Radeon RADV Driver's Emulated Ray-Tracing Achieves 100% Pass Rate

Mesa's Radeon Vulkan driver "RADV" supports native hardware ray-tracing with RDNA2 and RDNA3 graphics cards where it's matured quite nicely over the past number of months. With the upcoming Mesa 23.2, RADV RT support is enabled by default for all supported GPUs. RADV also has emulated ray-tracing support for older generations of AMD GPUs and as of today it's finally hit a 100% pass rate.

Going off the Vulkan conformance test suite (CTS) tests around Vulkan ray-tracing, with the latest code now in Mesa 23.2-devel the optional emulated RT path can achieve a 100% pass rate.

This merge request landed today that provided a fix for the water tightness CTS test and gets the 100% pass mark now. Friedrich Vock wrote with his code change:

I'm a bit bewildered that the hardware actually just makes all rays that hit one particular edge of a triangle miss.

It raises the CTS pass rate with emulated RT to 100% though, so I guess I can't complain. ¯\_(ツ)_/¯

Vock has opened a new merge request yesterday that is still open and would enable the emulated RT code path by default for pre-RDNA2 GPUs. The merge request also adds a "emulate_rt" debug option for forcing on/off the behavior -- including emulation on RDNA2 / RDNA3 GPUs if desired for comparison/testing purposes.

Right now it isn't clear if that emulated-RT-by-default will be merged though as some objections have been raised how it could adversely impact the user experience for those on older Radeon GPUs when moving to newer Mesa and then suddenly finding some games running very slow if the game suddenly starts trying to utilize ray-tracing. We'll see what happens though but otherwise can be easily enabled by those on RDNA1 hardware and older.