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 3127 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 215 matching lines @@
   // is not the case here. We eventually want to have the same behaviour on both
   // sides but it may become a non issue if we get rid of scroll chaining (see
   // crbug.com/526462)
   std::list<ScrollNode*> current_scroll_chain;
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
   ScrollNode* viewport_scroll_node =
       viewport()->MainScrollLayer()
           ? scroll_tree.Node(viewport()->MainScrollLayer()->scroll_tree_index())
           : nullptr;
+

[majidvp, 2017/07/14 14:29:43]

nit: remove the unnecessary blank line.

[sunyunjia, 2017/07/14 22:07:23]

Done.

   if (scroll_node) {
     // TODO(bokan): The loop checks for a null parent but don't we still want to
     // distribute to the root scroll node?
     for (; scroll_tree.parent(scroll_node);
          scroll_node = scroll_tree.parent(scroll_node)) {
       if (scroll_node == viewport_scroll_node) {
         // Don't chain scrolls past the outer viewport scroll layer. Once we
         // reach that, we should scroll the viewport which is represented by the
         // main viewport scroll layer.
         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 22 matching lines @@
     }
     delta_to_scroll = local_scroll_delta;
   }
 
   if (ComputeScrollDelta(scroll_node, delta_to_scroll) != gfx::Vector2dF())
     return true;
 
   return false;
 }
 
+bool LayerTreeHostImpl::CanPropagate(ScrollNode* scroll_node,

[majidvp, 2017/07/14 14:29:43]

This function is not using any state in LayerTreeHostImpl so 
it does not need to be a member function.

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

Done.

+                                     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 node
+  // should be scrolled.

[majidvp, 2017/07/14 14:29:43]

The last sentence is not accurate. We don't decide which node should be
scrolled here. Rather we decide if scroll should be propagate from this node
given its relevant* ScrollBoundaryBehavior value.


* relevant here depends on the the dominant axis of scroll gesture.

[sunyunjia, 2017/07/14 22:07:23]

Done.

+  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);
+}
+
 InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
     ScrollState* scroll_state) {
   DCHECK(scroll_state);
 
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBy");
   ScrollTree& scroll_tree = active_tree_->property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
 
   if (!scroll_node)
     return InputHandlerScrollResult();
@@ skipping 955 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc