[Interest] ItemIgnoresTransform slowness

Brad Pepers bpepers at me.com
Sun Dec 22 21:11:38 CET 2013

I was trying to figure out why my code using QGraphicsScene was slow for scrolling and the chip example was so fast.  My example has 75,000 pixmap graphics items and to scroll is very laggy but the chip example is very smooth.  I added a pixmap graphics item on top of each chip and it was still fast.  Then I changed those pixmaps to have ItemIgnoresTransform set and suddenly I got the same laggy performance when scrolling.

Is it expected that performance takes such a hit by setting this?  Any ideas on how to get the same result without using this flag?  The pixmaps are all symbols that need to be the same size no matter what the zoom level is on the view and ItemIgnoresTransform gives this effect nicely but at a huge cost in performance!


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