Bug 479952

Summary: Adjusting primary screen's scale factor and then plugging in a previously-attached secondary screen can results in gaps or overlaps between them
Product: [Plasma] kwin Reporter: Nate Graham <nate>
Component: multi-screenAssignee: KWin default assignee <kwin-bugs-null>
Status: CONFIRMED ---    
Severity: normal CC: a.samberg, fanzhuyifan, kde, mail, postix, sergio.callegari
Priority: NOR Keywords: multiscreen
Version First Reported In: master   
Target Milestone: ---   
Platform: Other   
OS: Linux   
See Also: https://bugs.kde.org/show_bug.cgi?id=506777
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description Nate Graham 2024-01-17 16:38:16 UTC 
Today's git master of Plasma 6 Wayland built form source on top of Fedora KDE 39.


STEPS TO REPRODUCE
1. Have two screens, and arrange them in the KScreen KCM horizontally so that they are touching
2. Unplug the screen on the right
3. Raise the scale factor of the screen on the left (e.g. from 200% to 225% in my case)
4. Plug in the second screen again


OBSERVED RESULT
There is now a gap between the screens and the cursor can't cross the gap from one screen to the other! The KCM displays a warning message about this, as though I somehow did it on purpose. :) 


EXPECTED RESULT
The screens keep touching on their common edge


ADDITIONAL INFORMATION
Does not happen if the secondary screen has never been connected before (or at least, if there are no pre-existing KScreen configs for it). It only happens if the prior KScreen config for the secondary screen is available for use. What happens is that the secondary screen's prior absolute position is retained, despite that absolute position no longer resulting in it touching the primary screen anymore.
Comment 1 Nate Graham 2024-03-01 20:32:04 UTC 
*** Bug 481946 has been marked as a duplicate of this bug. ***
Comment 2 fanzhuyifan 2024-03-19 18:10:01 UTC 
Probably an issue in kscreen/libkscreen rather than kwin. This could be a candidate for junior job.
Comment 3 fanzhuyifan 2024-03-30 17:32:56 UTC 
Conversely, if the screen's scale factor is lowered, plugging in a previously-attached secondary screen results in overlaps between the two screens.
Comment 4 fanzhuyifan 2024-03-30 18:11:51 UTC 
https://invent.kde.org/plasma/kwin/-/issues/217
Comment 5 Nate Graham 2024-06-12 18:50:08 UTC 
*** Bug 488422 has been marked as a duplicate of this bug. ***