Refactor root element background painting

Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #include "config.h"
 #include "core/layout/LayoutBoxModelObject.h"
 
+#include "core/dom/NodeComputedStyle.h"
+#include "core/html/HTMLBodyElement.h"
 #include "core/layout/ImageQualityController.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutFlowThread.h"
 #include "core/layout/LayoutGeometryMap.h"
 #include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutObject.h"
 #include "core/layout/LayoutTextFragment.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/CompositedDeprecatedPaintLayerMapping.h"
 #include "core/layout/compositing/DeprecatedPaintLayerCompositor.h"
@@ skipping 203 matching lines @@
     // gets the same layout after changing position property, although no
     // re-raster (rect-based invalidation) is needed, display items should
     // still update their paint offset.
     if (RuntimeEnabledFeatures::slimmingPaintEnabled() && oldStyle) {
         bool newStyleIsFixedPosition = style()->position() == FixedPosition;
         bool oldStyleIsFixedPosition = oldStyle->position() == FixedPosition;
         if (newStyleIsFixedPosition != oldStyleIsFixedPosition)
             invalidateDisplayItemClientForNonCompositingDescendants();
     }
 
+    // The used style for body background may change due to computed style change
+    // on the document element because of background stealing.
+    // Refer to backgroundStolenForBeingBody() and
+    // http://www.w3.org/TR/css3-background/#body-background for more info.
+    if (isDocumentElement()) {
+        HTMLBodyElement* body = document().firstBodyElement();
+        LayoutObject* bodyLayout = body ? body->layoutObject() : nullptr;
+        if (bodyLayout && bodyLayout->isBoxModelObject()) {
+            bool newStoleBodyBackground = toLayoutBoxModelObject(bodyLayout)->backgroundStolenForBeingBody(style());
+            bool oldStoleBodyBackground = oldStyle && toLayoutBoxModelObject(bodyLayout)->backgroundStolenForBeingBody(oldStyle);
+            if (newStoleBodyBackground != oldStoleBodyBackground
+                && bodyLayout->style() && bodyLayout->style()->hasBackground()) {
+                bodyLayout->setShouldDoFullPaintInvalidation();
+            }
+        }
+    }
+
     if (FrameView *frameView = view()->frameView()) {
         bool newStyleIsViewportConstained = style()->hasViewportConstrainedPosition();
         bool oldStyleIsViewportConstrained = oldStyle && oldStyle->hasViewportConstrainedPosition();
         if (newStyleIsViewportConstained != oldStyleIsViewportConstrained) {
             if (newStyleIsViewportConstained && layer())
                 frameView->addViewportConstrainedObject(this);
             else
                 frameView->removeViewportConstrainedObject(this);
         }
     }
@@ skipping 668 matching lines @@
 
     ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
     for (LayoutObject* child = startChild; child && child != endChild; ) {
         // Save our next sibling as moveChildTo will clear it.
         LayoutObject* nextSibling = child->nextSibling();
         moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
         child = nextSibling;
     }
 }
 
+bool LayoutBoxModelObject::backgroundStolenForBeingBody(const ComputedStyle* rootElementStyle) const
+{
+    // http://www.w3.org/TR/css3-background/#body-background
+    // If the root element is <html> with no background, and a <body> child element exists,
+    // the root element steals the first <body> child element's background.
+    if (!isBody())
+        return false;
+
+    Element* rootElement = document().documentElement();
+    if (!isHTMLHtmlElement(rootElement))
+        return false;
+
+    if (!rootElementStyle)
+        rootElementStyle = rootElement->ensureComputedStyle();
+    if (rootElementStyle->hasBackground())
+        return false;
+
+    if (node() != document().firstBodyElement())
+        return false;
+
+    return true;
+}
+
 } // namespace blink