Refactor root element background painting

Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 177 matching lines @@
     if (!style()->isHorizontalWritingMode())
         return true;
 
     // The width/height checks below assume horizontal writing mode.
     ASSERT(style()->isHorizontalWritingMode());
 
     if (size().width() != viewLogicalWidthForBoxSizing())
         return true;
 
     if (size().height() != viewLogicalHeightForBoxSizing()) {
-        if (LayoutObject* backgroundLayoutObject = this->backgroundLayoutObject()) {
-            // When background-attachment is 'fixed', we treat the viewport (instead of the 'root'
-            // i.e. html or body) as the background positioning area, and we should full paint invalidation
-            // viewport resize if the background image is not composited and needs full paint invalidation on
-            // background positioning area resize.
-            if (!m_compositor || !m_compositor->needsFixedRootBackgroundLayer(layer())) {
-                if (backgroundLayoutObject->style()->hasFixedBackgroundImage()
-                    && mustInvalidateFillLayersPaintOnHeightChange(backgroundLayoutObject->style()->backgroundLayers()))
-                    return true;
-            }
+        // When background-attachment is 'fixed', we treat the viewport (instead of the 'root'
+        // i.e. html or body) as the background positioning area, and we should full paint invalidation
+        // viewport resize if the background image is not composited and needs full paint invalidation on
+        // background positioning area resize.
+        if (!m_compositor || !m_compositor->needsFixedRootBackgroundLayer(layer())) {
+            if (style()->hasFixedBackgroundImage()
+                && mustInvalidateFillLayersPaintOnHeightChange(style()->backgroundLayers()))
+                return true;
         }
     }
 
     return false;
 }
 
 void LayoutView::layout()
 {
     if (!document().paginated())
         setPageLogicalHeight(0);
@@ skipping 45 matching lines @@
                 rootObject->setShouldDoFullPaintInvalidation();
         }
     }
 
 #if ENABLE(ASSERT)
     checkLayoutState();
 #endif
     clearNeedsLayout();
 }
 
+LayoutRect LayoutView::visualOverflowRect() const
+{
+    // In root layer scrolling mode, the LayoutView performs overflow clipping
+    // like a regular scrollable div.
+    if (document().settings() && document().settings()->rootLayerScrolls())
+        return LayoutBlockFlow::visualOverflowRect();
+
+    // Ditto when not in compositing mode.
+    if (!usesCompositing())
+        return LayoutBlockFlow::visualOverflowRect();
+
+    // In normal compositing mode, LayoutView doesn't actually apply clipping
+    // on its descendants. Instead their visual overflow is propagated to
+    // compositor()->m_rootContentLayer for accelerated scrolling.
+    return LayoutRect(unscaledDocumentRect());
+}
+
 void LayoutView::mapLocalToContainer(const LayoutBoxModelObject* paintInvalidationContainer, TransformState& transformState, MapCoordinatesFlags mode, bool* wasFixed, const PaintInvalidationState* paintInvalidationState) const
 {
     ASSERT_UNUSED(wasFixed, !wasFixed || *wasFixed == static_cast<bool>(mode & IsFixed));
 
     if (!paintInvalidationContainer && mode & UseTransforms && shouldUseTransformFromContainer(0)) {
         TransformationMatrix t;
         getTransformFromContainer(0, LayoutSize(), t);
         transformState.applyTransform(t);
     }
 
@@ skipping 554 matching lines @@
 
 IntRect LayoutView::unscaledDocumentRect() const
 {
     LayoutRect overflowRect(layoutOverflowRect());
     flipForWritingMode(overflowRect);
     return pixelSnappedIntRect(overflowRect);
 }
 
 bool LayoutView::rootBackgroundIsEntirelyFixed() const
 {
-    if (LayoutObject* backgroundLayoutObject = this->backgroundLayoutObject())
-        return backgroundLayoutObject->style()->hasEntirelyFixedBackground();
-    return false;
-}
-
-LayoutObject* LayoutView::backgroundLayoutObject() const
-{
-    if (Element* documentElement = document().documentElement()) {
-        if (LayoutObject* rootObject = documentElement->layoutObject())
-            return rootObject->layoutObjectForRootBackground();
-    }
-    return nullptr;
+    return style()->hasEntirelyFixedBackground();
 }
 
 LayoutRect LayoutView::backgroundRect(LayoutBox* backgroundLayoutObject) const
 {
     return LayoutRect(unscaledDocumentRect());
 }
 
 IntRect LayoutView::documentRect() const
 {
     FloatRect overflowRect(unscaledDocumentRect());
@@ skipping 105 matching lines @@
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 void LayoutView::willBeDestroyed()
 {
     LayoutBlockFlow::willBeDestroyed();
     m_compositor.clear();
 }
 
 } // namespace blink