1GL_EXT_texture_compression_rgtc 2http://developer.download.nvidia.com/opengl/specs/GL_EXT_texture_compression_rgtc.txt 3GL_EXT_texture_compression_rgtc 4 5 GL_COMPRESSED_RED_RGTC1_EXT 0x8DBB 6 GL_COMPRESSED_SIGNED_RED_RGTC1_EXT 0x8DBC 7 GL_COMPRESSED_RED_GREEN_RGTC2_EXT 0x8DBD 8 GL_COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT 0x8DBE 9