Paint local background colors onto foreground layer.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 291 matching lines @@
         if (!context->hasAlpha())
             m_graphicsLayer->setContentsOpaque(true);
         else if (WebLayer* layer = context->platformLayer())
             m_graphicsLayer->setContentsOpaque(!Color(layer->backgroundColor()).hasAlpha());
         else
             m_graphicsLayer->setContentsOpaque(false);
     } else if (m_backgroundLayer) {
         m_graphicsLayer->setContentsOpaque(false);
         m_backgroundLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     } else {
-        // For non-root layers, background is always painted by the primary graphics layer.
-        m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
+        // For non-root layers, background is painted by the scrolling contents layer if all backgrounds
+        // are background attachment local, otherwise background is painted by the primary graphics layer.
+        if (hasScrollingLayer() && shouldPaintBackgroundOntoScrollingContentsLayer()) {
+            // Backgrounds painted onto the foreground are clipped by the padding box rect.
+            // TODO(flackr): This should actually check the entire overflow rect within the
+            // scrolling contents layer but since we currently only trigger this for solid
+            // color backgrounds the answer will be the same.
+            m_scrollingContentsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(toLayoutBox(layoutObject())->paddingBoxRect()));
+
+            // When we paint the background onto the scrolling contents layer we are going
+            // to leave a hole in the m_graphicsLayer where the background is so it is
+            // not opaque.
+            m_graphicsLayer->setContentsOpaque(false);
+        } else {
+            m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
+        }
     }
 }
 
 void CompositedLayerMapping::updateCompositedBounds()
 {
     ASSERT(m_owningLayer.compositor()->lifecycle().state() == DocumentLifecycle::InCompositingUpdate);
     // FIXME: if this is really needed for performance, it would be better to store it on Layer.
     m_compositedBounds = m_owningLayer.boundingBoxForCompositing();
     m_contentOffsetInCompositingLayerDirty = true;
 }
@@ skipping 2082 matching lines @@
     // FIXME: once the state machine is ready, this can be removed and we can refer to that instead.
     if (Page* page = layoutObject()->frame()->page())
         page->setIsPainting(true);
 #endif
 
     TRACE_EVENT1("devtools.timeline", "Paint", "data", InspectorPaintEvent::data(m_owningLayer.layoutObject(), LayoutRect(interestRect), graphicsLayer));
 
     PaintLayerFlags paintLayerFlags = 0;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintBackground)
         paintLayerFlags |= PaintLayerPaintingCompositingBackgroundPhase;
+    else
+        paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintForeground)
         paintLayerFlags |= PaintLayerPaintingCompositingForegroundPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintMask)
         paintLayerFlags |= PaintLayerPaintingCompositingMaskPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintChildClippingMask)
         paintLayerFlags |= PaintLayerPaintingChildClippingMaskPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintOverflowContents)
         paintLayerFlags |= PaintLayerPaintingOverflowContents;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll)
         paintLayerFlags |= PaintLayerPaintingCompositingScrollingPhase;
 
     if (graphicsLayer == m_backgroundLayer.get())
         paintLayerFlags |= (PaintLayerPaintingRootBackgroundOnly | PaintLayerPaintingCompositingForegroundPhase); // Need PaintLayerPaintingCompositingForegroundPhase to walk child layers.
-    else if (compositor()->fixedRootBackgroundLayer())
+    else if (compositor()->fixedRootBackgroundLayer() && m_owningLayer.isRootLayer())
         paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
 
     if (graphicsLayer == m_graphicsLayer.get()
         || graphicsLayer == m_foregroundLayer.get()
         || graphicsLayer == m_backgroundLayer.get()
         || graphicsLayer == m_maskLayer.get()
         || graphicsLayer == m_childClippingMaskLayer.get()
         || graphicsLayer == m_scrollingContentsLayer.get()) {
 
+        bool paintRootBackgroundOntoScrollingContentsLayer = shouldPaintBackgroundOntoScrollingContentsLayer();
+        DCHECK(!paintRootBackgroundOntoScrollingContentsLayer || (!m_backgroundLayer && !m_foregroundLayer));
+        if (paintRootBackgroundOntoScrollingContentsLayer) {
+            if (graphicsLayer == m_scrollingContentsLayer.get())
+                paintLayerFlags &= ~PaintLayerPaintingSkipRootBackground;
+            else
+                paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
+        }
         GraphicsLayerPaintInfo paintInfo;
         paintInfo.paintLayer = &m_owningLayer;
         paintInfo.compositedBounds = compositedBounds();
         paintInfo.offsetFromLayoutObject = graphicsLayer->offsetFromLayoutObject();
         adjustForCompositedScrolling(graphicsLayer, paintInfo.offsetFromLayoutObject);
 
         // We have to use the same root as for hit testing, because both methods can compute and cache clipRects.
         doPaintTask(paintInfo, *graphicsLayer, paintLayerFlags, context, interestRect);
     } else if (graphicsLayer == m_squashingLayer.get()) {
         for (size_t i = 0; i < m_squashedLayers.size(); ++i)
@@ skipping 91 matching lines @@
         if (m_squashedLayers[previousIndex].paintLayer == layerToRemove)
             break;
     }
     if (previousIndex == indexToClear && layerToRemove->groupedMapping() == this) {
         compositor()->paintInvalidationOnCompositingChange(layerToRemove);
         return true;
     }
     return false;
 }
 
+bool CompositedLayerMapping::shouldPaintBackgroundOntoScrollingContentsLayer() const
+{
+    // TODO(flackr): Add support for painting locally attached background images. https://crbug.com/625882
+    const FillLayer& backgroundLayer = m_owningLayer.layoutObject()->style()->backgroundLayers();
+    return !m_owningLayer.isRootLayer()
+        && m_owningLayer.scrollsOverflow()
+        && !backgroundLayer.image()
+        && !backgroundLayer.next()
+        && (backgroundLayer.attachment() == LocalBackgroundAttachment
+            || backgroundLayer.clip() == PaddingFillBox)
+        && !m_owningLayer.stackingNode()->hasNegativeZOrderList();
+}
+
 bool CompositedLayerMapping::updateSquashingLayerAssignment(PaintLayer* squashedLayer, size_t nextSquashedLayerIndex)
 {
     GraphicsLayerPaintInfo paintInfo;
     paintInfo.paintLayer = squashedLayer;
     // NOTE: composited bounds are updated elsewhere
     // NOTE: offsetFromLayoutObject is updated elsewhere
 
     // Change tracking on squashing layers: at the first sign of something changed, just invalidate the layer.
     // FIXME: Perhaps we can find a tighter more clever mechanism later.
     if (nextSquashedLayerIndex < m_squashedLayers.size()) {
@@ skipping 100 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink