Bug 417566

Summary:	Bouncing when changing virtual desktop through touchpad scroll
Product:	[Plasma] plasmashell	Reporter:	Guo Yunhe <i>
Component:	Containment	Assignee:	Marco Martin <notmart>
Status:	RESOLVED DUPLICATE
Severity:	major	CC:	bugseforuns, kde, nate, plasma-bugs
Priority:	VHI	Keywords:	regression
Version:	5.18.0
Target Milestone:	1.0
Platform:	openSUSE
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	desktop jumping when scroll with touchpad

Description Guo Yunhe 2020-02-13 13:55:46 UTC

SUMMARY


STEPS TO REPRODUCE
1. Close all app windows
2. Use touchpad (two finger scroll) to switch virtual desktop
3. Observe the transition

OBSERVED RESULT
The desktop is jumping, check the video

EXPECTED RESULT
The desktop should move smoothly

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20200211
KDE Plasma Version: 5.18.0
KDE Frameworks Version: 5.66.0
Qt Version: 5.14.1
Kernel Version: 5.5.2-1-default
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 31.1 GiB


ADDITIONAL INFORMATION

Comment 1 Guo Yunhe 2020-02-13 13:59:27 UTC

Created attachment 125951 [details]
desktop jumping when scroll with touchpad

Comment 2 Nate Graham 2020-02-15 22:55:33 UTC

Can reproduce. This makes switching using a touchpad scroll almost impossible and very frustrating.

Comment 3 David Edmundson 2020-03-04 23:12:05 UTC

Investigated. We haven't changed anything our side. 

Scrolling momentum is being faked at a lower level. 
angleDelta and pixelDelta keep being sent after a physical scroll finishes which adds up and goes psycho.

We don't have QWheelEvent::phase() data which would be ideal for detecting these fake events.

At best, I can bodge it by checking for pixelDelta and setting a different target to trigger the action, but it's not a proper fix and that could break setups without the fake scrolls. Which means I'm stuck.

Comment 4 Nate Graham 2020-03-04 23:14:24 UTC

The Synaptics touchpad drivers can send fake scroll events, but Libinput deliberately does not, delegating that to the UI toolkit. Yunhe, which drivers were you using? I was able to reproduce this using Libinput, which means the culprit would be somewhere in Qt.

Comment 5 Guo Yunhe 2020-03-05 08:28:22 UTC

Hi Nate, I am using libinput.

Comment 6 Vlad Zahorodnii 2020-03-10 12:54:41 UTC

I'm able to reproduce this bug even with a regular mouse. It seems like the switch desktop action is invoked per each wheel tick, which can be a lot! 

Either way, this bug doesn't belong here.

Comment 7 Guo Yunhe 2020-03-10 12:59:37 UTC

I can also reproduce it with Thinkpad track point, which is similar to a mouse wheel without ticks. Maybe it should detect wheel scroll distance instead of number of ticks.

Comment 8 Nate Graham 2020-03-10 14:23:13 UTC

> Either way, this bug doesn't belong here.
Where does it belong? Plasma? Qt?

Comment 9 Vlad Zahorodnii 2020-03-10 14:58:04 UTC

plasmashell

Comment 10 Nate Graham 2020-06-23 16:11:53 UTC

Exact same symptoms and workaround as Bug 419867; marking as a duplicate.

*** This bug has been marked as a duplicate of bug 419867 ***

Comment 11 Nate Graham 2022-12-14 22:24:51 UTC


*** This bug has been marked as a duplicate of bug 419878 ***