Make touch events uncancelable during fling when they are on the current active scroll layer

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 137 matching lines @@
   bool scroll_on_main_thread = (scroll_thread == MAIN_THREAD);
   if (IsWheelBasedScroll(type)) {
     UMA_HISTOGRAM_BOOLEAN("Renderer4.CompositorWheelScrollUpdateThread",
                           scroll_on_main_thread);
   } else {
     UMA_HISTOGRAM_BOOLEAN("Renderer4.CompositorTouchScrollUpdateThread",
                           scroll_on_main_thread);
   }
 }
 
+// Similar to LayerImpl::HasAncestor, but walks up the scroll parents.
+static bool HasScrollAncestor(LayerImpl* child, LayerImpl* scroll_ancestor) {
+  DCHECK(scroll_ancestor);
+  if (!child)
+    return false;
+  ScrollTree& scroll_tree =
+      child->layer_tree_impl()->property_trees()->scroll_tree;
+  ScrollNode* scroll_node = scroll_tree.Node(child->scroll_tree_index());
+  for (; scroll_tree.parent(scroll_node);

[bokan, 2016/11/04 19:32:55]

This will avoid comparing against the root layer. I would change this to just
check that scroll_node is non-null

+       scroll_node = scroll_tree.parent(scroll_node)) {
+    if (scroll_node->scrollable)
+      return scroll_node->owner_id == scroll_ancestor->id();
+  }
+  return false;
+}
+
 }  // namespace
 
 DEFINE_SCOPED_UMA_HISTOGRAM_TIMER(PendingTreeDurationHistogramTimer,
                                   "Scheduling.%s.PendingTreeDuration");
 
 LayerTreeHostImpl::FrameData::FrameData()
     : render_surface_layer_list(nullptr),
       has_no_damage(false),
       may_contain_video(false) {}
 
@@ skipping 416 matching lines @@
   }
 
   return false;
 }
 
 EventListenerProperties LayerTreeHostImpl::GetEventListenerProperties(
     EventListenerClass event_class) const {
   return active_tree_->event_listener_properties(event_class);
 }
 
-bool LayerTreeHostImpl::DoTouchEventsBlockScrollAt(
+InputHandler::TouchStartHitResult LayerTreeHostImpl::DoTouchEventsBlockScrollAt(
     const gfx::Point& viewport_point) {
   gfx::PointF device_viewport_point = gfx::ScalePoint(
       gfx::PointF(viewport_point), active_tree_->device_scale_factor());
 
   // Now determine if there are actually any handlers at that point.
   // TODO(rbyers): Consider also honoring touch-action (crbug.com/347272).
   LayerImpl* layer_impl =
       active_tree_->FindLayerThatIsHitByPointInTouchHandlerRegion(
           device_viewport_point);
-  return layer_impl != NULL;
+  if (layer_impl == NULL)
+    return TouchStartHitResult::HANDLER;
+
+  if (!CurrentlyScrollingLayer())
+    return TouchStartHitResult::SAME_LAYER;

[tdresser, 2016/11/04 17:15:20]

I don't understand this, but I might just be confused by the naming.

[bokan, 2016/11/04 19:32:55]

+1, I don't know what these returns mean.

+
+  bool is_ancestor =
+      HasScrollAncestor(layer_impl, active_tree_->CurrentlyScrollingLayer());

[bokan, 2016/11/04 19:32:55]

What should happen if layer_impl == CurrentlyScrollingLayer? HasScrollAncestor
will return false but maybe that's by design?

+  return is_ancestor ? TouchStartHitResult::SAME_LAYER
+                     : TouchStartHitResult::DIFFERENT_LAYER;
 }
 
 std::unique_ptr<SwapPromiseMonitor>
 LayerTreeHostImpl::CreateLatencyInfoSwapPromiseMonitor(
     ui::LatencyInfo* latency) {
   return base::WrapUnique(
       new LatencyInfoSwapPromiseMonitor(latency, NULL, this));
 }
 
 ScrollElasticityHelper* LayerTreeHostImpl::CreateScrollElasticityHelper() {
@@ skipping 1953 matching lines @@
     if (IsMainThreadScrolling(status, scroll_node)) {
       *scroll_on_main_thread = true;
       *main_thread_scrolling_reasons = status.main_thread_scrolling_reasons;
       return NULL;
     }
   }
 
   return potentially_scrolling_layer_impl;
 }
 
-// Similar to LayerImpl::HasAncestor, but walks up the scroll parents.
-static bool HasScrollAncestor(LayerImpl* child, LayerImpl* scroll_ancestor) {
-  DCHECK(scroll_ancestor);
-  if (!child)
-    return false;
-  ScrollTree& scroll_tree =
-      child->layer_tree_impl()->property_trees()->scroll_tree;
-  ScrollNode* scroll_node = scroll_tree.Node(child->scroll_tree_index());
-  for (; scroll_tree.parent(scroll_node);
-       scroll_node = scroll_tree.parent(scroll_node)) {
-    if (scroll_node->scrollable)
-      return scroll_node->owner_id == scroll_ancestor->id();
-  }
-  return false;
-}
-
 InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBeginImpl(
     ScrollState* scroll_state,
     LayerImpl* scrolling_layer_impl,
     InputHandler::ScrollInputType type) {
   DCHECK(scroll_state);
   DCHECK(scroll_state->delta_x() == 0 && scroll_state->delta_y() == 0);
 
   InputHandler::ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
@@ skipping 74 matching lines @@
   LayerImpl* scrolling_layer_impl = FindScrollLayerForDeviceViewportPoint(
       device_viewport_point, type, layer_impl, &scroll_on_main_thread,
       &scroll_status.main_thread_scrolling_reasons);
 
   if (scrolling_layer_impl)
     scroll_affects_scroll_handler_ =
         scrolling_layer_impl->layer_tree_impl()->have_scroll_event_handlers();
 
   if (scroll_on_main_thread) {
     RecordCompositorSlowScrollMetric(type, MAIN_THREAD);
-
     scroll_status.thread = SCROLL_ON_MAIN_THREAD;
     return scroll_status;
   }
 
   return ScrollBeginImpl(scroll_state, scrolling_layer_impl, type);
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimatedBegin(
     const gfx::Point& viewport_point) {
   InputHandler::ScrollStatus scroll_status;
@@ skipping 1389 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc