Implement CSS: scroll-boundary-behavior

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 59 matching lines @@
 #include "platform/graphics/CompositorFilterOperations.h"
 #include "platform/graphics/CompositorMutableProperties.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/ClipDisplayItem.h"
 #include "platform/graphics/paint/CullRect.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
 #include "platform/graphics/paint/PaintController.h"
 #include "platform/graphics/paint/PaintRecordBuilder.h"
 #include "platform/graphics/paint/TransformDisplayItem.h"
 #include "public/platform/WebLayerStickyPositionConstraint.h"
+#include "public/platform/WebScrollBoundaryBehavior.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 static IntRect clipBox(LayoutBox& layoutObject);
 
 static IntRect contentsRect(const LayoutObject& layoutObject) {
@@ skipping 983 matching lines @@
   updateBackgroundColor();
   updateDrawsContent();
   updateElementIdAndCompositorMutableProperties();
   updateBackgroundPaintsOntoScrollingContentsLayer();
   updateContentsOpaque();
   updateAfterPartResize();
   updateRenderingContext();
   updateShouldFlattenTransform();
   updateChildrenTransform();
   updateScrollParent(scrollParent());
+  updateScrollBoundaryBehavior();

[bokan, 2017/03/23 13:18:26]

Hmm...I'm not sure CLM::updateGraphicsLayerGeometry will get called if you just
change the scrollBoundaryBehavior. Do you know how that happens? If not, I think
you'll need to add a call to CLM::setNeedsGraphicsLayerUpdate. This gets called
when the scroll offset is changed so it might work in most cases but we should
probably do it explicitly when the CSS value changes. Is there another CSS
feature that needs to communicate behavior to the compositor like this so we can
reuse its path?

[sunyunjia, 2017/03/23 20:16:54]

I checked the call stack, and found both CLM::updateGraphicsLayerGeometry and
CLM::setNeedsGraphicsLayerUpdate are called from
FrameView::updateAllLifecyclePhases

   registerScrollingLayers();
 
   updateCompositingReasons();
 }
 
+void CompositedLayerMapping::updateScrollBoundaryBehavior() {
+  ScrollBoundaryBehavior behavior =
+      layoutObject().styleRef().getScrollBoundaryBehavior();
+  if (m_scrollingContentsLayer) {
+    m_scrollingContentsLayer->setScrollBoundaryBehavior(
+        static_cast<WebScrollBoundaryBehavior>(behavior));
+  }
+}
+
 void CompositedLayerMapping::updateMainGraphicsLayerGeometry(
     const IntRect& relativeCompositingBounds,
     const IntRect& localCompositingBounds,
     const IntPoint& graphicsLayerParentLocation) {
   m_graphicsLayer->setPosition(FloatPoint(relativeCompositingBounds.location() -
                                           graphicsLayerParentLocation));
   m_graphicsLayer->setOffsetFromLayoutObject(
       toIntSize(localCompositingBounds.location()));
 
   FloatSize oldSize = m_graphicsLayer->size();
@@ skipping 2400 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink