Bug 450329

Summary: Screen sometimes flickers (strobe like) (most likely after unlocking session)
Product: [Plasma] kwin Reporter: postix <postix>
Component: wayland-genericAssignee: KWin default assignee <kwin-bugs-null>
Severity: normal CC: nate, postix
Priority: NOR Keywords: wayland
Version: 5.24.2   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed In:
Attachments: Recording: Screen Flickers
KWin Support Information (openSUSE TW)
Recording 2: Secondary monitor, flickering synchronized to mouse movement
Recording 3

Description postix 2022-02-15 18:44:08 UTC
Created attachment 146783 [details]
Recording: Screen Flickers


I have noticed that sometimes after unlocking the session one of my screens flickers until I press the left mouse button. Please see the screen recording.

This happens both under KDE Neon Testing in VBox and openSUSE TW with Wayland and Plasma 5.24.0. I haven't experienced it under X11 yet.

Operating System: openSUSE Tumbleweed 20220213
KDE Plasma Version: 5.24.0
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2
Kernel Version: 5.16.8-1-default (64-bit)
Graphics Platform: Wayland
Graphics Processor: AMD Radeon RX 580 Series
Comment 1 postix 2022-02-15 18:46:17 UTC
Created attachment 146784 [details]
KWin Support Information (openSUSE TW)
Comment 2 postix 2022-02-16 13:37:00 UTC
Yesterday, short after I have posted the bug report and unlocking the session, the 3/4 (from left to right) of the Dolphin's titlebar on the secondary screen flickered, whereby the frequency increased when I moved the mouse on the secondary screen. 

Today, the whole secondary screen flickered after unlocking the session. It indeed happens occasionally.
Comment 3 postix 2022-02-17 12:50:15 UTC
Created attachment 146863 [details]
Recording 2: Secondary monitor, flickering synchronized to mouse movement

This shall be the last example or recording I attach for now: 

When I unlocked the screen, the secondary monitor seemed not to come back to live as the screen was black. 
However, once I moved the mouse over it, it started to flicker synchronized with the mouse movement. 

I am not sure what mad the strobe effect vanish, but after < minute, when I moved the mouse to the primary monitor again or opened kickoff there, the issue was gone again.
Comment 4 postix 2022-02-19 19:45:35 UTC
Created attachment 146943 [details]
Recording 3

I promised not to upload another recording ;), but the today's issue may give some useful insights:

You can see the unlocked screen, which is partly overlayed with the lock screen wallpaper and clock. The clock changes from 15:06 to 15:07 during the flickering back and forth: As I had unlocked it at exactly this time, my guess is that the last two frames (15:06, 15:07) are somehow still in the buffer and not cleared but drawn on top of the scene. KWin experts probably know it better. :)

When I moved the mouse over the flickering part, a rectangle was "cut out" and the actual unlocked scene became visible in this area. Clicking somewhere made the flickering go away as usual.

You can of course download the video and let it run frame by frame via the VLC or other media player.
Comment 5 postix 2022-02-19 20:10:25 UTC
Apparently it also happens during normal usage: This time the left screen starte to flicker d(while I was working on the right)  showing, the lockscreen wallpaper + clock again (this time in full screen, but it's also only fullhd@100%). However and that's interesting, the clock dated 21:00, while it happened at 21:05!

When I moved the mouse to the left screen, most of the flickering image went away, but the taskbar of Thunderbird continued flickering, until I clicked somewhere ... fortunately I'm not epileptic. All in all, very mysterious.
Comment 6 postix 2022-03-04 12:54:13 UTC
Looks like someone has already reported the same issue before me.

*** This bug has been marked as a duplicate of bug 447705 ***