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/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();
     }
 
+    if (isDocumentElement() && isHTMLHtmlElement(node())) {
+        // Refers to backgroundStolenForBeingBody().

[chrishtr, 2015/06/05 23:54:18]

Is this code to handle when backgroundStolenForBeingBody() might change? Can you
instead compare the value of backgroundStolenForBeingBody() before and after?

[trchen, 2015/06/06 05:30:02]

Acknowledged.

+        bool newStyleHasBackground = style()->hasBackground();
+        bool oldStyleHasBackground = oldStyle && oldStyle->hasBackground();
+        if (newStyleHasBackground != oldStyleHasBackground) {
+            Element* body = document().body();
+            LayoutObject* bodyLayout = isHTMLBodyElement(body) ? body->layoutObject() : nullptr;
+            if (bodyLayout) {
+                const ComputedStyle* bodyStyle = bodyLayout->style();
+                if (bodyStyle && bodyStyle->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 440 matching lines @@
             return false;
     }
 
     if (!hasOneNormalBoxShadow)
         return false;
 
     Color backgroundColor = resolveColor(CSSPropertyBackgroundColor);
     if (backgroundColor.hasAlpha())
         return false;
 
+    // TODO(trchen): Mask layers are painted with the same code path as background layers.
+    // We shouldn't paint shadow to the mask by accident.
+    if (style()->maskImage())

[chrishtr, 2015/06/05 23:54:18]

This seems a little random. Is it fixing a particular layout test?

[trchen, 2015/06/06 05:30:02]

Nope. Just feel dangerous when I see this. I can split this to another CL.

+        return false;
+
     const FillLayer* lastBackgroundLayer = &style()->backgroundLayers();
     for (const FillLayer* next = lastBackgroundLayer->next(); next; next = lastBackgroundLayer->next())
         lastBackgroundLayer = next;
 
     if (lastBackgroundLayer->clip() != BorderFillBox)
         return false;
 
     if (lastBackgroundLayer->image() && style()->hasBorderRadius())
         return false;
 
@@ skipping 210 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
+{
+    // 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) || rootElement->ensureComputedStyle()->hasBackground())
+        return false;
+
+    if (node() != document().body())
+        return false;
+
+    return true;
+}
+
 } // namespace blink