Bug 489342

Summary:	Desktop frame rate drops when fractional scaling is enabled on wayland with a maximised Firefox window in focus.
Product:	[Plasma] kwin	Reporter:	kreds <nerig18328>
Component:	performance	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED WORKSFORME
Severity:	normal	CC:	xaver.hugl
Priority:	NOR
Version First Reported In:	6.1.1
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description kreds 2024-06-27 22:49:32 UTC

SUMMARY
When I open and maximise a Firefox window in wayland, while fractional scaling is enabled, desktop animations have dropped frames. Animations such as minimising and maximising other windows, opening and closing start menu, opening new application windows and such.

STEPS TO REPRODUCE
1. Enable fractional scaling to any % on wayland
2. Open Firefox, maximise it and make sure no other window is in front or in focus.
3. Open and close start menu or do anything else that has a desktop animation.

OBSERVED RESULT
Animations seem to have dropped frames / are laggy.

EXPECTED RESULT
Animations are smooth.

SOFTWARE/OS VERSIONS
OS: Arch Linux
KDE Plasma Version: 6.1.1
KDE Frameworks Version: 6.3.0
Qt Version: 6.7.2

ADDITIONAL INFORMATION
Occurs on other distros that I have tried on USB.

Does not occur with scaling at 100%

Does not occur in X11 with or without fractional scaling.

If another window is in front of Firefox (FF is not in focus) the animations are smooth as expected.

Does not occur if FF is windowed / not maximised

If you set FF to work under Xwayland instead, the bug does not occur.

Comment 1 kreds 2024-07-02 01:51:20 UTC

I'd just like to add that at 100% scaling, so fractional scaling disabled, some animations have dropped frames while FF is in focus and maximised. For instance, the opening animation for dolphin has dropped frames but the closing animation is smooth.

Another weird thing I noticed with 100% scaling was when you have FF in focus+maximised and have a video iframe on the active tab like the homepage video of a youtube channel, doesn't matter if the video is actively playing or not, the desktop has dropped frames when switching virtual desktops via keyboard shortcuts. Specifically when going from another virtual desktop back to the desktop with FF in focus. If you switch desktops fast enough, it seems like only the first animation back to the desktop with FF lags and the rest are smooth. However, if you switch desktops with a 3 second-ish delay, then each animation going back to the desktop with FF has dropped frames.

Comment 2 Zamundaaa 2025-10-17 12:06:40 UTC

Is this on an integrated GPU?
Unfortunately Firefox doesn't properly support fractional scaling and thus renders at a higher resolution than native. As GPU drivers don't do proper prioritization of GPU tasks, it can in some cases simply take away the rendering power KWin needs to render animations smoothly.

Comment 3 Bug Janitor Service 2025-11-01 03:47:57 UTC

🐛🧹 ⚠️ This bug has been in NEEDSINFO status with no change for at least 15 days. Please provide the requested information, then set the bug status to REPORTED. If there is no change for at least 30 days, it will be automatically closed as RESOLVED WORKSFORME.

For more information about our bug triaging procedures, please read https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging.

Thank you for helping us make KDE software even better for everyone!

Comment 4 Bug Janitor Service 2025-11-16 03:48:21 UTC

🐛🧹 This bug has been in NEEDSINFO status with no change for at least 30 days. Closing as RESOLVED WORKSFORME.