[Webkit-unassigned] [Bug 86383] Scrolling is sluggish on pages with many relative elements

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=86383





--- Comment #7 from Allan Sandfeld Jensen <allan.jensen at nokia.com>  2012-08-24 08:41:50 PST ---
(In reply to comment #6)
> After profiling it, it looks like most of the time spend scrolling is spend inside
> RenderBox::mapLocalToContainer  and RenderLayer::convertToLayerCoords.
> 
> RenderBox::mapLocalToContainer is called indirectly RenderLayer::computeRepaintRects.
> 
> RenderLayer::convertToLayerCoords is called from several places.

Specifically it is RenderBox::outlineBoundsForRepaint that is the problem. clippedOverflowRectForRepaint are fast enough, but outlineBoundsForRepaint is really slow, probably because it uses a generic method to build up the transformation matrix and applies it, instead of using a custom build algorithm like RenderBox::computeRectForRepaint does.

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