[Webkit-unassigned] [Bug 104981] New: Element is displayed behind a composited layer when clipping is used on a previous element

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=104981

           Summary: Element is displayed behind a composited layer when
                    clipping is used on a previous element
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: achicu at adobe.com


Created an attachment (id=179385)
 --> (https://bugs.webkit.org/attachment.cgi?id=179385&action=review)
test case

Look at the attached test case. "Layer3" needs to be displayed on top of everything else, but instead it is displayed behind. The element needs to be promoted to composited layer, but it is not.

The problem is in RenderLayerCompositor::computeCompositingRequirements at the following line:

> // We're done processing an element that clips. The container can keep testing overlap.
> compositingState.m_testingOverlap = true;

The problem is that there's another animation behind it that requested to skip testing for overlaps, but the overflow:hidden element that comes right in the middle will reset the flag and will force the top-most element incorrectly check for overlaps again.

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