Let only the root layer paint root background

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
@@ skipping 185 matching lines @@
     // foreground phase. Since scrolled contents are moved by paint invalidation in this
     // case, the outline won't get 'dragged along'.
     bool shouldPaintSelfOutline = isSelfPaintingLayer && !isPaintingOverlayScrollbars
         && ((isPaintingScrollingContent && isPaintingCompositedBackground)
             || (!isPaintingScrollingContent && isPaintingCompositedForeground))
         && m_paintLayer.layoutObject()->styleRef().hasOutline();
     bool shouldPaintContent = m_paintLayer.hasVisibleContent() && isSelfPaintingLayer && !isPaintingOverlayScrollbars;
 
     PaintResult result = FullyPainted;
 
-    if (paintFlags & PaintLayerPaintingRootBackgroundOnly && !m_paintLayer.layoutObject()->isLayoutView() && !m_paintLayer.layoutObject()->isDocumentElement())
+    if (paintFlags & PaintLayerPaintingRootBackgroundOnly && !m_paintLayer.layoutObject()->isLayoutView())
         return result;
 
     if (m_paintLayer.layoutObject()->view()->frame() && m_paintLayer.layoutObject()->view()->frame()->shouldThrottleRendering())
         return result;
 
     // Ensure our lists are up to date.
     m_paintLayer.stackingNode()->updateLayerListsIfNeeded();
 
     LayoutSize subpixelAccumulation = m_paintLayer.compositingState() == PaintsIntoOwnBacking ? m_paintLayer.subpixelAccumulation() : paintingInfoArg.subPixelAccumulation;
     ShouldRespectOverflowClipType respectOverflowClip = shouldRespectOverflowClip(paintFlags, m_paintLayer.layoutObject());
@@ skipping 340 matching lines @@
                 childPaintingInfo.scrollOffsetAccumulation += parentLayer->layoutBox()->scrolledContentOffset();
         }
 
         if (childPainter.paintLayer(context, childPaintingInfo, paintFlags) == MayBeClippedByPaintDirtyRect)
             result = MayBeClippedByPaintDirtyRect;
     }
 
     return result;
 }
 
-// FIXME: inline this.
-static bool paintForFixedRootBackground(const PaintLayer* layer, PaintLayerFlags paintFlags)
-{
-    return layer->layoutObject()->isDocumentElement() && (paintFlags & PaintLayerPaintingRootBackgroundOnly);
-}
-
 bool PaintLayerPainter::shouldPaintLayerInSoftwareMode(const GlobalPaintFlags globalPaintFlags, PaintLayerFlags paintFlags)
 {
     DisableCompositingQueryAsserts disabler;
 
     return m_paintLayer.compositingState() == NotComposited
         || (globalPaintFlags & GlobalPaintFlattenCompositingLayers)
-        || ((paintFlags & PaintLayerPaintingReflection) && !m_paintLayer.has3DTransform())
-        || paintForFixedRootBackground(&m_paintLayer, paintFlags);
+        || ((paintFlags & PaintLayerPaintingReflection) && !m_paintLayer.has3DTransform());
 }
 
 void PaintLayerPainter::paintOverflowControlsForFragments(const PaintLayerFragments& layerFragments, GraphicsContext& context, const PaintLayerPaintingInfo& localPaintingInfo, PaintLayerFlags paintFlags)
 {
     PaintLayerScrollableArea* scrollableArea = m_paintLayer.getScrollableArea();
     if (!scrollableArea)
         return;
 
     Optional<DisplayItemCacheSkipper> cacheSkipper;
     if (layerFragments.size() > 1)
@@ skipping 79 matching lines @@
         cacheSkipper.emplace(context);
 
     for (auto& fragment : layerFragments)
         paintFragmentWithPhase(PaintPhaseSelfBlockBackgroundOnly, fragment, context, fragment.backgroundRect, localPaintingInfo, paintFlags, HasNotClipped);
 }
 
 void PaintLayerPainter::paintForegroundForFragments(const PaintLayerFragments& layerFragments,
     GraphicsContext& context, const LayoutRect& transparencyPaintDirtyRect,
     const PaintLayerPaintingInfo& localPaintingInfo, bool selectionOnly, PaintLayerFlags paintFlags)
 {
+    DCHECK(!(paintFlags & PaintLayerPaintingRootBackgroundOnly));
+
     // Optimize clipping for the single fragment case.
     bool shouldClip = localPaintingInfo.clipToDirtyRect && layerFragments.size() == 1 && !layerFragments[0].foregroundRect.isEmpty();
     ClipState clipState = HasNotClipped;
     Optional<LayerClipRecorder> clipRecorder;
     if (shouldClip && needsToClip(localPaintingInfo, layerFragments[0].foregroundRect)) {
         clipRecorder.emplace(context, *m_paintLayer.layoutObject(), DisplayItem::kClipLayerForeground, layerFragments[0].foregroundRect, &localPaintingInfo, layerFragments[0].paginationOffset, paintFlags);
         clipState = HasClipped;
     }
 
     // We have to loop through every fragment multiple times, since we have to issue paint invalidations in each specific phase in order for
@@ skipping 65 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize());
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink