Initializing GLEW

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:

#include <GL/glew.h>

#include <GL/glut.h>

...

glutInit(&argc, argv);

glutCreateWindow("GLEW Test");

GLenum err = glewInit();

if (GLEW_OK != err)

{

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

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

  ...

}

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

Checking for Extensions

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>:

if (GLEW_ARB_vertex_program)

{

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

  glGenProgramsARB(...);

}

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.

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

see if OpenGL 1.3 is supported, do the following:

if (GLEW_VERSION_1_3)

{

  /* Yay! OpenGL 1.3 is supported! */

}

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

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

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:

if (glewIsSupported("GL_VERSION_1_4  GL_ARB_point_sprite"))

{

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

}

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

(GLEW 1.0.x-1.2.x). Note that in the 1.3.0 release 

<tt>glewGetExtension</tt> was replaced with 

<tt>glewIsSupported</tt>.

if (glewGetExtension("GL_ARB_fragment_program"))

{

  /* Looks like ARB_fragment_program is supported. */

}

Experimental Drivers

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.

Platform Specific Extensions

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:

#include <GL/wglew.h>

if (WGLEW_ARB_pbuffer)

{

  /* OK, we can use pbuffers. */

}

else

{

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

}

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

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

if (wglewIsSupported("WGL_ARB_pbuffer"))

{

  /* OK, we can use pbuffers. */

}

Utilities

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

available extensions and visuals; and another for verifying extension

entry points.

visualinfo: extensions and visuals

<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>.

glewinfo: extension verification utility

<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>.

Windows usage:

 
glewinfo [-pf <id>]

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

capabilities are displayed.

Unix usage:

glewinfo [-display <dpy>] [-visual <id>]

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

the visual id for which the capabilities are displayed.