Bug 469056

(In reply to Guillaume DE BURE from comment #0)
> Created attachment 158485 [details]
> Screencast showing visual glitches on cover switch
> 
> SUMMARY
> Cover Switch effect has background glitches on my external 4k monitor :
> * wallpaper is not fullscreen
> * window artefact
> I found it difficult to describe in words or even with a picture, please
> refer to the attached screencast.
> 
> I noticed this ever since the new QML based cover switch effect has been
> released, only taking the time today to report it.
> 
> 
> SOFTWARE/OS VERSIONS
> Linux/KDE Plasma: Archlinux, kernel 6.2.12
> KDE Plasma Version: 5.27.4
> KDE Frameworks Version:  5.105.0
> Qt Version: 5.15.9

If I understood the screencast correctly, this would be in fact two separate bugs:

1 - The wallpaper does not fill the whole fullscreen: Do you have scaling factor > 1?

2 - Is the window artifact you refer to the initial/final "magic-lamp" kind of effect on the desktop layer? 
This is caused because the Cover Switch window also gets the effects for show/hide window applied on top of it. Can you try to disable those effects on "Desktop Effects" and see if that part gets fixed? This is just to check the cause of the bug. We should not apply those effects here.

Thanks!

Thanks for coming back to me :) 

1- My wallpaper is actually not really a wallpaper. My desktop is set to have a plain color background, and the picture is a media frame widget resized to cover a large portion of the screen. (The reason for this is that this image actually shows packages installed on my machine and their dependencies as a graph. The image is recomputed every time the system checks for updates on the repositories, so setting up this way allows to reload it every time it is updated). If that is unclear, I can provide screenshots of systemsettings, or even config files.
 
2- No, I was referring to the fact that window previews stay in the background. The magic lamp effect is indeed intended when minimizing the window.

(In reply to Guillaume DE BURE from comment #2)
> Thanks for coming back to me :) 
> 
> 1- My wallpaper is actually not really a wallpaper. My desktop is set to
> have a plain color background, and the picture is a media frame widget
> resized to cover a large portion of the screen. (The reason for this is that
> this image actually shows packages installed on my machine and their
> dependencies as a graph. The image is recomputed every time the system
> checks for updates on the repositories, so setting up this way allows to
> reload it every time it is updated). If that is unclear, I can provide
> screenshots of systemsettings, or even config files.
JFYI In Plasma 6 this will be supported with the built-in wallpaper plugin; see https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/2840. We might even be able to backport it to Plasma 5.27.5.

> 2- No, I was referring to the fact that window previews stay in the background. 

Thanks! I think I understand now. The actual bug is that the Wallpaper Item does not get the correct size for your set-up, and doesn't cover the whole screen.  This means the actual windows are still visible behind this region.

This bug is closed in 6.x :)