Created attachment 155378 [details] Lag when changing focus from Qalculate SUMMARY Kwin on X11 lags a lot when changing focus between some windows. Maybe those windows do a lot of repainting when focusing/defocusing. This effect is more seen with GTK apps with the "Default" theme. Also seen in the maximized System Monitor & System Settings apps which have several elements visible at once. Interestingly, this does not happen on Wayland. I have attached a video to demonstrate this issue. The lag doesn't seem to be much worse in my situation, but think, if an application has more GUI elements, then it can freeze up Kwin for a significant amount of time. STEPS TO REPRODUCE 1. Open a GTK app such as Qalculate, System settings or System monitor, then maximize it. 2. Try opening any panel menu (to take away focus from the application). 3. See the animation lagging. OBSERVED RESULT Kwin lags & hence, the animations also lag. EXPECTED RESULT Kwin should not lag even if an application does some graphic-intensive task during focusing/defocusing. SOFTWARE/OS VERSIONS Linux/KDE Plasma: 5.15.88-1-LTS (64-bit) KDE Plasma Version: 5.26.5 KDE Frameworks Version: 5.102.0 Qt Version: 5.15.8 ADDITIONAL INFORMATION In my opinion, this can be fixed if Kwin ignores the frames which do not come at the proper time from a particular window.