GL_MESAX_texture_stack http://www.opengl.org/registry/specs/MESAX/texture_stack.txt GL_MESAX_texture_stack GL_TEXTURE_1D_STACK_MESAX 0x8759 GL_TEXTURE_2D_STACK_MESAX 0x875A GL_PROXY_TEXTURE_1D_STACK_MESAX 0x875B GL_PROXY_TEXTURE_2D_STACK_MESAX 0x875C GL_TEXTURE_1D_STACK_BINDING_MESAX 0x875D GL_TEXTURE_2D_STACK_BINDING_MESAX 0x875E