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Horizontal shift/Staircase graphic artifacts with vblank_mode=xpresent on let...


Description alexo 2019-12-23 17:14:40 CET
Hey there,

on my amdgpu laptop, I've applied a non-native (1650x1050 instead of native 1920x1080) resolution to the display settings.
Now, shifting-artifacts occur like shown in the attachment.

To produce this behaviour, I switched from the vblank_mode=auto to xpresent, then restarted xfwm.
When switching back to the default blanking mode, this behaviour disappears.

I suspect that the xpresent component erroneously calculates vertical black bar widths/heights into the wrong offsets.
It might also attempt to redraw too many parts of the screen, or assumes a too big screen (not paying attention to the vertical bars left and right from the drawn desktop parts), hence the empty yet drawn background of the left cascade.

See also this thread: https://forum.xfce.org/viewtopic.php?id=13632

Cheers, and thanks in advance for the good work being done here! :)
Comment 1 alexo 2019-12-23 17:16:27 CET
The attachment upload failed due to file size; I did upload the image over here, however: https://i.imgur.com/AsmBTyt.jpg
Comment 2 Olivier Fourdan editbugs 2019-12-24 16:09:51 CET
That looks a lot like a driver bug, not the client (xfwm4).
Comment 3 Olivier Fourdan editbugs 2019-12-24 16:11:31 CET
FTR, the client (xfwm4) does not calculate anything, it just submits the pixmap for flipping on next vblank, waits for the vblank notification, submits the other pixmap buffer, so forth and so on.
Comment 4 alexo 2020-05-27 10:02:43 CEST
(In reply to Olivier Fourdan from comment #2)
> That looks a lot like a driver bug, not the client (xfwm4).

Okay then, thanks for the answer. Do you have a hint on where to file a bug or to ask?
Like, in the official amdgpu driver forum or somewhere?
Comment 6 alexo 2020-05-27 10:10:57 CEST
(In reply to Olivier Fourdan from comment #5)
> There
> https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/issues/10
> And the fix is already merged upstream
> https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/-/
> merge_requests/52

Fantastic, thank you very much! :)

Bug #16299

Reported by:
Reported on: 2019-12-23
Last modified on: 2020-05-27


Olivier Fourdan
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