[webkit-qt] [Qt] Strong performance degradation with DirectFB since r122720

Simon Hausmann simon.hausmann at nokia.com
Mon Sep 17 05:39:19 PDT 2012

On Thursday, September 13, 2012 05:31:57 PM ext Brianceau, Julien wrote:
> Hello all,
> I wonder why this changeset has been made :
> http://trac.webkit.org/changeset/122720
> QPixmap and QImage are not the same with QPA platforms plugins (e.g.
> DirectFB).
> To give you an idea of the performance issue, I performed the following test
> on my ST armv7 board :
> -          using a Qt 4.8 using QPA with DirectFB platform
> -          using WebKit r122719 and r122720
> -          using this URL :
> http://www.craftymind.com/factory/guimark3/bitmap/GM3_JS_Bitmap.html in a
> QWebView sized to 1280x720 (with webkit 1 build)
> With r122719, I get 50,7 displayed fps with a CPU usage of about 25%
> With r122720, I fall to 25,3 displayed fps with a CPU usage of more than 90%
> Is it possible to revert this commit, or at last provide a compilation
> option to keep QPixmap as native images ?

Instead of reverting the whole change I wonder how the performance would be if 
ImageBuffer / ImageBufferData would be backed by a QPixmap instead.

This should also significantly accelerate CSS animations when used in such a 
DirectFB based platform, because the layers can go through the blitter.

It wouldn't make the individual paints of <img> elements (the sprites) go 
through the blitter, but the blit onto the screen should get quicker. It might 
be that that already fixes the speed regression for you, given that the canvas 
is huge for you. (compared to the size of the sprites)


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