How to Check for OpenGL Extension Availability

How to Check for OpenGL Extension Availability

All supported extensions have a corresponding definition in gl.h and a token in the extensions string returned by glGetString(). For example, if the ABGR extension (EXT_abgr) is supported, it is defined in gl.h as follows:

#define GL_EXT_abgr 1

GL_EXT_abgr appears in the extensions string returned by glGetString(). Use the definitions in gl.h at compile time to determine if procedure calls corresponding to an extension exist in the library.

Applications should do compile-time checking--for example, making sure GL_EXT_abgr is defined; and run-time checking--for example, making sure GL_EXT_abgr is in the extension string returned by glGetString().

Compile-time checking ensures that entry points such as new functions or new enums are supported. You can't compile or link a program that uses a certain extension if the client side development environment does not support it.
Run-time checking ensures that the extension is supported for the OpenGL server and run-time library you are using.
Note that availability depends not only on the operating system but also on the particular hardware you are using: even though the 5.3 OpenGL library supports GL_CONVOLUTION_2D_EXT, you get an GL_INVALID_OPERATION error if you call glConvolutionFilter2DEXT() on an Indy system.