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 63 matching lines @@
 #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 "platform/wtf/CurrentTime.h"
 #include "platform/wtf/text/StringBuilder.h"
 #include "public/platform/WebLayerStickyPositionConstraint.h"
+#include "public/platform/WebScrollBoundaryBehavior.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 static IntRect ClipBox(LayoutBox& layout_object);
 
 static IntRect ContentsRect(const LayoutObject& layout_object) {
   if (!layout_object.IsBox())
     return IntRect();
@@ skipping 1038 matching lines @@
   UpdateDrawsContent();
   UpdateElementId();
   UpdateBackgroundPaintsOntoScrollingContentsLayer();
   UpdateContentsOpaque();
   UpdateRasterizationPolicy();
   UpdateAfterPartResize();
   UpdateRenderingContext();
   UpdateShouldFlattenTransform();
   UpdateChildrenTransform();
   UpdateScrollParent(ScrollParent());
+  UpdateScrollBoundaryBehavior();
   RegisterScrollingLayers();
 
   UpdateCompositingReasons();
 }
 
+void CompositedLayerMapping::UpdateScrollBoundaryBehavior() {
+  EScrollBoundaryBehavior behavior_x =
+      GetLayoutObject().StyleRef().ScrollBoundaryBehaviorX();
+  EScrollBoundaryBehavior behavior_y =
+      GetLayoutObject().StyleRef().ScrollBoundaryBehaviorY();
+  if (scrolling_contents_layer_) {
+    using ScrollBoundaryBehavior =
+        WebScrollBoundaryBehavior::ScrollBoundaryBehaviorType;

[majidvp, 2017/07/05 21:30:03]

nit: I don't feel like this using declaration is helping much with
the readability of this code. It is just saving typing
'WebScrollBoundaryBehavior' twice below. Also the naming is confusing
as it removes the Type prefix. I suggest not having it and just specifying the
exact type below.

[sunyunjia, 2017/07/14 02:59:01]

Done.

+    scrolling_contents_layer_->SetScrollBoundaryBehavior(
+        WebScrollBoundaryBehavior(
+            static_cast<ScrollBoundaryBehavior>(behavior_x),
+            static_cast<ScrollBoundaryBehavior>(behavior_y)));
+  }
+}
+
 void CompositedLayerMapping::UpdateMainGraphicsLayerGeometry(
     const IntRect& relative_compositing_bounds,
     const IntRect& local_compositing_bounds,
     const IntPoint& graphics_layer_parent_location) {
   // Find and remove the offset applied for sticky position if the compositor
   // will shift the layer for sticky position to avoid offsetting the layer
   // twice.
   FloatSize offset_for_sticky_position;
   if (UsesCompositedStickyPosition()) {
     const StickyConstraintsMap& constraints_map =
@@ skipping 2442 matching lines @@
   } else if (graphics_layer == decoration_outline_layer_.get()) {
     name = "Decoration Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink