OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Global Shader-Compilation Option

One final #pragma directive that is available is STDGL. This option is currently used to enable invariance in the output of varying values.

Extension Processing in Shaders

GLSL, like OpenGL itself, may be enhanced by extensions. As vendors may include extensions specific to their OpenGL implementation, it’s useful to have some control over shader compilation in light of possible extensions that a shader may use.

The GLSL preprocessor uses the #extension directive to provide instructions to the shader compiler regarding how extension availability should be handled during compilation. For any, or all, extensions, you can specify how you would like the compiler to proceed with compilation.

#extension extension_name ...