Bug 489422

Summary:	KDE Plasma's touchscreen "automatic" target screen settings redirects touch to the other monitor
Product:	[Plasma] kwin	Reporter:	Yorimirus <misawalach00>
Component:	input	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED FIXED
Severity:	normal	CC:	nate, xaver.hugl
Priority:	NOR
Version First Reported In:	6.1.1
Target Milestone:	---
Platform:	openSUSE
OS:	Linux
Latest Commit:	https://invent.kde.org/plasma/kwin/-/commit/19a00948b1a6768eaa508ee93d8773f9584f169f	Version Fixed/Implemented In:	6.4.5
Sentry Crash Report:

Description Yorimirus 2024-06-29 09:09:16 UTC

SUMMARY

I have a portable monitor, 1920x1080@60Hz, connected to my laptop via USB-C. It supports touch input. However, when I connect this monitor to my laptop, the touch input from that monitor is redirected to my built-in screen for some reason. Therefore, every time I connect this monitor, I need to go to the settings and change it to the external display.

STEPS TO REPRODUCE
1. Connect an external monitor with touch support
2. Make sure that in system settings > touch screen > target display is set to "automatic"

OBSERVED RESULT

Wherever I press with my finger on the external screen, instead of that touch input being registered on the external screen, it's instead registered in my built-in screen.

EXPECTED RESULT

Touch input should happen on the external screen. Because that's the screen with touch support.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: openSUSE Tumbleweed
(available in About System)
KDE Plasma Version: 6.1.1
KDE Frameworks Version: 6.3.0
Qt Version: 6.7.2

ADDITIONAL INFORMATION

I don't think it's important, but the screen is a VERBATIM PMT-15. In the touch settings, the device is detected as "Silicon Integrated System Co. SiS HID Touch Controller". When I change the setting to "Verbatim MT15/demoset-1 - (0,0 1536x864)", then touch works like it should with no bugs that I am currently aware of. 
I am not sure why it says the resolution is 1536x864. The screen is 1920x1080. May be caused by the 200% scaling on the built-in screen.

Comment 1 Zamundaaa 2025-10-14 12:47:06 UTC

The setting should be remembered properly in Plasma 6.4.5, it was saved using an unreliable display identifier before.

The "automatic" mode could still be improved, but as it's lacking any actual information about the touchscreen<->display association, it's unfortunately merely heuristics that will just sometimes be wrong.