Bug 505184

Summary: With fractional scaling on one screen, XWayland applications maximized on other screen can have 1px gap on top
Product: [Plasma] kwin Reporter: Robin Kertels <robin.kertels>
Component: coreAssignee: KWin default assignee <kwin-bugs-null>
Status: REPORTED ---    
Severity: normal CC: kde, nate
Priority: NOR Keywords: multiscreen
Version First Reported In: 6.3.5   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: Video showcasing the bug.

Description Robin Kertels 2025-06-03 20:32:09 UTC
Created attachment 182012 [details]
Video showcasing the bug.

# SUMMARY

I have 2 monitors.
Monitor 1 is a 32" 4k monitor with 125% scaling.
Monitor 2 is a 27" 1440p monitor with 100% scaling.

When I maximize an XWayland application on the secondary (27") screen, there's a 1px gap at the top. Clicking there unfocusses the maximized application because the click registers on the desktop.

I can reproduce this with Chromium and CLion (both XWayland) but Wayland applications (like the KDE settings or Konsole) don't seem to have this problem.

The attached video demonstrates the problem.

# STEPS TO REPRODUCE

1.  Maximize XWayland window on second screen
2. Move mouse to the very top
3. click

# OBSERVED RESULT

Window is unfocussed

# EXPECTED RESULT

Click should register with the window

 # SOFTWARE/OS VERSIONS

Linux/KDE Plasma: 6.3.5
Comment 1 David Edmundson 2025-06-04 06:21:16 UTC
Unfortunately this is expected at certain resolutions and scales. There isn't anything we can do about it with the current architecture. The X11 windows are run at 125% scale then resized to the 100% screen.

Choosing a slightly different scale on the first monitor would give you a workaround.
Comment 2 Robin Kertels 2025-06-04 07:26:43 UTC
Could the window at least get snapped to the top so the gap is at the bottom?

The current behavior is terrible for usability because I keep flicking up to hit the window bar and the click doesn't register. Having the gap on the bottom would be less problematic.
Comment 3 Robin Kertels 2025-06-05 17:59:48 UTC
See my question above.