QGraphicsView: How to efficiently get the viewport coordinates of QGraphicsItems?

Question

Is there a fast way to get the viewport coordinates of QGraphicsItems in a QGraphicsView? The only way I can think of is to call QGraphicsView::items(), and then QGraphicsItem::pos() followed by QGraphicsView::mapFromScene.

I must be missing something, though, because items are already converted to viewport coordinates to position them correctly on the QGraphicsView, so converting it to viewport coordinates again with mapFromScene seems inefficient--especially because in my case this is occurring often and for many items. Is there a more direct approach?

Answer 1

Probably not. A QGraphicScene can be rendered by more than one QGraphicsView simultaneously. It makes no sense to keep only one set of view port coordinates.

Also. All operation between QGraphicsItems are calculated in scene coordinate directly. Events from view port are convert to scene before processing. Working off view port which is only integer-based can also loose precision. A QGraphicsView is only a representation of the mathematical model of a scene. It's not the actual model.

Maybe you can ask a more specific question on what exactly you are trying to accomplish. There may be a better way to do it in scene coordinate.