Bug 499881

Summary:	Mouse scrolling too fast and inconsistent
Product:	[Plasma] kwin	Reporter:	fbleichrodt
Component:	libinput	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	CLOSED INTENTIONAL
Severity:	normal	CC:	kde, nate
Priority:	NOR
Version First Reported In:	6.2.5
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description fbleichrodt 2025-02-12 14:06:51 UTC

SUMMARY
The mouse wheel scrolls a lot further per click compared to gnome with wayland (around 5 lines vs 3 lines). Qt apps like dolphin do seem to scroll the correct amount, but not in Firefox of Chrome. When on gnome, all apps scroll a similar amount. Reducing the scoll speed makes the scroll amount good for chrome, but way too slow for qt apps like dolphin. This is inconsistent behavior. Also, my  two mouses scroll a different amount for 1 click of the mouse wheel.

STEPS TO REPRODUCE
1. Scroll in chrome, scroll in dolphin.

OBSERVED RESULT
Scroll amount is inconsistent, too much.

EXPECTED RESULT
Scroll behavior should be exactly the same as in gnome 3 with wayland (since both use libinput) for any app independent of the framework used, qt/gtk etc.

SOFTWARE/OS VERSIONS

Linux/KDE Plasma:  Arch linux
KDE Plasma Version: 6.2


ADDITIONAL INFORMATION

Comment 1 fbleichrodt 2025-02-14 20:12:07 UTC

I noticed the scroll amount for firefox is now the same. There is only a fast difference between scrolling in Chrome with kde plasma compared to Chrome on gnome.

Comment 2 Nate Graham 2025-02-18 23:33:45 UTC

> but not in Firefox of Chrome
We have no ability to control how non-KDE apps react to scrolling.

> When on gnome, all apps scroll a similar amount
This will be coincidence, the result of only using GTK apps or apps whose toolkits happened to, by chance or design) manually synchronize their scrolling speeds to one another.

> Also, my  two mouses scroll a different amount for 1 click of the mouse wheel.
This will be due to a hardware difference in your mice.

> Scroll behavior should be exactly the same as in gnome 3 with wayland (since both use libinput)
> for any app independent of the framework used, qt/gtk etc.
Unfortunately this goal is fundamentally impossible; it's up to each toolkit how it reacts to scroll events from Libinput. Libinput can't control how much they decide to scroll in response to the events it sends to them through the compositor. And toolkits (and even apps) can also adjust their scroll behavior based on the environment they detect, whether the app is being run as a Native Wayland app or through XWayland, etc.

Basically, it's impossible, sorry. :( Just a mostly unavoidable side effect of a heterogenous environment.