1GL_ATI_texture_env_combine3 2https://www.khronos.org/registry/OpenGL/extensions/ATI/ATI_texture_env_combine3.txt 3GL_ATI_texture_env_combine3 4 5 GL_MODULATE_ADD_ATI 0x8744 6 GL_MODULATE_SIGNED_ADD_ATI 0x8745 7 GL_MODULATE_SUBTRACT_ATI 0x8746 8