So this one is a bit tricky. When I start a fresh kwin session, everything works as expected, there is no flickering, tearing. However, after some time (sorry, couldn't find an exact way to trigger), on focus changes, it starts flickering. It looks a bit like some sort of race condition, where the focus between two windows changes back and forth very fast a few times until it eventually settles. Sometimes, it was triggered by the screensaver (blanking of the screen after some time), but not every time. This issue is gone (until triggered again) when switching the rendering backend or restarting kwin. It happens with both the 2.0 and the 3.1 rendering backend¹. Haven't tried the XRender backend, but if that would be interesting, I can try. Without compositing, I haven't observed such behaviour. ¹ When using the 3.1 backend, I still get the message that it's using OpenGL 2? Initialization information: Initializing OpenGL compositing Drawable visual (depth 24 ): 0x "210" Drawable visual (depth 32 ): 0x "6d" Buffer visual (depth 24 ): 0x "212" Direct rendering: true Color correction: false OpenGL 2 compositing successfully initialized Vertical Refresh rate 60 Hz Reproducible: Sometimes
Created attachment 86811 [details] Output of glxinfo
Could you please run KWin from a terminal and check the output for: "Triple buffering detection" when the problem arises. If you see something like that, please paste the debug output of that line into the bug report. Please also provide the output of: qdbus org.kde.KWin /KWin supportInformation
(In reply to comment #2) > Could you please run KWin from a terminal and check the output for: > > "Triple buffering detection" > > when the problem arises. If you see something like that, please paste the > debug output of that line into the bug report. Triple buffering detection: "NOT available" - Mean block time: 5.60969 ms
Created attachment 86837 [details] qdbus org.kde.KWin /KWin supportInformation
The output will occur unconditionally - the interesting question is whether it occurs coincidental with the prooblem (ie. no problem before detection, but arises after) Can you prevent the problem by export KWIN_TRIPLE_BUFFER=1 kwin --replace & ?
(In reply to comment #5) > The output will occur unconditionally - the interesting question is whether > it occurs coincidental with the prooblem (ie. no problem before detection, > but arises after) Well, this is the only time I got that message, afaics. It was one of the last lines when the problem first occurred in this session, so I think it's correlated. > export KWIN_TRIPLE_BUFFER=1 > kwin --replace & Will try tomorrow.
(In reply to comment #6) > > export KWIN_TRIPLE_BUFFER=1 > > kwin --replace & > Will try tomorrow. Ok, so I tried with KWIN_TRIPLE_BUFFER=1 for a couple of days and didn't observe and flickering anymore, so that seems to work around the issue. On a related note, I get similar (but not quite the same) issues when switching the platform interface to EGL (which doesn't work that well over here) and back to GLX again. Then the compositor goes berserk, shows lot of flickering and some areas are not or not properly updated anymore. This goes on until vsync is deactivated. (Backend change doesn't help here) Don't know if that is a different issue or if the two are related.
> Ok, so I tried with KWIN_TRIPLE_BUFFER=1 for a couple of days and didn't > observe and flickering anymore, so that seems to work around the issue. hmm, I think I need to try that :-) > > On a related note, I get similar (but not quite the same) issues when > switching the platform interface to EGL (which doesn't work that well over > here) and back to GLX again. > Then the compositor goes berserk, shows lot of flickering and some areas are > not or not properly updated anymore. I can confirm that, experienced that as well. I do not think that they are related, but might indicate that we either do not tear down the egl backend correctly or need to restart KWin when switching the interface.
Actually, this problem went away completely now, even without exporting KWIN_TRIPLE_BUFFER=1 as suggested above. Unfortunately, I can't tell you if the update of Mesa (10.1.3 -> 10.1.4) fixed it or some commit in KF5/kwin. Anyway, I didn't observe this anymore, so feel free to mark as fixed.
Do you have 902e424f8171719a07f6376a9b1ebe47ecb322b0 ?
No, the currently installed and used id is 0bf9ed5317540eb14c8d0a1554471ba6cbd42b9f.
On a second glance, I noted that I was running kwin with vsync turned off for the last few days. Let me try git master with vsync set to automatic again and see what happens.
Ok, so at abe620 I still observe this unless setting KWIN_TRIPLE_BUFFER=1 or disabling tearing prevention.
Thank you for the bug report. As this report hasn't seen any changes in 5 years or more, we ask if you can please confirm that the issue still persists. If this bug is no longer persisting or relevant please change the status to resolved.
I do still see some flickering in kwin, but I don't think it's related to this bug, so closing this as resolved.