https://bugs.kde.org/show_bug.cgi?id=528179
Bug ID: 528179
Summary: KWin 6.8.2: blinking-line artifacts on cursor-shape
changes with NVIDIA rendering and Intel eDP scanout
Classification: Plasma
Product: kwin
Version First 6.8.2
Reported In:
Platform: Gentoo Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: platform-drm
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
Created attachment 197936
--> https://bugs.kde.org/attachment.cgi?id=197936&action=edit
KWin support details and display configuration — KWIN_FORCE_SW_CURSOR=1 working
session
DESCRIPTION
The cursor briefly shows blinking-line artifacts when its icon changes while
hovering over links, buttons, or text. It happens across the desktop and
multiple applications while moving the pointer.
Setup: MSI GS76 Stealth, MUX-less laptop. NVIDIA RTX 3070 Laptop GPU renders
the desktop; Intel Tiger Lake-H UHD/i915 drives the internal 1920x1080 panel at
360 Hz, scale 1. No external display. KWIN_DRM_DEVICES is NVIDIA-first:
KWIN_DRM_DEVICES=/dev/dri/by-gpu/nvidia:/dev/dri/by-gpu/intel
These are local udev aliases for the NVIDIA and Intel DRM devices respectively.
STEPS TO REPRODUCE
1. Start a Plasma Wayland session in the above NVIDIA-render / Intel-scanout
configuration, with KWIN_FORCE_SW_CURSOR unset.
2. Move the pointer across controls or text that cause the cursor image to
change.
3. Observe the brief blinking-line artifacts during cursor-shape transitions.
OBSERVED RESULT
Cursor-shape changes cause brief blinking-line artifacts. The issue reproduces
with both Catppuccin Mocha Mauve and stock Breeze cursors, at cursor size 24.
EXPECTED RESULT
Cursor images change cleanly, without corruption or blinking lines.
TESTS AND WORKAROUND
- Switching from Catppuccin to Breeze did not remove the artifacts.
- Enabling desktop zoom at 1.2x stopped the artifacts. DRM debug state showed
the Intel hardware cursor plane disabled during this test (cursor A:
crtc=(null), fb=0).
- Returning zoom to 1x restored the hardware cursor plane and the artifacts
returned.
- Setting KWIN_FORCE_SW_CURSOR=1, then logging out and back in, eliminated the
artifacts at normal zoom. KWin supportInformation confirms that the new session
has this variable set. The same hover transitions now work cleanly.
SOFTWARE/OS VERSIONS
Operating System: Gentoo Linux 2.18
KWin: 6.8.2 (Gentoo package kwin-6.8.2-r1)
KDE Plasma: 6.8.2
KDE Frameworks: 6.31.0
Qt: 6.11.3
Kernel: 7.2.11-zen1-gentoo-dist (64-bit)
Graphics Platform: Wayland, DRM atomic modesetting on both GPUs
Compositing: OpenGL ES / EGL; renderer NVIDIA GeForce RTX 3070 Laptop GPU
NVIDIA driver: 615.78.08, open kernel module
Intel driver: i915; Mesa 26.2.6
libdrm: 2.4.134
ADDITIONAL INFORMATION
The regression window and exact compositor/driver cause are not established.
The tests above identify a working cursor-compositing workaround; they do not
establish the underlying fault.
My earlier bug 527544 is fixed on this setup; the old black-wallpaper /
no-repaint problem is not the symptom being reported here. Bug 527163 also
mentioned cursor corruption on Intel-connected outputs, but I have not
established whether this is the same remaining issue.
Attached diagnostic excerpts from supportInformation and the display
configuration were captured after enabling the workaround, in the working
session with KWIN_FORCE_SW_CURSOR=1. No supportInformation dump from the
earlier failing session was preserved.
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