Zink OpenGL-On-Vulkan Lands Tessellation Shader Support In Mesa 21.0

Landing in Mesa 21.0 on Tuesday was support for OpenGL tessellation shaders (ARB_tessellation_shader) with the Zink Gallium3D code implementing generic OpenGL support atop Vulkan.

Tessellation support is one of the key requirements for OpenGL 4.0 and one of the remaining extensions for Zink in hitting GL 4.0 on mainline Mesa besides ARB_gpu_shader5 and ARB_texture_gather.

For months already there have been experimental patches taking Zink up to OpenGL 4.6 but that code has been out-of-tree while now Mike Blumenkrantz -- thanks to funding from Valve -- and others have been working to upstream all of the GL4 work as well as the significant performance optimizations.

This merge from yesterday has the OpenGL tessellation support now working properly for Zink atop Vulkan drivers.

There still is just over one month to go for Mesa 21.0 development until the feature freeze begins so we'll see what more of the Zink OpenGL 4.x support and performance optimizations get review and merged in time for this next quarterly Mesa3D update.