Bug 88386 – shouldSuppressPaintingLayer shouldn't be called on every RenderLayers

• Status: NEW
• Component: Layout and Rendering

[Julien Chaffraix]

After doing some archeology (see r16129), the code is used to avoid FOUCs by preventing paints to propagate to child RenderLayers (meaning that there will be a flash to white instead). It was later extended to allow for paints suppression. All the conditions that the function checks are tied to the document - the exception being that it checks for child layer - which means that instead of having a fixed cost per paint phase, it's a cost per RenderLayer::paintLayer. On http://dglazkov.github.com/performance-tests/biggrid.html, this is an ~8 - 10% cost as we need to do a lot of paintLayer calls.

At the time the function was introduced, it's unclear if the painting went through a single point as it does now but we can easily move the code to the FrameView now.

Patch forthcoming.

[Julien Chaffraix]

Created attachment 145917 [details]
Proposed change v1.

[Simon Fraser (smfr)]

Comment on attachment 145917 [details]
Proposed change v1.

What happens when there are compositing layers, which can enter painting on a non-root RenderLayer? Or do we never have compositing layers this early on?

[Simon Fraser (smfr)]

Comment on attachment 145917 [details]
Proposed change v1.

r- until we resolve the compositing issue.

[Julien Chaffraix]

(In reply to comment #2)
> (From update of attachment 145917 [details])
> What happens when there are compositing layers, which can enter painting on a non-root RenderLayer? Or do we never have compositing layers this early on?

The compositing code is bypassing the checks for the owning layer already as RenderLayerBacking::paintContents calls directly RenderLayer::paintLayerContents. However you would not paint the descendant layers as you would need to go through RenderLayer::paintLayer.

I don't think anything prevents us from having compositing layers during a potential FOUC so the logic needs to be changed.

[Julien Chaffraix]

Mhh, it also looks like the new logic wouldn't repaint the RenderView or the document's element which means we wouldn't paint the background and do a "flash to white" like the old code. It doesn't sound like a good idea to change that.