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

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<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
succeeded and you can use the available extensions as well as core
OpenGL functionality. For example:
</p>

<p class="pre">
#include &lt;GL/glew.h&gt;<br>
#include &lt;GL/glut.h&gt;<br>
...<br>
glutInit(&amp;argc, argv);<br>
glutCreateWindow("GLEW Test");<br>
GLenum err = glewInit();<br>
if (GLEW_OK != err)<br>
{<br>
&nbsp;&nbsp;/* Problem: glewInit failed, something is seriously wrong. */<br>
&nbsp;&nbsp;fprintf(stderr, "Error: %s\n", glewGetErrorString(err));<br>
&nbsp;&nbsp;...<br>
}<br>
fprintf(stdout, "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION));<br>
</p>

<h2>Checking for Extensions</h2>

<p>
Starting from GLEW 1.1.0, you can find out if a particular extension
is available on your platform by querying globally defined variables
of the form <tt>GLEW_{extension_name}</tt>:
</p>

<p class="pre">
if (GLEW_ARB_vertex_program)<br>
{<br>
&nbsp;&nbsp;/* It is safe to use the ARB_vertex_program extension here. */<br>
&nbsp;&nbsp;glGenProgramsARB(...);<br>
}<br>
</p>

<p>
<b>In GLEW 1.0.x, a global structure was used for this task. To ensure
binary compatibility between releases, the struct was replaced with a
set of variables.</b>
</p>

<p>
You can also check for core OpenGL functionality.  For example, to
see if OpenGL 1.3 is supported, do the following:
</p>

<p class="pre">
if (GLEW_VERSION_1_3)<br>
{<br>
&nbsp;&nbsp;/* Yay! OpenGL 1.3 is supported! */<br>
}<br>
</p>

<p>
In general, you can check if <tt>GLEW_{extension_name}</tt> or
<tt>GLEW_VERSION_{version}</tt> is true or false.
</p>

<p>
It is also possible to perform extension checks from string
input. Starting from the 1.3.0 release, use <tt>glewIsSupported</tt>
to check if the required core or extension functionality is
available:
</p>

<p class="pre">
if (glewIsSupported("GL_VERSION_1_4&nbsp;&nbsp;GL_ARB_point_sprite"))<br>
{<br>
&nbsp;&nbsp;/* Great, we have OpenGL 1.4 + point sprites. */<br>
}<br>
</p>

<p>
For extensions only, <tt>glewGetExtension</tt> provides a slower alternative
(GLEW 1.0.x-1.2.x). <b>Note that in the 1.3.0 release </b>
<tt>glewGetExtension</tt> <b>was replaced with </b>
<tt>glewIsSupported</tt>.
</p>

<p class="pre">
if (glewGetExtension("GL_ARB_fragment_program"))<br>
{<br>
&nbsp;&nbsp;/* Looks like ARB_fragment_program is supported. */<br>
}<br>
</p>

<h2>Experimental Drivers</h2>

<p>
GLEW obtains information on the supported extensions from the graphics
driver.  Experimental or pre-release drivers, however, might not
report every available extension through the standard mechanism, in
which case GLEW will report it unsupported.  To circumvent this
situation, the <tt>glewExperimental</tt> global switch can be turned
on by setting it to <tt>GL_TRUE</tt> before calling
<tt>glewInit()</tt>, which ensures that all extensions with valid
entry points will be exposed.
</p>

<h2>Platform Specific Extensions</h2>

<p>
Platform specific extensions are separated into two header files:
<tt>wglew.h</tt> and <tt>glxew.h</tt>, which define the available
<tt>WGL</tt> and <tt>GLX</tt> extensions.  To determine if a certain
extension is supported, query <tt>WGLEW_{extension name}</tt> or
<tt>GLXEW_{extension_name}</tt>.  For example:
</p>

<p class="pre">
#include &lt;GL/wglew.h&gt;<br>
<br>
if (WGLEW_ARB_pbuffer)<br>
{<br>
&nbsp;&nbsp;/* OK, we can use pbuffers. */<br>
}<br>
else<br>
{<br>
&nbsp;&nbsp;/* Sorry, pbuffers will not work on this platform. */<br>
}<br>
</p>

<p>
Alternatively, use <tt>wglewIsSupported</tt> or
<tt>glxewIsSupported</tt> to check for extensions from a string:
</p>

<p class="pre">
if (wglewIsSupported("WGL_ARB_pbuffer"))<br>
{<br>
&nbsp;&nbsp;/* OK, we can use pbuffers. */<br>
}<br>
</p>

<h2>Utilities</h2>

<p>
GLEW provides two command-line utilities: one for creating a list of
available extensions and visuals; and another for verifying extension
entry points.
</p>

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

<p>
<tt>visualinfo</tt> is an extended version of <tt>glxinfo</tt>. The
Windows version creates a file called <tt>visualinfo.txt</tt>, which
contains a list of available OpenGL, WGL, and GLU extensions as well
as a table of visuals aka. pixel formats. Pbuffer and MRT capable
visuals are also included. For additional usage information, type
<tt>visualinfo -h</tt>.
</p>

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

<p>
<tt>glewinfo</tt> allows you to verify the entry points for the
extensions supported on your platform. The Windows version
reports the results to a text file called <tt>glewinfo.txt</tt>. The
Unix version prints the results to <tt>stdout</tt>.
</p>

<p>Windows usage:</p>
 <blockquote><pre>glewinfo [-pf &lt;id&gt;]</pre></blockquote>

<p>where <tt>&lt;id&gt;</tt> is the pixel format id for which the
capabilities are displayed.</p>

<p>Unix usage:</p>
<blockquote><pre>glewinfo [-display &lt;dpy&gt;] [-visual &lt;id&gt;]</pre></blockquote>

<p>where <tt>&lt;dpy&gt;</tt> is the X11 display and <tt>&lt;id&gt;</tt> is
the visual id for which the capabilities are displayed.</p>

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