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 58 matching lines @@
   return GetAutoscrollController() &&
          GetAutoscrollController()->MiddleClickAutoscrollInProgress();
 }
 
 AutoscrollController* ScrollManager::GetAutoscrollController() const {
   if (Page* page = frame_->GetPage())
     return &page->GetAutoscrollController();
   return nullptr;
 }
 
+static bool CanPropagate(const ScrollState& scroll_state,
+                         const Element& element) {
+  // 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 node's ScrollBoundaryBehavior should be applied, i.e. which the
+  // scroll should be propagated from this node given its relevant*
+  // ScrollBoundaryBehavior value. * relevant here depends on the dominant
+  // axis of scroll gesture.
+  bool x_dominant =
+      std::abs(scroll_state.deltaXHint()) > std::abs(scroll_state.deltaYHint());
+  return (x_dominant && element.GetComputedStyle()->ScrollBoundaryBehaviorX() ==
+                            EScrollBoundaryBehavior::kAuto) ||
+         (!x_dominant &&
+          element.GetComputedStyle()->ScrollBoundaryBehaviorY() ==
+              EScrollBoundaryBehavior::kAuto);
+}
+
 void ScrollManager::RecomputeScrollChain(const Node& start_node,
                                          const ScrollState& scroll_state,
                                          std::deque<int>& scroll_chain) {
   DCHECK(!scroll_chain.size());
   scroll_chain.clear();
 
   DCHECK(start_node.GetLayoutObject());
   LayoutBox* cur_box = start_node.GetLayoutObject()->EnclosingBox();
   Element* document_element = frame_->GetDocument()->documentElement();
 
@@ skipping 13 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 576 matching lines @@
                                 &should_update_capture)) {
       if (should_update_capture)
         scrollbar_handling_scroll_gesture_ = scrollbar;
       return true;
     }
   }
   return false;
 }
 
 }  // namespace blink