inform QWidget that the screen dimensions changed

[wysota]

So how do you implement screen geometry change?

[Dzha]

So how do you implement screen geometry change?

Right, the orientation is implemented in the hardware. The app commands the driver to rotate, the driver changes how pixels are written to the screen and changes what geometry (w,h) is reported to the screen driver plugin. As a result, the dimensions of the screen are different, but the full screen window does not pick them up until it re-enters the full screen mode.
So only the refresh of the screen width and height is required.