https://bugs.kde.org/show_bug.cgi?id=411877
Bug ID: 411877
Summary: Touchscreen input locked to first screen
Product: kwin
Version: 5.16.4
Platform: Gentoo Packages
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: input
Assignee: kwin-bugs-n...@kde.org
Reporter: lo...@kde.bt.alestan.publicvm.com
Target Milestone: ---
SUMMARY
kwin uses a size-based heuristic to map touchscreens (absolute pointing
devices) to their physical screen. This heuristic fails when the size of the
screen, as reported by xrandr or similar, doesn't match the size of the
pointing device, as reported by libinput. When the heuristic fails, the
pointing device is mapped to the first screen, regardless of the presence of a
different touch input device on the first screen, and with no way to change the
mapping.
STEPS TO REPRODUCE
1. To the first slot of a GPU, attach a normal monitor.
1. To the second slot of a GPU, attach a touchscreen monitor, which reports
inconsistent sizes between the screen and touch device, the Asus VT229H is one
such device, a Wacom Bamboo would be another.
2. Note that the input is mapped to the wrong (first) monitor.
3. Swap the monitor slots.
4. Note that the input is mapped to the correct (first) monitor.
OBSERVED RESULT
The touch input is always mapped to the first monitor, unless the first monitor
is hot-plugged, at which point it remains mapped to the correct monitor until
kwin restarts. Virtual display positioning does not matter.
EXPECTED RESULT
Some way to override the (failed) heuristic to manually map an absolute
positioning input device to an arbitrary section of the virtual display.
SOFTWARE/OS VERSIONS
Linux: gentoo 17.0/desktop/plasma
Kernel: 5.2.1
KDE Plasma Version: 5.16.4
KDE Frameworks Version: 5.16.4
Qt Version: 5.12
ADDITIONAL INFORMATION
Also tried it on an old touchscreen laptop, both the integrated screen and the
Asus map to the integrated screen. For laptop users, the workaround of
changing screen order is not possible.
A way to manually specify the mapping also would support non-screen absolute
positioning devices, like the Wacom bamboo, where there is no clear map between
the input device and a screen.
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