How to make sure Qt Widget.repaint has finished running?
//Scene is a QGraphicScene
//View is a QGraphicView
//Camera is a camera object
Scene.setBackgroundBrush(Qt::Blue)
View.repaint()
Camera.Capture()

View->setCaptureInProgress(true);
Scene.setBackgroundBrush(Qt::Blue);

void view::paintEvent(QPaintEvent *event) {
   // let the original painting occur
   QGraphicsView::paintEvent(event);

   if (captureInProgress) {
       Camera.Capture();
       captureInProgress = false;
       // reset the background
       // ...
   }
}