[Webkit-unassigned] [Bug 96584] New: Logic to not composite fixed elements outside the viewport is wrong

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=96584

           Summary: Logic to not composite fixed elements outside the
                    viewport is wrong
           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: simon.fraser at apple.com
                CC: bdakin at apple.com, jamesr at chromium.org,
                    wangxianzhu at chromium.org


Created an attachment (id=163746)
 --> (https://bugs.webkit.org/attachment.cgi?id=163746&action=review)
Testcase

RenderLayerCompositor::requiresCompositingForPosition() has:

    FrameView* frameView = m_renderView->frameView();
    if (frameView && !layer->absoluteBoundingBox().intersects(IntRect(IntPoint(frameView->scrollOffsetForFixedPosition()), frameView->layoutSize())))
        return false;

This is incorrect, since the fixed element may have abs pos children that lie outside its bounds, but they can be visible in the viewport.

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