Fullscreen button for ImageDisplay

[ClementLeBihan]

Hi !
I'm trying to add a fullscreen button for ImageDisplay, without success.
I think it could be a good feature.

I've created a fullscreen button in the titlebar of the widget :

QToolButton* fullscreen_button = new QToolButton();

  fullscreen_button->setText("FullScreen");
  fullscreen_button->setIconSize(QSize(10, 10));

  connect(fullscreen_button, SIGNAL(clicked()), this, SLOT(updateFullScreen()));

  dynamic_cast<QHBoxLayout*>(getAssociatedWidgetPanel()->titleBarWidget()->layout())
      ->insertWidget(2, fullscreen_button);

and implemented the updateFullScreen function :

void ImageDisplay::updateFullScreen()
{
  if (!(getAssociatedWidgetPanel()->windowState() & Qt::WindowFullScreen)) {
    getAssociatedWidgetPanel()->setFloating(
        true);
    getAssociatedWidgetPanel()->showFullScreen();
  } else {
    getAssociatedWidgetPanel()->setFloating(false);
    getAssociatedWidgetPanel()->showNormal();
  }
}

Unfortunately, something weird happen.
The first time I click, the widget start floating but not fullscreen.
The second time I click, the widget doesn't move
The third time I click, the widget stop floating
The Fourth time I click, the widget goes fullscreen as expected.

Do you have an idea why It needs 4 clicks ?
I have no idea how QtWidget works, I may forgot to call a function ...

Thank you for your help,
Best regards,
Clément

[rhaschke]

I'm afraid that is a Qt limitation. See the corresponding note in the docs.
Maximizing the window works as expected: #1803
Note that you should remember the previous state of the display (floating or not) and restore that state.

[ClementLeBihan]

In my side maximizing also need 4 clicks before beeing maximized. But there is the same warning about maximizing. Thank you for giving me the link, I wasn't aware of the limitation.

It says On X11, a window does not have a frame until the window manager decorates it. This happens asynchronously at some point in time after calling [QWidget::show](https://doc.qt.io/qt-5/qwidget.html#show)() and the first paint event the window receives, or it does not happen at all. It seems to correspond the fact that I need to click 4 times on my button to see window maximizing or fullscreening.

Thanks a lot for your quick answer and for your help @rhaschke !!!

[rhaschke]

On my side maximizing also needs 4 clicks before being maximized.

I was using Qt 5.15 on Ubuntu Jammy. Maybe on Focal with Qt 5.12 it doesn't (yet) work?

[ClementLeBihan]

That's may be the point ! Thank you @rhaschke