Collision detection QGraphicsItem

[wysota]

I wanted to do this by writing a new QGraphicsItem::shape() function.

Yes, that's a correct approach.

But for this i need to do a QPainterPath from my map and I think theres no function to do a QPainterPath of a QPixmap?

You have to find a way to scan your pixmap and create a path for it. You can for example try to do that by first detecting edges of the shape by using high frequency filtering algorithms (like Sodel, Laplace or even a simple convolution filter) and then approximate the shape by "walking" through the edge. Simply speaking - you need to trace the image