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<tr><td align="center"><i>Last Update: 11-03-08</i></td></tr>

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<h1>The OpenGL Extension Wrangler Library</h1>

<h2>Initializing GLEW</h2>

<p>

First you need to create a valid OpenGL rendering context and call

<tt>glewInit()</tt> to initialize the extension entry points. If

<tt>glewInit()</tt> returns <tt>GLEW_OK</tt>, the initialization

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succeeded and you can use the available extensions as well as core

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OpenGL functionality. For example:

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</p>

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#include <GL/glew.h><br>

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#include <GL/glut.h><br>

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...<br>

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glutInit(&argc, argv);<br>

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glutCreateWindow("GLEW Test");<br>

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GLenum err = glewInit();<br>

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if (GLEW_OK != err)<br>

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{<br>

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  /* Problem: glewInit failed, something is seriously wrong. */<br>

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  fprintf(stderr, "Error: %s\n", glewGetErrorString(err));<br>

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  ...<br>

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}<br>

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fprintf(stdout, "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION));<br>

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</p>

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<h2>Checking for Extensions</h2>

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<p>

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Starting from GLEW 1.1.0, you can find out if a particular extension

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is available on your platform by querying globally defined variables

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of the form <tt>GLEW_{extension_name}</tt>:

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</p>

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if (GLEW_ARB_vertex_program)<br>

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{<br>

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  /* It is safe to use the ARB_vertex_program extension here. */<br>

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  glGenProgramsARB(...);<br>

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}<br>

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</p>

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<p>

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<b>In GLEW 1.0.x, a global structure was used for this task. To ensure

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binary compatibility between releases, the struct was replaced with a

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set of variables.</b>

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</p>

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<p>

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You can also check for core OpenGL functionality. For example, to

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see if OpenGL 1.3 is supported, do the following:

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</p>

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if (GLEW_VERSION_1_3)<br>

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{<br>

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  /* Yay! OpenGL 1.3 is supported! */<br>

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}<br>

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</p>

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<p>

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In general, you can check if <tt>GLEW_{extension_name}</tt> or

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<tt>GLEW_VERSION_{version}</tt> is true or false.

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</p>

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<p>

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It is also possible to perform extension checks from string

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input. Starting from the 1.3.0 release, use <tt>glewIsSupported</tt>

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to check if the required core or extension functionality is

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available:

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</p>

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if (glewIsSupported("GL_VERSION_1_4  GL_ARB_point_sprite"))<br>

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{<br>

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  /* Great, we have OpenGL 1.4 + point sprites. */<br>

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}<br>

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</p>

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<p>

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For extensions only, <tt>glewGetExtension</tt> provides a slower alternative

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(GLEW 1.0.x-1.2.x). <b>Note that in the 1.3.0 release </b>

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<tt>glewGetExtension</tt> <b>was replaced with </b>

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<tt>glewIsSupported</tt>.

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</p>

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if (glewGetExtension("GL_ARB_fragment_program"))<br>

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{<br>

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  /* Looks like ARB_fragment_program is supported. */<br>

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}<br>

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</p>

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<h2>Experimental Drivers</h2>

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<p>

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GLEW obtains information on the supported extensions from the graphics

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driver. Experimental or pre-release drivers, however, might not

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report every available extension through the standard mechanism, in

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which case GLEW will report it unsupported. To circumvent this

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situation, the <tt>glewExperimental</tt> global switch can be turned

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on by setting it to <tt>GL_TRUE</tt> before calling

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<tt>glewInit()</tt>, which ensures that all extensions with valid

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entry points will be exposed.

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</p>

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<h2>Platform Specific Extensions</h2>

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<p>

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Platform specific extensions are separated into two header files:

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<tt>wglew.h</tt> and <tt>glxew.h</tt>, which define the available

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<tt>WGL</tt> and <tt>GLX</tt> extensions. To determine if a certain

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extension is supported, query <tt>WGLEW_{extension name}</tt> or

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<tt>GLXEW_{extension_name}</tt>. For example:

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</p>

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#include <GL/wglew.h><br>

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<br>

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if (WGLEW_ARB_pbuffer)<br>

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{<br>

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  /* OK, we can use pbuffers. */<br>

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}<br>

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else<br>

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{<br>

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  /* Sorry, pbuffers will not work on this platform. */<br>

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}<br>

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</p>

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<p>

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Alternatively, use <tt>wglewIsSupported</tt> or

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<tt>glxewIsSupported</tt> to check for extensions from a string:

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</p>

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if (wglewIsSupported("WGL_ARB_pbuffer"))<br>

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{<br>

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  /* OK, we can use pbuffers. */<br>

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}<br>

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</p>

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<h2>Utilities</h2>

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<p>

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GLEW provides two command-line utilities: one for creating a list of

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available extensions and visuals; and another for verifying extension

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entry points.

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</p>

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<h3>visualinfo: extensions and visuals</h3>

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<p>

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<tt>visualinfo</tt> is an extended version of <tt>glxinfo</tt>. The

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Windows version creates a file called <tt>visualinfo.txt</tt>, which

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contains a list of available OpenGL, WGL, and GLU extensions as well

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as a table of visuals aka. pixel formats. Pbuffer and MRT capable

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visuals are also included. For additional usage information, type

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<tt>visualinfo -h</tt>.

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</p>

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<h3>glewinfo: extension verification utility</h3>

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<p>

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<tt>glewinfo</tt> allows you to verify the entry points for the

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extensions supported on your platform. The Windows version

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reports the results to a text file called <tt>glewinfo.txt</tt>. The

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Unix version prints the results to <tt>stdout</tt>.

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</p>

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<p>Windows usage:</p>

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<blockquote><pre>glewinfo [-pf <id>]</pre></blockquote>

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<p>where <tt><id></tt> is the pixel format id for which the

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capabilities are displayed.</p>

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<p>Unix usage:</p>

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<blockquote><pre>glewinfo [-display <dpy>] [-visual <id>]</pre></blockquote>

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<p>where <tt><dpy></tt> is the X11 display and <tt><id></tt> is

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the visual id for which the capabilities are displayed.</p>

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