Bug 386725

Summary:	Two finger scrolling needs three fingers
Product:	[Plasma] kwin	Reporter:	sgat_bugs
Component:	libinput	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	nate
Priority:	NOR	Flags:	mgraesslin: Wayland+ mgraesslin: X11-
Version First Reported In:	5.11.3
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Screenshot of KWin debug console

Description sgat_bugs 2017-11-10 22:02:50 UTC

Hello.
I have installed Plasma 5.11.3 packages from Kubuntu backports PPA over Kubuntu 17.10. In a wayland session the two finger scrolling needs three fingers to work properly on my Lenovo Laptop. In a X11-session the two finger scrolling works properly.
Best regards

Comment 1 Martin Flöser 2017-11-11 07:35:10 UTC

In an X11 session KWin is not responsible for the touchscreen device configuration. Only on Wayland KWin is responsible.

Comment 2 sgat_bugs 2017-11-11 13:38:30 UTC

You have closed the bug, but let me explain another time: The function "TWO finger scrolling" behaves differently in Wayland and X11.

X11: In the X11-session the function behaves according to it's specification: you need only TWO fingers to scroll.

Wayland: If you need THREE fingers to scroll and the function is called TWO finger scrolling, either the function has the wrong name (rename it to THREE finger scrolling) or the function does not behave according to it's specification.

If KWin is responsible on Wayland for the touchscreen device configuration, it is in my point of view a bug of KWin.

Comment 3 Martin Flöser 2017-11-11 15:32:15 UTC

Sorry I misread the bug report. I only saw X11 session and didn't read properly.

Comment 4 Martin Flöser 2017-11-11 18:07:19 UTC

Please open KRunner (Alt+Space) and enter:
KWin

It will offer to "Open KWin debug console". Please do that. A window will open in the top left corner and it has an "Input Devices" tab. Navigate to that, find your touchpad and expand it. It will list all the options available on the touchpad device and how they are configured.

I'm mostly interested in:
supportsScrollTwoFinger and scrollTwoFinger. Both should be true.

Comment 5 sgat_bugs 2017-11-11 21:53:38 UTC

Created attachment 108800 [details]
Screenshot of KWin debug console

input device: SynPS/2 Synaptics TouchPad

supportsScrollTwoFinger: true
scrollTwoFinger: true

Comment 6 Martin Flöser 2017-11-12 07:25:13 UTC

I fear it's a bug in the underlying libinput library. We don't do anything special except telling libinput to activate it. That code on our side works. E.g. I'm also using two finger scrolling and it works.

Comment 7 sgat_bugs 2017-11-12 21:13:21 UTC

I have investigated in the meantime that my X11 session still uses the synaptics input driver rather than libinput. It seems that some quirks for my touchpad model needs to be ported from synaptics to libinput. Thank you though for investing time in this issue.