Getting QWindow back into parent QWidget from the fullscreen

[SGaist]

Can you provide a minimal compilable example that shows that behaviour ?

[sasmaster]

Yes,sure.

Inside MainWindow (QMainWindow):

myWindow = new MyWindow(); // inherits from QWindow
myWinContainer= QWidget::createWindowContainer(myWindow ,this);
myWinContainer->setFixedSize(640,360);
//layouts:
vbox = new QVBoxLayout();
vbox->setAlignment(Qt::AlignHCenter);
vbox->addWidget(myWinContainer);
ui->centralWidget->setLayout(vbox);

Slot that enters/exits fullscreen mode for myWinContainer:

    if( myWinContainer->windowState() == Qt::WindowFullScreen )
    {
        myWinContainer->setParent(this);
        myWinContainer->setWindowState(Qt::WindowNoState);
        vbox->insertWidget(0,myWinContainer);
    }
    else
    {
        vbox->removeWidget(myWinContainer);
        //  myWinContainer->setParent(nullptr);//doesn't help either
        myWinContainer->setParent(this,Qt::Tool);
        myWinContainer->showFullScreen();
    }

[SGaist]

That's not a compilable example.

[sasmaster]

Hey SGaist,Here is a complete runnable program with the problem.Thanks

[sasmaster]

Oops,it appears I don't have enough privilege to upload files. How do I pass the code to you?

[mrjj]

@sasmaster
Hi
it dont like some files. ( not for anyone at all )

If possible use googledrive/dropbox or Github etc.

[sasmaster]

Hmm,indeed, DropBox is the option... Here is the link to the test prog that show the issue:
https://www.dropbox.com/s/dxow1ye9fo6r1ap/FullScrTest.rar?dl=0

Thanks.

[SGaist]

I don't know whether you are hitting an unusual code path or if there's really a bug. You should check the bug report system to see if there's something related.

In any case, since you are doing OpenGL with widgets, did you consider using QOpenGLWidget ?

On a side note, there's QOpenGLWindow that might also interest you.

[sasmaster]

If you check the code you see that the full screen problem error has no relation to OpenGL at all. What I see here is SDK bug. The reason I don't use any sort of widget is because I don't need all the pile of code which comes with QWidget. All I need is a thin GL surface to render to very very fast.So I guess that I need to file a bug?

[SGaist]

What I see is that the assert comes from QWindowContainer which for some reason can't get a window handle from the top level widget. Hence my question whether you are hitting an unusual code path using QWindow as you do.

If you don't want widgets, then why are you using a QMainWindow ?

[sasmaster]

I do need widgets for some UI around the rendering window.
"Hence my question whether you are hitting an unusual code path using QWindow as you do" - what do you mean by that?

[SGaist]

Simply that I don't know whether the top level widget handling works as expected and you are doing something wrong with your QWindow or if in fact you uncovered a use case not handled properly.

[sasmaster]

And therefore I uploaded for you a full program depicting the use case. Have you tested it?

[mrjj]

@sasmaster

Hi i did run it on win 10, Qt 5.9/Qt 5.5 and
did have it crash consistently.
Also i removed much of the openGL code and seems not related to that at all unless
its some sort of hidden use or something i missed.

It does smells like a (Qt) bug but I didn't get 100% proof.

[sasmaster]

Hi mrjj. Thanks for your input. If QT CHAMPION says it smells like a bug, then probably it's a bug :)

[SGaist]

Yes I did after having to remove some stuff to make it start like @mrjj did.

Hence you can also mention that the problem appears on macOS 10.12.6.

[sasmaster]

Thanks for collaboration, guys. Submitted a bug:
https://bugreports.qt.io/browse/QTBUG-63168