Bug 503747

Summary:	Janky middle mouse scroll functionality
Product:	[Plasma] kwin	Reporter:	honkanen.ap
Component:	libinput	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	john.kizer, nate
Priority:	NOR
Version First Reported In:	6.3.4
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
URL:	https://gitlab.freedesktop.org/libinput/libinput/-/issues/1049
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description honkanen.ap 2025-05-04 11:46:13 UTC

SUMMARY
Middle mouse scroll has overall a janky functionality which is in some applications leads to unexpected behaviour. Particularly the slight delay between the button press and beginning of the scrolling causes a user to overexaggerate the mouse movement which leads to an uncontrolled amount of scrolling initially. In most programs the delay makes it feel that the middle mouse scrolling gets stuck.

SUGGESTION
To maintain the backwards compatible behaviour, add options to adjust the initial delay and perhaps the scroll speed to System settings 

STEPS TO REPRODUCE
1.  Check on "Press middle button and move mouse to scroll" under "System settings" > "Mouse & Touchpad"
2.  Press mouse middle button and scroll

OBSERVED RESULT
Middle mouse scrolling starts after a slight delay which is bothersome in most applications

EXPECTED RESULT
Scrolling starts smoothly after the button press

SOFTWARE/OS VERSIONS
Linux: Arch Linux w/ 6.14.4-arch1-2 kernel  
KDE Plasma Version: 6.3.4 
KDE Frameworks Version: 6.13.0
Qt Version:  6.9.0
Graphics Platform: Wayland

Comment 1 honkanen.ap 2025-05-04 13:00:16 UTC

To elaborate the suggestion for scroll speed further, I know that the current scroll speed option does affect the middle mouse scrolling as well. However, there should be separate speeds for the mouse wheel scrolling and the middle mouse scrolling.

Comment 2 John Kizer 2025-05-11 04:31:54 UTC

Hi - while Plasma exposes the setting to toggle middle mouse button scrolling functionality on or off, the functionality itself lives in the libinput driver - so changes in its behavior would have to be made there.

I'm no expert on that front, but I would suspect that what you're observing is a mouse-based version of this issue, reported by a touchpad user: https://gitlab.freedesktop.org/libinput/libinput/-/issues/1049

Thanks!