Wayland : Creating a fake screen in order for Qt not to crash

The Qt Mayssa

I'am having a trouble turning on off screen on wyaland .
Using these commands on my RPI5, ( using labwc)

wlr-randr --output HDMI-A-1 --on
wlr-randr --output HDMI-A-1 --off
Makes my app crash the last log i can see as important is ;

QCoreApplication::postEvent: Unexpected null receiver
qt.qpa.wayland: Creating a fake screen in order for Qt not to crash
MainWindow::processExited Le processus NeoScheduler a termine par lui-meme

Is there any solution ? is it a known issue ?
Thank you

Axel Spoerl

Hi, @The-Qt-Mayssa ,
can you please post a minimal compilable reproducer?

The Qt Mayssa

Hello @Axel-Spoerl ,

I’m running a Qt Widgets application on Wayland (Raspberry Pi 5, wlroots-based compositor).
Qt version : 5.15.17

The app is started with:

export QT_QPA_PLATFORM=wayland
export WAYLAND_DISPLAY=wayland-0
./myApp

When I disable the display using:

wlr-randr --output HDMI-A-1 --off

the application crashes or becomes unstable.

This also happens when the command is executed via SSH.

When I re-enable the output:

wlr-randr --output HDMI-A-1 --on

the issue still occurs.

It seems that removing the output entirely from Wayland causes Qt to crash.

Questions:

Is this a known limitation of Qt Widgets on Wayland?
What is the recommended way to handle display power management in this setup?
Should outputs be avoided from being fully disabled when using Qt?

Thanks for your help.

Axel Spoerl

Well, that's not a reproducer.
It's how you start the app that crashes.
However, Qt 5.15 has been EOL for a long time.
The wayland implementation has been hardened recently.
Please use Qt 6.8 or later.

The Qt Mayssa

@Axel-Spoerl Passing to qt6 , is more complicated then that. The idea is to keep app working , fixing some bugs ( the eolution to qt6 is not an option today :// )
i start the app manually via a script launch.sh , that sets the exports values then ./myapp.

Knowing the app crashes only when doing wlr-randr command to turn on off screen.
I already added logs to debug ( since i'm cross compiling to deploy on a light version of tirixie :') ) , i'm getting this as a last log


2026.03.25 13:16:08 Creating a fake screen in order for Qt not to crash
2026.03.25 13:16:08[D] step Primary screen changed: QScreen(0x73a0270, name="")
2026.03.25 13:16:08[D] step Screen removed: QScreen(0x6ec0510, name="HDMI-A-1")

the code:

    QObject::connect(&app, &QGuiApplication::screenRemoved,
                     [](QScreen *screen){
                         qDebug() << "step Screen removed:" << screen;
                     });

    QObject::connect(&app, &QGuiApplication::primaryScreenChanged,
                     [](QScreen *screen){
                         qDebug() << "step Primary screen changed:" << screen;
                     });

Axel Spoerl

@The-Qt-Mayssa
I think we're talking in circles.
If you want someone in the forum to analyze the problem, you need to provide a minimal reproducer. In the unlikely case that it's a bug in Qt, it won't be fixed in an EOL version.
You will have to upgrade at some point anyway.