Rendering rectangles speed issue

[macbeth]

Thanks for your answer!

I'm just thinking about rewriting some code to see how would it behave with QGraphicsScene, it looks like it has many good features and supports printing and rendering to QPaintDevice, which is crucial for me...

[macbeth]

Hm, another strange thing that showed up: when I add 250 000 small (5x5pix) rectangles on the GraphicsScene and then want to show it using GraphicsView, the cpu 'user' load rises to ~90%. Not just during plotting, but for all the time after the rectangles are drawn. That's looks quite strange to me... (If I draw ~50 000 rectangles, the cpu usage is about 50%)

Does anybody know, what is GraphicsView doing in the background? Still updating the view?
I'm quite disappointed, because they say in Qt docs:

Graphics View uses a BSP (Binary Space Partitioning) tree to provide very fast item discovery, and as a result of this, it can visualize large scenes in real-time, even with millions of items.

But how can one use it, if the cpu load is 90% :/

Well, maybe I've made a mistake somewhere, but I just tried to edit one of the examples (portedcanvas in examples/graphicsview) and instead of adding one rectangle I added many of them, so I don't know what's wrong...

Any advice appreciated, thanks...