Set an OpenGL window attribute before window creation.
Defined in SDL_video.h
int SDL_GL_SetAttribute(SDL_GLattr attr, int value);| SDL_GLattr | attr | an SDL_GLattr enum value specifying the OpenGL attribute to set. | 
| int | value | the desired value for the attribute. | 
(int) Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.
This function sets the OpenGL attribute attr to value. The requested attributes should be set before creating an OpenGL window. You should use SDL_GL_GetAttribute() to check the values after creating the OpenGL context, since the values obtained can differ from the requested ones.
This function is available since SDL 2.0.0.