GL_SGIX_subsample http://www.opengl.org/registry/specs/SGIX/subsample.txt GL_SGIX_subsample GL_PACK_SUBSAMPLE_RATE_SGIX 0x85A0 GL_UNPACK_SUBSAMPLE_RATE_SGIX 0x85A1 GL_PIXEL_SUBSAMPLE_4444_SGIX 0x85A2 GL_PIXEL_SUBSAMPLE_2424_SGIX 0x85A3 GL_PIXEL_SUBSAMPLE_4242_SGIX 0x85A4