[Interest] QApplication::ApplicationStateChanged Signal Not Emitted With -platform EGLFS

[Mcnally (Journals)]

Hi all, 

I have a QApplication object have connected its QApplicationStateChanged
signal to a slot in a custom object. In the slot, I test on the
Qt::ApplicationState parameter and, if the QApplication is in the
ApplicationReady state I begin drawing objects on my interface.


This works fine when run with the default plugin (I am assuming XCB but not
sure how to confirm that) but when run with -platform eglfs the signal
doesn't seem to be emitted. Or, perhaps more accurately, the connected slot
is not called.

I can verify that the application state changes by querying and printing the
QApplication::ApplicationState() at different times - the state certainly
does change from 2 (ApplicationInactive) to 4 (ApplicationReady) but the
signal is never emitted.

I can emit the signal myself before the call to app.exec() but this results
in drawing being done before the window is initialised and positioning,
scaling etc. doesn't behave as it should. I can create a single-shot timer
and connect the QTimer::timeout() signal to a slot which emits the
QApplication::ApplicationStateChanged signal with the correct state, but
this feels a bit of a nasty hack around it.

Is there something I'm missing?

I'm developing in Debian Jessie 64bit and Qt 5.9. Also running on an Odroid
XU4 but the described behaviour is evident in both environments

In case it's of benefit, I can provide some example code:

int main(int argc, char *argv[])

{

   QApplication app(argc, argv);

   std::cout << "Application state: " << app.applicationState();//Output
here is: Application state: 2

   std::cin.ignore();

   

   MyObject* mObject = new MyObject(&engine, window, mPrint_info,
&app);//App only passed here to be used in timed ApplicationState slot 

   

   QThread::connect(&app,
SIGNAL(applicationStateChanged(Qt::ApplicationState )), MyObject,
SLOT(app_state(Qt::ApplicationState )));//Connect application's
StateChanged() signal to handler in MyObject. Using this mechanism, we can
draw elements on the view when the window has initialised. This connection
works with the default platform but doesn't seem to work in eglfs.

 

   QTimer* myTimer = new QTimer();

   myTimer->setInterval(1000);

   QThread::connect(myTimer, SIGNAL(timeout()), MyObject, SLOT(temp()));

   myTimer->start(); //Inside temp() is an
emit->app->applicationStateChanged(Qt::ApplicationReady). This is a
(hopefully) temporary workaround to get drawing working properly in EGLFS.

   rc = app.exec();

 

  delete component;

   return rc;

}

 

And in MyObject:

 

void MyObject::app_state(Qt::ApplicationState state)//This needs to be
called after the UI has initialised and all widths, heights etc. have valid
values. Works well in default platform
{
    if(state == Qt::ApplicationState::ApplicationActive)
    {
        if(!this->work_set)
        {
            //Draw to GUI
            //Other logic
            this->sensors_set = true;
        }
    }
}
 
void LabelUpdater::temp()//When called from the QTimer slot after 1second,
this allows drawing to be performed as expected running in EGLFS
{
    std::cout << "[LabelUpdater::temp()]: In temp();" << std::endl;
    if( app->applicationState() == Qt::ApplicationActive )
            emit this->app->applicationStateChanged(Qt::ApplicationActive);
}

 

 

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