GL_ANGLE_texture_compression_dxt1 https://code.google.com/p/angleproject/source/browse/#git%2Fextensions GL_ANGLE_texture_compression_dxt1 GL_COMPRESSED_RGB_S3TC_DXT1_ANGLE 0x83F0 GL_COMPRESSED_RGBA_S3TC_DXT1_ANGLE 0x83F1 GL_COMPRESSED_RGBA_S3TC_DXT3_ANGLE 0x83F2 GL_COMPRESSED_RGBA_S3TC_DXT5_ANGLE 0x83F3