Qt 5 Apps on Wayland

[Dr. Zenzic]

I have a qt 5 application that I'm trying to run on Fedora 29 running
Wayland. The app was built from source and was working correctly on
Fedora 28. After upgrading to 29 I am receiving the following warning
and the application doesn't start

"Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use
QT_QPA_PLATFORM=wayland to run on Wayland anyway."

If I run it as root using sudo I get

"QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
No protocol specified
qt.qpa.screen: QXcbConnection: Could not connect to display :0
Could not connect to any X display."

Running the command with QT_QPA_PLATFORM=wayland-egl (per
https://fedoraproject.org/wiki/How_to_debug_Wayland_problems#Looking_for_...)
I get the error

"QSocketNotifier: Can only be used with threads started with QThread"

I have the WAYLAND_DEBUG=1 output as well but it means nothing to me. I
dont know much about display backends and compsitors, but it seems like
the QT application is trying to connect to an XWayland display but can't
find one in Fedora 29. Does anyone have any suggestions to try and get
the application to display?

[Samuel Sieb]

On 11/11/18 9:43 PM, Dr. Zenzic wrote:
>  I have a qt 5 application that I'm trying to run on Fedora 29
> running
>  Wayland. The app was built from source and was working correctly on
>  Fedora 28. After upgrading to 29 I am receiving the following warning
>  and the application doesn't start
>  
>  "Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use
>  QT_QPA_PLATFORM=wayland to run on Wayland anyway." 
Did you try using that?

>  If I run it as root using sudo I get
>  
>  "QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
>  No protocol specified
>  qt.qpa.screen: QXcbConnection: Could not connect to display :0
>  Could not connect to any X display." 
Right, you can't easily run applications as root on Wayland.

>  Running the command with QT_QPA_PLATFORM=wayland-egl (per
>
> https://fedoraproject.org/wiki/How_to_debug_Wayland_problems#Looking_for_...)
>  I get the error
>  
>  "QSocketNotifier: Can only be used with threads started with QThread" 
That looks like an application bug.

>  I have the WAYLAND_DEBUG=1 output as well but it means nothing to me.
> I
>  dont know much about display backends and compsitors, but it seems like
>  the QT application is trying to connect to an XWayland display but can't
>  find one in Fedora 29. Does anyone have any suggestions to try and get
>  the application to display? 
If you want it to try connecting to XWayland, then run it with 
XDG_SESSION_TYPE=x11. Like:
"XDG_SESSION_TYPE=x11 myapp"