如何确保Qt Widget.repaint已完成运行？

Question

I am currently having a problem with Qt graphics view framework namely, I want to clear my QGraphicScene background color and then run a function to take a webcam picture. So far when I use QWidget.repaint the screen only got repaint after about 1 second and by then the camera function has been called and the image captured is always off. Here is how my code currently look like.

//Scene is a QGraphicScene
//View is a QGraphicView
//Camera is a camera object
Scene.setBackgroundBrush(Qt::Blue)
View.repaint()
Camera.Capture()

I have tried wrapping the repaint() call with another function and use signal and slot call but it still fail. I want to know if there is a way to pause the program until the screen has been refreshed.

Answer 1

A QGraphicsView has a bit more going on than most QWidget subclasses and I'm not familiar enough with it to say what is going on for sure but I might venture a guess that your problem is related to the fact that the scene is actually rendered onto the view port widget. Perhaps calling viewport->repaint() will give you the results you are looking for?

Also, unless you really need to be using the webcam in this scenario, you could call ::render() on your scene and pass it a QImage which you could save directly to a file.