We recently setup Dolphin's automated rendering tests on Fiji XT with Mesa/amdgpu. It started detected a random rendering issue which I think we can attribute to a driver bug.
See https://fifoci.dolphin-emu.org/compare/1086020-1085934/ . Left side has the "bad" rendering, right side the "good" rendering.
The issue is properly captured in this apitrace: http://delroth.net/radeon-unpredictable.trace -- rendering it on my Fiji XT system shows the lines but rendering it on i965 doesn't.
We have also had reports of users seeing this in action on Pitcairn GPUs: https://bugs.dolphin-emu.org/issues/9239
Someone on IRC just reported something that sounds like the same issue, but on r600.
It's likely that this issue comes from geometry shaders, which we are using to generate stripes from lines. Disabling the use of geometry shaders breaks some features in Dolphin but fixes that particular problem.
I haven't been able to test that myself, but other Dolphin users have reported the same symptoms on Intel Sandybridge IGPs. Our automated tests on Broadwell don't seem see that issue however, and my own laptop on Haswell doesn't see that issue either.
I tested on a SNB and couldn't reproduce any artifacts on the apitrace (after forcing ARB_conservative_depth on). Even if I could, it'd be very surprising if the issues were related. Unless you have concrete evidence to the contrary, I'd keep it to one bug per issue that you see. Issues can be combined later on, but are difficult to break apart. Switching this one back to radeonsi.
Any issues you see on other hardware should include an apitrace taken on that hw.
(In reply to Ilia Mirkin from comment #3)
> I tested on a SNB and couldn't reproduce any artifacts on the apitrace
> (after forcing ARB_conservative_depth on). Even if I could, it'd be very
> surprising if the issues were related. Unless you have concrete evidence to
> the contrary, I'd keep it to one bug per issue that you see. Issues can be
> combined later on, but are difficult to break apart. Switching this one back
> to radeonsi.
> Any issues you see on other hardware should include an apitrace taken on
> that hw.
I think Pierre was referring to bug #93418 it already has an apitrace for SNB I tried it a while ago on my Ivy Bridge and it also worked fine there.
Thanks again for the report. Analysing the apitrace suggests we're not handling geometry shader primitive types correctly, I'm looking into it.
Found the bug: we didn't properly update a piece of state in a specific (but not all that unusual) sequence of operations involving geometry shaders.
I have a preliminary series containing the fix at http://cgit.freedesktop.org/~nh/mesa/log/?h=shader-state
I remember that you mentioned other rendering bugs in Dolphin that showed up using your automated tests, but I don't think you've filed bug reports for them. Of course they may well have had the same root cause, but if any of them persist after the fix for this bug, I appreciate similarly high quality bug reports in the future :)
The fix is now in Mesa master:
Author: Nicolai Hähnle <firstname.lastname@example.org>
Date: Fri Jan 22 17:04:48 2016 -0500
radeonsi: ensure that VGT_GS_MODE is sent when necessary
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