Implement CSS: scroll-boundary-behavior

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3039 matching lines @@
 
   mutator_host_->ImplOnlyScrollAnimationCreate(
       scroll_node->element_id, target_offset, current_offset, delayed_by,
       animation_start_offset);
 
   SetNeedsOneBeginImplFrame();
 
   return true;
 }
 
+static bool CanPropagate(ScrollNode* scroll_node, float x, float y) {
+  // 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(x) > std::abs(y);
+  return (x_dominant &&
+          scroll_node->scroll_boundary_behavior.x ==
+              ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto) ||
+         (!x_dominant &&
+          scroll_node->scroll_boundary_behavior.y ==
+              ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto);
+}
+
 InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
     const gfx::Point& viewport_point,
     const gfx::Vector2dF& scroll_delta,
     base::TimeDelta delayed_by) {
   InputHandler::ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
 
@@ skipping 68 matching lines @@
       }
 
       gfx::Vector2dF scroll_delta =
           ComputeScrollDelta(scroll_node, pending_delta);
       if (ScrollAnimationCreate(scroll_node, scroll_delta, delayed_by)) {
         scroll_animating_latched_node_id_ = scroll_node->id;
         return scroll_status;
       }
 
       pending_delta -= scroll_delta;
+
+      if (!CanPropagate(scroll_node, pending_delta.x(), pending_delta.y()))
+        break;
     }
   }
   scroll_state.set_is_ending(true);
   ScrollEnd(&scroll_state);
   if (settings_.is_layer_tree_for_subframe &&
       scroll_status.thread == SCROLL_ON_IMPL_THREAD) {
     // If we get to here, we shouldn't return SCROLL_ON_IMPL_THREAD as otherwise
     // we'll mark the scroll as handled and the scroll won't bubble.
     scroll_status.thread = SCROLL_IGNORED;
     scroll_status.main_thread_scrolling_reasons =
@@ skipping 234 matching lines @@
         DCHECK(viewport_scroll_node);
         current_scroll_chain.push_front(viewport_scroll_node);
         break;
       }
 
       if (!scroll_node->scrollable)
         continue;
 
       if (CanConsumeDelta(scroll_node, *scroll_state))
         current_scroll_chain.push_front(scroll_node);
+
+      float delta_x = scroll_state->is_beginning()
+                          ? scroll_state->delta_x_hint()
+                          : scroll_state->delta_x();
+      float delta_y = scroll_state->is_beginning()
+                          ? scroll_state->delta_y_hint()
+                          : scroll_state->delta_y();
+
+      if (!CanPropagate(scroll_node, delta_x, delta_y))
+        break;
     }
   }
   active_tree_->SetCurrentlyScrollingNode(
       current_scroll_chain.empty() ? nullptr : current_scroll_chain.back());
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,
                                                 active_tree());
   scroll_state->DistributeToScrollChainDescendant();
 }
 
 bool LayerTreeHostImpl::CanConsumeDelta(ScrollNode* scroll_node,
@@ skipping 997 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc