Bug 57571

Summary: We spend time in updateLayerPositions() for every layout, whether or not layers changed
Product: WebKit Reporter: Simon Fraser (smfr) <simon.fraser>
Component: Layout and RenderingAssignee: Nobody <webkit-unassigned>
Status: NEW ---    
Severity: Normal CC: hyatt, jamesr, jchaffraix, koivisto, mitz, simon.fraser
Priority: P2 Keywords: InRadar
Version: 528+ (Nightly build)   
Hardware: All   
OS: OS X 10.5   
URL: http://cnn.com

Description Simon Fraser (smfr) 2011-03-31 13:24:42 PDT 
When cnn.com does layout, there are a lot of calls to RenderBox::computeRectForRepaint(), via RenderLayer::updateLayerPositions(). It's inefficient for the following reasons:

1. We don't track whether any layers actually changed, so we may not actually have to do any work
2. We're walking down the RenderLayer tree, but for each layer walking back up the renderers doing computeRectForRepaint(), so it's > O(N)
Comment 1 Simon Fraser (smfr) 2011-03-31 13:25:51 PDT 
<rdar://problem/9216902>
Comment 2 Simon Fraser (smfr) 2011-03-31 13:50:01 PDT 
Ideas here:
1. remove the repaint code from layers (hyatt says it's old)
2. have layout detect when a layer is moved or resized