masks */
+
+ /* Map the window on the screen */
+ XCBMapWindow (c, win.window);
+
+
+ /* We flush the request */
+ XCBSync (c, 0);
+
+ while ((e = XCBWaitEvent (c)))
+ {
+ switch (e-&gt;response_type)
+ {
+ case XCBExpose:
+ {
+ /* We draw the points */
+ XCBPolyPoint (c, CoordModeOrigin, win, foreground, 4, points);
+
+ /* We draw the polygonal line */
+ XCBPolyLine (c, CoordModeOrigin, win, foreground, 4, polyline);
+
+ /* We draw the segements */
+ XCBPolySegment (c, win, foreground, 2, segments);
+
+ /* We draw the rectangles */
+ XCBPolyRectangle (c, win, foreground, 2, rectangles);
+
+ /* We draw the arcs */
+ XCBPolyArc (c, win, foreground, 2, arcs);
+
+ /* We flush the request */
+ XCBSync (c, 0);
+
+ break;
+ }
+ default:
+ {
+ /* Unknown event type, ignore it */
+ break;
+ }
+ }
+ /* Free the Generic Event */
+ free (e);
+ }
+
+ return 1;
+}
+</pre>
+ </ol>
+ <li class="title"><a name="xevents">X Events</a></li>
+ <p>
+ In an X program, everything is driven by events. Event painting
+ on the screen is sometimes done as a response to an event (an
+ <span class="code">Expose</span> event). If part of a program's
+ window that was hidden, gets exposed (e.g. the window was raised
+ above other widows), the X server will send an "expose" event to
+ let the program know it should repaint that part of the
+ window. User input (key presses, mouse movement, etc) is also
+ received as a set of events.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="register">Registering for event types using event masks</a></li>
+ <p>
+ During the creation of a window, you should give it what kind
+ of events it wishes to receive. Thus, you may register for
+ various mouse (also called pointer) events, keyboard events,
+ expose events, and so on. This is done for optimizing the
+ server-to-client connection (i.e. why send a program (that
+ might even be running at the other side of the globe) an event
+ it is not interested in ?)
+ </p>
+ <p>
+ In XCB, you use the "value_mask" and "value_list" data in the
+ <span class="code">XCBCreateWindow()</span> function to
+ register for events. Here is how we register for
+ <span class="code">Expose</span> event when creating a window:
+ </p>
+ <pre class="code">
+ mask = XCBCWEventMask;
+ valwin[0] = ExposureMask;
+ win.window = XCBWINDOWNew (c);
+ XCBCreateWindow (c, depth, win.window, root-&gt;root,
+ 0, 0, 150, 150, 10,
+ InputOutput, root-&gt;root_visual,
+ mask, valwin);
+</pre>
+ <p>
+ <span class="code">ExposureMask</span> is a constant defined
+ in the "X.h" header file. If we wanted to register to several
+ event types, we can logically "or" them, as follows:
+ </p>
+ <pre class="code">
+ mask = XCBCWEventMask;
+ valwin[0] = ExposureMask | ButtonPressMask;
+ win.window = XCBWINDOWNew (c);
+ XCBCreateWindow (c, depth, win.window, root-&gt;root,
+ 0, 0, 150, 150, 10,
+ InputOutput, root-&gt;root_visual,
+ mask, valwin);
+</pre>
+ <p>
+ This registers for <span class="code">Expose</span> events as
+ well as for mouse button presses insode the created
+ window. You should note that a mask may represent several
+ event sub-types.
+ </p>
+ <p>
+ The values that a mask could take are given
+ by the <span class="code">XCBCW</span> enumeration:
+ </p>
+ <pre class="code">
+typedef enum {
+ XCBCWBackPixmap = 1L<<0,
+ XCBCWBackPixel = 1L<<1,
+ XCBCWBorderPixmap = 1L<<2,
+ XCBCWBorderPixel = 1L<<3,
+ XCBCWBitGravity = 1L<<4,
+ XCBCWWinGravity = 1L<<5,
+ XCBCWBackingStore = 1L<<6,
+ XCBCWBackingPlanes = 1L<<7,
+ XCBCWBackingPixel = 1L<<8,
+ XCBCWOverrideRedirect = 1L<<9,
+ XCBCWSaveUnder = 1L<<10,
+ XCBCWEventMask = 1L<<11,
+ XCBCWDontPropagate = 1L<<12,
+ XCBCWColormap = 1L<<13,
+ XCBCWCursor = 1L<<14
+} XCBCW;
+</pre>
+ <div class="emph">
+ <p>Note: we must be careful when setting the values of the valwin
+ parameter, as they have to follow the order the
+ <span class="code">XCBCW</span> enumeration. Here is an
+ example:
+ </p>
+ </div>
+ <pre class="code">
+ mask = XCBCWEventMask | XCBCWBackPixmap;
+ valwin[0] = None; /* for XCBCWBackPixmap (whose value is 1) */
+ valwin[1] = ExposureMask | ButtonPressMask; /* for XCBCWEventMask, whose value (2048) */
+ /* is superior to the one of XCBCWBackPixmap */
+</pre>
+ <p>
+ If the window has already been created, we can use the
+ <span class="code">XCBConfigureWindow()</span> function to set
+ the events that the window will receive. The subsection
+ <a href="#winconf">Configuring a window</a> shows its
+ prototype. As an example, here is a piece of code that
+ configures the window to receive the
+ <span class="code">Expose</span> and
+ <span class="code">ButtonPressMask</span> events:
+ </p>
+ <pre class="code">
+const static CARD32 values[] = { ExposureMask | ButtonPressMask };
+
+/* The connection c and the window win are supposed to be defined */
+
+XCBConfigureWindow (c, win, XCBCWEventMask, values);
+</pre>
+ <div class="emph">
+ <p>
+ Note: A common bug programmers do is adding code to handle new
+ event types in their program, while forgetting to add the
+ masks for these events in the creation of the window. Such a
+ programmer then should sit down for hours debugging his
+ program, wondering "Why doesn't my program notice that I
+ released the button?", only to find that they registered for
+ button press events but not for button release events.
+ </p>
+ </div>
+ <li class="subtitle"><a name="loop">Receiving events: writing the events loop</a></li>
+ <p>
+ After we have registered for the event types we are interested
+ in, we need to enter a loop of receiving events and handling
+ them. There are two ways to receive events: a blocking way and
+ a non blocking way:
+ </p>
+ <ul>
+ <li>
+ <span class="code">XCBWaitEvent (XCBConnection *c)</span>
+ is the blocking way. It waits (so blocks...) until an event is
+ queued in the X server. Then it retrieves it into a newly
+ allocated structure (it dequeues it from the queue) and returns
+ it. This structure has to be freed. The function returns
+ <span class="code">NULL</span> if an error occurs.
+ </li>
+ <br />
+ <li>
+ <span class="code">XCBPollForEvent (XCBConnection *c, int
+ *error)</span> is the non blocking way. It looks at the event
+ queue and returns (and dequeues too) an existing event into
+ a newly allocated structure. This structure has to be
+ freed. It returns <span class="code">NULL</span> if there is
+ no event. If an error occurs, the parameter <span
+ class="code">error</span> will be filled with the error
+ status.
+ </li>
+ </ul>
+ <p>
+ There are various ways to write such a loop. We present two
+ ways to write such a loop, with the two functions above. The
+ first one uses <span class="code">XCBWaitEvent</span>, which
+ is similar to an event Xlib loop using only <span
+ class="code">XNextEvent</span>:
+ </p>
+ <pre class="code">
+ XCBGenericEvent *e;
+
+ while ((e = XCBWaitEvent (c)))
+ {
+ switch (e-&gt;response_type)
+ {
+ case XCBExpose:
+ {
+ /* Handle the Expose event type */
+ XCBExposeEvent *ev = (XCBExposeEvent *)e;
+
+ /* ... */
+
+ break;
+ }
+ case XCBButtonPress:
+ {
+ /* Handle the ButtonPress event type */
+ XCBButtonPressEvent *ev = (XCBButtonPressEvent *)e;
+
+ /* ... */
+
+ break;
+ }
+ default:
+ {
+ /* Unknown event type, ignore it */
+ break;
+ }
+ }
+ /* Free the Generic Event */
+ free (e);
+ }
+</pre>
+ <p>
+ You will certainly want to use <span
+ class="code">XCBPollForEvent(XCBConnection *c, int
+ *error)</span> if, in Xlib, you use <span
+ class="code">XPending</span>:
+ </p>
+ <pre class="code">
+ while (XPending (display))
+ {
+ XEvent ev;
+
+ XNextEvent(d, &ev);
+
+ /* Manage your event */
+ }
+</pre>
+ <p>
+ Such a loop in XCB looks like:
+ </p>
+ <pre class="code">
+ XCBGenericEvent *ev;
+
+ while ((ev = XCBPollForEvent (conn, 0)))
+ {
+ /* Manage your event */
+ }
+</pre>
+ <p>
+ The events are managed in the same way as with <span
+ class="code">XCBWaitEvent</span>.
+ Obviously, we will need to give the user some way of
+ terminating the program. This is usually done by handling a
+ special "quit" event, as we will soon see.
+ </p>
+ <div class="comp">
+ <div class="title">
+ Comparison Xlib/XCB
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XNextEvent ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBWaitEvent ()</li>
+ </ul>
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XPending ()</li>
+ <li>XNextEvent ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBPollForEvent ()</li>
+ <br />
+ </ul>
+ </div>
+ </div>
+ <p />
+ <li class="subtitle"><a name="expose">Expose events</a></li>
+ <p>
+ The <span class="code">Expose</span> event is one of the most
+ basic (and most used) events an application may receive. It
+ will be sent to us in one of several cases:
+ <ul>
+ <li>A window that covered part of our window has moved
+ away, exposing part (or all) of our window.</li>
+ <li>Our window was raised above other windows.</li>
+ <li>Our window mapped for the first time.</li>
+ <li>Our window was de-iconified.</li>
+ </ul>
+ </p>
+ <p>
+ You should note the implicit assumption hidden here: the
+ contents of our window is lost when it is being obscured
+ (covered) by either windows. One may wonder why the X server
+ does not save this contents. The answer is: to save
+ memory. After all, the number of windows on a display at a
+ given time may be very large, and storing the contents of all
+ of them might require a lot of memory. Actually, there is a
+ way to tell the X server to store the contents of a window in
+ special cases, as we will see later.
+ </p>
+ <p>
+ When we get an <span class="code">Expose</span> event, we
+ should take the event's data from the members of the following
+ structure:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type; /* The type of the event, here it is XCBExpose */
+ CARD8 pad0;
+ CARD16 sequence;
+ XCBWINDOW window; /* The Id of the window that receives the event (in case */
+ /* our application registered for events on several windows */
+ CARD16 x; /* The x coordinate of the top-left part of the window that needs to be redrawn */
+ CARD16 y; /* The y coordinate of the top-left part of the window that needs to be redrawn */
+ CARD16 width; /* The width of the part of the window that needs to be redrawn */
+ CARD16 height; /* The height of the part of the window that needs to be redrawn */
+ CARD16 count;
+} XCBExposeEvent;
+</pre>
+ <li class="subtitle"><a name="userinput">Getting user input</a></li>
+ <p>
+ User input traditionally comes from two sources: the mouse
+ and the keyboard. Various event types exist to notify us of
+ user input (a key being presses on the keyboard, a key being
+ released on the keyboard, the mouse moving over our window,
+ the mouse entering (or leaving) our window, and so on.
+ </p>
+ <ol>
+ <li class="subsubtitle"><a name="mousepressrelease">Mouse button press and release events</a></li>
+ <p>
+ The first event type we will deal with is a mouse
+ button-press (or button-release) event in our window. In
+ order to register to such an event type, we should add one
+ (or more) of the following masks when we create our window:
+ </p>
+ <ul>
+ <li><span class="code">ButtonPressMask</span>: notify us
+ of any button that was pressed in one of our windows.</li>
+ <li><span class="code">ButtonReleaseMask</span>: notify us
+ of any button that was released in one of our windows.</li>
+ </ul>
+ <p>
+ The structure to be checked for in our events loop is the
+ same for these two events, and is the following:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type; /* The type of the event, here it is XCBButtonPressEvent or XCBButtonReleaseEvent */
+ XCBBUTTON detail;
+ CARD16 sequence;
+ XCBTIMESTAMP time; /* Time, in milliseconds the event took place in */
+ XCBWINDOW root;
+ XCBWINDOW event;
+ XCBWINDOW child;
+ INT16 root_x;
+ INT16 root_y;
+ INT16 event_x; /* The x coordinate where the mouse has been pressed in the window */
+ INT16 event_y; /* The y coordinate where the mouse has been pressed in the window */
+ CARD16 state; /* A mask of the buttons (or keys) during the event */
+ BOOL same_screen;
+} XCBButtonPressEvent;
+
+typedef XCBButtonPressEvent XCBButtonReleaseEvent;
+</pre>
+ <p>
+ The <span class="code">time</span> field may be used to calculate "double-click"
+ situations by an application (e.g. if the mouse button was
+ clicked two times in a duration shorter than a given amount
+ of time, assume this was a double click).
+ </p>
+ <p>
+ The <span class="code">state</span> field is a mask of the buttons held down during
+ the event. It is a bitwise OR of any of the following:
+ </p>
+ <ul>
+ <li><span class="code">Button1Mask</span></li>
+ <li><span class="code">Button2Mask</span></li>
+ <li><span class="code">Button3Mask</span></li>
+ <li><span class="code">Button4Mask</span></li>
+ <li><span class="code">Button5Mask</span></li>
+ <li><span class="code">ShiftMask</span></li>
+ <li><span class="code">LockMask</span></li>
+ <li><span class="code">ControlMask</span></li>
+ <li><span class="code">Mod1Mask</span></li>
+ <li><span class="code">Mod2Mask</span></li>
+ <li><span class="code">Mod3Mask</span></li>
+ <li><span class="code">Mod4Mask</span></li>
+ <li><span class="code">Mod5Mask</span></li>
+ </ul>
+ <p>
+ Their names are self explanatory, where the first 5 refer to
+ the mouse buttons that are being pressed, while the rest
+ refer to various "special keys" that are being pressed (Mod1
+ is usually the 'Alt' key or the 'Meta' key).
+ </p>
+ <p>
+ <b>TODO:</b> Problem: it seems that the state does not
+ change when clicking with various buttons.
+ </p>
+ <li class="subsubtitle"><a name="mousemvnt">Mouse movement events</a></li>
+ <p>
+ Similar to mouse button press and release events, we also
+ can be notified of various mouse movement events. These can
+ be split into two families. One is of mouse pointer
+ movement while no buttons are pressed, and the second is a
+ mouse pointer motion while one (or more) of the buttons are
+ pressed (this is sometimes called "a mouse drag operation",
+ or just "dragging"). The following event masks may be added
+ during the creation of our window:
+ </p>
+ <ul>
+ <li><span class="code">PointerMotionMask</span>: events of
+ the pointer moving in one of the windows controlled by our
+ application, while no mouse button is held pressed.</li>
+ <li><span class="code">ButtonMotionMask</span>: Events of
+ the pointer moving while one or more of the mouse buttons
+ is held pressed.</li>
+ <li><span class="code">Button1MotionMask</span>: same as
+ <span class="code">ButtonMotionMask</span>, but only when
+ the 1st mouse button is held pressed.</li>
+ <li><span class="code">Button2MotionMask</span>,
+ <span class="code">Button3MotionMask</span>,
+ <span class="code">Button4MotionMask</span>,
+ <span class="code">Button5MotionMask</span>: same as
+ <span class="code">Button1MotionMask</span>, but
+ respectively for 2nd, 3rd, 4th and 5th mouse button.</li>
+ </ul>
+ <p>
+ The structure to be checked for in our events loop is the
+ same for these events, and is the following:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type; /* The type of the event */
+ BYTE detail;
+ CARD16 sequence;
+ XCBTIMESTAMP time; /* Time, in milliseconds the event took place in */
+ XCBWINDOW root;
+ XCBWINDOW event;
+ XCBWINDOW child;
+ INT16 root_x;
+ INT16 root_y;
+ INT16 event_x; /* The x coordinate of the mouse when the event was generated */
+ INT16 event_y; /* The y coordinate of the mouse when the event was generated */
+ CARD16 state; /* A mask of the buttons (or keys) during the event */
+ BOOL same_screen;
+} XCBMotionNotifyEvent;
+</pre>
+ <li class="subsubtitle"><a name="mouseenter">Mouse pointer enter and leave events</a></li>
+ <p>
+ Another type of event that applications might be interested
+ at, is a mouse pointer entering a window the program
+ controls, or leaving such a window. Some programs use these
+ events to show the user tht the applications is now in
+ focus. In order to register for such an event type, we
+ should add one (or more) of the following masks when we
+ create our window:
+ </p>
+ <ul>
+ <li><span class="code">EnterWindowMask</span>: notify us
+ when the mouse pointer enters any of our controlled
+ windows.</li>
+ <li><span class="code">LeaveWindowMask</span>: notify us
+ when the mouse pointer leaves any of our controlled
+ windows.</li>
+ </ul>
+ <p>
+ The structure to be checked for in our events loop is the
+ same for these two events, and is the following:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type; /* The type of the event */
+ BYTE detail;
+ CARD16 sequence;
+ XCBTIMESTAMP time; /* Time, in milliseconds the event took place in */
+ XCBWINDOW root;
+ XCBWINDOW event;
+ XCBWINDOW child;
+ INT16 root_x;
+ INT16 root_y;
+ INT16 event_x; /* The x coordinate of the mouse when the event was generated */
+ INT16 event_y; /* The y coordinate of the mouse when the event was generated */
+ CARD16 state; /* A mask of the buttons (or keys) during the event */
+ BYTE mode; /* The number of mouse button that was clicked */
+ BYTE same_screen_focus;
+} XCBEnterNotifyEvent;
+
+typedef XCBEnterNotifyEvent XCBLeaveNotifyEvent;
+</pre>
+ <li class="subsubtitle"><a name="focus">The keyboard focus</a></li>
+ <p>
+ There may be many windows on a screen, but only a single
+ keyboard attached to them. How does the X server then know
+ which window should be sent a given keyboard input ? This is
+ done using the keyboard focus. Only a single window on the
+ screen may have the keyboard focus at a given time. There
+ is a XCB function that allow a program to set the keyboard
+ focus to a given window. The user can usually set the
+ keyboard ficus using the window manager (often by clicking
+ on the title bar of the desired window). Once our window
+ has the keyboard focus, every key press or key release will
+ cause an event to be sent to our program (if it regsitered
+ for these event types...).
+ </p>
+ <li class="subsubtitle"><a name="keypress">Keyboard press and release events</a></li>
+ <p>
+ If a window controlled by our program currently holds the
+ keyboard focus, it can receive key press and key release
+ events. So, we should add one (or more) of the following
+ masks when we create our window:
+ </p>
+ <ul>
+ <li><span class="code">KeyPressMask</span>: notify us when
+ a key was pressed while any of our controlled windows had
+ the keyboard focus.</li>
+ <li><span class="code">KeyReleaseMask</span>: notify us
+ when a key was released while any of our controlled
+ windows had the keyboard focus.</li>
+ </ul>
+ <p>
+ The structure to be checked for in our events loop is the
+ same for these two events, and is the following:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type; /* The type of the event */
+ XCBKEYCODE detail;
+ CARD16 sequence;
+ XCBTIMESTAMP time; /* Time, in milliseconds the event took place in */
+ XCBWINDOW root;
+ XCBWINDOW event;
+ XCBWINDOW child;
+ INT16 root_x;
+ INT16 root_y;
+ INT16 event_x;
+ INT16 event_y;
+ CARD16 state;
+ BOOL same_screen;
+} XCBKeyPressEvent;
+
+typedef XCBKeyPressEvent XCBKeyReleaseEvent;
+</pre>
+ <p>
+ The <span class="code">detail</span> field refer to the
+ physical key on the keyboard.
+ </p>
+ <p>
+ <b>TODO:</b> Talk about getting the ASCII code from the key code.
+ </p>
+ </ol>
+ <li class="subtitle"><a name="eventex">X events: a complete example</a></li>
+ <p>
+ As an example for handling events, we show a program that
+ creates a window, enter an events loop and check for all the
+ events described above, and write on the terminal the relevant
+ characteristics of the event. With this code, it should be
+ easy to add drawing operations, like those which have been
+ described above.
+ </p>
+ <pre class="code">
+#include &lt;malloc.h&gt;
+#include &lt;stdio.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBDRAWABLE win;
+ XCBGenericEvent *e;
+ CARD32 mask = 0;
+ CARD32 values[2];
+
+ /* Open the connection to the X server */
+ c = XCBConnect (NULL, NULL);
+
+ /* Get the first screen */
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* Ask for our window's Id */
+ win.window = XCBWINDOWNew(c);
+
+ /* Create the window */
+ mask = XCBCWBackPixel | XCBCWEventMask;
+ values[0] = screen-&gt;white_pixel;
+ values[1] = ExposureMask | ButtonPressMask | ButtonReleaseMask |
+ PointerMotionMask | EnterWindowMask | LeaveWindowMask |
+ KeyPressMask | KeyReleaseMask;
+ XCBCreateWindow (c, /* Connection */
+ 0, /* depth */
+ win.window, /* window Id */
+ screen-&gt;root, /* parent window */
+ 0, 0, /* x, y */
+ 150, 150, /* width, height */
+ 10, /* border_width */
+ InputOutput, /* class */
+ screen-&gt;root_visual, /* visual */
+ mask, values); /* masks */
+
+ /* Map the window on the screen */
+ XCBMapWindow (c, win.window);
+
+ XCBSync (c, 0);
+ while ((e = XCBWaitEvent (c)))
+ {
+ switch (e-&gt;response_type)
+ {
+ case XCBExpose:
+ {
+ XCBExposeEvent *ev = (XCBExposeEvent *)e;
+
+ printf ("Window %ld exposed. Region to be redrawn at location (%d,%d), with dimension (%d,%d)\n",
+ ev-&gt;window.xid, ev-&gt;x, ev-&gt;y, ev-&gt;width, ev-&gt;height);
+ break;
+ }
+ case XCBButtonPress:
+ {
+ XCBButtonPressEvent *ev = (XCBButtonPressEvent *)e;
+ int button_num = 0;
+
+ if ((ev-&gt;state | Button1Mask) == Button1Mask)
+ button_num = 1;
+ if ((ev-&gt;state | Button2Mask) == Button2Mask)
+ button_num = 2;
+ if ((ev-&gt;state | Button3Mask) == Button3Mask)
+ button_num = 3;
+ if ((ev-&gt;state | Button4Mask) == Button4Mask)
+ button_num = 4;
+ if ((ev-&gt;state | Button5Mask) == Button5Mask)
+ button_num = 5;
+
+ switch (ev-&gt;detail.id)
+ {
+ case 4:
+ {
+ printf ("Wheel Button up in window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ case 5:
+ {
+ printf ("Wheel Button down in window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ default:
+ printf ("Button %d pressed in window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;detail.id, ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ }
+ break;
+ }
+ case XCBButtonRelease:
+ {
+ XCBButtonReleaseEvent *ev = (XCBButtonReleaseEvent *)e;
+ int button_num = 0;
+
+ if ((ev-&gt;state | Button1Mask) == Button1Mask)
+ button_num = 1;
+ if ((ev-&gt;state | Button2Mask) == Button2Mask)
+ button_num = 2;
+ if ((ev-&gt;state | Button3Mask) == Button3Mask)
+ button_num = 3;
+ if ((ev-&gt;state | Button4Mask) == Button4Mask)
+ button_num = 4;
+ if ((ev-&gt;state | Button5Mask) == Button5Mask)
+ button_num = 5;
+
+ printf ("Button %d released in window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;detail.id, ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ case XCBMotionNotify:
+ {
+ XCBMotionNotifyEvent *ev = (XCBMotionNotifyEvent *)e;
+
+ printf ("Mouse moved in window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ case XCBEnterNotify:
+ {
+ XCBEnterNotifyEvent *ev = (XCBEnterNotifyEvent *)e;
+
+ printf ("Mouse entered window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ case XCBLeaveNotify:
+ {
+ XCBLeaveNotifyEvent *ev = (XCBLeaveNotifyEvent *)e;
+
+ printf ("Mouse leaved window %ld, at coordinates (%d,%d)\n",
+ ev-&gt;event.xid, ev-&gt;event_x, ev-&gt;event_y);
+ break;
+ }
+ case XCBKeyPress:
+ {
+ XCBKeyPressEvent *ev = (XCBKeyPressEvent *)e;
+
+ printf ("Key pressed in window %ld\n",
+ ev-&gt;event.xid);
+ break;
+ }
+ case XCBKeyRelease:
+ {
+ XCBKeyReleaseEvent *ev = (XCBKeyReleaseEvent *)e;
+
+ printf ("Key releaseed in window %ld\n",
+ ev-&gt;event.xid);
+ break;
+ }
+ default:
+ {
+ /* Unknown event type, ignore it */
+ break;
+ }
+ }
+ /* Free the Generic Event */
+ free (e);
+ }
+
+ return 1;
+}
+</pre>
+ </ol>
+ <li class="title"><a name="font">Handling text and fonts</a></li>
+ <p>
+ Besides drawing graphics on a window, we often want to draw
+ text. Text strings have two major properties: the characters to
+ be drawn and the font with which they are drawn. In order to
+ draw text, we need to first request the X server to load a
+ font. We the assign a font to a Graphic Context, and finally, we
+ draw the text in a window, using the Graphic Context.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="fontstruct">The Font structure</a></li>
+ <p>
+ In order to support flexible fonts, a font structure is
+ defined. You know what ? Its an Id:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBFONT;
+</pre>
+ <p>
+ It is used to contain information about a font, and is passed
+ to several functions that handle fonts selection and text drawing.
+ </p>
+ </ol>
+ <li class="title"><a name="wm">Interacting with the window manager</a></li>
+ <p>
+ After we have seen how to create windows and draw on them, we
+ take one step back, and look at how our windows are interacting
+ with their environment (the full screen and the other
+ windows). First of all, our application needs to interact with
+ the window manager. The window manager is responsible to
+ decorating drawn windows (i.e. adding a frame, an iconify
+ button, a system menu, a title bar, etc), as well as handling
+ icons shown when windows are being iconified. It also handles
+ ordering of windows on the screen, and other administrative
+ tasks. We need to give it various hints as to how we want it to
+ treat our application's windows.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="wmprop">Window properties</a></li>
+ <p>
+ Many of the parameters communicated to the window manager are
+ passed using data called "properties". These properties are
+ attached by the X server to different windows, and are stores
+ in a format that makes it possible to read them from different
+ machines that may use different architectures (remember that
+ an X client program may run on a remote machine).
+ </p>
+ <p>
+ The property and its type (a string, an integer, etc) are
+ Id. Their type are <span class="code">XCBATOM</span>:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBATOM;
+</pre>
+ <p>
+ To change the property of a window, we use the following
+ function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBChangeProperty (XCBConnection *c, /* Connection to the X server */
+ CARD8 mode, /* Property mode */
+ XCBWINDOW window, /* Window */
+ XCBATOM property, /* Property to change */
+ XCBATOM type, /* Type of the property */
+ CARD8 format, /* Format of the property (8, 16, 32) */
+ CARD32 data_len, /* Length of the data parameter */
+ const void *data); /* Data */
+</pre>
+ <p>
+ The <span class="code">mode</span> parameter coud be one of
+ the following value (defined in the X.h header file):
+ </p>
+ <ul>
+ <li>PropModeReplace</li>
+ <li>PropModePrepend</li>
+ <li>PropModeAppend</li>
+ </ul>
+ <p></p>
+ <li class="subtitle"><a name="wmname">Setting the window name and icon name</a></li>
+ <p>
+ The firt thing we want to do would be to set the name for our
+ window. This is done using the
+ <span class="code">XCBChangeProperty()</span> function. This
+ name may be used by the window manager as the title of the
+ window (in the title bar), in a task list, etc. The property
+ atom to use to set the name of a window is
+ <span class="code">WM_NAME</span> (and
+ <span class="code">WM_ICON_NAME</span> for the iconified
+ window) and its type is <span class="code">STRING</span>. Here
+ is an example of utilization:
+ </p>
+ <pre class="code">
+#include &lt;string.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+#include &lt;X11/XCB/xcb_atom.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBDRAWABLE win;
+ char *title = "Hello World !";
+ char *title_icon = "Hello World ! (iconified)";
+
+
+
+ /* Open the connection to the X server */
+ c = XCBConnect (NULL, NULL);
+
+ /* Get the first screen */
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* Ask for our window's Id */
+ win.window = XCBWINDOWNew(c);
+
+ /* Create the window */
+ XCBCreateWindow (c, /* Connection */
+ 0, /* depth */
+ win.window, /* window Id */
+ screen-&gt;root, /* parent window */
+ 0, 0, /* x, y */
+ 250, 150, /* width, height */
+ 10, /* border_width */
+ InputOutput, /* class */
+ screen-&gt;root_visual, /* visual */
+ 0, NULL); /* masks, not used */
+
+ /* Set the title of the window */
+ XCBChangeProperty(c, PropModeReplace, win.window,
+ WM_NAME, STRING, 8,
+ strlen(title), title);
+
+ /* Set the title of the window icon */
+ XCBChangeProperty(c, PropModeReplace, win.window,
+ WM_ICON_NAME, STRING, 8,
+ strlen(title_icon), title_icon);
+
+ /* Map the window on the screen */
+ XCBMapWindow (c, win.window);
+
+ XCBSync (c, 0);
+
+ while (1) {}
+
+ return 1;
+}
+</pre>
+ <div class="emph">
+ <p>Note: the use of the atoms needs our program to be compiled
+ and linked against xcb_atom, so that we have to use
+ </p>
+ </div>
+ <pre class="text">
+gcc prog.c -o prog `pkg-config --cflags --libs xcb_atom`
+</pre>
+ <div class="emph">
+ <p>
+ for the program to compile fine.
+ </p>
+ </div>
+ </ol>
+ <li class="title"><a name="winop">Simple window operations</a></li>
+ <p>
+ One more thing we can do to our window is manipulate them on the
+ screen (resize them, move them, raise or lower them, iconify
+ them, and so on). Some window operations functions are supplied
+ by XCB for this purpose.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="winmap">Mapping and un-mapping a window</a></li>
+ <p>
+ The first pair of operations we can apply on a window is
+ mapping it, or un-mapping it. Mapping a window causes the
+ window to appear on the screen, as we have seen in our simple
+ window program example. Un-mapping it causes it to be removed
+ from the screen (although the window as a logical entity still
+ exists). This gives the effect of making a window hidden
+ (unmapped) and shown again (mapped). For example, if we have a
+ dialog box window in our program, instead of creating it every
+ time the user asks to open it, we can create the window once,
+ in an un-mapped mode, and when the user asks to open it, we
+ simply map the window on the screen. When the user clicked the
+ 'OK' or 'Cancel' button, we simply un-map the window. This is
+ much faster than creating and destroying the window, however,
+ the cost is wasted resources, both on the client side, and on
+ the X server side.
+ </p>
+ <p>
+ To map a window, you use the following function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBMapWindow(XCBConnection *c, XCBWINDOW window);
+</pre>
+ <p>
+ To have a simple example, see the <a href="#helloworld">example</a>
+ above. The mapping operation will cause an
+ <span class="code">Expose</span> event to be sent to our
+ application, unless the window is completely covered by other
+ windows.
+ </p>
+ <p>
+ Un-mapping a window is also simple. You use the function
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBUnmapWindow(XCBConnection *c, XCBWINDOW window);
+</pre>
+ <p>
+ The utilization of this function is the same as
+ <span class="code">XCBMapWindow()</span>.
+ </p>
+ <li class="subtitle"><a name="winconf">Configuring a window</a></li>
+ <p>
+ As we have seen when we have created our first window, in the
+ X Events subsection, we can set some attributes to the window
+ (that is, the position, the size, the events the window will
+ receive, etc). If we want to modify them, but the window is
+ already created, we can change them by using hte following
+ function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBConfigureWindow (XCBConnection *c, /* The connection to the X server*/
+ XCBWINDOW window, /* The window to configure */
+ CARD16 value_mask, /* The mask */
+ const CARD32 *value_list); /* The values to set */
+</pre>
+ <p>
+ We set the <span class="code">value_mask</span> to one or
+ several mask values that are in the X.h header:
+ <ul>
+ <li><span class="code">CWX</span>: new x coordinate of the window's top left corner</li>
+ <li><span class="code">CWY</span>: new y coordinate of the window's top left corner</li>
+ <li><span class="code">CWWidth</span>: new width of the window</li>
+ <li><span class="code">CWHeight</span>: new height of the window</li>
+ <li><span class="code">CWBorderWidth</span>: new width of the border of the window</li>
+ <li><span class="code">CWSibling</span></li>
+ <li><span class="code">CWStackMode</span>: the new stacking order</li>
+ </ul>
+ </p>
+ <p>
+ We then give to <span class="code">value_mask</span> the new
+ value. We now describe how to use
+ <span class="code">XCBConfigureWindow</span> in some useful
+ situations.
+ </p>
+ <li class="subtitle"><a name="winmove">Moving a window around the screen</a></li>
+ <p>
+ An operation we might want to do with windows is to move them
+ to a different location. This can be done like this:
+ </p>
+ <pre class="code">
+const static CARD32 values[] = { 10, 20 };
+
+/* The connection c and the window win are supposed to be defined */
+
+/* Move the window to coordinates x = 10 and y = 20 */
+XCBConfigureWindow (c, win, CWX | CWY, values);
+</pre>
+ <p>
+ Note that when the window is moved, it might get partially
+ exposed or partially hidden by other windows, and thus we
+ might get <span class="code">Expose</span> events due to this
+ operation.
+ </p>
+ <li class="subtitle"><a name="winsize">Resizing a window</a></li>
+ <p>
+ Yet another operation we can do is to change the size of a
+ window. This is done using the following code:
+ </p>
+ <pre class="code">
+const static CARD32 values[] = { 200, 300 };
+
+/* The connection c and the window win are supposed to be defined */
+
+/* Resize the window to width = 10 and height = 20 */
+XCBConfigureWindow (c, win, CWWidth | CWHeight, values);
+</pre>
+ <p>
+ We can also combine the move and resize operations using one
+ single call to <span class="code">XCBConfigureWindow</span>:
+ </p>
+ <pre class="code">
+const static CARD32 values[] = { 10, 20, 200, 300 };
+
+/* The connection c and the window win are supposed to be defined */
+
+/* Move the window to coordinates x = 10 and y = 20 */
+/* and resize the window to width = 10 and height = 20 */
+XCBConfigureWindow (c, win, CWX | CWY | CWWidth | CWHeight, values);
+</pre>
+ <li class="subtitle"><a name="winstack">Changing windows stacking order: raise and lower</a></li>
+ <p>
+ Until now, we changed properties of a single window. We'll see
+ that there are properties that relate to the window and other
+ windows. One of hem is the stacking order. That is, the order
+ in which the windows are layered on top of each other. The
+ front-most window is said to be on the top of the stack, while
+ the back-most window is at the bottom of the stack. Here is
+ how to manipulate our windows stack order:
+ </p>
+ <pre class="code">
+const static CARD32 values[] = { Above };
+
+/* The connection c and the window win are supposed to be defined */
+
+/* Move the window on the top of the stack */
+XCBConfigureWindow (c, win, CWStackMode, values);
+</pre>
+ <pre class="code">
+const static CARD32 values[] = { Below };
+
+/* The connection c and the window win are supposed to be defined */
+
+/* Move the window on the bottom of the stack */
+XCBConfigureWindow (c, win, CWStackMode, values);
+</pre>
+ <li class="subtitle"><a name="wingetinfo">Getting information about a window</a></li>
+ <p>
+ Just like we can set various attributes of our windows, we can
+ also ask the X server supply the current values of these
+ attributes. For example, we can chewk where a window is
+ located on the screen, what is its current size, wheter it is
+ mapped or not, etc. The structure that contains some of this
+ information is
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type;
+ CARD8 depth; /* depth of the window */
+ CARD16 sequence;
+ CARD32 length;
+ XCBWINDOW root; /* Id of the root window *>
+ INT16 x; /* X coordinate of the window's location */
+ INT16 y; /* Y coordinate of the window's location */
+ CARD16 width; /* Width of the window */
+ CARD16 height; /* Height of the window */
+ CARD16 border_width; /* Width of the window's border */
+} XCBGetGeometryRep;
+</pre>
+ <p>
+ XCB fill this structure with two functions:
+ </p>
+ <pre class="code">
+XCBGetGeometryCookie XCBGetGeometry (XCBConnection *c,
+ XCBDRAWABLE drawable);
+XCBGetGeometryRep *XCBGetGeometryReply (XCBConnection *c,
+ XCBGetGeometryCookie cookie,
+ XCBGenericError **e);
+</pre>
+ <p>
+ You use them as follows:
+ </p>
+ <pre class="code">
+ XCBConnection *c;
+ XCBDRAWABLE win;
+ XCBGetGeometryRep *geom;
+
+ /* You initialize c and win */
+
+ geom = XCBGetGeometryReply (c, XCBGetGeometry (c, win), 0);
+
+ /* Do something with the fields of geom */
+
+ free (geom);
+</pre>
+ <p>
+ Remark that you have to free the structure, as
+ <span class="code">XCBGetGeometryReply</span> allocates a
+ newly one.
+ </p>
+ <p>
+ One problem is that the returned location of the window is
+ relative to its parent window. This makes these coordinates
+ rather useless for any window manipulation functions, like
+ moving it on the screen. In order to overcome this problem, we
+ need to take a two-step operation. First, we find out the Id
+ of the parent window of our window. We then translate the
+ above relative coordinates to the screen coordinates.
+ </p>
+ <p>
+ To get the Id of the parent window, we need this structure:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type;
+ CARD8 pad0;
+ CARD16 sequence;
+ CARD32 length;
+ XCBWINDOW root;
+ XCBWINDOW parent; /* Id of the parent window */
+ CARD16 children_len;
+ CARD8 pad1[14];
+} XCBQueryTreeRep;
+</pre>
+ <p>
+ To fill this structure, we use these two functions:
+ </p>
+ <pre class="code">
+XCBQueryTreeCookie XCBQueryTree (XCBConnection *c,
+ XCBWINDOW window);
+XCBQueryTreeRep *XCBQueryTreeReply (XCBConnection *c,
+ XCBQueryTreeCookie cookie,
+ XCBGenericError **e);
+</pre>
+ <p>
+ The translated coordinates will be found in this structure:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type;
+ BOOL same_screen;
+ CARD16 sequence;
+ CARD32 length;
+ XCBWINDOW child;
+ CARD16 dst_x; /* Translated x coordinate */
+ CARD16 dst_y; /* Translated y coordinate */
+} XCBTranslateCoordinatesRep;
+</pre>
+ <p>
+ As usual, we need two functions to fill this structure:
+ </p>
+ <pre class="code">
+XCBTranslateCoordinatesCookie XCBTranslateCoordinates (XCBConnection *c,
+ XCBWINDOW src_window,
+ XCBWINDOW dst_window,
+ INT16 src_x,
+ INT16 src_y);
+XCBTranslateCoordinatesRep *XCBTranslateCoordinatesReply (XCBConnection *c,
+ XCBTranslateCoordinatesCookie cookie,
+ XCBGenericError **e);
+</pre>
+ <p>
+ We use them as follows:
+ </p>
+ <pre class="code">
+ XCBConnection *c;
+ XCBDRAWABLE win;
+ XCBGetGeometryRep *geom;
+ XCBQueryTreeRep *tree;
+ XCBTranslateCoordinatesRep *trans;
+
+ /* You initialize c and win */
+
+ geom = XCBGetGeometryReply (c, XCBGetGeometry (c, win), 0);
+ if (!geom)
+ return 0;
+
+ tree = XCBQueryTreeReply (c, XCBQueryTree (c, win), 0);
+ if (!tree)
+ return 0;
+
+ trans = XCBTranslateCoordinatesReply (c,
+ XCBTranslateCoordinates (c,
+ win,
+ tree-&gt;parent,
+ geom-&gt;x, geom-&gt;y),
+ 0);
+ if (!trans)
+ return 0;
+
+ /* the translated coordinates are in trans-&gt;dst_x and trans-&gt;dst_y */
+
+ free (trans);
+ free (tree);
+ free (geom);
+</pre>
+ <p>
+ Of course, as for <span class="code">geom</span>,
+ <span class="code">tree</span> and
+ <span class="code">trans</span> have to be freed.
+ </p>
+ <p>
+ The work is a bit hard, but XCB is a very low-level library.
+ </p>
+ <p>
+ <b>TODO:</b> the utilization of these functions should be a
+ prog, which displays the coordinates of the window.
+ </p>
+ <p>
+ There is another structure that gives informations about our window:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type;
+ CARD8 backing_store;
+ CARD16 sequence;
+ CARD32 length;
+ XCBVISUALID visual; /* Visual of the window */
+ CARD16 _class;
+ CARD8 bit_gravity;
+ CARD8 win_gravity;
+ CARD32 backing_planes;
+ CARD32 backing_pixel;
+ BOOL save_under;
+ BOOL map_is_installed;
+ CARD8 map_state; /* Map state of the window */
+ BOOL override_redirect;
+ XCBCOLORMAP colormap; /* Colormap of the window */
+ CARD32 all_event_masks;
+ CARD32 your_event_mask;
+ CARD16 do_not_propagate_mask;
+} XCBGetWindowAttributesRep;
+</pre>
+ <p>
+ XCB supplies these two functions to fill it:
+ </p>
+ <pre class="code">
+XCBGetWindowAttributesCookie XCBGetWindowAttributes (XCBConnection *c,
+ XCBWINDOW window);
+XCBGetWindowAttributesRep *XCBGetWindowAttributesReply (XCBConnection *c,
+ XCBGetWindowAttributesCookie cookie,
+ XCBGenericError **e);
+</pre>
+ <p>
+ You use them as follows:
+ </p>
+ <pre class="code">
+ XCBConnection *c;
+ XCBDRAWABLE win;
+ XCBGetWindowAttributesRep *attr;
+
+ /* You initialize c and win */
+
+ attr = XCBGetWindowAttributesReply (c, XCBGetWindowAttributes (c, win), 0);
+
+ if (!attr)
+ return 0;
+
+ /* Do something with the fields of attr */
+
+ free (attr);
+</pre>
+ <p>
+ As for <span class="code">geom</span>,
+ <span class="code">attr</span> has to be freed.
+ </p>
+ </ol>
+ <li class="title"><a name="usecolor">Using colors to paint the rainbow</a></li>
+ <p>
+ Up until now, all our painting operation were done using black
+ and white. We will (finally) see now how to draw using colors.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="colormap">Color maps</a></li>
+ <p>
+ In the beginning, there were not enough colors. Screen
+ controllers could only support a limited number of colors
+ simultaneously (initially 2, then 4, 16 and 256). Because of
+ this, an application could not just ask to draw in a "light
+ purple-red" color, and expect that color to be available. Each
+ application allocated the colors it needed, and when all the
+ color entries (4, 16, 256 colors) were in use, the next color
+ allocation would fail.
+ </p>
+ <p>
+ Thus, the notion of "a color map" was introduced. A color map
+ is a table whose size is the same as the number of
+ simultaneous colors a given screen controller. Each entry
+ contained the RGB (Red, Green and Blue) values of a different
+ color (all colors can be drawn using some combination of red,
+ green and blue). When an application wants to draw on the
+ screen, it does not specify which color to use. Rather, it
+ specifies which color entry of some color map to be used
+ during this drawing. Change the value in this color map entry
+ and the drawing will use a different color.
+ </p>
+ <p>
+ In order to be able to draw using colors that got something to
+ do with what the programmer intended, color map allocation
+ functions are supplied. You could ask to allocate entry for a
+ color with a set of RGB values. If one already existed, you
+ would get its index in the table. If none existed, and the
+ table was not full, a new cell would be allocated to contain
+ the given RGB values, and its index returned. If the table was
+ full, the procedure would fail. You could then ask to get a
+ color map entry with a color that is closest to the one you
+ were asking for. This would mean that the actual drawing on
+ the screen would be done using colors similar to what you
+ wanted, but not the same.
+ </p>
+ <p>
+ On today's more modern screens where one runs an X server with
+ support for 16 million colors, this limitation looks a little
+ silly, but remember that there are still older computers with
+ older graphics cards out there. Using color map, support for
+ these screen becomes transparent to you. On a display
+ supporting 16 million colors, any color entry allocation
+ request would succeed. On a display supporting a limited
+ number of colors, some color allocation requests would return
+ similar colors. It won't look as good, but your application
+ would still work.
+ </p>
+ <li class="subtitle"><a name="colormapalloc">Allocating and freeing Color Maps</a></li>
+ <p>
+ When you draw using XCB, you can choose to use the standard
+ color map of the screen your window is displayed on, or you
+ can allocate a new color map and apply it to a window. In the
+ latter case, each time the mouse moves onto your window, the
+ screen color map will be replaced by your window's color map,
+ and you'll see all the other windows on screen change their
+ colors into something quite bizzare. In fact, this is the
+ effect you get with X applications that use the "-install"
+ command line option.
+ </p>
+ <p>
+ In XCB, a color map is (as often in X) an Id:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBCOLORMAP;
+</pre>
+ <p>
+ In order to access the screen's default color map, you just
+ have to retrieve the <span class="code">default_colormap</span>
+ field of the <span class="code">XCBSCREEN</span> structure
+ (see Section
+ <a href="#screen">Checking basic information about a connection</a>):
+ </p>
+ <pre class="code">
+#include &lt;stdio.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBCOLORMAP colormap;
+
+ /* Open the connection to the X server and get the first screen */
+ c = XCBConnect (NULL, NULL);
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ colormap = screen-&gt;default_colormap;
+
+ return 1;
+}
+</pre>
+ <p>
+ This will return the color map used by default on the first
+ screen (again, remember that an X server may support several
+ different screens, each of which might have its own resources).
+ </p>
+ <p>
+ The other option, that of allocating a new colormap, works as
+ follows. We first ask the X server to give an Id to our color
+ map, with this function:
+ </p>
+ <pre class="code">
+XCBCOLORMAP XCBCOLORMAPNew (XCBConnection *c);
+</pre>
+ <p>
+ Then, we create the color map with
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBCreateColormap (XCBConnection *c, /* Pointer to the XCBConnection structure */
+ BYTE alloc, /* Colormap entries to be allocated (AllocNone or AllocAll) */
+ XCBCOLORMAP mid, /* Id of the color map */
+ XCBWINDOW window, /* Window on whose screen the colormap will be created */
+ XCBVISUALID visual); /* Id of the visual supported by the screen */
+</pre>
+ <p>
+ Here is an example of creation of a new color map:
+ </p>
+ <pre class="code">
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBWINDOW win;
+ XCBCOLORMAP cmap
+
+ /* Open the connection to the X server and get the first screen */
+ c = XCBConnect (NULL, NULL);
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* We create the window win here*/
+
+ cmap = XCBCOLORMAPNew (c);
+ XCBCreateColormap (c, AllocNone, cmap, win, screen-&gt;root_visual);
+
+ return 1;
+}
+</pre>
+ <p>
+ Note that the window parameter is only used to allow the X
+ server to create the color map for the given screen. We can
+ then use this color map for any window drawn on the same screen.
+ </p>
+ <p>
+ To free a color map, it suffices to use this function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBFreeColormap (XCBConnection *c, /* The connection */
+ XCBCOLORMAP cmap); /* The color map */
+</pre>
+ <div class="comp">
+ <div class="title">
+ Comparison Xlib/XCB
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XCreateColormap ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBCOLORMAPNew ()</li>
+ <li>XCBCreateColormap ()</li>
+ </ul>
+ </div>
+ <div class="xlib">
+ <ul>
+ <li>XFreeColormap ()</li>
+ </ul>
+ </div>
+ <div class="xcb">
+ <ul>
+ <li>XCBFreeColormap ()</li>
+ </ul>
+ </div>
+ </div>
+ <p></p>
+ <li class="subtitle"><a name="alloccolor">Allocating and freeing a color entry</a></li>
+ <p>
+ Once we got access to some color map, we can strat allocating
+ colors. The informations related to a color are stored in the
+ following structure:
+ </p>
+ <pre class="code">
+typedef struct {
+ BYTE response_type;
+ CARD8 pad0;
+ CARD16 sequence;
+ CARD32 length;
+ CARD16 red; /* The red component */
+ CARD16 green; /* The green component */
+ CARD16 blue; /* The blue component */
+ CARD8 pad1[2];
+ CARD32 pixel; /* The entry in the color map, supplied by the X server */
+} XCBAllocColorRep;
+</pre>
+ <p>
+ XCB supplies these two functions to fill it:
+ </p>
+ <pre class="code">
+XCBAllocColorCookie XCBAllocColor (XCBConnection *c,
+ XCBCOLORMAP cmap,
+ CARD16 red,
+ CARD16 green,
+ CARD16 blue);
+XCBAllocColorRep *XCBAllocColorReply (XCBConnection *c,
+ XCBAllocColorCookie cookie,
+ XCBGenericError **e);
+</pre>
+ <p>
+ The fuction <span class="code">XCBAllocColor()</span> takes the
+ 3 RGB components as parameters (red, green and blue). Here is an
+ example of using these functions:
+ </p>
+ <pre class="code">
+#include &lt;malloc.h&gt;
+
+#include &lt;X11/XCB/xcb.h&gt;
+
+int
+main (int argc, char *argv[])
+{
+ XCBConnection *c;
+ XCBSCREEN *screen;
+ XCBWINDOW win;
+ XCBCOLORMAP cmap;
+ XCBAllocColorRep *rep;
+
+ /* Open the connection to the X server and get the first screen */
+ c = XCBConnect (NULL, NULL);
+ screen = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).data;
+
+ /* We create the window win here*/
+
+ cmap = XCBCOLORMAPNew (c);
+ XCBCreateColormap (c, AllocNone, cmap, win, screen-&gt;root_visual);
+
+ rep = XCBAllocColorReply (c, XCBAllocColor (c, cmap, 65535, 0, 0), 0);
+
+ if (!rep)
+ return 0;
+
+ /* Do something with r-&gt;pixel or the components */
+
+ free (rep);
+
+ return 1;
+}
+</pre>
+ <p>
+ As <span class="code">XCBAllocColorReply()</span> allocates
+ memory, you have to free <span class="code">rep</span>.
+ </p>
+ <p>
+ <b>TODO</b>: Talk about freeing colors.
+ </p>
+ </ol>
+ <li class="title"><a name="pixmaps">X Bitmaps and Pixmaps</a></li>
+ <p>
+ One thing many so-called "Multi-Media" applications need to od,
+ is display images. In the X world, this is done using bitmaps
+ and pixmaps. We have already seen some usage of them when
+ setting an icon for our application. Lets study them further,
+ and see how to draw these images inside a window, along side the
+ simple graphics and text we have seen so far.
+ </p>
+ <p>
+ One thing to note before delving further, is that XCB (nor Xlib)
+ supplies no means of manipulating popular image formats, such as
+ gif, png, jpeg or tiff. It is up to the programmer (or to higher
+ level graphics libraries) to translate these image formats into
+ formats that the X server is familiar with (x bitmaps and x
+ pixmaps).
+ </p>
+ <ol>
+ <li class="subtitle"><a name="pixmapswhat">What is a X Bitmap ? An X Pixmap ?</a></li>
+ <p>
+ An X bitmap is a two-color image stored in a format specific
+ to the X window system. When stored in a file, the bitmap data
+ looks like a C source file. It contains variables defining the
+ width and the height of the bitmap, an array containing the
+ bit values of the bitmap (the size of the array is
+ weight*height), and an optional hot-spot location (that will
+ be explained later, when discussing mouse cursors).
+ </p>
+ <p>
+ An X pixmap is a format used to stored images in the memory of
+ an X server. This format can store both black and white images
+ (such as x bitmaps) as well as color images. It is the only
+ image format supported by the X protocol, and any image to be
+ drawn on screen, should be first translated into this format.
+ </p>
+ <p>
+ In actuality, an X pixmap can be thought of as a window that
+ does not appear on the screen. Many graphics operations that
+ work on windows, will also work on pixmaps. Indeed, the type
+ of X pixmap in XCB is an Id like a window:
+ </p>
+ <pre class="code">
+typedef struct {
+ CARD32 xid;
+} XCBPIXMAP;
+</pre>
+ <p>
+ In order to make the difference between a window and a pixmap,
+ XCB introduces a drawable type, which is a <b>union</b>
+ </p>
+ <pre class="code">
+typedef union {
+ XCBWINDOW window;
+ XCBPIXMAP pixmap;
+} XCBDRAWABLE;
+</pre>
+ <p>
+ in order to avoid confusion between a window and a pixmap.The
+ operations that will work indifferently on a window or a pixmap
+ will require a <span class="code">XCBDRAWABLE</span>
+ </p>
+ <div class="emph">
+ <p>
+ Remark: In Xlib, there is no specific difference between a
+ <span class="code">Drawable</span>, a
+ <span class="code">Pixmap</span> or a
+ <span class="code">Window</span>: all are 32 bit long
+ integer.
+ </p>
+ </div>
+ <li class="subtitle"><a name="pixmapscreate">Creating a pixmap</a></li>
+ <p>
+ Sometimes we want to create an un-initialized pixmap, so we
+ can later draw into it. This is useful for image drawing
+ programs (creating a new empty canvas will cause the creation
+ of a new pixmap on which the drawing can be stored). It is
+ also useful when reading various image formats: we load the
+ image data into memory, create a pixmap on the server, and
+ then draw the decoded image data onto that pixmap.
+ </p>
+ <p>
+ To create a new pixmap, we first ask the X server to give an
+ Id to our pixmap, with this function:
+ </p>
+ <pre class="code">
+XCBPIXMAP XCBPIXMAPNew (XCBConnection *c);
+</pre>
+ <p>
+ Then, XCB supplies the following function to create new pixmaps:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBCreatePixmap (XCBConnection *c, /* Pointer to the XCBConnection structure */
+ CARD8 depth, /* Depth of the screen */
+ XCBPIXMAP pid, /* Id of the pixmap */
+ XCBDRAWABLE drawable,
+ CARD16 width, /* Width of the window (in pixels) */
+ CARD16 height); /* Height of the window (in pixels) */
+</pre>
+ <p>
+ <b>TODO</b>: Explain the drawable parameter, and give an
+ example (like xpoints.c)
+ </p>
+ <li class="subtitle"><a name="pixmapsdraw"></a>Drawing a pixmap in a window</li>
+ <p>
+ Once we got a handle to a pixmap, we can draw it on some
+ window, using the following function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBCopyArea (XCBConnection *c, /* Pointer to the XCBConnection structure */
+ XCBDRAWABLE src_drawable, /* The Drawable we want to paste */
+ XCBDRAWABLE dst_drawable, /* The Drawable on which we copy the previous Drawable */
+ XCBGCONTEXT gc, /* A Graphic Context */
+ INT16 src_x, /* Top left x coordinate of the region we want to copy */
+ INT16 src_y, /* Top left y coordinate of the region we want to copy */
+ INT16 dst_x, /* Top left x coordinate of the region where we want to copy */
+ INT16 dst_y, /* Top left y coordinate of the region where we want to copy */
+ CARD16 width, /* Width of the region we want to copy */
+ CARD16 height); /* Height of the region we want to copy */
+</pre>
+ <p>
+ As you can see, we could copy the whole pixmap, as well as
+ only a given rectangle of the pixmap. This is useful to
+ optimize the drawing speed: we could copy only what we have
+ modified in the pixmap.
+ </p>
+ <p>
+ <b>One important note should be made</b>: it is possible to
+ create pixmaps with different depths on the same screen. When
+ we perform copy operations (a pixmaap onto a window, etc), we
+ should make sure that both source and target have the same
+ depth. If they have a different depth, the operation would
+ fail. The exception to this is if we copy a specific bit plane
+ of the source pixmap using the
+ <span class="code">XCBCopyPlane</span> function. In such an
+ event, we can copy a specific plain to the target window (in
+ actuality, setting a specific bit in the color of each pixel
+ copied). This can be used to generate strange graphic effects
+ in widow, but beyond the scope of this tutorial.
+ </p>
+ <li class="subtitle"><a name="pixmapsfree"></a>Freeing a pixmap</li>
+ <p>
+ Finally, when we are done using a given pixmap, we should free
+ it, in order to free resources of the X server. This is done
+ using this function:
+ </p>
+ <pre class="code">
+XCBVoidCookie XCBFreePixmap (XCBConnection *c, /* Pointer to the XCBConnection structure */
+ XCBPIXMAP pixmap); /* A given pixmap */
+</pre>
+ <p>
+ Of course, after having freed it, we must not try accessing
+ the pixmap again.
+ </p>
+ <p>
+ <b>TODO</b>: Give an example, or a link to xpoints.c
+ </p>
+ </ol>
+ <li class="title"><a name="translation">Translation of basic Xlib functions and macros</a></li>
+ <p>
+ The problem when you want to port an Xlib program to XCB is that
+ you don't know if the Xlib function that you want to "translate"
+ is a X Window one or an Xlib macro. In that section, we describe
+ a way to translate the usual functions or macros that Xlib
+ provides. It's usually just a member of a structure.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="displaystructure">Members of the Display structure</a></li>
+ In this section, we look at how to translate the macros that
+ returns some members of the <span class="code">Display</span>
+ structure. They are obtain by using a function that requires a
+ <span class="code">XCBConnection *</span> or a member of the
+ <span class="code">XCBConnSetupSuccessRep</span> structure
+ (via the function <span class="code">XCBGetSetup</span>), or
+ a function that requires that structure.
+ <ol>
+ <li class="subtitle"><a name="ConnectionNumber">ConnectionNumber</a></li>
+ <p>
+ This number is the file descriptor that connects the client
+ to the server. You just have to use that function:
+ </p>
+ <pre class="code">
+int XCBGetFileDescriptor(XCBConnection *c);
+</pre>
+ <li class="subtitle"><a name="DefaultScreen"></a>DefaultScreen</li>
+ <p>
+ That number is not stored by XCB. It is returned in the
+ second parameter of the function <span class="code"><a href="#openconn">XCBConnect</a></span>.
+ Hence, you have to store it yourself if you want to use
+ it. Then, to get the <span class="code">XCBSCREEN</span>
+ structure, you have to iterate on the screens.
+ The equivalent function of the Xlib's
+ <span class="code">ScreenOfDisplay</span> function can be
+ found <a href="#ScreenOfDisplay">below</a>. OK, here is the
+ small piece of code to get that number:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+int screen_default_nbr;
+
+/* you pass the name of the display you want to XCBConnect */
+
+c = XCBConnect (display_name, &screen_default_nbr);
+
+/* screen_default_nbr contains now the number of the default screen */
+</pre>
+ <li class="subtitle"><a name="QLength"></a>QLength</li>
+ <p>
+ Not documented yet.
+ </p>
+ <li class="subtitle"><a name="ScreenCount"></a>ScreenCount</li>
+ <p>
+ You get the count of screens with the functions
+ <span class="code">XCBGetSetup</span>
+ and
+ <span class="code">XCBConnSetupSuccessRepRootsIter</span>
+ (if you need to iterate):
+ </p>
+ <pre class="code">
+XCBConnection *c;
+int screen_count;
+
+/* you init the connection */
+
+screen_count = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c)).rem;
+
+/* screen_count contains now the count of screens */
+</pre>
+ <p>
+ If you don't want to iterate over the screens, a better way
+ to get that number is to use
+ <span class="code">XCBConnSetupSuccessRepRootsLength</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+int screen_count;
+
+/* you init the connection */
+
+screen_count = XCBConnSetupSuccessRepRootsLength (XCBGetSetup (c));
+
+/* screen_count contains now the count of screens */
+</pre>
+ <li class="subtitle"><a name="ServerVendor"></a>ServerVendor</li>
+ <p>
+ You get the name of the vendor of the server hardware with
+ the functions <span class="code">XCBGetSetup</span>
+ and
+ <span
+ class="code">XCBConnSetupSuccessRepVendor</span>. Beware
+ that, unlike Xlib, the string returned by XCB is not
+ necessarily null-terminaled:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+char *vendor = NULL;
+int length;
+
+/* you init the connection */
+length = XCBConnSetupSuccessRepVendorLength (XCBGetSetup (c));
+vendor = (char *)malloc (length + 1);
+if (vendor)
+memcpy (vendor, XCBConnSetupSuccessRepVendor (XCBGetSetup (c)), length);
+vendor[length] = '\0';
+
+/* vendor contains now the name of the vendor. Must be freed when not used anymore */
+</pre>
+ <li class="subtitle"><a name="ProtocolVersion"></a>ProtocolVersion</li>
+ <p>
+ You get the major version of the protocol in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD16 protocol_major_version;
+
+/* you init the connection */
+
+protocol_major_version = XCBGetSetup (c)-&gt;protocol_major_version;
+
+/* protocol_major_version contains now the major version of the protocol */
+</pre>
+ <li class="subtitle"><a name="ProtocolRevision"></a>ProtocolRevision</li>
+ <p>
+ You get the minor version of the protocol in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD16 protocol_minor_version;
+
+/* you init the connection */
+
+protocol_minor_version = XCBGetSetup (c)-&gt;protocol_minor_version;
+
+/* protocol_minor_version contains now the minor version of the protocol */
+</pre>
+ <li class="subtitle"><a name="VendorRelease"></a>VendorRelease</li>
+ <p>
+ You get the number of the release of the server hardware in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD32 release_number;
+
+/* you init the connection */
+
+release_number = XCBGetSetup (c)-&gt;release_number;
+
+/* release_number contains now the number of the release of the server hardware */
+</pre>
+ <li class="subtitle"><a name="DisplayString"></a>DisplayString</li>
+ <p>
+ The name of the display is not stored in XCB. You have to
+ store it by yourself.
+ </p>
+ <li class="subtitle"><a name="BitmapUnit"></a>BitmapUnit</li>
+ <p>
+ You get the bitmap scanline unit in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD8 bitmap_format_scanline_unit;
+
+/* you init the connection */
+
+bitmap_format_scanline_unit = XCBGetSetup (c)-&gt;bitmap_format_scanline_unit;
+
+/* bitmap_format_scanline_unit contains now the bitmap scanline unit */
+</pre>
+ <li class="subtitle"><a name="BitmapBitOrder"></a>BitmapBitOrder</li>
+ <p>
+ You get the bitmap bit order in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD8 bitmap_format_bit_order;
+
+/* you init the connection */
+
+bitmap_format_bit_order = XCBGetSetup (c)-&gt;bitmap_format_bit_order;
+
+/* bitmap_format_bit_order contains now the bitmap bit order */
+</pre>
+ <li class="subtitle"><a name="BitmapPad"></a>BitmapPad</li>
+ <p>
+ You get the bitmap scanline pad in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD8 bitmap_format_scanline_pad;
+
+/* you init the connection */
+
+bitmap_format_scanline_pad = XCBGetSetup (c)-&gt;bitmap_format_scanline_pad;
+
+/* bitmap_format_scanline_pad contains now the bitmap scanline pad */
+</pre>
+ <li class="subtitle"><a name="ImageByteOrder"></a>ImageByteOrder</li>
+ <p>
+ You get the image byte order in the
+ <span class="code">XCBConnSetupSuccessRep</span>
+ structure, with the function <span class="code">XCBGetSetup</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+CARD8 image_byte_order;
+
+/* you init the connection */
+
+image_byte_order = XCBGetSetup (c)-&gt;image_byte_order;
+
+/* image_byte_order contains now the image byte order */
+</pre>
+ </ol>
+ <li class="subtitle"><a name="screenofdisplay">ScreenOfDisplay related functions</a></li>
+ <p>
+ in Xlib, <span class="code">ScreenOfDisplay</span> returns a
+ <span class="code">Screen</span> structure that contains
+ several characteristics of your screen. XCB has a similar
+ structure (<span class="code">XCBSCREEN</span>),
+ but the way to obtain it is a bit different. With
+ Xlib, you just provide the number of the screen and you grab it
+ from an array. With XCB, you iterate over all the screens to
+ obtain the one you want. The complexity of this operation is
+ O(n). So the best is to store this structure if you often use
+ it. See <a href="#ScreenOfDisplay">ScreenOfDisplay</a> just below.
+ </p>
+ <p>
+ Xlib provides generally two functions to obtain the characteristics
+ related to the screen. One with the display and the number of
+ the screen, which calls <span class="code">ScreenOfDisplay</span>,
+ and the other that uses the <span class="code">Screen</span> structure.
+ This might be a bit confusing. As mentioned above, with XCB, it
+ is better to store the <span class="code">XCBSCREEN</span>
+ structure. Then, you have to read the members of this
+ structure. That's why the Xlib functions are put by pairs (or
+ more) as, with XCB, you will use the same code.
+ </p>
+ <ol>
+ <li class="subtitle"><a name="ScreenOfDisplay">ScreenOfDisplay</a></li>
+ <p>
+ This function returns the Xlib <span class="code">Screen</span>
+ structure. With XCB, you iterate over all thee screens and
+ once you get the one you want, you return it:
+ </p>
+ <pre class="code"><a name="ScreenOfDisplay"></a>
+XCBSCREEN *ScreenOfDisplay (XCBConnection *c,
+ int screen)
+{
+ XCBSCREENIter iter;
+
+ iter = XCBConnSetupSuccessRepRootsIter (XCBGetSetup (c));
+ for (; iter.rem; --screen, XCBSCREENNext (&iter))
+ if (screen == 0)
+ return iter.data;
+
+ return NULL;
+}
+</pre>
+ <p>
+ As mentioned above, you might want to store the value
+ returned by this function.
+ </p>
+ <p>
+ All the functions below will use the result of that
+ fonction, as they just grab a specific member of the
+ <span class="code">XCBSCREEN</span> structure.
+ </p>
+ <li class="subtitle"><a name="DefaultScreenOfDisplay"></a>DefaultScreenOfDisplay</li>
+ <p>
+ It is the default screen that you obtain when you connect to
+ the X server. It suffices to call the <a href="#ScreenOfDisplay">ScreenOfDisplay</a>
+ function above with the connection and the number of the
+ default screen.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+int screen_default_nbr;
+XCBSCREEN *default_screen; /* the returned default screen */
+
+/* you pass the name of the display you want to XCBConnect */
+
+c = XCBConnect (display_name, &screen_default_nbr);
+default_screen = ScreenOfDisplay (c, screen_default_nbr);
+
+/* default_screen contains now the default root window, or a NULL window if no screen is found */
+</pre>
+ <li class="subtitle"><a name="RootWindow">RootWindow / RootWindowOfScreen</a></li>
+ <p>
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+XCBWINDOW root_window = { 0 }; /* the returned window */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ root_window = screen-&gt;root;
+
+/* root_window contains now the root window, or a NULL window if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DefaultRootWindow">DefaultRootWindow</a></li>
+ <p>
+ It is the root window of the default screen. So, you call
+ <a name="ScreenOfDisplay">ScreenOfDisplay</a> with the
+ default screen number and you get the
+ <a href="#RootWindow">root window</a> as above:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_default_nbr;
+XCBWINDOW root_window = { 0 }; /* the returned root window */
+
+/* you pass the name of the display you want to XCBConnect */
+
+c = XCBConnect (display_name, &screen_default_nbr);
+screen = ScreenOfDisplay (c, screen_default_nbr);
+if (screen)
+ root_window = screen-&gt;root;
+
+/* root_window contains now the default root window, or a NULL window if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DefaultVisual">DefaultVisual / DefaultVisualOfScreen</a></li>
+ <p>
+ While a Visual is, in Xlib, a structure, in XCB, there are
+ two types: <span class="code">XCBVISUALID</span>, which is
+ the Id of the visual, and <span class="code">XCBVISUALTYPE</span>,
+ which corresponds to the Xlib Visual. To get the Id of the
+ visual of a screen, just get the
+ <span class="code">root_visual</span>
+ member of a <span class="code">XCBSCREEN</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+XCBVISUALID root_visual = { 0 }; /* the returned visual Id */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ root_visual = screen-&gt;root_visual;
+
+/* root_visual contains now the value of the Id of the visual, or a NULL visual if no screen is found */
+</pre>
+ <p>
+ To get the <span class="code">XCBVISUALTYPE</span>
+ structure, it's a bit less easier. You have to get the
+ <span class="code">XCBSCREEN</span> structure that you want,
+ get its <span class="code">root_visual</span> member,
+ then iterate on the <span class="code">XCBDEPTH</span>s
+ and the <span class="code">XCBVISUALTYPE</span>s, and compare
+ the <span class="code">XCBVISUALID</span> of these <span class="code">XCBVISUALTYPE</span>s:
+ with <span class="code">root_visual</span>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+XCBVISUALID root_visual = { 0 };
+XCBVISUATYPE *visual_type = NULL; /* the returned visual type */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ {
+ XCBDEPTHIter depth_iter;
+
+ depth_iter = XCBSCREENAllowedDepthsIter (screen);
+ for (; depth_iter.rem; XCBDEPTHNext (&depth_iter))
+ {
+ XCBVISUALTYPEIter visual_iter;
+
+ visual_iter = XCBDEPTHVisualsIter (depth_iter.data);
+ for (; visual_iter.rem; XCBVISUALTYPENext (&visual_iter))
+ {
+ if (screen-&gt;root_visual.id == visual_iter.data-&gt;visual_id.id)
+ {
+ visual_type = visual_iter.data;
+ break;
+ }
+ }
+ }
+ }
+
+/* visual_type contains now the visual structure, or a NULL visual structure if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DefaultGC">DefaultGC / DefaultGCOfScreen</a></li>
+ <p>
+ This default Graphic Context is just a newly created Graphic
+ Context, associated to the root window of a
+ <span class="code">XCBSCREEN</span>,
+ using the black white pixels of that screen:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+XCBGCONTEXT gc = { 0 }; /* the returned default graphic context */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ {
+ XCBDRAWABLE draw;
+ CARD32 mask;
+ CARD32 values[2];
+
+ gc = XCBGCONTEXTNew (c);
+ draw.window = screen-&gt;root;
+ mask = GCForeground | GCBackground;
+ values[0] = screen-&gt;black_pixel;
+ values[1] = screen-&gt;white_pixel;
+ XCBCreateGC (c, gc, draw, mask, values);
+ }
+
+/* gc contains now the default graphic context */
+</pre>
+ <li class="subtitle"><a name="BlackPixel">BlackPixel / BlackPixelOfScreen</a></li>
+ <p>
+ It is the Id of the black pixel, which is in the structure
+ of an <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 black_pixel = 0; /* the returned black pixel */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ black_pixel = screen-&gt;black_pixel;
+
+/* black_pixel contains now the value of the black pixel, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="WhitePixel">WhitePixel / WhitePixelOfScreen</a></li>
+ <p>
+ It is the Id of the white pixel, which is in the structure
+ of an <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 white_pixel = 0; /* the returned white pixel */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ white_pixel = screen-&gt;white_pixel;
+
+/* white_pixel contains now the value of the white pixel, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DisplayWidth">DisplayWidth / WidthOfScreen</a></li>
+ <p>
+ It is the width in pixels of the screen that you want, and
+ which is in the structure of the corresponding
+ <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 width_in_pixels = 0; /* the returned width in pixels */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ width_in_pixels = screen-&gt;width_in_pixels;
+
+/* width_in_pixels contains now the width in pixels, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DisplayHeight">DisplayHeight / HeightOfScreen</a></li>
+ <p>
+ It is the height in pixels of the screen that you want, and
+ which is in the structure of the corresponding
+ <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 height_in_pixels = 0; /* the returned height in pixels */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ height_in_pixels = screen-&gt;height_in_pixels;
+
+/* height_in_pixels contains now the height in pixels, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DisplayWidthMM">DisplayWidthMM / WidthMMOfScreen</a></li>
+ <p>
+ It is the width in millimeters of the screen that you want, and
+ which is in the structure of the corresponding
+ <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 width_in_millimeters = 0; /* the returned width in millimeters */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ width_in_millimeters = screen-&gt;width_in_millimeters;
+
+/* width_in_millimeters contains now the width in millimeters, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DisplayHeightMM">DisplayHeightMM / HeightMMOfScreen</a></li>
+ <p>
+ It is the height in millimeters of the screen that you want, and
+ which is in the structure of the corresponding
+ <span class="code">XCBSCREEN</span>.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 height_in_millimeters = 0; /* the returned height in millimeters */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ height_in_millimeters = screen-&gt;height_in_millimeters;
+
+/* height_in_millimeters contains now the height in millimeters, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DisplayPlanes">DisplayPlanes / DefaultDepth / DefaultDepthOfScreen / PlanesOfScreen</a></li>
+ <p>
+ It is the depth (in bits) of the root window of the
+ screen. You get it from the <span class="code">XCBSCREEN</span> structure.
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD8 root_depth = 0; /* the returned depth of the root window */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ root_depth = screen-&gt;root_depth;
+
+/* root_depth contains now the depth of the root window, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DefaultColormap">DefaultColormap / DefaultColormapOfScreen</a></li>
+ <p>
+ This is the default colormap of the screen (and not the
+ (default) colormap of the default screen !). As usual, you
+ get it from the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+XCBCOLORMAP default_colormap = { 0 }; /* the returned default colormap */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ default_colormap = screen-&gt;default_colormap;
+
+/* default_colormap contains now the default colormap, or a NULL colormap if no screen is found */
+</pre>
+ <li class="subtitle"><a name="MinCmapsOfScreen"></a>MinCmapsOfScreen</li>
+ <p>
+ You get the minimum installed colormaps in the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD16 min_installed_maps = 0; /* the returned minimum installed colormaps */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ min_installed_maps = screen-&gt;min_installed_maps;
+
+/* min_installed_maps contains now the minimum installed colormaps, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="MaxCmapsOfScreen"></a>MaxCmapsOfScreen</li>
+ <p>
+ You get the maximum installed colormaps in the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD16 max_installed_maps = 0; /* the returned maximum installed colormaps */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ max_installed_maps = screen-&gt;max_installed_maps;
+
+/* max_installed_maps contains now the maximum installed colormaps, or 0 if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DoesSaveUnders"></a>DoesSaveUnders</li>
+ <p>
+ You know if <span class="code">save_unders</span> is set,
+ by looking in the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+BOOL save_unders = 0; /* the returned value of save_unders */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ save_unders = screen-&gt;save_unders;
+
+/* save_unders contains now the value of save_unders, or FALSE if no screen is found */
+</pre>
+ <li class="subtitle"><a name="DoesBackingStore"></a>DoesBackingStore</li>
+ <p>
+ You know the value of <span class="code">backing_stores</span>,
+ by looking in the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+BYTE backing_stores = 0; /* the returned value of backing_stores */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ backing_stores = screen-&gt;backing_stores;
+
+/* backing_stores contains now the value of backing_stores, or FALSE if no screen is found */
+</pre>
+ <li class="subtitle"><a name="EventMaskOfScreen"></a>EventMaskOfScreen</li>
+ <p>
+ To get the current input masks,
+ you look in the <span class="code">XCBSCREEN</span> structure:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBSCREEN *screen;
+int screen_nbr;
+CARD32 current_input_masks = 0; /* the returned value of current input masks */
+
+/* you init the connection and screen_nbr */
+
+screen = ScreenOfDisplay (c, screen_nbr);
+if (screen)
+ current_input_masks = screen-&gt;current_input_masks;
+
+/* current_input_masks contains now the value of the current input masks, or FALSE if no screen is found */
+</pre>
+ </ol>
+ <li class="subtitle"><a name="misc">Miscellaneous macros</a></li>
+ <ol>
+ <li class="subtitle"><a name="DisplayOfScreen"></a>DisplayOfScreen</li>
+ <p>
+ in Xlib, the <span class="code">Screen</span> structure
+ stores its associated <span class="code">Display</span>
+ structure. This is not the case in the X Window protocol,
+ hence, it's also not the case in XCB. So you have to store
+ it by yourself.
+ </p>
+ <li class="subtitle"><a name="DisplayCells"></a>DisplayCells / CellsOfScreen</li>
+ <p>
+ To get the colormap entries,
+ you look in the <span class="code">XCBVISUALTYPE</span>
+ structure, that you grab like <a class="subsection" href="#DefaultVisual">here</a>:
+ </p>
+ <pre class="code">
+XCBConnection *c;
+XCBVISUALTYPE *visual_type;
+CARD16 colormap_entries = 0; /* the returned value of the colormap entries */
+
+/* you init the connection and visual_type */
+
+if (visual_type)
+ colormap_entries = visual_type-&gt;colormap_entries;
+
+/* colormap_entries contains now the value of the colormap entries, or FALSE if no screen is found */
+</pre>
+ </ol>
+ </ol>
+ </ol>
+ </div>
+</body>
+
+</html>
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