Bug 505427

Summary:	Cursor surfaces don't get fractional scale events
Product:	[Plasma] kwin	Reporter:	pbs3141
Component:	wayland-generic	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	CONFIRMED ---
Severity:	normal	CC:	nate, xaver.hugl
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description pbs3141 2025-06-10 10:57:44 UTC

SUMMARY

Under KWin + wayland, GTK4's cursors demo has incorrectly scaled cursors.

STEPS TO REPRODUCE

1. Run gtk4-demo under KWin + wayland
2. Select the Cursors demo
3. In the third row (named "gtk-logo"), place the mouse over the third triangle (with hover-text "A callback cursor for the GTK logo").
4. Observe the cursor.
5. Do steps 1-4 at scale 100% and 200%.

OBSERVED RESULT

When the scale is increased from 100% to 200%, the cursor increases in size by a factor of 2 (correct), but it is blurry.

EXPECTED RESULT

It should be sharp.

SOFTWARE/OS VERSIONS

KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.12.0
Qt Version: 6.9.0
Graphics Platform: Wayland

ADDITIONAL INFORMATION

See https://gitlab.gnome.org/GNOME/gtk/-/issues/7587 for some analysis on why this is believed to be a kwin bug.

Note that this issue also happens on X11, but there it's a GTK bug.

Comment 1 Nate Graham 2025-06-10 15:26:12 UTC

From the GTK bug report:

> Sounds like a kwin issue, then. We rely on pointer_surface_fractional_scale_preferred_scale_cb to get
> information about the desired scale for cursors. If kwin doesn't send any, it evidently prefers cursors
> of scale 1.

Comment 2 Nate Graham 2025-06-10 15:41:02 UTC

Can confirm.