https://bugs.kde.org/show_bug.cgi?id=485409
Bug ID: 485409
Summary: Pointer escapes confinement when moving over surface
above the one it is confined to
Classification: Plasma
Product: kwin
Version: git master
Platform: openSUSE
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: input
Assignee: kwin-bugs-n...@kde.org
Reporter: aaronkirsc...@gmail.com
Target Milestone: ---
Created attachment 168408
--> https://bugs.kde.org/attachment.cgi?id=168408&action=edit
c program which creates a window with surface that can constrain the pointer by
pressing "l" or unconstrain by pressing "u". I edited this from a different bug
report by Mark Bolhuis (bug id=449620)
SUMMARY
The pointer can escape its confinement from a constrained window when moved
over another window's surface that is above the one it is confined to.
STEPS TO REPRODUCE
(With Wayland windows)
1. Run the provided C program to create a window.
2. Move another window partially over the window created by the program so
that it overlaps the window and crosses over the edge of the window.
3. Set the overlapping window to "Keep Above Others" using a KWin Window
Rule, so that it remains above the window created by the program.
4. Constrain the pointer to the window created by the program by pressing
"l" when the pointer is on the surface.
5. Move the pointer outside of the confined window surface by moving it
over the "Keep Above Others" window’s surface.
OBSERVED RESULT
(With Wayland windows)
The pointer, though still constrained when it returns to the original window,
can escape its confinement by passing over the window set to "Keep Above
Others."
EXPECTED RESULT
The pointer should remain confined within the original window’s boundaries
while it is constrained, regardless of its interaction with any overlapping
window above it.
SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20240410
KDE Plasma Version: 6.0.80
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.8.4-rc1-1-default (64-bit)
Graphics Platform: Wayland
ADDITIONAL INFORMATION
This issue presents differently depending on whether the surface the pointer is
confined to is managed by Wayland or XWayland.
Behavior Summary:
• In Wayland windows, the pointer can escape confinement by passing over
another window above it which extends beyond the confined window’s boundary.
• In XWayland windows, the pointer escapes confinement more readily; simply
passing over any part of a window surface above it (whether it extends beyond
the confined window’s boundary or not) breaks the confinement entirely.
Moreover, the cursor shape change from the confined window is retained when the
pointer is over other XWayland windows.
Wayland Window Confinement:
If the surface the pointer is confined to is a Wayland window, the pointer
remains confined to all visible edges of the window. However, it can escape
this confinement by moving over any surface that is positioned above the
confined surface and extends beyond its boundaries.
This behavior can be demonstrated with the provided program that creates a
Wayland window with pointer constraints by following the steps to reproduce.
XWayland Window Confinement:
For a window managed by XWayland and confined using XGrabPointer, the behavior
diverges significantly. Here, the pointer remains confined until it moves over
a surface that is above it.
Upon moving over this surface, regardless of whether it extends beyond the
confined surface's boundaries or not, the pointer constraint is completely
broken, allowing the pointer to freely cross the originally confined
boundaries.
When the pointer is over other XWayland windows, the cursor retains the shape
it had during the confinement. However, this effect does not persist when the
pointer moves over native Wayland windows, where the cursor shape reverts to
normal.
I have not included steps to reproduce with XWayland windows, but I can make a
sample program for that if it would help.
My use case is not very common: I'm trying to confine the pointer to a game
which is in windowed mode that has an overlay window on top of it. The overlay
is not injected into the game; it is running as a seperate process with its own
window which passes through input to the game’s window. Both the game and the
overlay are running through WINE and are XWayland windows.
I think there may be other use cases such as watching a video in a window set
to “Keep Above Others” above another window that the pointer is confined too.
The program I’ve included I got from a different bug report on KWin (id=449620
by Mark Bolhuis) and slightly edited it to only have constrain/unconstrain
functionality. To constrain the pointer, press the “l” key. To unconstrain,
press the “u” key.
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