Bug 330812

Summary:	"Tearing" when scrolling a window that is covering a playing video
Product:	[Plasma] kwin	Reporter:	Michael Marley <michael>
Component:	compositing	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	REPORTED ---
Severity:	normal	CC:	andrew.crouthamel, kde.org
Priority:	NOR
Version:	4.11.6
Target Milestone:	---
Platform:	Kubuntu
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	Output of "qdbus org.kde.kwin /KWin supportInformation"

Description Michael Marley 2014-02-05 18:36:49 UTC

If I have a 30fps video file playing in an mplayer window and put it directly behind another window, when I start scrolling in the other window, the section of that window that covers up the mplayer window updates before the rest, causing a rectangular box of "tearing". This "tearing" goes away after one or two frames of animation, but it is definitely there.  Stopping and starting scrolling causes the "tearing" to show up again.

Reproducible: Always

Steps to Reproduce:
1. Play a 30fps video in an mplayer window (not fullscreen)
2. Place another window (such as Firefox) on top of the mplayer window
3. Scroll in the other window
Actual Results:  
When the scrolling first starts in the window on top, there is a "tearing" effect as the area of the top window that covers the mplayer window updates before the rest of the window.  After one or two frames, the "tearing" goes away.

Expected Results:  
No tearing should occur.

Comment 1 Michael Marley 2014-02-05 18:37:17 UTC

Created attachment 85009 [details]
Output of "qdbus org.kde.kwin /KWin supportInformation"

Comment 2 Michael Marley 2014-02-16 21:25:34 UTC

I have two new bits of information about this:

First, it doesn't have to be a 30fps video; the same thing happens with 60fps things like glxgears.

Second, it does appear to be caused by buffer age support.  If set KWIN_USE_BUFFER_AGE=0 and restart kwin, the "tearing" no longer occurs.

Comment 3 Andrew Crouthamel 2018-11-11 04:26:14 UTC

Dear Bug Submitter,

This bug has been stagnant for a long time. Could you help us out and re-test if the bug is valid in the latest version? I am setting the status to NEEDSINFO pending your response, please change the Status back to REPORTED when you respond.

Thank you for helping us make KDE software even better for everyone!

Comment 4 Michael Marley 2018-11-11 12:11:30 UTC

Yes, this still happens with Plasma 5.14.3 and KF5 5.52.

Comment 5 Andrew Crouthamel 2018-11-12 03:08:20 UTC

Thanks for the update!

Comment 6 kde.org 2021-11-07 10:10:59 UTC

There have recently been fixes for more smooth rendering. Can you still reproduce the problem with Plasma 5.23?

Comment 7 Michael Marley 2021-11-07 12:39:07 UTC

This does still happen, though it doesn't seem quite as bad as it used to be.  It is, in fact, noticeably better than Windows® in the same scenario now.

Comment 8 kde.org 2021-11-07 12:43:11 UTC

Thank you for reporting back. Have you tried changing the latency in Compositor system settings top see if that makes any difference? Is this on X11 and/or Wayland now?

Comment 9 Michael Marley 2021-11-07 13:24:21 UTC

I did some more in-depth testing and found that the problem only occurs on Xorg, not on Wayland (though using Wayland isn't possible for me right now due to another bug I am about to open).  I also tested the latency settings while running in Xorg and found that they didn't have any effect.

Comment 10 kde.org 2021-11-07 14:43:47 UTC

Thank you for your quick feedback. I'm not sure how much effort is still going in X11, as it's on it's way out. I'll leave the issue report open for now.