Mesa Support For ETC1 Texture Compression

With commits this afternoon by Intel, there's now support for handling ETC1 texture compression within Mesa.

The commits from Chad Versace of Intel provide a function for decoding ETC1 textures (this commit) and then another commit enables the GL_OES_compressed_ETC1_RGB8_texture extension for all hardware using the Intel DRI driver. Intel hardware doesn't currently handle ETC1 so the data is converted instead to RGBX data.

ETC1 is the original version of Ericsson Texture Compression, which was conceived about a half-decade ago and based upon the original PACKMAN texture compression design for mobile phones. ETC1 provides six times compression of 24-bit RGB data, but doesn't support alpha components while a newer ETC2 provides higher-quality RGB compression along with alpha support. However, this newer ETC2 implementation isn't yet supported by software or hardware and is only months old.

Ericsson Texture Compression is part of the OpenGL ES specification and is also part of the WebGL specification too. It's nice that there's support for a new texture compression scheme within Mesa, but too bad there's no progress to report at this time of S3TC texture compression support within mainline Mesa. S3TC is still only available as a third-party source library over patent/legal concerns, although this means of texture compression is widely used and relied upon within the professional/gaming desktop world.