[Webkit-unassigned] [Bug 140183] New: Failed to display background image when body is composited

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=140183

            Bug ID: 140183
           Summary: Failed to display background image when body is
                    composited
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: j.isorce at samsung.com

Usually body's RenderBox skip to paint the background (see skipBodyBackground function in RenderBox) because it assumes HTML's Render will do.
Problem happens when these 2 renders are composited (isComposited() return true).
Indeed if HTML's Render does not draw its content (RenderLayerBacking::isSimpleContainerCompositingLayer() returns true) then body's render should not skip painting the background.

In the following patch I improved the condition in "skipBodyBackground" function regarding explanation above.
But it not enough, the CachedImage has to be marked isLoaded when CachedImage::finishLoading is called and before notifying observers.
Moreover the RenderLayerBacking has to redisplay its content once the background is loaded.

Also see layout test in the following attached patch. The negative zIndex and the video tag are there to hit the call "layer.setIndirectCompositingReason(RenderLayer::IndirectCompositingReason::BackgroundLayer);" in RenderLayerCompositor::computeCompositingRequirements which one makes the body's RenderBox to be composited.
Without the patch the background of this layout test is not displayed.

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