HiDPI: interface Auto scaling picks a too large factor on fractional Wayland (KDE Plasma 6.7)

[ed3e11]

This issue is unique.

• I have used the search tool and did not find an issue describing my bug.

Operating System

Linux

Architecture

x86_64

Package Type

deb

Version information

9.3.1-dev.0, git main, commit 16d1a01

Expected Behavior

With Interface scaling on Auto, the app matches the desktop fractional scale and looks normal sized.

Actual Behavior

On KDE Plasma 6 Wayland with fractional scaling (my display is 3072x1920 at 1.65x), Interface scaling set to Auto makes everything way too big. Setting Interface scaling to a fixed value fixes it completely and stays sharp (150% is right for my setup), so it looks like the Auto detection just overshoots on fractional scale factors.

I am fairly sure this is inherited from ONLYOFFICE, there are older reports there like ONLYOFFICE/DesktopEditors #393 and #217. Just wanted to note it for the fork too. Not urgent since the manual setting works, it is only a slightly rough first impression before you find that option.

Reproduction Steps

1. KDE Plasma 6 on Wayland with fractional display scaling (e.g. 1.65x).
2. Open the app with Interface scaling on Auto.
3. The UI renders much larger than the rest of the desktop.
4. Set Interface scaling to a fixed value (150% here) and restart. Now it is correct and sharp.

Additional information

Arch Linux, KDE Plasma 6.7 Wayland, built from source through the AUR euro-office-desktopeditors-git.

[pplupo]

Hi @ed3e11 ! Thank you for your report.
We are still working on wayland support on a separate branch. We are not done yet. However, I just tested with 1.65%. I could not see the issue.
I'm on CachyOS, KDE Plasma Version 6.7.2, I've tested it with multiple fractional scales (I myself use it 1.15%).

The thing is that this version "works" on wayland, but it doesn't support it fully yet. Although your report is super relevant, I think the fix is coming already.

And you are right, ONLYOFFICE has the same issue for the same reason. They are also still stuck on qt5, we have just moved to qt6. We are pulling ahead. :-)

Be patient, it's coming. :-) Once again, thank you for your report.

Fixed by #42

@rikled FYI