SUMMARY After enabling "Blur titlebars that have transparency" in Klassy Window Decoration settings, (with Blur effect in System Settings enabled), full screen window can no longer trigger direct scanout. STEPS TO REPRODUCE 1. Enable "Show Compositing" in System Settings > Windows Management > Desktop Effects 2. Also enable the "Blur" effect 3. Install Klassy[1] and enable it in Window Decorations 4. Open Klassy's setting, Open Titlebar tab > Titlebar Opacity 5. Set both transparency to 80%, and check "Blur titlebars that have transparency" below, click apply 6. Full screen a window (MPV or F11 in browsers) [1] https://github.com/paulmcauley/klassy/ OBSERVED RESULT The compositing indicator still displays EXPECTED RESULT The compositing indicator should disappear. SOFTWARE/OS VERSIONS Operating System: Arch Linux KDE Plasma Version: 6.4.0 KDE Frameworks Version: 6.15.0 Qt Version: 6.9.1 Kernel Version: 6.15.2-arch1-1 (64-bit) Graphics Platform: Wayland Processors: 16 × AMD Ryzen 7 PRO 6850HS with Radeon Graphics Memory: 16 GiB of RAM (14.9 GiB usable) Graphics Processor: AMD Radeon Graphics Manufacturer: HP Product Name: HP EliteBook 845 14 inch G9 Notebook PC ADDITIONAL INFORMATION I am not quite sure whether this is in kwin or klassy, but blur effect in background window probably should not prevent direct scanout? Also, the problem does not go away by simply switching back to Breeze decoration. I have to disable and re-enable Blur effect to make compositing indicator to disappear for full screen window.
Created attachment 182480 [details] Blurred bar stretched out behind Breeze's title bar I played with window decorations a bit, switching between Breeze and Klassy, and this blurred background stretched out behind title bar after switching from Klassy (with blurred titlebar) to Breeze. The blurred bar moves and resizes with the window, and its color changes according to contents behind, just like a working blurred titlebar. Not sure if it is related to preventing direct scanout, but it also disappears after turning off blur effect.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/7806
Git commit b5a1a61970589725e7688f0cbfbdd2f785d5572b by Vlad Zahorodnii. Committed on 23/06/2025 at 14:45. Pushed by vladz into branch 'master'. plugins/blur: Update blur region when decoration is destroyed Otherwise the blur effect will keep the ItemEffect around, which will block direct scanout. M +4 -1 src/plugins/blur/blur.cpp https://invent.kde.org/plasma/kwin/-/commit/b5a1a61970589725e7688f0cbfbdd2f785d5572b
I don't think this is fixed in 6.4.1? I've updated to 6.4.1 on Arch Linux, but the bug still appears.
Git commit d180b9dacbe4728dd31db7f1671929de2f5fa895 by Vlad Zahorodnii. Committed on 28/07/2025 at 11:24. Pushed by vladz into branch 'master'. plugins/blur: Update blur region when decoration is destroyed Otherwise the blur effect will keep the ItemEffect around, which will block direct scanout. (cherry picked from commit b5a1a61970589725e7688f0cbfbdd2f785d5572b) M +4 -1 src/plugins/blur/blur.cpp https://invent.kde.org/plasma/kwin-x11/-/commit/d180b9dacbe4728dd31db7f1671929de2f5fa895