I'm using my own style, subclassing QWindowsStyle, and I'd like to make the background of a QWidget semi-transparent.

I've been re-drawing my own scrollbars and other widgets, so I'm somewhat familiar with QPainter and its setOpacity() method, but I can't seem to find the correct flag to override the QWidget's background.

What I'd basically like to do is have the main window's background semi-transparent and all the other widgets inside it opaque.

Can someone point me in the right direction?