Perf issue in QGraphicsItem::ItemClipsChildrenToShape

Issue :

If the child rect is bigger than the parent rect and parent has the QGraphicsItem::ItemClipsChildrenToShape flag set. then by updating the child , the whole child rect is updated/dirty and the whole child rect gets repainted. This has a perfformance issue as only part of the child rect is visible because of the above flag set in parent and parent has a smaller rect than child.

This has a major performance issue in ORBIT/HB itemviews as they are implemented using this concept. (ie container is the child of ItemView, and it holds all the view items and the container size is bigger than the ItemView size and the ItemView has QGraphicsItem::ItemClipsChildrenToShape flag set on it.).

I have attached a small video and a mail to show the above issue.