On 06/10/15 00:48, Boettger, Heiko wrote: > 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/
That's quite an old article (2008). I think there are talking about these: http://doc.qt.io/qt-5/qgraphicsitem.html#setBoundingRegionGranularity http://doc.qt.io/qt-5/qgraphicsitem.html#boundingRegion They have been added in Qt 4.4, which is the Qt version mentioned in the article. A simple optimisation is to cache the values returned by boundingRect() and shape() since these function members are called very often (at least in my case). How you tune your view/scene/items depends on the typical use case (animated or not, few vs millions of items, big vs small items, ...) My 2 cents, Krys > > 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 > > > > _______________________________________________ > Interest mailing list > [email protected] > http://lists.qt-project.org/mailman/listinfo/interest > _______________________________________________ Interest mailing list [email protected] http://lists.qt-project.org/mailman/listinfo/interest
