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