GL_S3_s3tc http://www.opengl.org/registry/specs/S3/s3tc.txt GL_S3_s3tc GL_RGB_S3TC 0x83A0 GL_RGB4_S3TC 0x83A1 GL_RGBA_S3TC 0x83A2 GL_RGBA4_S3TC 0x83A3 GL_RGBA_DXT5_S3TC 0x83A4 GL_RGBA4_DXT5_S3TC 0x83A5