SUMMARY I reported this to kitty, and the developer there said this is likely a compositor issue. I can help fix this if someone can point me to the right direction (I've contributed a bugfix to kwin a long time ago in the past!) https://github.com/kovidgoyal/kitty/issues/8429 STEPS TO REPRODUCE 1. Set fractional scaling to 1.25x (e.g. using kscreen-doctor output.DP-1.scale."1.25" ) 2. Resize the window so that the surface width, when multipled by the scaling factor, ends up .00, .50, or 0.75 3. notice the blurry fonts This is all in the github bug above, with screenshots and logs. I also put some debug statements in kwin (I think I have the right spot), and as far as I can tell, kwin and kitty both agree on the pixel-perfect size of the buffer. As a workaround, I've been setting the screen scale to 1.26 (which actually gets set as 1.2583333333333333), presumably so it's a lot less likely to run into whatever rounding error is causing this. OBSERVED RESULT Blurry fonts EXPECTED RESULT Not blurry fonts SOFTWARE/OS VERSIONS Operating System: Arch Linux KDE Plasma Version: 6.3.2 KDE Frameworks Version: 6.11.0 Qt Version: 6.8.2 Kernel Version: 6.13.5-arch1-1 (64-bit) Graphics Platform: Wayland Processors: 32 × AMD Ryzen 9 5950X 16-Core Processor Memory: 62.7 GiB of RAM Graphics Processor: NVIDIA GeForce RTX 4090 ADDITIONAL INFORMATION See the bug in: https://github.com/kovidgoyal/kitty/issues/8429
Created attachment 179281 [details] patch I used on kwin to match the the sizes This is the patch I used to check the sizes, kitty uses the wayland xdg_toplevel::configure message and multiplies the fractional scaling value (rounding up at 0.5 according to the spec), and that value matches the buffer size here, but I'm not sure if this is the value that's off by one or more pixels.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/7319
Turns out it was this the rounded corners plugin that causes this, weirdly: https://github.com/matinlotfali/KDE-Rounded-Corners/issues/149 I still think it is off by a pixel in certain (much rarer) cases though.