[Bug] Plasmazones being active prevents "direct scanout" mode for fullscreen or borderless fullscreen applications

[laundmo]

Description

With plasmazones enabled, direct scanout doesn't activate for fullscreen or borderless windowed but fullscreen applications.

Direct scanout is a mode where kwin directly passes through the swapchain image buffer of the fullscreen window to the display/hardware directly, without compositing. This reduces latency and improves performance.

Expected Behavior

I expected plasmazones to not cause direct scanout issues or disable whatever causes direct scanout issues when a window is fullscreen or a borderless window fills the entire screen.

Steps to Reproduce

1. Make sure plasmazones is running and working
2. Run qdbus org.kde.KWin /Effects org.kde.kwin.Effects.toggleEffect showcompositing
3. Now, every window should have a red border around it. This shows that the window is being composited.
4. Make sure you have mpv and ffmpeg installed.
5. Run mpv --no-config --fullscreen --vo=gpu-next --hwdec=auto-safe "av://lavfi:color=c=black:s=1920x1080:r=60:d=60" which plays a generated black video stream for 60 seconds, fullscreen.
6. Observe that the black fullscreen mpv player has the "showcompositing" red border
7. Open Plasmazones settings and in the top-right corner stop the daemon.
8. Observe that the black fullscreen mpv player does not have a red border anymore. This means direct scanout is working.

If at step 8. it still shows the red border, some other overlay application or setting is blocking direct scanout.

Heres what to check if direct scanout is not working even with plasmazones daemon disabled:

• There is no window rules applying translucency
• Plasma display settings:
  • Scale: 100%
  • Color profile: None
  • HDR disabled
  • Color accuracy: prefer efficiency
  • Brightness: control hardware brightness with DDC/CI and/or 100%
• Disable/turn off "Night Light"
• ensure KWIN_DRM_NO_DIRECT_SCANOUT=1 is NOT set.
• currently displaying/active Desktop Effects, known culprits:
  • Dim Inactive
  • Highlight Screen Edges and Hot Corners

report which cant be sent in the intended field: plasmazones-report-20261027-132232.tar.gz

PlasmaZones Version

cachyos/plasmazones 3.5.3-1

Display Server

Wayland

Desktop Environment

Plasma 6.8.1

Distribution

CachyOS

Support Report

This field in the template does not allow uploading files, and markdown is not supported.

Checklist

• I searched existing discussions and issues
• I can reproduce this with default settings

[fuddlesworth]

Thanks for the detailed report and the repro steps, they made this quick to track down.

PlasmaZones was the cause. The daemon keeps one transparent, full-screen overlay surface per monitor that the OSD, layout picker, zone overlay and snap assist all draw into. It stayed mapped on the overlay layer for as long as the daemon ran, so it sat above every window, fullscreen ones included. KWin only scans out a fullscreen window when nothing visible is stacked on top of it, so that idle overlay forced compositing on every monitor. That's why stopping the daemon fixed it.

The fix in #1170 takes the overlay down whenever nothing is showing on it, and puts it back when an OSD or overlay actually appears.

If you can build from source, I'd appreciate a check on your setup, since I could only verify it in a nested KWin session, which has no real display planes:

git clone https://github.com/fuddlesworth/PlasmaZones.git
cd PlasmaZones
git checkout fix/passive-shell-idle-unmap
cmake --preset release
cmake --build --preset release
sudo cmake --install build-release

Then restart the daemon (or log out and back in) and run your mpv + showcompositing steps again. The red border should disappear from the fullscreen video while the daemon is running. One more thing worth checking: whether it comes back as it should once an OSD has shown and faded, for example after switching layouts.

If building isn't convenient, the fix will be in the next release.

On borderless windowed games that fill the screen without being real fullscreen: with "Show border" on, PlasmaZones draws its border around them, and that also forces compositing. A rule with the "Exclude from decorations" action matching the game avoids it.

[laundmo]

Nice, i just got around to testing this, i've just been stopping the daemon while a game is starting till now... (mpv is only the easiest test setup)

I'm happy to report that it seems to work, with mpv and the game i initially noticed this with, Deadlock.

One thing about borderless windowed though: Couldn't plasmazones detect if a window is at the right position and size to exactly fill a monitor, and disable decorations while this is the case? In any case, thats more a nitpick, tho if this limitation stays, it should be documented somwhere people can find, imo. Well, besides in this discussion.

Thank you!

[fuddlesworth]

Fixed in 3.5.4 (#1170). The overlay is taken down once nothing is showing on it, so fullscreen windows can go straight to the display again. Thanks for testing it. The borderless windowed idea is a separate request, so feel free to open it as its own idea. Closing this, but reply here if you still see it on 3.5.4.