Mesa's LLVMpipe Driver Adds 4x MSAA Support

David Airlie's "multi-sample support extravaganza" for the LLVMpipe software driver has been merged into Mesa 20.2-devel.

This big set of patches for LLVMpipe enables working 4x multi-sample anti-aliasing and includes window system multi-sampling and support for the OpenGL extensions of EXT_framebuffer_multisample, ARB_texture_multisample, ARB_sample_shading, and ARM_shader_texture_image_samples.

Airlie noted in the merge request this support has been tested with the Piglit test cases as well as Unigine Heaven.

Finishing up ARB_sample_shading clears out another blocker from LLVMpipe in reaching OpenGL 4.0 support but still needs ARB_gpu_shader5 before crossing that milestone. For OpenGL 4.1, LLVMpipe is blocked by ARB_shader_precision and ARB_get_program_binary. But after that it's quite close to OpenGL 4.3+4.4 once tacking on ARB_robust_buffer_access_behavior. So it's possible we could finally be seeing LLVMpipe achieving a more recent GL4 version in the months ahead after being stuck on OpenGL 3.3 for the past few years for this CPU-based OpenGL software driver.

In addition to LLVMpipe, Airlie has also been working on Vallium as a new Vulkan-based software driver.