QGraphicsView: Strange performance (at least on Mac)

[Greger]

Hi,

I have the following, somewhat strange--at least to me, behavior of a QGraphicsView: When the window with the view is active the performance is significantly worse than when the window is deselected.

To sum my situation up, I have a QGraphicsView with a number of QGraphicsObjects that I pan using the standard mouse panning action (the default mouseWheelEvent handler). All the objects are cached with DeviceCoordinateCache and neither case (window active or inactive) they are getting paint events, so I would expect them to redraw equally quickly from the pixmap buffer. However, when the window is selected, scrolling lags so bad it can take many seconds to catch up.

If I start the application with -graphicssystem raster, the performance difference is much less subtle but still noticeable.

Any tips on how to improve on this situation?

I use Qt 4.7.4 (macports).