Implement CSS: scroll-boundary-behavior

third_party/WebKit/Source/core/input/ScrollManager.cpp

 // Copyright 2016 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/input/ScrollManager.h"
 
 #include <memory>
 #include "core/dom/DOMNodeIds.h"
+#include "core/dom/NodeComputedStyle.h"
 #include "core/events/GestureEvent.h"
 #include "core/frame/BrowserControls.h"
 #include "core/frame/LocalFrameView.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/input/EventHandler.h"
 #include "core/input/EventHandlingUtil.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutEmbeddedContent.h"
 #include "core/layout/api/LayoutViewItem.h"
 #include "core/loader/DocumentLoader.h"
@@ skipping 91 matching lines @@
       // that'll be the document node rather than the element.
       cur_element = document_element;
     }
 
     if (cur_element) {
       if (CanScroll(scroll_state, *cur_element))
         scroll_chain.push_front(DOMNodeIds::IdForNode(cur_element));
       if (IsViewportScrollingElement(*cur_element) ||
           cur_element == document_element)
         break;
+
+      if (!CanPropagate(scroll_state, *cur_element))
+        break;
     }
 
     cur_box = cur_box->ContainingBlock();
   }
 }
 
 bool ScrollManager::CanScroll(const ScrollState& scroll_state,
                               const Element& current_element) {
   const double delta_x = scroll_state.isBeginning() ? scroll_state.deltaXHint()
                                                     : scroll_state.deltaX();
@@ skipping 15 matching lines @@
   if (!scrollable_area)
     return false;
 
   ScrollOffset current_offset = scrollable_area->GetScrollOffset();
   ScrollOffset target_offset = current_offset + ScrollOffset(delta_x, delta_y);
   ScrollOffset clamped_offset =
       scrollable_area->ClampScrollOffset(target_offset);
   return clamped_offset != current_offset;
 }
 
+bool ScrollManager::CanPropagate(const ScrollState& scroll_state,
+                                 const Element& current_element) {

[majidvp, 2017/07/14 14:29:44]

ditto. This function does not need to be a member function.

nit: The name |current_element| is not very appropriate here.
There is no other element so just calling it scrolling_element
or just element is better IMHO. 

[sunyunjia, 2017/07/14 22:07:24]

Done.

+  // ScrollBoundaryBehavior may have different values on x-axis and y-axis.
+  // We need to find out the dominant axis of user's intended scroll to decide
+  // which ScrollBoundaryBehavior should be applied, i.e. which node should
+  // be scrolled.

[majidvp, 2017/07/14 14:29:44]

ditto. the last sentence of the comment is not accurate.

[sunyunjia, 2017/07/14 22:07:24]

Done.

+  bool x_dominant =
+      std::abs(scroll_state.deltaXHint()) > std::abs(scroll_state.deltaYHint());
+  return (x_dominant &&
+          current_element.GetComputedStyle()->ScrollBoundaryBehaviorX() ==
+              EScrollBoundaryBehavior::kAuto) ||
+         (!x_dominant &&
+          current_element.GetComputedStyle()->ScrollBoundaryBehaviorY() ==
+              EScrollBoundaryBehavior::kAuto);
+}
+
 bool ScrollManager::LogicalScroll(ScrollDirection direction,
                                   ScrollGranularity granularity,
                                   Node* start_node,
                                   Node* mouse_press_node) {
   Node* node = start_node;
 
   if (!node)
     node = frame_->GetDocument()->FocusedElement();
 
   if (!node)
@@ skipping 541 matching lines @@
                                 &should_update_capture)) {
       if (should_update_capture)
         scrollbar_handling_scroll_gesture_ = scrollbar;
       return true;
     }
   }
   return false;
 }
 
 }  // namespace blink