https://bugs.kde.org/show_bug.cgi?id=480684
Bug ID: 480684
Summary: Window restore via mouse-drag appears non-atomic due
to delayed resize
Classification: Plasma
Product: kwin
Version: 5.27.10
Platform: openSUSE
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: bugs.7n...@aleeas.com
Target Milestone: ---
Created attachment 165440
--> https://bugs.kde.org/attachment.cgi?id=165440&action=edit
Slow-motion screen recording
SUMMARY
When de-maximizing windows by dragging them with the mouse, the window-restore
effect is spread across multiple presentation frames: First, the window
"unsnaps" from the top of the screen, and it only shortly after that it resizes
to its original size.
In effect, it looks as if the window jumped around before restoring its actual
size. This is particularly noticeable with the wobbly windows effect, where the
window corners will be unevenly stretched at its corners.
I attached a slow-motion video to illustrate: Stepping through it frame by
frame you can see that 1. The window unsnaps (note the top-left corner being on
a different height than the top-right one), 2. The wobbliness calms down but
the window is still in maximum size, 3. The window resize kicks in, triggering
another wobble.
This might be a Wayland-specific issue.
STEPS TO REPRODUCE
(0. Test on Wayland)
1. Maximize a window
2. Drag the window from its title bar to restore its size
3. Closely observe the result, as this glitch happens within 2-3 presentation
frames
OBSERVED RESULT
The restore operation is non-atomic: The window unsnaps before being resized
EXPECTED RESULT
The window should start resizing in the same frame that its top-left corner
moves.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.27.10
KDE Plasma Version: 5.27.10
KDE Frameworks Version: 5.114.0
Qt Version: 5.15.12
ADDITIONAL INFORMATION
I'm also observing this glitch in a Parallels VM, where it can be prolonged by
continuously moving the mouse cursor. This will delay the window resize until
the cursor stops moving. Maybe this gives a hint on the nature of the issue?
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