QT under wayland causes painter to fail

[jakob1379]

Describe the bug
the regular issues with Qt on wayland

To Reproduce

❯ python main/python/main.py 
Initialising RootPainter
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: linuxfb, minimal, offscreen, vnc, webgl, xcb.

Aborted (core dumped)

Additional context

root painter version: "0.2.27.0"
system info:

OS: NixOS 25.05 (Warbler) x86_64
Host: 20S1S8KN00 (ThinkPad T14 Gen 1)
Kernel: Linux 6.12.10
Uptime: 3 hours, 29 mins
Packages: 1397 (nix-system), 967 (nix-user)
Shell: bash 5.2.37
Display (PHL 346E2C): 3440x1440 @ 75 Hz in 34" [External]
DE: KDE Plasma
WM: KWin (Wayland)
WM Theme: Breeze
Theme: Breeze (Light) [Qt]
Icons: breeze [Qt], breeze [GTK2/3/4]
Font: Noto Sans (10pt) [Qt], Noto Sans (10pt) [GTK2/3/4]
Cursor: breeze (24px)
Terminal: ghostty 1.0.1
Terminal Font: JetBrainsMono Nerd Font (13pt)
CPU: Intel(R) Core(TM) i7-10610U (8) @ 4.90 GHz
GPU 1: NVIDIA GeForce MX330 [Discrete]
GPU 2: Intel UHD Graphics @ 1.15 GHz [Integrated]
Memory: 10.01 GiB / 30.98 GiB (32%)
Swap: Disabled
Disk (/): 226.86 GiB / 928.65 GiB (24%) - ext4
Local IP (wlp0s20f3): 10.18.6.215/21
Battery (5B10W13906): 100% [AC Connected]
Locale: en_DK.UTF-8

[Abe404]

Thanks for reporting:

I'm wondering if the solutions available here (for the issue with 'error related to xcb') might help:

https://github.com/Abe404/root_painter/blob/master/docs/FAQ.md#question---on-ubuntu-i-get-an-error-related-to-xcb

[jakob1379]

You can force windows to start in x using

QT_QPA_PLATFORM=xcb python <path to painter main>.py

Changing this forces the program to start under X, and works if added in the .desktop file as well.

[jakob1379]

I already have libxcb-xinerama0 installed on Ubuntu 24/wayland. It is some x-bindings so that will not fix the issue. I would imagine qt would have a proper solution in place by now

[Abe404]

What do you feel our plan should be to address this? I don't get the issue myself so it's a bit tricky for me to work on it.

[jakob1379]

For this I am unsure. I have to do a bit of testing as I do not like the workaround which would be to just tell the Qt5 application to run as x11 no matter what.

I believe Qt has a "correct" way to handle this so it would work out of the box.

The Issue currently is that the failure when launching the application is silent, so if you open Painter from a launcher, you will not see any errors unless you go into a syslog.

[jakob1379]

I tried updating pyqt5 and the issue seems to have been resolved upstream.