Blurry qt5 app in Plasma 6 wayland


I have installed Open Suse Tumbleweed with KDE plasma 6 on my pc. Previously I always had installed Tumbleweed, but the system had not yet updated to plasma 6. As before, I select the options scale by the system for legacy X11 apps (from display and monitor settings) because I have a two screen configuration with mixed dpi. Some applications that before (with plasma 5 wayland) were scaled properly (without blurriness) like LibreOffice and TeXstudio are now, with plasma 6, blurry (in the 2x scaling monitor). I noticed that such applications use QT5. Is this normal?


When you use “Scaled by the system” for “Legacy applications (X11)” then X11 applications that need to be scaled will look blurry - this is explained in the system settings application where you enabled that setting:


If you see a blurry application, it means that its an X11 application that was not built with Wayland support. Qt 5 does support Wayland so the problem is likely that the application was built for an older version of the operating system that did not have Wayland support (which seems weird - I’m pretty sure Tumbleweed had Wayland support for quite a few years now).

Qt 5 applications should also know how to scale themselves well - it was a problem with GTK until very recently, but Qt apps should handle scaling themselves just fine and should behave well if you set the “Legacy Applications (X11)” setting to let applications scale themselves.

Thanks for your reply.
I already know the functionality of Legacy application(x11) options in system settings. The strange things is that qt5 apps (like TeXStudio or LibreOffice) that were scaled correctly (without blurriness) in tumbleweed with plasma 5 wayland with the option Scaled by the system selected are now blurry with plasma 6 (always with the same config: tumbleweed wayland with the option Scaled by the system selected)

That does not sound reasonable - “scale by system” by definition will cause blurriness. The only reason that applications in one case are scaled correctly and in another case they are blurry is because they switched from Wayland rendering to X11 rendering.

Can you verify that the applications under Plasma 5, that are scaled there without blurriness are running as X11? I believe the answer to that is “no”, but please verify.

If that is the case then we need to ask ourselves why do applications that should support Wayland are running using X11 on Plasma 6 - Qt should be able to easily detect the the Wayland compositor.

BTW - on my system (Neon testing) the Qt5 LO interface doesn’t even load - it current detects Wayland and then fails because of internal compatibility issues between the Qt version compiled into LibreOffice and the version installed, and I can only use the GTK interface that is running under X11 (supposedly the GTK theme should support Wayland but that is not happening for me).

The only reason that applications in one case are scaled correctly and in another case they are blurry is because they switched from Wayland rendering to X11 rendering.

I agree with you: with the command xwininfo I verified that in my actual configuration (Plasma 6) the blurry apps (TeXstudio and LibreOffice) are running in Xwayland instead of wayland.

I apologize if I caused confusion in the previous message.

If I try to open TeXstudio or LibreOffice from the command line the following message is printed:

qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""


Can you check if any of the answers in this Stack Overflow question are helpful?

I solved the problem by installing the package


thanks for your help

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BTW - on my system, KDE Neon, I need to set the environment variable SAL_USE_VCLPLUGIN=qt5 to force LibreOffice to use the Qt plugin, and with that - and assuming the Qt5 Wayland plugin is also installed - LibreOffice runs on Wayland: