Refactor root element background painting

Source/core/layout/LayoutView.cpp

Index: Source/core/layout/LayoutView.cpp
diff --git a/Source/core/layout/LayoutView.cpp b/Source/core/layout/LayoutView.cpp
index f100481a8ab8727510cb2745c1dc77de5c6c09f4..71f8f06ac67bdc4125aee779cacd12112b3299b3 100644
--- a/Source/core/layout/LayoutView.cpp
+++ b/Source/core/layout/LayoutView.cpp
@@ -195,16 +195,14 @@ bool LayoutView::shouldDoFullPaintInvalidationForNextLayout() const
         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;
         }
     }
 
@@ -221,8 +219,6 @@ void LayoutView::layout()
 
     SubtreeLayoutScope layoutScope(*this);
 
-    LayoutRect oldLayoutOverflowRect = layoutOverflowRect();
-
     // Use calcWidth/Height to get the new width/height, since this will take the full page zoom factor into account.
     bool relayoutChildren = !shouldUsePrintingLayout() && (!m_frameView
         || logicalWidth() != viewLogicalWidthForBoxSizing()
@@ -254,22 +250,64 @@ void LayoutView::layout()
 
     layoutContent();
 
-    if (RuntimeEnabledFeatures::slimmingPaintEnabled() && layoutOverflowRect() != oldLayoutOverflowRect) {
-        // The document element paints the viewport background, so we need to invalidate it when
-        // layout overflow changes.
-        // FIXME: Improve viewport background styling/invalidation/painting. crbug.com/475115
-        if (Element* documentElement = document().documentElement()) {
-            if (LayoutObject* rootObject = documentElement->layoutObject())
-                rootObject->setShouldDoFullPaintInvalidation();
-        }
-    }
-
 #if ENABLE(ASSERT)
     checkLayoutState();
 #endif
     clearNeedsLayout();
 }
 
+void LayoutView::styleDidChange(StyleDifference diff, const ComputedStyle* oldStyle)
+{
+    const ComputedStyle& newStyle = styleRef();
+
+    if (oldStyle && oldStyle->hasEntirelyFixedBackground() != newStyle.hasEntirelyFixedBackground())
+        compositor()->setNeedsUpdateFixedBackground();
+
+    LayoutBlockFlow::styleDidChange(diff, oldStyle);
+}
+
+PaintInvalidationReason LayoutView::invalidatePaintIfNeeded(PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& newPaintInvalidationContainer)
+{
+    const LayoutObject* rootObject = document().documentElement() ? document().documentElement()->layoutObject() : nullptr;
+    TransformationMatrix newTransform;
+    LayoutSize newBorderBoxSize;
+    LayoutRect newPaddingBoxRect;
+    LayoutRect newContentBoxRect;
+
+    if (rootObject && rootObject->isBox()) {
+        const LayoutBox& rootBox = toLayoutBox(*rootObject);
+        if (rootBox.hasLayer()) {
+            const DeprecatedPaintLayer& rootLayer = *rootBox.layer();
+            LayoutPoint offset;
+            rootLayer.convertToLayerCoords(nullptr, offset);
+            newTransform.translate(offset.x(), offset.y());
+            newTransform.multiply(rootLayer.currentTransform());
+        }
+        newBorderBoxSize = rootBox.size();
+        newPaddingBoxRect = rootBox.paddingBoxRect();
+        newContentBoxRect = rootBox.contentBoxRect();
+    }
+
+    if (m_previousRootBackgroundPositioning.transform != newTransform)
+        setShouldDoFullPaintInvalidation(PaintInvalidationLocationChange);
+
+    const FillLayer& backgroundLayers = style()->backgroundLayers();
+    if (mustInvalidateFillLayersPaintOnWidthChange(backgroundLayers) || mustInvalidateFillLayersPaintOnHeightChange(backgroundLayers)) {
+        if (m_previousRootBackgroundPositioning.borderBoxSize != newBorderBoxSize
+            || m_previousRootBackgroundPositioning.paddingBoxRect != newPaddingBoxRect
+            || m_previousRootBackgroundPositioning.contentBoxRect != newContentBoxRect) {
+            setShouldDoFullPaintInvalidation(PaintInvalidationBorderBoxChange);
+        }
+    }

[Xianzhu, 2015/06/05 03:44:51]

We don't allow setShouldDoFullPaintInvalidation() during paint invalidation to
prevent invalidation flags set after clearing. Though there is no problem for
LayoutView, the above code looks to me more proper to be executed during
setStyle and layout.

I'm also confused about how root box's border, padding, content box affect
layout view's background painting. Can you explain more?

+
+    m_previousRootBackgroundPositioning.transform = newTransform;
+    m_previousRootBackgroundPositioning.borderBoxSize = newBorderBoxSize;
+    m_previousRootBackgroundPositioning.paddingBoxRect = newPaddingBoxRect;
+    m_previousRootBackgroundPositioning.contentBoxRect = newContentBoxRect;
+
+    return LayoutBox::invalidatePaintIfNeeded(paintInvalidationState, newPaintInvalidationContainer);
+}
+
 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));
@@ -844,18 +882,7 @@ IntRect LayoutView::unscaledDocumentRect() const
 
 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 0;
+    return style()->hasEntirelyFixedBackground();
 }
 
 LayoutRect LayoutView::backgroundRect(LayoutBox* backgroundLayoutObject) const