Tiling regression in the blur effect of KWin (≥ 6.5)

[tsujan]

Since KWin 6.5 (or probably a little before it), KWin's blur effect has got this regression: When QTerminal is tiled or maximized under kwin_wayland, the blurring may randomly flicker until the window is unfocused and focused again.

This tiling regression may happen in Konsole (and perhaps some other apps) too, but I haven't encountered it in other Qt apps.

I opened this page for two reasons:

1. To tell Kvantum users that the cause of the problem is in KWin (or KWindowEffects or both), not in Kvantum, which just makes use of KWindowEffects::enableBlurBehind() if KWin's blur wffect is available, as it always did; and
2. To see in which version of KWin the regression might be fixed.

As for QTerminal, a small workaround is possible in its code, but hiding the bugs of other apps isn't an option in LXQt.