Paint solid color background into both scrolling contents layer and graphics layer.

third_party/WebKit/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
@@ skipping 93 matching lines @@
 }
 
 LayoutBoxModelObject::LayoutBoxModelObject(ContainerNode* node)
     : LayoutObject(node) {}
 
 bool LayoutBoxModelObject::usesCompositedScrolling() const {
   return hasOverflowClip() && hasLayer() &&
          layer()->getScrollableArea()->usesCompositedScrolling();
 }
 
-bool LayoutBoxModelObject::hasLocalEquivalentBackground() const {
+BackgroundPaintLocation LayoutBoxModelObject::backgroundPaintLocation() const {
   bool hasCustomScrollbars = false;
   // TODO(flackr): Detect opaque custom scrollbars which would cover up a
   // border-box background.
   if (PaintLayerScrollableArea* scrollableArea = getScrollableArea()) {
     if ((scrollableArea->horizontalScrollbar() &&
          scrollableArea->horizontalScrollbar()->isCustomScrollbar()) ||
         (scrollableArea->verticalScrollbar() &&
          scrollableArea->verticalScrollbar()->isCustomScrollbar())) {
       hasCustomScrollbars = true;
     }
   }
 
   // TODO(flackr): When we correctly clip the scrolling contents layer we can
   // paint locally equivalent backgrounds into it. https://crbug.com/645957
   if (!style()->hasAutoClip())
-    return false;
+    return BackgroundPaintInGraphicsLayer;
 
   // TODO(flackr): Remove this when box shadows are still painted correctly when
   // painting into the composited scrolling contents layer.
   // https://crbug.com/646464
   if (style()->boxShadow())
-    return false;
+    return BackgroundPaintInGraphicsLayer;
 
+  // Assume optimistically that the background can be painted in the scrolling
+  // contents until we find otherwise.
+  BackgroundPaintLocation paintLocation = BackgroundPaintInScrollingContents;
   const FillLayer* layer = &(style()->backgroundLayers());
   for (; layer; layer = layer->next()) {
     if (layer->attachment() == LocalBackgroundAttachment)
       continue;
 
     // Solid color layers with an effective background clip of the padding box
     // can be treated as local.
     if (!layer->image() && !layer->next() &&
         resolveColor(CSSPropertyBackgroundColor).alpha() > 0) {
       EFillBox clip = layer->clip();
       if (clip == PaddingFillBox)
         continue;
       // A border box can be treated as a padding box if the border is opaque or
       // there is no border and we don't have custom scrollbars.
-      if (clip == BorderFillBox && !hasCustomScrollbars &&
-          (style()->borderTopWidth() == 0 ||
-           !resolveColor(CSSPropertyBorderTopColor).hasAlpha()) &&
-          (style()->borderLeftWidth() == 0 ||
-           !resolveColor(CSSPropertyBorderLeftColor).hasAlpha()) &&
-          (style()->borderRightWidth() == 0 ||
-           !resolveColor(CSSPropertyBorderRightColor).hasAlpha()) &&
-          (style()->borderBottomWidth() == 0 ||
-           !resolveColor(CSSPropertyBorderBottomColor).hasAlpha())) {
+      if (clip == BorderFillBox) {
+        if (!hasCustomScrollbars &&
+            (style()->borderTopWidth() == 0 ||
+             !resolveColor(CSSPropertyBorderTopColor).hasAlpha()) &&
+            (style()->borderLeftWidth() == 0 ||
+             !resolveColor(CSSPropertyBorderLeftColor).hasAlpha()) &&
+            (style()->borderRightWidth() == 0 ||
+             !resolveColor(CSSPropertyBorderRightColor).hasAlpha()) &&
+            (style()->borderBottomWidth() == 0 ||
+             !resolveColor(CSSPropertyBorderBottomColor).hasAlpha())) {
+          continue;
+        }
+        // If we have an opaque background color only, we can safely paint it
+        // into both the scrolling contents layer and the graphics layer to
+        // preserve LCD text.
+        if (layer == (&style()->backgroundLayers()) &&
+            resolveColor(CSSPropertyBackgroundColor).alpha() < 255)
+          return BackgroundPaintInGraphicsLayer;
+        paintLocation |= BackgroundPaintInGraphicsLayer;
         continue;
       }
       // A content fill box can be treated as a padding fill box if there is no
       // padding.
       if (clip == ContentFillBox && style()->paddingTop().isZero() &&
           style()->paddingLeft().isZero() && style()->paddingRight().isZero() &&
           style()->paddingBottom().isZero()) {
         continue;
       }
     }
-    return false;
+    return BackgroundPaintInGraphicsLayer;
   }
-  return true;
+  return paintLocation;
 }
 
 LayoutBoxModelObject::~LayoutBoxModelObject() {
   // Our layer should have been destroyed and cleared by now
   ASSERT(!hasLayer());
   ASSERT(!m_layer);
 }
 
 void LayoutBoxModelObject::willBeDestroyed() {
   ImageQualityController::remove(*this);
@@ skipping 1130 matching lines @@
   if (rootElementStyle->hasBackground())
     return false;
 
   if (node() != document().firstBodyElement())
     return false;
 
   return true;
 }
 
 }  // namespace blink