[Webkit-unassigned] [Bug 76486] New: RenderLayer ClipRect not accounting for transforms

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=76486

           Summary: RenderLayer ClipRect not accounting for transforms
           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: shawnsingh at chromium.org
                CC: simon.fraser at apple.com, jamesr at chromium.org,
                    enne at google.com


A reduced test case is attached.  It reproduces on both Chromium tip-of-tree and Webkit nightly.  On chromium, this bug is the cause of http://code.google.com/p/chromium/issues/detail?id=102943 but that maps bug does not reproduce on Safari.

Explanation: the ClipRect computed by the backgroundClipRect() does not include transforms.  If the layer is translated far enough, the intersection between layerbounds and cliprect is empty, and an empty rect is stored in the overlapMap.  As a result, the layer on top does not realize it should be composited, because it thinks it doesn't overlap anything.

Simon, can you please suggest the "correct" way to fix this is?  The fixes I've tried so far break other layout tests, and I'm probably just missing some simple detail about clipRect usage.   Thanks in advance!

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