kawazoe: No, you missed the point. My solution fixes the problem where the background wasn't erased by Qt (it was just painted over). Now with this solution, everytime the window wants to repaint itself, it will resize itself first (thus erasing the garbage painted before), and then paint the stuff.

marcel: Stuff like shadows is exactly what I'm trying to do the whole time You scaled your screenshot a little bit too much and I can't see if your circle is anti aliased or not. But I guess not, since this would be equal to shadows

Anyway, I can finally do that now. But here comes the kinda weird part:
I paint text and circles (anti aliased) in my widget and everything looks smooth. But if I paint a pixmap first and then the text and the circles, the circles are still smooth but now the text is crispy as hell
Weird, I can paint every type of form/shape smooth on my png pixmap window, but not text...