[Webkit-unassigned] [Bug 89899] New: Don't collect non-self-painting subtree in RenderLayer's normal flow list

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=89899

           Summary: Don't collect non-self-painting subtree in
                    RenderLayer's normal flow list
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jchaffraix at webkit.org
                CC: simon.fraser at apple.com, jamesr at chromium.org
            Blocks: 75001


Following bug 88888, we don't walk the non-self-painting subtree as an optimization. We could go one step further and don't collect them altogether. That should save some memory and remove some of the explicit checks that we have during painting. This also means that the optimization from bug 88888 would apply more broadly - it is an all-or-nothing optimization - as we will only walk the needed layer subtree.

One of the points to be careful with is that the compositing code requires to know if there are any non-composited visible descendant. Because non-self-painting layers are normal flow and cannot be composited, this is just a matter of storing when we skip one in our parent.

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