https://bugs.kde.org/show_bug.cgi?id=526812
Bug ID: 526812
Summary: Keyboard-only portal sessions falsely advertise
touchscreen support
Classification: Plasma
Product: xdg-desktop-portal-kde
Version First 6.7.91
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 196951
--> https://bugs.kde.org/attachment.cgi?id=196951&action=edit
Standalone reproducer that opens a keyboard-only RemoteDesktop portal session,
prints Wayland seat capabilities before, during, and after the session, and
closes it on Enter. Sends no input events.
SUMMARY
Keyboard-only portal sessions falsely advertise touchscreen support
On KDE Plasma Wayland, starting a keyboard-only RemoteDesktop portal session
adds touch support to the Wayland seat on a laptop without a touchscreen.
Chromium/Electron then reports a coarse pointer and 10 touch points.
KDE's tablet mode is disabled.
STEPS TO REPRODUCE
Dependencies: Python 3, dbus-python, PyGObject, and wayland-info.
1. Run the attached standalone reproducer:
python3 keyboard-portal-repro.py
2. Approve the keyboard access request.
3. Leave the reproducer waiting for Enter.
4. In a native Wayland Chromium/Electron window, evaluate:
matchMedia('(any-pointer: coarse)').matches
navigator.maxTouchPoints
5. Press Enter in the reproducer to close the session.
6. Check the browser values again.
OBSERVED RESULT
The reproducer requests keyboard access with SelectDevices types=1. The portal
confirms granted device types=1.
The reproducer prints:
before: capabilities: pointer keyboard
Granted device types: 1
active: capabilities: pointer keyboard touch
closed: capabilities: pointer keyboard
Before the session opens, the same Electron window reports:
- any-pointer: coarse is false.
- navigator.maxTouchPoints is 0.
While the session is open:
- any-pointer: coarse is true.
- navigator.maxTouchPoints is 10.
After the session closes:
- any-pointer: coarse is false.
- navigator.maxTouchPoints is 0.
matchMedia('(pointer: fine)').matches remains true throughout.
EXPECTED RESULT
A keyboard-only portal session should not advertise touchscreen support or
change applications' touch detection.
SOFTWARE/OS VERSIONS
OS: Arch Linux
Graphics platform: Wayland
Running KWin version: 6.7.90
Installed xdg-desktop-portal-kde package: 6.7.91
Electron version: 43.7.9
Chromium version: 150.0.7871.250
Hardware: Laptop without a touchscreen
ADDITIONAL INFORMATION
The reproducer sends no input events. Starting the session is enough to trigger
the problem.
The portal creates a KWin fake-input device. FakeInputDevice::isTouch() always
returns true:
https://github.com/KDE/kwin/blob/v6.7.90/src/backends/fakeinput/fakeinputdevice.cpp
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