https://bugs.kde.org/show_bug.cgi?id=523851
Bug ID: 523851
Summary: Tablet stylus events are routed to the surface under
the mouse pointer instead of the surface under the
stylus
Classification: Plasma
Product: kwin
Version First unspecified
Reported In:
Platform: Kubuntu
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: input
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
SUMMARY
On Wayland, stylus input is delivered to whichever surface the mouse
pointer currently sits over, not to the surface the stylus is actually
hovering. The tablet cursor visibly follows the stylus with no offset,
but tip-down events do not reach the window under it. Moving the
physical mouse pointer over the target window — without clicking —
immediately makes the stylus work.
This only affects applications that support the tablet protocol
(tablet_v2). Applications that do not receive emulated pointer events
instead, and behave correctly.
STEPS TO REPRODUCE
1. Open Krita and Kate side by side (two screens or one, both reproduce).
2. Leave the mouse pointer over the Kate window.
3. Activate Krita, either by clicking its titlebar or via a KWin window
shortcut, so it has keyboard focus.
4. Hover and press the stylus inside the Krita canvas.
OBSERVED RESULT
The tablet cursor tracks the stylus correctly over Krita, and hover
feedback works (tooltips appear). Tip-down does nothing: no strokes, no
button presses, no interaction of any kind. Krita has keyboard focus at
this point, so focus is not the deciding factor.
Moving the mouse pointer over the Krita window, without clicking,
immediately restores full stylus functionality.
EXPECTED RESULT
Stylus events should be delivered to the surface under the stylus,
independently of where the mouse pointer happens to be.
ADDITIONAL INFORMATION
The behaviour differs by application, which appears to isolate the cause:
Mouse over Kate, stylus on Krita -> does not work
Mouse over Kate, stylus on SAI (Wine) -> does not work
Mouse over Kate, stylus on Chrome -> works
Mouse over Krita, stylus on Kate -> works
Krita and SAI implement tablet support; Kate and Chrome do not and
receive emulated pointer events, which are delivered normally. This
suggests the tablet_v2 event path uses the pointer focus surface rather
than the tablet focus surface.
Things tried without effect:
- Focus policy set to "Focus follows mouse"
- Focus stealing prevention set to "None"
- KWin per-window activation shortcut (window is activated, stylus
still does nothing)
Workaround: binding the "Move Mouse to Focus" KWin shortcut to a tablet
pad button, which moves the pointer onto the active window.
Possibly related to Bug 505663, though the symptom there is cursor
position teleporting, which does not occur here.
SOFTWARE/OS VERSIONS
Operating System: Kubuntu 26.04
KDE Plasma Version: 6.6.5
KWin Version: 6.6.6
Graphics Platform: Wayland
Kernel Version: 7.0.0-29-generic
Graphics Processor: 1060 gtx
Tablet: Huion Kamvas 13 gen 3
OpenTabletDriver: last, Artist Mode
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