[Interest] QGraphicsItem/QGraphicsView - boundingRegion

[Boettger, Heiko]

Hi,

while looking for a way to optimize the performance on out hardware I found the following blog entry:

http://blog.qt.io/blog/2008/01/08/accurate-update-regions-for-thin-qgraphicsitems/

It's about using a boundingRegion which consist out of multiple rectangle in order to reduce the number of pixel to be painted. However after looking deeper I got stuck when trying to find out where this method is actually called. I used grep to find occurencies of "boundingRegion" but the only related call which I could found was in

QRegion QGraphicsViewPrivate::mapToViewRegion(const QGraphicsItem *item, const QRectF &rect) const

and that method doesn't seem to be called from code inside qt.

My question is now, does this still work in qt 4.8.7 or 5.4.0? If yes, can someone point out where to find information how it works? I am interested in the requirements for the CacheMode or other properties to make it work. Does the QGraphicsView automatically create such a boundingRegion based on the existing QGraphicItems places inside?

Many thanks in advanced.

Heiko Böttger
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