https://bugs.kde.org/show_bug.cgi?id=470497
Bug ID: 470497
Summary: Compositor-provided V-Sync is active on fullscreen
applications even when turned off in the settings
Classification: Plasma
Product: kwin
Version: 5.27.5
Platform: unspecified
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: apri...@posteo.net
Target Milestone: ---
Created attachment 159376
--> https://bugs.kde.org/attachment.cgi?id=159376&action=edit
Compositor option to disable V-Sync in fullscreen applications
KWin as a Wayland compositor provides V-Sync over all screen content to prevent
tearing. As high performance graphics applications like video games often
provide their own V-Sync implementation the compositor-provided V-Sync should
be disabled to avoid two V-Sync operations in a row and to give the application
the option to disable V-Sync alltogether to favor latency over image quality.
To achieve this behavior KWin has a checkbox in the System Settings under
"Display and Monitor -> Compositor" called "Reduce latency by allowing screen
tearing artifacts in fullscreen applications", so basically "Disable compositor
V-Sync in fullscreen applications". Unfortunately this checkbox does nothing,
as Nate Graham looked up in the code. Therefore currently applications in KWin
Wayland are not able to run without forced V-Sync, which they should be able
to.
STEPS TO REPRODUCE
1. Go to the system settings "Display and Monitor -> Compositor" and test with
the activated and deactivated check box "Reduce latency by allowing screen
tearing artifacts in fullscreen applications"
2. Open different fullscreen applications which do not have internal V-Sync
like "glxgears -fullscreen"
OBSERVED RESULT
I can not get fullscreen applications to tear, suggesting that KWin forces
V-Sync itself, even if it should not.
EXPECTED RESULT
The applications should tear and KWin should not apply V-Sync leaving them the
option to figure it out themselves.
SOFTWARE/OS VERSIONS
Linux: 6.3.4-arch1-1 (64-bit)
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9
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