Re: [Traverso-devel] playhead cpu usage, crosshair like implementation needed ?

[Nicola Döbelin]

> > I must admit I'm surprised (or disappointed for that matter) by the poor
> > performance of QGraphicsView. After all it is advertised as a very
> > powerfull framework, designed to work with large numbers of 2D objects.
> 
> There has been an extremely lengthy discussion on qt4-preview mailinglist
> on 
> exactly this issue.
> 
> To clarify things a bit:
> 
> QGraphicsView doesn't paint _at all_ !
> It manages in combination with QGraphicsScene the graphics items, and it's
> doing a _great_ job at that, no doubt!
> 
> The painting is done by the arthur paint engine, which is called by the 
> ViewItems, like painter->drawRect(), painter->drawLines() and so on, so to
> some degree, we have to blame that piece of code ?
> Unfortunately, it's not that simple. We the user want vector based
> drawing, so 
> the engine has to be vector based.
> This imposes a certain amount of overhead!
> This overhead is reduced to some very little cpu load in Qt 4.3, so that's
> very good news.
> 
> Why does painting then still take so much cpu time? 
> What became clear on that lengthy discussion on qt4-prevew ml is that the
> very 
> same application that took ~ 80% cpu load in X11 only took ~ 5% max on 
> windows .....

Thanks for the explanation. It seems we have to live with it for now. Just out 
of curiosity: Do you know if the 3D desktop stuff (Xgl, Aixgl, compiz, beryll 
etc.) could solve these problems? If I understood correctly the painting is 
hardware accellerated, but I've never tried it out since I don't care that much 
about these gimmicks.

Nic

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