Bug 499533

Created attachment 177981 [details]
OBSERVED RESULT: flickering when toggling full-screen

SUMMARY
If I continuously press full-screen toggling shortcut, frequently switch between full-screen modes, occasionally the underlying window is revealed, causing flickering.
Regarding the use case, there isn’t any particular scenario that demands rapid switching full-screen. So not a big deal anyway. Just Kwin would be better without the flickering. 

STEPS TO REPRODUCE
For firefox:
    1. Open Firefox
    2. Toggle fullscreen mode frequently (For firefox it’s long-press F11)
For other app (like mpv or konsole):
    1. Bind fullscreen shortcut key to whatever U like.
    2. Rapidly tap the full screen key (long-pressing seems works too).

OBSERVED RESULT
There will be split-second of exposing the window underneath the current one, causing flickering.
See upload gif:OBSERVED_RESULT.gif

EXPECTED RESULT
Getting window always showup and follow right z-index when switching full-screen mode.
For comparison, There is a Win11 24h2 one. Win11 not behave the best, there also some drawback on compositor.
See upload gif:EXPECTED_RESULT.gif

SOFTWARE/OS VERSIONS
Windows: Not affected
macOS: Not affected
Linux/KDE Plasma: Manjaro KDE Plasma 6.2.5 Wayland and X11
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1
Kernel Version: 6.13.0-1-MANJARO (AMD64)

ADDITIONAL INFORMATION
    Initial conversation: https://discuss.kde.org/t/frequently-toggling-fullscreen-causing-window-flickering/29153
    Can reproduced on both:
        AMD 7840HS Laptop
        AMD Ryzen 3700x, Radeon Vega56 platform
    More system information, See upload txt: inxi.txt