You know, tonnot, the more questions you ask, the more it sounds like you are going about designing your application completely the wrong way.

If you have to resort to all sorts of "outside the box" tricks to prevent Qt from doing what it was designed to do, then maybe you should question why your design seems to *require* all these tricks in order to have adequate performance. I gave you one piece of advice on how to avoid excessive repaints; you didn't like that idea, so you're still trying to find ways to defeat Qt.

Why? You'll likely end up with an application that completely breaks next time a new release of Qt comes out or if you have to change it to add some new feature, because you've had to write it in a way that doesn't conform to standard Qt expectations.