Linux - Doesn't work on Wayland (natively)

[JordanL2]

Version: QT5 1.137.2.1-0 installed on Arch Linux via AUR
Using Wayfire (Wayland) compositor

On startup I just get this error:

[FORMS.PP] ExceptionOccurred
  Sender=EAccessViolation
  Exception=Access violation
  Stack trace:
  $000000000061E8F2
  $0000000000600191
  $0000000000752491
  $0000000000751E7D
  $000000000074DF73
  $0000000000689E21
  $0000000000689D38
  $000000000047C2B8
  $000000000044BE30
  $000000000043A39C
[FORMS.PP] ExceptionOccurred

I can successfully start and run it via XWayland if I start like this:

QT_QPA_PLATFORM=xcb cudatext

Since Qt5 supports Wayland natively it would be better if it worked without the XWayland compatibility layer.

[Alexey-T]

What Qt5 version do you have? Arch, so the latest?
I can run on Ubuntu:

apt list libqt5*

[JordanL2]

Yes, latest:

extra/qt5-base 5.15.2+kde+r210-1 (qt qt5) [installed]
    A cross-platform application and UI framework

Also this is the version of qt5pas installed:

community/qt5pas 2.6.r65219-1
    Free Pascal Qt5 binding library updated by lazarus IDE

[JordanL2]

@Alexey-T I take it you're testing with Gnome Wayland?

[Alexey-T]

yes, and I see that on Gnome + Wayland app works - it shows weird UI theme but works.

[Alexey-T]

@JordanL2 What if you try these 2 test programs? (app from Lazarus 'examples'- compiled for gtk2 + qt5).
scroll-synedit.zip

[JordanL2]

@Alexey-T Much like Cudatext - GTK2 launches (vai Xwayland) after some delay, while the QT5 one outputs this error (but works via Xwayland):

[FORMS.PP] ExceptionOccurred
  Sender=EObjectCheck
  Exception=Object reference is Nil
  Stack trace:
  $0000000000567D75
  $00000000004A1FE6
  $0000000000770DBA
  $0000000000770625
  $000000000076B989
  $00000000006E0BEC
  $00000000006E0ADB
  $000000000047E3A2
  $00000000004CDAC0
  $000000000043AB6C
[FORMS.PP] ExceptionOccurred

Interestingly, the app works with Sway, so it doesn't even seem to be a wlroots issue.

[Alexey-T]

OK, so it is some Lazarus Qt5-code issue, I will report it to Lazarus devs, thanks.

[JordanL2]

Oh weird. It works if I reset my Wayfire config to pretty much default. It must be caused by some config or plugin I'm using. Will try to narrow it down.

[JordanL2]

Sorry - My mistake. That just unset the QT_QPA_PLATFORM environment variable so it defaulted to using Xwayland.

[JordanL2]

I've raised a bug on the Wayfire tracker, maybe the devs there will have some idea of why this is happening:
WayfireWM/wayfire#1249

[JordanL2]

Quite bizarre, but changing QT_QPA_PLATFORM=wayland-egl to QT_QPA_PLATFORM=wayland has made it work :)

I'll close this issue, thanks for your help!

[JordanL2]

@Alexey-T - Exactly what version of FPC and Lazarus do you use to compile the Linux+Qt5 build? I think you use FPC 3.2.1 from the about dialog.

I only ask because I'm trying to build Cudatext from source (I'm investigating making a Flatpak) and the build I'm making is throwing this error with QT_QPA_PLATFORM=wayland - only thing I can think could be causing it is the Lazarus version. I'm using 2.0.12.

[Alexey-T]

Of course the reason is Laz version, not FPC. I use the trunk 2.2 which was pulled about a 2-3 weeks ago.