SUMMARY This is a bug that I've seen on different systems for quite some time on both Intel and NVIDIA GPUs (and I think radeon too). After reenabling compositing (I disable compositing for games) the screen is filled with black areas after opening new windows, on Intel GPUs those black areas start to flicker while on NVIDIA GPUs the black areas remain still until you move the windows to such areas. I don't know what is exactly causing this bugs but it should have something to do with kwin and OpenGL compositing because when compositing disabled those black areas do not appear. The issue is gone after I login again. SOFTWARE/OS VERSIONS Linux: Kubuntu 19.04 (Linux 5.0.0-13-generic) (present in previous versions too) KDE Plasma Version: 5.15.4 KDE Frameworks Version: 5.56.0 Qt Version: 5.12.2 ADDITIONAL INFORMATION I've seen this bug appear in the next GPUs: Intel HD Graphics 5500 (Broadwell GT2) (OpenGL 4.5/Mesa 19.0.2) Intel HD Graphics 500 (Broxton 2x6) (OpenGL 4.5/Mesa 19.0.2) AMD Radeon R5 230 (CAICOS) (OpenGL 3.3/Mesa 19.0.2) NVIDIA GeForce 840M (OpenGL 4.6/NVIDIA binary driver 418.56)
If you run kwin with KWIN_USE_BUFFER_AGE=0, does flickering occur?
(In reply to Vlad Zagorodniy from comment #1) > If you run kwin with KWIN_USE_BUFFER_AGE=0, does flickering occur? I restarted kwin using that variable but I still have the same problem. I open a game, disable compositing after it started, close the game, reenable compositing and when I open a new window I can see black artifacts in the border that are gone when I move the mouse over the affected areas. The bug is quite arbitrary, sometimes it creates black artifacts in the window borders, other times it cause flickering when opening widnows.
I can't reproduce exactly this bug. However, for some period of time I was noticing similar bug. If you toggle compositing couple times, the screen becomes completely black. The only thing that's visible is the cursor. After recent updates (BTW, I use Arch) the issue seem to be gone. In either case, I'm not sure that this is a kwin bug, e.g. buffer age related. It's worth looking down the stack.
*** This bug has been marked as a duplicate of bug 404375 ***