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 3219 matching lines @@
         delta, viewport_point, scroll_state->is_direct_manipulation(),
         !wheel_scrolling_, scrolls_main_viewport_scroll_layer);
 
     applied_delta = result.consumed_delta;
     delta_applied_to_content = result.content_scrolled_delta;
   } else {
     applied_delta = ScrollSingleNode(
         scroll_node, delta, viewport_point,
         scroll_state->is_direct_manipulation(),
         &scroll_state->layer_tree_impl()->property_trees()->scroll_tree);
+    if (scroll_node->scroll_boundary_behavior.x !=

[bokan, 2017/05/19 19:35:57]

I believe you'll also need similar logic in LTHI::ScrollAnimated which is used
by smooth wheel scrolls and is a separate path from this.

[sunyunjia, 2017/05/25 20:07:10]

Done.

+            ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto &&
+        std::abs(delta.x()) > std::abs(delta.y()))
+      applied_delta.set_x(delta.x());
+    if (scroll_node->scroll_boundary_behavior.y !=
+            ScrollBoundaryBehavior::kScrollBoundaryBehaviorTypeAuto &&
+        std::abs(delta.y()) > std::abs(delta.x()))
+      applied_delta.set_y(delta.y());

[bokan, 2017/05/19 19:35:57]

I think we should do this in DistributeScrollDelta where we calculate the scroll
chain.

[sunyunjia, 2017/05/25 20:07:10]

Done.

   }
 
   // If the layer wasn't able to move, try the next one in the hierarchy.
   bool scrolled = std::abs(applied_delta.x()) > kEpsilon;
   scrolled = scrolled || std::abs(applied_delta.y()) > kEpsilon;
   if (!scrolled) {
     // TODO(bokan): This preserves existing behavior by not allowing tiny
     // scrolls to produce overscroll but is inconsistent in how delta gets
     // chained up. We need to clean this up.
     if (scrolls_main_viewport_scroll_layer)
@@ skipping 41 matching lines @@
          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;
-
-      current_scroll_chain.push_front(scroll_node);
+      if (scroll_node->scrollable)
+        current_scroll_chain.push_front(scroll_node);
     }
   }
   scroll_state->set_scroll_chain_and_layer_tree(current_scroll_chain,
                                                 active_tree());
   scroll_state->DistributeToScrollChainDescendant();
 }
 
 InputHandlerScrollResult LayerTreeHostImpl::ScrollBy(
     ScrollState* scroll_state) {
   DCHECK(scroll_state);
@@ skipping 1033 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc