Of course, just slightly modified portedcanvas example -- try to add rectangle using Edit menu (or Alt + R), it should draw +-100 000 rects (some of them maybe cut out) quite fast, but afterwards the cpu load remains high (according to top or KDE task manager), on my machie around 90%...

here is an archive
just try to run qmake && make/gmake on it, it should be compiled & able to run...

and let me know how it works on your machine...

And thank you for the fruitful discussion