https://bugs.kde.org/show_bug.cgi?id=459733
Bug ID: 459733
Summary: Kwin applies integer scaling instead of fractional
when calculating output boundaries for wl_surface
enter and leave events
Classification: Plasma
Product: kwin
Version: 5.25.5
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: m...@bolhuis.dev
Target Milestone: ---
SUMMARY
A wl_surface will receive enter and leave events based on a region that is the
output's physical resolution divided by the integer scaling factor, not the
fractional scaling factor.
For example, for a fractional scale of 1.25 the wl_output scale used is 2,
which means that for an output of 2560x1440 physical pixels the region that
triggers surface enter and leave events is 1280x720, anchored at the top left.
Instead the bounds should be calculated based on the physical size divided by
the fractional scale.
STEPS TO REPRODUCE
1. Configure a 2560x1440 physical pixel output to use 125% fractional scaling.
2. Create a small window (idealy less than
3. Log wl_surface.{enter,leave} events of the window
4. Place the window at the top left corner of the output
5. Drag the window down, or horizontally and observe surface events
OBSERVED RESULT
Once the the entire surface is past 1280 logical pixels in the x axis or 720 in
the y the surface receives a leave event.
EXPECTED RESULT
The surface should receive a leave event once it fully passes 2048 logical
pixels in the x and 1152 in the y.
NOTES
The bug applies equally for different output resolutions and fractional scaling
factors, not just the example values I've used above. The bug does not appear
when outputs use integer scaling.
SOFTWARE/OS VERSIONS
Linux: Arch
KDE Plasma Version: 5.25.5
KDE Frameworks Version: 5.98.0
Qt Version: 5.15.6
NVIDIA Driver: 515.76
Wayland Version: 1.21
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