Created attachment 144551 [details]
Screenshot showing artifacts

This game worked perfectly for me around a year ago. Now it shows strange flashing/moving mostly black squares in the upper half of the screen when HDAO is enabled. Please see the attached screenshot. It looks worse when you move. Choosing "standard" SSAO instead makes the problem go away.

I'm not alone, here is another Steam user reporting the same thing:
https://steamcommunity.com/app/214490/discussions/0/1735468061769831062/

Here are my system details:
OpenGL vendor string: X.Org
OpenGL renderer string: AMD Radeon (TM) RX 480 Graphics (POLARIS10, DRM 3.30.0, 5.1.10-00004-g8b7bb440229b, LLVM 8.0.0)
OpenGL core profile version string: 4.5 (Core Profile) Mesa 19.2.0-devel (git-749c544b84)
OpenGL core profile shading language version string: 4.50

It still happens with Mesa as far back as 18.2.0. Anything earlier just crashes on my system but the other user reported he was using 18.1.9. I have tried against LLVM 6, 7, and 8 with no change. I have also booted into a Fedora 28 Live USB system, chrooted into my Gentoo system, and it still happens. It's possibly down a change in the game itself although I can't verify that and I don't think it's seeing many changes these days.

Sorry if I've assigned this to the wrong component but it's hard to say where the problem lies.