Bug 420754

Summary: Non-Plasma Notifications flicker when fading out with KWin as the window manager in Xubuntu
Product: [Plasma] kwin Reporter: Ruslan Kabatsayev <b7.10110111>
Component: compositingAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED UNMAINTAINED    
Severity: minor CC: nate
Priority: NOR    
Version: 5.16.5   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed In:
Sentry Crash Report:

Description Ruslan Kabatsayev 2020-04-29 14:35:25 UTC 
SUMMARY
When a desktop notification fades out after being shown for several seconds, the fadeout animation flickers. I've also seen this happen with other kinds of windows, not only notifications.
A screencast can be seen here: https://youtu.be/l1xR3aAy0Uw . It was taken by recordmydesktop.

STEPS TO REPRODUCE
1. This bug is hard to catch, but usually it appears after multiple cycles of suspend/resume. So, try suspending and resuming the system with KWin compositing turned on.
2. Run
    notify-send Test 'Hello world'
3. Wait until the notification displayed begins to fade out

OBSERVED RESULT
The fadeout animation flickers. If compositing is turned off and back on again, the flicker disappears.

EXPECTED RESULT
The fadeout animation should be smooth, with notification's transparency changing monotonically in time.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Xubuntu 19.10
KDE Plasma Version: (Plasma shell not running)
KDE Frameworks Version: 5.62.0
Qt Version: 5.12.4

ADDITIONAL INFORMATION
This particular instance was seen on Intel UHD Graphics 620 (Whiskey Lake), but I've also had this on Kubuntu 18.04.3 with Intel HD Graphics 530 (rev 06), and on some systems with Nvidia GeForce GTX 750Ti and GTX 460.

This has been happening for many years (since at least 2014) with ever-upgrading Linux distribution versions on many machines I've been using. So, although the problem is hard to trigger, it does happen once in a while (maybe several times a month), and I can do some inspection of internal state of KWin when I get this flicker again—if you tell me what to look for.
Comment 1 Nate Graham 2020-05-01 13:31:39 UTC 
Those notifications are sent by something in xubuntu, I assume?
Comment 2 Ruslan Kabatsayev 2020-05-01 13:36:18 UTC 
(In reply to Nate Graham from comment #1)
> Those notifications are sent by something in xubuntu, I assume?

See reproduction step 2: they can be sent by notify-send.
On the other side, the service displaying the notification windows is xfce4-notifyd.
Comment 3 Ruslan Kabatsayev 2020-05-01 13:59:44 UTC 
Actually I wouldn't restrict the title of the report to Xubuntu+KWin: I've also seen this on Kubuntu with complete KDE-based workspace. It's just that I've been able to screencast the problem on the Xubuntu machine. Moreover, on the Kubuntu system I saw this with e.g. tooltips, which get the same fade in and out animation.
Comment 4 David Edmundson 2023-09-06 10:38:24 UTC 
This bug was reported against an outdated version of KWin. We have made many changes since the. 
If the issue persists in newer versions can you reopen the bug report updating the version number.