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);
 
     if (shouldUsePrintingLayout())
         m_minPreferredLogicalWidth = m_maxPreferredLogicalWidth = logicalWidth();
 
     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()
         || logicalHeight() != viewLogicalHeightForBoxSizing());
     if (relayoutChildren) {
         layoutScope.setChildNeedsLayout(this);
         for (LayoutObject* child = firstChild(); child; child = child->nextSibling()) {
             if (child->isSVGRoot())
                 continue;
 
@@ skipping 11 matching lines @@
     ASSERT(!m_layoutState);
     if (!needsLayout())
         return;
 
     LayoutState rootLayoutState(pageLogicalHeight(), pageLogicalHeightChanged(), *this);
 
     m_pageLogicalHeightChanged = false;
 
     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);
+}
+
+void LayoutView::getBackgroundPositioningFromDocumentElement(BackgroundPositioning& position) const
+{
+    const LayoutObject* rootObject = document().documentElement() ? document().documentElement()->layoutObject() : nullptr;
+    if (!rootObject || !rootObject->isBox())
+        return;
+
+    const LayoutBox& rootBox = toLayoutBox(*rootObject);
+    position.borderBoxSize = rootBox.size();
+    position.paddingBoxRect = rootBox.paddingBoxRect();
+    position.contentBoxRect = rootBox.contentBoxRect();
+    if (rootBox.hasLayer()) {
+        const DeprecatedPaintLayer& rootLayer = *rootBox.layer();
+        LayoutPoint offset;
+        rootLayer.convertToLayerCoords(nullptr, offset);
+        position.transform.translate(offset.x(), offset.y());
+        position.transform.multiply(rootLayer.currentTransform());
+    }
+}
+
+PaintInvalidationReason LayoutView::paintInvalidationReason(const LayoutBoxModelObject& paintInvalidationContainer,
+    const LayoutRect& oldBounds, const LayoutPoint& oldLocation,
+    const LayoutRect& newBounds, const LayoutPoint& newLocation) const
+{
+    const BackgroundPositioning& oldPosition = m_previousRootBackgroundPositioning;
+    BackgroundPositioning newPosition;
+    getBackgroundPositioningFromDocumentElement(newPosition);
+
+    if (oldPosition.transform != newPosition.transform)
+        return PaintInvalidationLocationChange;
+
+    const FillLayer& backgroundLayers = style()->backgroundLayers();
+    if (mustInvalidateFillLayersPaintOnWidthChange(backgroundLayers) || mustInvalidateFillLayersPaintOnHeightChange(backgroundLayers)) {
+        if (oldPosition.borderBoxSize != newPosition.borderBoxSize
+            || oldPosition.paddingBoxRect != newPosition.paddingBoxRect
+            || oldPosition.contentBoxRect != newPosition.contentBoxRect) {
+            return PaintInvalidationBorderBoxChange;
+        }
+    }
+
+    return LayoutBlockFlow::paintInvalidationReason(paintInvalidationContainer, oldBounds, oldLocation, newBounds, newLocation);
+}
+
+PaintInvalidationReason LayoutView::invalidatePaintIfNeeded(PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& newPaintInvalidationContainer)
+{
+    getBackgroundPositioningFromDocumentElement(m_previousRootBackgroundPositioning);

[Xianzhu, 2015/06/05 05:08:28]

This seems incorrect. m_previousRootBackgroundPositioning and newPosition will
be got in the same cycle and always equal.

I think it would be better to do this in LayoutView::layout(). We can save old
position in stack before layoutContent() and get new position after, and check
the positions and set paint invalidation flags. 

For rootObject transform, I think we can check it in
LayoutObject::styleWillChange() (by checking
styleDifference.transformChanged()). Though we will invalidate when both offset
and transform change but the combined transform doesn't change, I think this is
acceptable.

In addition, I suggest to separate these code into another CL and add tests.
This CL has been too big.

+
+    return LayoutBlockFlow::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));
 
     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 0;
+    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