https://bugs.kde.org/show_bug.cgi?id=521764
Bug ID: 521764
Summary: rapid flashing and cut-off window geometry on a
secondary monitor only when it is configured in
portrait mode
Classification: Plasma
Product: kwin
Version First 6.7.0
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: multi-screen
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 193368
--> https://bugs.kde.org/attachment.cgi?id=193368&action=edit
Picture of multimonitor setup with my secondary monitor in portrait mode afer
pressing META+W (Present windows)
DESCRIPTION
After upgrading to Plasma 6.7.0, using the "Present Windows" effect (Meta+W)
causes severe rendering regressions on a multi-monitor configuration utilizing
mixed orientations and fractional scaling. Specifically, when a secondary
monitor is rotated into portrait mode, entering the Present Windows view causes
rapid, aggressive screen flashing/flickering and cleanly cuts off the window
geometry on that display.
This issue appears to be directly tied to the DRM Direct Scanout optimization
layer on AMD hardware under Wayland. Forcing the compositor to bypass direct
scanout completely eliminates the geometry clipping and flashing.
STEPS TO REPRODUCE
Set up a dual-monitor configuration with an AMD RX 580 GPU on Wayland.
Configure the primary display in landscape mode (2560x1440) and the
secondary display in portrait mode (1200x1600, 1.33x fractional scaling).
Open several application windows across both displays.
Trigger the "Present Windows" effect using Meta+W.
OBSERVED RESULT
The windows on the landscape monitor scale normally, but the secondary portrait
display experiences rapid buffer flashing/flickering. The window previews on
the portrait display are visually cut off, misaligned with the actual screen
geometry, and unusable until the effect is dismissed.
EXPECTED RESULT
The Present Windows effect should cleanly and smoothly tile open windows across
all displays simultaneously, respecting the vertical/horizontal boundaries and
scaling factors of mixed-orientation layouts without flickering.
SOFTWARE/OS VERSIONS
Operating System: CachyOS x86_64 (Kernel: Linux 7.0.12-1-cachyos)
KDE Plasma Version: 6.7.0
KDE Frameworks Version: 6.7.0
Qt Version: 6.7.0
Graphics Platform: Wayland
ADDITIONAL INFORMATION
Hardware: Intel Xeon E5-2673 v4 | AMD Radeon RX 580 Series
Monitor Setup: LG QHD (2560x1440 @ 144Hz, Landscape) + DELL 2007FP
(1200x1600 @ 60Hz, Portrait, 1.33x Scaling)
Workaround Identified: Adding KWIN_DRM_NO_DIRECT_SCANOUT=1 to
/etc/environment and restarting the session completely resolves the bug.
Present Windows functions flawlessly with this flag active, strongly pointing
to an issue with how scene-drm handles coordinate scaling calculations for
rotated buffers during direct scanout handoffs on Polaris/AMD open-source
drivers.
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