A Decade Later, Mesa Wiring In Support For Qualcomm/AMD's ATC Texture Compression
AMD_compressed_ATC_texture is the extension worked on a decade ago by AMD/Qualcomm for ATC compressed texture formats. ATC was AMD's proprietary compression algorithm with a focus on mobile devices for power and memory bandwidth savings. That was right around the time ATI/AMD Imageon IP was sold off to Qualcom to form the Adreno graphics processors for the company's SoCs.
ATC isn't to be confused with the newer Adaptive Scalable Texture Compression (ASTC) that was also developed in part by AMD but isn't proprietary and has already been part of OpenGL for years as well as being supported by Mesa.
Now in 2019, the open-source, largely reverse-engineered Freedreno Gallium3D driver has picked up support for the ATC texture extension. The code merged today into Mesa Git plumbs the GL_AMD_compressed_ATC_texture support into core Mesa as well as the Mesa Gallium state tracker, adding support for the ATC formats, and wiring it through for the Freedreno driver on older Adreno 200/300 series hardware.
It's likely not to be too useful today as better, non-proprietary texture compression alternatives exist, but it looks like ATC textures may still have some relevance in the WebGL/GLES space on old hardware, so for anyone interested it's now in Git ahead of Mesa 19.1.