RADV Driver Adds VK_EXT_line_rasterization In Preparing For Eventual Vulkan CAD Apps

Added to the Vulkan API last summer was VK_EXT_line_rasterization for line rasterization like employed by CAD applications. The open-source Mesa Radeon Vulkan "RADV" driver is now supporting this extension.

AMD's AMDVLK Vulkan driver has supported VK_EXT_line_rasterization since last September while finally a few days ago the RADV support was added for Mesa 20.1. Granted, without any major Linux software yet using VK_EXT_line_rasterization, this hasn't been a particularly pressing extension to support.

With the initial RADV code, only Bresenham lines are supported. Besides Bresenham lines, the VK_EXT_line_rasterization specification also is designed to handle smooth rectangular lines with coverage to alpha and stippled lines.

As another initial caveat, Vega/GFX9 support is currently disabled due to some Vulkan conformance test suite failures for "weird reasons" being explored.

It's hopefully not too far out before seeing CAD software powered by Vulkan. Last year before the introduction of VK_EXT_line_rasterization was introduced, Autodesk did join The Khronos Group raising hopes their impressive suite of software will one day move past OpenGL for Vulkan.