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26 KiB
HTML
535 lines
26 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Mini GLX Specification</title>
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</head>
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<body>
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<h1>
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<center>Mini GLX Specification</center>
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</h1>
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<h2>
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<center>Tungsten Graphics, Inc.<br>
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<br>
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January 20, 2003<br>
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<br>
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</center>
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</h2>
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<p> Copyright © 2002-2003 by Tungsten Graphics, Inc., Cedar Park,
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Texas. All Rights Reserved. <br>
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<br>
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Permission is granted to make and distribute verbatim copies of this
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document provided the copyright notice and this permission notice are
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preserved on all copies.<br>
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<br>
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</p>
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<h1>1. Introduction</h1>
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<p>The Mini GLX interface facilitates OpenGL rendering on embedded
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devices. The interface is a subset of the GLX interface, plus a minimal
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set of Xlib-like functions.</p>
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<p>Programs written to the Mini GLX specification should run unchanged
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on systems with the X Window System and the GLX extension. The intention
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is to allow flexibility for prototyping and testing.</p>
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<p>This document serves as both the reference guide and programming
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guide for Mini GLX.<br>
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<br>
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</p>
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<h1>2. Mini GLX Concepts</h1>
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<p>The OpenGL specification does not describe how OpenGL rendering
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contexts and drawing surfaces (i.e. the frame buffer) are created and
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managed. Rather, this is handled by an OpenGL window system interface,
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such as Mini GLX.</p>
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<p>There are three main datatypes or resources managed by Mini GLX. The
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resources and their corresponding GLX or Xlib data types are:</p>
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<table cellspacing="10" align="center">
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<tbody>
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<tr>
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<td><u>Resource</u></td>
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<td><u>Data type</u></td>
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</tr>
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<tr>
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<td>pixel formats</td>
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<td>X Visual and XVisualInfo</td>
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</tr>
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<tr>
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<td>drawing surfaces</td>
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<td>X Window or GLXDrawable</td>
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</tr>
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<tr>
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<td>rendering contexts</td>
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<td>GLXContext</td>
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</tr>
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</tbody>
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</table>
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<p>Pixel formats or X Visuals describe the per-pixel attributes of the
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frame buffer. For example, bits per color component, Z buffer size,
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stencil size, TrueColor vs PseudoColor, etc.</p>
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<p>Drawing surfaces or X Windows typically describe a spatial
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allocation of the frame buffer (i.e. the position and size of a
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rectangular region of pixels). Since MiniGLX doesn't really support a
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window system, the window is effectively the entire frame buffer.</p>
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<p>A rendering context represents the current OpenGL state such as
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current drawing color, line width, blending mode, texture parameters,
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etc. Several rendering contexts can be created but only one can be in
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use at any given time.</p>
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<p>The Mini GLX interface provides all the functions needed for
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choosing pixel formats, create drawing surfaces, creating rendering
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contexts and binding rendering contexts to drawing surfaces.<br>
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<br>
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</p>
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<h1>3. Using Mini GLX</h1>
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<p>To use the Mini GLX interface in your application, include the
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GL/miniglx.h header file at compile time:</p>
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<blockquote><code> #include <GL/miniglx.h><br>
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</code></blockquote>
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<code></code>Applications should link with libGL.so (i.e. <code>gcc
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myprogram.o -lGL -o myprogram</code>). libGL.so implements the
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MiniGLX API functions and, in turn, loads a hardware-specific device
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driver (such as <code>radeon_dri.so</code>) at runtime. The
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environment variable <code>LIBGL_DRIVERS_PATH</code> should name the
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directory where these modules are located.<br>
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<br>
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The remainder of this section describes the MiniGLX API functions.<br>
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<br>
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<h2>3.1 Initialization</h2>
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<p>The XOpenDisplay function is used to initialize the graphics system:</p>
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<blockquote>
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<pre>Display *XOpenDisplay(const char *displayname)<br></pre>
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</blockquote>
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<p>The <code>displayName</code> parameter is currently ignored in Mini
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GLX. It is recommended that <code>NULL</code> be passed as the<code>displayName</code>
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parameter.</p>
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<p>If XOpenDisplay is able to initialize the graphics system a pointer
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to a Display will be returned. Otherwise, NULL will be returned.</p>
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<h2>3.2 Choosing a Visual</h2>
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<p>A visual (i.e. pixel format) must be chosen before a drawing surface
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or rendering context can be created. This is done with the
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glXChooseVisual function:</p>
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<blockquote>
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<pre>XVisualInfo *glXChooseVisual(Display *dpy, int screen, const int *attribList)<br></pre>
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</blockquote>
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<p><code>dpy</code> is a pointer to the display returned by
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XOpenDisplay. </p>
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<p><code>screen</code> is currently ignored by Mini GLX and should be
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zero. </p>
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<p><code>attribList</code> is a list of GLX attributes which describe
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the desired pixel format. It is terminated by the token <code>None</code>.
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The attributes are as follows:</p>
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<blockquote>
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<dl>
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<dt><code>GLX_USE_GL</code></dt>
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<dd>This attribute should always be present in order to maintain
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compatibility with GLX.</dd>
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<dt><code>GLX_RGBA</code></dt>
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<dd>If present, only RGBA pixel formats will be considered.
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Otherwise, only color index formats are considered.</dd>
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<dt><code>GLX_DOUBLEBUFFER</code></dt>
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<dd>if present, only double-buffered pixel formats will be chosen.</dd>
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<dt><code>GLX_RED_SIZE n</code></dt>
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<dd>Must be followed by a non-negative integer indicating the
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minimum number of bits per red pixel component that is acceptable.</dd>
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<dt><code>GLX_GREEN_SIZE n</code></dt>
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<dd>Must be followed by a non-negative integer indicating the
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minimum number of bits per green pixel component that is acceptable.</dd>
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<dt><code>GLX_BLUE_SIZE n</code></dt>
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<dd>Must be followed by a non-negative integer indicating the
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minimum number of bits per blue pixel component that is acceptable.</dd>
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<dt><code>GLX_ALPHA_SIZE n</code></dt>
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<dd>Must be followed by a non-negative integer indicating the
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minimum number of bits per alpha pixel component that is acceptable.</dd>
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<dt><code>GLX_STENCIL_SIZE n</code></dt>
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<dd>Must be followed by a non-negative integer indicating the
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minimum number of bits per stencil value that is acceptable.</dd>
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<dt><code>None</code></dt>
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<dd>This token is used to terminate the attribute list.</dd>
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</dl>
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</blockquote>
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<p>glXChooseVisual will return a pointer to an XVisualInfo object which
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most closely matches the requirements of the attribute list. If there
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is no visual which matches the request, NULL will be returned.</p>
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<p>Note that visuals with accumulation buffers and depth buffers are
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not available.<br>
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<br>
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</p>
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<h2>3.3 Creating a Drawing Surface</h2>
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<p>Drawing surfaces are created as X windows. For Mini GLX,
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windows are <i>full-screen</i>; they cover the entire frame buffer.
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Also, Mini GLX imposes a limit of one window. A second window
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cannot be created until the first one is destroyed.</p>
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<h3>3.3.1 Window Creation</h3>
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<p>The XCreateWindow function is used to create a drawing surface:</p>
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<blockquote>
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<pre>Window XCreateWindow( Display *display,<br> Window parent,<br> int x, int y,<br> unsigned int width, unsigned int height,<br> unsigned int borderWidth,<br> int depth,<br> unsigned int class,<br> Visual *visual,<br> unsigned long valuemask,<br> XSetWindowAttributes *attributes )<br></pre>
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</blockquote>
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<p>The parameters are as follows:</p>
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<blockquote>
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<dl>
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<dt><code>display</code></dt>
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<dd>A Display pointer, as returned by XOpenDisplay.</dd>
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<dt><code>parent</code></dt>
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<dd>The parent window for the new window. For Mini GLX, this
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should be<code>RootWindow(dpy, 0)</code>.</dd>
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<dt><code>x, y</code></dt>
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<dd>The position of the window. For Mini GLX, both values should
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be zero.</dd>
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<dt><code>width, height</code></dt>
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<dd>The size of the window. For Mini GLX, this specifies the
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desired screen size such as 1024, 768 or 1280, 1024.</dd>
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<dt><code>borderWidth</code></dt>
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<dd>This parameter should be zero.</dd>
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<dt><code>depth</code></dt>
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<dd>The pixel depth for the window. For Mini GLX this should be
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the depth found in the XVisualInfo object returned by <code>glxChooseVisual</code>.</dd>
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<dt><code>class</code></dt>
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<dd>The window class. For Mini GLX this value should be <code>InputOutput</code>.</dd>
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<dt><code>visual</code></dt>
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<dd>This parameter should be the <code>visual</code> field of the <code>XVisualInfo</code>
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object returned by <code>glxChooseVisual</code>.</dd>
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<dt><code>valuemask</code></dt>
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<dd>This parameter indicates which fields of the <code>XSetWindowAttributes</code>
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are to be used. For Mini GLX this is typically the bitmask<code>CWBackPixel
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| CWBorderPixel | CWColormap</code>.</dd>
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<dt><code>attributes</code></dt>
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<dd>Initial window attributes. Of the fields in the <code>XSetWindowAttributes</code>
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structure, the<code>background_pixel</code>, <code>border_pixel</code>
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and <code>colormap</code> fields should be set. See the discussion
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below regarding colormaps.</dd>
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</dl>
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</blockquote>
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<p><code>XCreateWindow</code> will return a window handle if it succeeds
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or zero if it fails.</p>
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<h3>3.3.2 Window Mapping</h3>
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<p>To display the window the XMapWindow function must be called:</p>
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<blockquote>
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<pre>void XMapWindow(Display *dpy, Window w)</pre>
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</blockquote>
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<p>This function does nothing in Mini GLX but is required for Xlib/GLX
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compatibility</p>
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<h3>3.3.3 Colormaps<br>
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</h3>
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<p>Xlib requires specification of a colormap when creating a window.
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For purposes of interoperability, Mini GLX requires this as well,
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though the colormap is not actually used. The XCreateColormap
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function is used to create a colormap:</p>
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<blockquote><code>Colormap XCreateColormap(Display *dpy, Window window,
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Visual *visual, int alloc)</code><br>
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<code></code></blockquote>
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<p>The parameters are as follows:<br>
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</p>
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<blockquote>
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<dl>
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<dt><code>dpy</code></dt>
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<dd>The display handle as returned by XOpenDisplay.</dd>
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<dt><code>window</code></dt>
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<dd> This parameter is ignored by Mini GLX but should be the value
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returned by the <code>RootWindow(dpy, 0)</code> macro.<br>
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</dd>
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<dt><code>visual</code></dt>
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<dd>This parameter is ignored by Mini GLX but should be the visual
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field of the XVisualInfo object returned by glXChooseVisual. </dd>
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<dt><code>alloc</code></dt>
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<dd>This parameter is ignored by Mini GLX but should be set to <code>AllocNone</code>.</dd>
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</dl>
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</blockquote>
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<br>
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<h2>3.4 Creating a Rendering Context</h2>
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<p>An OpenGL rendering context is created with the <code>glXCreateContext</code>
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function:</p>
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<blockquote>
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<pre>GLXContext glXCreateContext(Display *dpy, XVisualInfo *visInfo, GLXContext shareList, Bool direct)<br></pre>
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</blockquote>
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<p>The parameters are as follows:</p>
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<blockquote>
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<dl>
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<dt><code>dpy</code></dt>
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<dd>The display handle as returned by XOpenDisplay.</dd>
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<dt><code>visInfo</code></dt>
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<dd>The visual as returned by glXChooseVisual.</dd>
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<dt><code>shareList</code></dt>
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<dd>If non-zero, texture objects and display lists are shared with
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the named rendering context. If zero, texture objects and display lists
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will (initially) be private to this context. They may be shared when a
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subsequent context is created.</dd>
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<dt><code>direct</code></dt>
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<dd>Specifies whether direct or indirect rendering is desired. For
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Mini GLX this value is ignored but it should be set to <code>True</code>.</dd>
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</dl>
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</blockquote>
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<p><code>glXCreateContext</code> will return a GLXContext handle if it
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succeeds or zero if it fails due to invalid parameter or insufficient
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resources.<br>
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<br>
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</p>
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<h2>3.5 Binding a Rendering Context</h2>
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<p>The final step before beginning OpenGL rendering is to bind (i.e.
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activate) a rendering context and drawing surface with the
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glXMakeCurrent function:</p>
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<blockquote>
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<pre>Bool glXMakeCurrent(Display *dpy, GLXDrawable drawable, GLXContext ctx)<br></pre>
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</blockquote>
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<p>The parameters are as follows:</p>
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<blockquote>
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<dl>
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<dt><code>dpy</code></dt>
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<dd>The display handle, as returned by XOpenDisplay.</dd>
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<dt><code>drawable</code></dt>
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<dd>The window or drawable to bind to the rendering context. This
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should be the value returned by XCreateWindow.</dd>
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<dt><code>ctx</code></dt>
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<dd>The rendering context to bind, as returned by glXCreateContext.</dd>
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</dl>
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</blockquote>
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<p>If glXMakeCurrent succeeds True is returned. Otherwise False is
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returned to indicate an invalid display, window or context parameter.</p>
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<p>After the rendering context has been bound to the drawing surface
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OpenGL rendering can begin.</p>
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<p>The current rendering context may be unbound by calling
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glXMakeCurrent with the window and context parameters set to zero.</p>
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<p>An application may create any number of rendering contexts and bind
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them as needed. Note that binding a rendering context is generally not a
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light-weight operation. Most simple OpenGL applications create
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only one rendering context.<br>
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<br>
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</p>
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<h2>3.6 Color Buffer Swapping</h2>
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<p>A double buffered window has two color buffers: a front buffer and a
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back buffer. Normally, rendering is directed to the back buffer while
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the front buffer is displayed. When rendering of a frame is finished
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the front and back buffers are swapped to provide the illusion of
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instanteous screen updates.</p>
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<p>The color buffers for a particular window (i.e. drawable) may be
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swapped with the glXSwapBuffers command:</p>
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<blockquote>
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<pre>void glXSwapBuffers(Display *dpy, GLXDrawable drawable)<br></pre>
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</blockquote>
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Any pending rendering commands will be completed before the buffer swap
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takes place.<br>
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<br>
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Calling glXSwapBuffers on a window which is single-buffered has no
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effect.<br>
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<br>
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<h2>3.7 Releasing Resources</h2>
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<h3>3.7.1 Releasing Rendering Contexts</h3>
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<p>A rendering context may be destroyed by calling glXDestroyContext:</p>
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<blockquote>
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<pre>void glXDestroyContext(Display *dpy, GLXContext ctx)<br></pre>
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|
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</blockquote>
|
||
|
|
<h3>3.7.2 Releasing Windows</h3>
|
||
|
|
<p>A window may be destroyed by calling XDestroyWindow:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>void XDestroyWindow(Display *dpy, Window window)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<h3>3.7.3 Releasing Visuals</h3>
|
||
|
|
<p>An XVisualInfo object may be freed by calling XFree:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>void XFree(void *data)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<h3>3.7.4 Releasing Colormaps</h3>
|
||
|
|
<p>A colormap may be freed by calling XFreeColormap:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>void XFreeColormap(Display *dpy, Colormap colormap)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<h3>3.7.4 Releasing Display Resources</h3>
|
||
|
|
<p>When the application is about to exit, the resources associated with
|
||
|
|
the graphics system can be released by calling XCloseDisplay:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>void XCloseDisplay(Display *dpy)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>The display handle becomes invalid at this point.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
<h2>3.8 Query Functions</h2>
|
||
|
|
<h3>3.8.1 Querying Available Visuals</h3>
|
||
|
|
A list of all available visuals can be obtained with the XGetVisualInfo
|
||
|
|
function:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><code>XVisualInfo
|
||
|
|
*XGetVisualInfo(Display *dpy, long vinfo_mask, XVisualInfo
|
||
|
|
*vinfo_template, int *nitems_return)<br>
|
||
|
|
</code></div>
|
||
|
|
<br>
|
||
|
|
The parameters are as follows:<br>
|
||
|
|
<blockquote>
|
||
|
|
<dl>
|
||
|
|
<dt><code>dpy</code></dt>
|
||
|
|
<dd>The display handle, as returned by XOpenDisplay.</dd>
|
||
|
|
<dt><code>vinfo_mask</code></dt>
|
||
|
|
<dd>A bitmask indicating which fields of the vinfo_template are to
|
||
|
|
be matched. The value must be VisualScreenMask.</dd>
|
||
|
|
<dt><code>vinfo_template</code></dt>
|
||
|
|
<dd>A template whose fields indicate which visual attributes must
|
||
|
|
be matched by the results. The screen field of this structure must
|
||
|
|
be zero.</dd>
|
||
|
|
<dt><code>nitems_return</code></dt>
|
||
|
|
<dd>Returns the number of visuals returned. </dd>
|
||
|
|
</dl>
|
||
|
|
</blockquote>
|
||
|
|
The return value is the address of an array of all available visuals.<br>
|
||
|
|
<br>
|
||
|
|
An example of using XGetVisualInfo to get all available visuals follows:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><code>XVisualInfo visTemplate, *results;</code><br>
|
||
|
|
<code>int numVisuals;</code><br>
|
||
|
|
<code>Display *dpy = XOpenDisplay(NULL);</code><br>
|
||
|
|
<code>visTemplate.screen = 0;</code><br>
|
||
|
|
<code>results = XGetVisualInfo(dpy, VisualScreenMask, &visTemplate,
|
||
|
|
&numVisuals);</code><br>
|
||
|
|
<code></code></div>
|
||
|
|
<br>
|
||
|
|
<h3>3.8.2 Querying Visual Attributes</h3>
|
||
|
|
<p>The GLX attributes of an X visual may be queried with the
|
||
|
|
glXGetConfig function:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>int glXGetConfig(Display *dpy, XVisualInfo *vis, int attribute, int *value)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>The parameters are as follows:</p>
|
||
|
|
<blockquote>
|
||
|
|
<dl>
|
||
|
|
<dt><code>dpy</code></dt>
|
||
|
|
<dd>The display handle, as returned by XOpenDisplay.</dd>
|
||
|
|
<dt><code>vis</code></dt>
|
||
|
|
<dd>The visual, as returned by glXChooseVisual.</dd>
|
||
|
|
<dt><code>attribute</code></dt>
|
||
|
|
<dd>The attribute to query. The attributes are listed below.</dd>
|
||
|
|
<dt><code>value</code></dt>
|
||
|
|
<dd>Pointer to an integer in which the result of the query will be
|
||
|
|
stored. </dd>
|
||
|
|
</dl>
|
||
|
|
</blockquote>
|
||
|
|
<p>The return value will be zero if no error occurs.<code>
|
||
|
|
GLX_INVALID_ATTRIBUTE</code> will be returned if the attribute
|
||
|
|
parameter is invalid.<code> GLX_BAD_VISUAL</code> will be returned
|
||
|
|
if the XVisualInfo parameter is invalid.</p>
|
||
|
|
<p>The following attributes may be queried:</p>
|
||
|
|
<blockquote>
|
||
|
|
<dl>
|
||
|
|
<dt><code>GLX_USE_GL</code></dt>
|
||
|
|
<dd>The result will be <code>True</code> or <code>False</code> to
|
||
|
|
indicate if OpenGL rendering is supported with the visual. Mini GLX
|
||
|
|
always return <code>True</code>.</dd>
|
||
|
|
<dt><code>GLX_RGBA</code></dt>
|
||
|
|
<dd>The result will be <code>True</code> for RGBA visuals or <code>False</code>
|
||
|
|
for color index visuals.</dd>
|
||
|
|
<dt><code>GLX_DOUBLEBUFFER</code></dt>
|
||
|
|
<dd>The result will be <code>True</code> if the visual has two
|
||
|
|
color buffers or <code>False</code> if the visual has one color buffer.</dd>
|
||
|
|
<dt><code>GLX_RED_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of red bits per pixel.</dd>
|
||
|
|
<dt><code>GLX_GREEN_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of green bits per pixel.</dd>
|
||
|
|
<dt><code>GLX_BLUE_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of blue bits per pixel.</dd>
|
||
|
|
<dt><code>GLX_ALPHA_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of alpha bits per pixel.</dd>
|
||
|
|
<dt><code>GLX_DEPTH_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of bits per Z value.</dd>
|
||
|
|
<dt><code>GLX_STENCIL_SIZE</code></dt>
|
||
|
|
<dd>The result will be the number of bits per stencil value.<br>
|
||
|
|
<br>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
</blockquote>
|
||
|
|
<h3>3.8.3 Querying the Current Rendering Context</h3>
|
||
|
|
<p>The current rendering context can be queried with
|
||
|
|
glXGetCurrentContext: </p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>GLXContext glXGetCurrentContext(void)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>Zero will be returned if no context is currently bound.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
<h3>3.8.4 Querying the Current Drawable</h3>
|
||
|
|
<p>The current drawable (i.e. window or drawing surface) can be queried
|
||
|
|
with glXGetCurrentDrawable:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>GLXDrawable glXGetCurrentDrawable(void)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>Zero will be returned if no drawable is currently bound.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
<h3>3.8.5 Function Address Queries</h3>
|
||
|
|
<p>The glXGetProcAddress function will return the address of any
|
||
|
|
available OpenGL or Mini GLX function:</p>
|
||
|
|
<blockquote>
|
||
|
|
<pre>void *glXGetProcAddress(const GLubyte *procName)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p>If <code>procName</code> is a valid function name, a pointer to that
|
||
|
|
function will be returned. Otherwise, NULL will be returned.</p>
|
||
|
|
<p>The purpose of glXGetProcAddress is to facilitate using future
|
||
|
|
extensions to OpenGL or Mini GLX. If a future version of the library
|
||
|
|
adds new extension functions they'll be accessible via
|
||
|
|
glXGetProcAddress. The alternative is to hard-code calls to the new
|
||
|
|
functions in the application but doing so will prevent linking the
|
||
|
|
application with older versions of the library.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
<h2>3.9 Versioning</h2>
|
||
|
|
The Mini GLX version can be queried at run time with glXQueryVersion:
|
||
|
|
<blockquote>
|
||
|
|
<pre>Bool glXQueryVersion(Display *dpy, int *major, int *minor)<br></pre>
|
||
|
|
</blockquote>
|
||
|
|
<p><code>major</code> will be set to the major version number and<code>minor</code>
|
||
|
|
will be set to the minor version number.<code>True</code> will be
|
||
|
|
returned if the function succeeds. <code>False</code> will be returned
|
||
|
|
if the function fails due to invalid parameters. The <code>dpy</code>
|
||
|
|
argument is currently ignored, but should be the value returned by
|
||
|
|
XOpenDisplay.</p>
|
||
|
|
<p>At compile time, the Mini GLX interface version can be tested with
|
||
|
|
the MINI_GLX_VERSION_1_<i>x</i> preprocessor tokens. For example, if
|
||
|
|
version 1.0 of Mini GLX is supported, then<code> MINI_GLX_VERSION_1_0</code>
|
||
|
|
will be defined. If version 1.1 of Mini GLX is supported, then<code>
|
||
|
|
MINI_GLX_VERSION_1_1</code> will be defined.</p>
|
||
|
|
<p>At the time of writing the current Mini GLX version is 1.0.<br>
|
||
|
|
<br>
|
||
|
|
</p>
|
||
|
|
<h1>4.0 Interoperability with GLX and Xlib</h1>
|
||
|
|
While Mini GLX strives to be compatible with GLX and Xlib there are
|
||
|
|
some unavoidable differences which must be taken into consideration.<br>
|
||
|
|
<h2>4.1 Public vs Private Structures</h2>
|
||
|
|
The structure of many X data types is public. For example, the <code>Display</code>
|
||
|
|
data type is defined as a structure in /usr/include/X11/Xlib.h and
|
||
|
|
programmers may access any fields of that structure at will. Mini
|
||
|
|
GLX also defines a Display data type but its fields are hidden and not
|
||
|
|
visiblein <code>miniglx.h</code>. Duplicating the Xlib
|
||
|
|
declaration for the <code>Display</code> data type in minigl.h would
|
||
|
|
require defining a large number of other superfluous Xlib datatypes.<br>
|
||
|
|
<br>
|
||
|
|
Mini GLX users are discouraged from directly accessing the fields of
|
||
|
|
Xlib data types to maximize portability - though this is unavoidable to
|
||
|
|
some extent. For example, the <code>XVisualInfo</code> and <code>XSetWindowAtttributes</code>
|
||
|
|
data types must be completely public.
|
||
|
|
<h2>4.2 Macros</h2>
|
||
|
|
In some cases, Xlib defines macros which are meant to be used instead
|
||
|
|
of direct structure accesses. For example, the <code>RootWindow(dpy,
|
||
|
|
screen)</code> macro returns the root window for a given screen on a
|
||
|
|
given display. Unfortunately, macros do nothing to aid in ABI
|
||
|
|
compatibility since they are resolved at compile time instead of at
|
||
|
|
link/run time.<br>
|
||
|
|
<br>
|
||
|
|
Mini GLX also defines a <code>RootWindow</code> macro since it's
|
||
|
|
essential for creating windows. But the implementation of this
|
||
|
|
macro by Xlib and Mini GLX is completely different.<br>
|
||
|
|
<h2>4.3 Summary</h2>
|
||
|
|
Because Xlib and Mini GLX define data types and macros differently,
|
||
|
|
Mini GLX applications must be recompiled when retargeting Mini GLX or
|
||
|
|
native Xlib/GLX. That is, applications can't simply be re-linked
|
||
|
|
because of ABI incompatibilities.<br>
|
||
|
|
<br>
|
||
|
|
Nevertheless, the fact that Mini GLX programs can be recompiled for
|
||
|
|
Xlib and GLX increases portability and flexibility for testing and
|
||
|
|
prototyping.<br>
|
||
|
|
<br>
|
||
|
|
<h1>5.0 Example Program</h1>
|
||
|
|
<p>This section shows an example program which uses the Mini GLX
|
||
|
|
interface. The program simply draws several frames of a rotating square.<br>
|
||
|
|
</p>
|
||
|
|
<p>The program may be compiled for use with Xlib/GLX or Mini GLX by
|
||
|
|
setting the <code>USE_MINIGLX</code> token to 0 or 1, respectively.
|
||
|
|
Note that the only difference is the header files which are
|
||
|
|
included.<br>
|
||
|
|
</p>
|
||
|
|
<p> </p>
|
||
|
|
<pre><code><br></code>#define USE_MINIGLX 1 /* 1 = use Mini GLX, 0 = use Xlib/GLX */<br><br>#include <stdio.h><br>#include <stdlib.h><br>#include <GL/gl.h><br><br>#if USE_MINIGLX<br>#include <GL/miniglx.h><br>#else<br>#include <GL/glx.h><br>#include <X11/Xlib.h><br>#endif<br><br><code>/*<br> * Create a simple double-buffered RGBA window.<br> */<br>static Window<br>MakeWindow(Display * dpy, unsigned int width, unsigned int height)<br>{<br> int visAttributes[] = {<br> GLX_RGBA,<br> GLX_RED_SIZE, 1,<br> GLX_GREEN_SIZE, 1,<br> GLX_BLUE_SIZE, 1,<br> GLX_DOUBLEBUFFER,<br> None<br> };<br> XSetWindowAttributes attr;<br> unsigned long attrMask;<br> Window root;<br> Window win;<br> GLXContext ctx;<br> XVisualInfo *visinfo;<br><br> root = RootWindow(dpy, 0);<br><br> /* Choose GLX visual / pixel format */<br> visinfo = glXChooseVisual(dpy, 0, visAttributes);<br> if (!visinfo) {<br> printf("Error: couldn't get an RGB, Double-buffered visual\n");<br> exit(1);<br> }<br><br> /* Create the window */<br> attr.background_pixel = 0;<br> attr.border_pixel = 0;<br> attr.colormap = XCreateColormap(dpy, root, visinfo->visual, AllocNone);<br> attrMask = CWBackPixel | CWBorderPixel | CWColormap;<br> win = XCreateWindow(dpy, root, 0, 0, width, height,<br> 0, visinfo->depth, InputOutput,<br> visinfo->visual, attrMask, &attr);<br> if (!win) {<br> printf("Error: XCreateWindow failed\n");<br> exit(1);<br> }<br><br> /* Display the window */<br> XMapWindow(dpy, win);<br><br> /* Create GLX rendering context */<br> ctx = glXCreateContext(dpy, visinfo, NULL, True);<br> if (!ctx) {<br> printf("Error: glXCreateContext failed\n");<br> exit(1);<br> }<br><br> /* Bind the rendering context and window */<br> glXMakeCurrent(dpy, win, ctx);<br><br> return win;<br>}<br><br><br>/*<br> * Draw a few frames of a rotating square.<br> */<br>static void<br>DrawFrames(Display * dpy, Window win)<br>{<br> int angle;<br> glShadeModel(GL_FLAT);<br> glClearColor(0.5, 0.5, 0.5, 1.0);<br> for (angle = 0; angle < 360; angle += 10) {<br> glClear(GL_COLOR_BUFFER_BIT);<br> glColor3f(1.0, 1.0, 0.0);<br> glPushMatrix();<br> glRotatef(angle, 0, 0, 1);<br> glRectf(-0.8, -0.8, 0.8, 0.8);<br> glPopMatrix();<br> glXSwapBuffers(dpy, win);<br> }<br>}<br><br><br>int<br>main(int argc, char *argv[])<br>{<br> Display *dpy;<br> Window win;<br><br> dpy = XOpenDisplay(NULL);<br> if (!dpy) {<br> printf("Error: XOpenDisplay failed\n");<br> return 1;<br> }<br><br> win = MakeWindow(dpy, 300, 300);<br><br> DrawFrames(dpy, win);<br><br> return 0;<br>}<br></code></pre>
|
||
|
|
<br>
|
||
|
|
</body>
|
||
|
|
</html>
|