[Interest] double-buffering, quality drop

Alexander Semke Alexander.Semke at web.de
Tue Feb 3 23:37:43 CET 2015


Am Dienstag, 3. Februar 2015, 10:59:44 schrieb René J.V. Bertin:
> I have no experience whatsoever in doing this kind of thing in Qt, but
> looking at the 2 images in the OP it strikes me that the image prepared in
> the background simply has (been scaled up from) a much lower resolution.
No, there's no scaling involved here. The pixmap has the same size as the 
bounding rectangulare of the graphics item.

> Has it occurred to you that the speed gain you're seeing might be related
> to doing the expensive operation (drawing a vast number of dots, circles
> and line segments with AA) at a much lower resolution?
It's really related to the loop over many points with all the painting inside. 

-- 
Alexander



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