SUMMARY Enabling Chromium CSD produces blurry buttons (maximize, close, etc). STEPS TO REPRODUCE 1. Install Chromium 2. Launch Chromium 3. In Settings set it to use CSD 4. Check that decorations are for your current theme OBSERVED RESULT Decorations follow the current Plasma theme but buttons are very blurry. EXPECTED RESULT Decorations follow the current Plasma theme and buttons are correctly rendered. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: Arch Linux (available in About System) KDE Plasma Version: 5.20 KDE Frameworks Version: 5.78.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION
Sorry, I forgot to mention that you should set a scaling factor different than 100%.
I believe this might be do to fractional scaling, every other GTK app seems to be scaled at 1x or 2x, but the titlebar of Chromium is similar in size to other Qt apps (currently at 150%). I know GTK can't handle fractional scales and I assume the CSD is rendered using GTK but, anyway, shouldn't them be rendered at 2x and the downscaled? If that were the case they shouldn't be as blurry as they are, given the blurriness they seem to be just upscaled from a small version.
Chromium uses auto-generated .png files whereas most other other GTK CSD apps use auto-generated SVGs. I think this blurriness is due to the auto-generation in kde-gtk-config scaling the titlebar button icons to too small a size as in bug 426074.
This isn't in kwin's control