Mesa Preparing Software Fallback For S3TC Texture Compression

Mesa recently landed BPTC software fallback handling that is a requirement for OpenGL 4.2 support but BPTC is not natively supported by all GPU hardware, particularly on the embedded side. That software emulation support for BPTC is similar to what already has existed within Mesa for the ASTC and ETC formats too. A merge request is pending that also adds S3TC software fallback handling, which helps out some of the smaller, embedded GPU drivers too for getting more games running that are dependent on S3 Texture Compression.

S3TC had been a headache for open-source GPU drivers due to patents around S3 Texture Compression. But the patents expired a few years ago and is no longer as much of a headache as it was years ago, especially with texture compression algorithms like ASTC coming about too.

Last week Erik Faye-Lund opened up a Mesa merge request adding the S3TC software fallback handling for cases where the graphics processor and/or driver lack the native S3TC handling. This software fallback can be used for getting more games running -- where they explicitly rely on S3TC support -- on the likes of the Arm Mali Panfrost driver, Raspberry Pi VC4, and other similar drivers.

This MR has the pending code for the S3TC software fallback that will hopefully be merged in time for next quarter's Mesa 22.3.