GL_ARB_texture_gather http://www.opengl.org/registry/specs/ARB/texture_gather.txt GL_ARB_texture_gather GL_MIN_PROGRAM_TEXTURE_GATHER_OFFSET_ARB 0x8E5E GL_MAX_PROGRAM_TEXTURE_GATHER_OFFSET_ARB 0x8E5F GL_MAX_PROGRAM_TEXTURE_GATHER_COMPONENTS_ARB 0x8F9F