Overscroll and Elasticity for views::ScrollView

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 265 matching lines @@
 
   DCHECK(!resource_provider_);
   DCHECK(!resource_pool_);
   DCHECK(!single_thread_synchronous_task_graph_runner_);
   DCHECK(!image_decode_controller_);
 
   if (input_handler_client_) {
     input_handler_client_->WillShutdown();
     input_handler_client_ = NULL;
   }
-  if (scroll_elasticity_helper_)
-    scroll_elasticity_helper_.reset();
+  root_scroll_elasticity_helper_.reset();
 
   // The layer trees must be destroyed before the layer tree host. We've
   // made a contract with our animation controllers that the animation_host
   // will outlive them, and we must make good.
   if (recycle_tree_)
     recycle_tree_->Shutdown();
   if (pending_tree_)
     pending_tree_->Shutdown();
   active_tree_->Shutdown();
   recycle_tree_ = nullptr;
@@ skipping 306 matching lines @@
   return layer_impl != NULL;
 }
 
 std::unique_ptr<SwapPromiseMonitor>
 LayerTreeHostImpl::CreateLatencyInfoSwapPromiseMonitor(
     ui::LatencyInfo* latency) {
   return base::WrapUnique(
       new LatencyInfoSwapPromiseMonitor(latency, NULL, this));
 }
 
-ScrollElasticityHelper* LayerTreeHostImpl::CreateScrollElasticityHelper() {
-  DCHECK(!scroll_elasticity_helper_);
+ScrollElasticityHelper* LayerTreeHostImpl::CreateRootScrollElasticityHelper() {
+  DCHECK(!root_scroll_elasticity_helper_);
   if (settings_.enable_elastic_overscroll) {
-    scroll_elasticity_helper_.reset(
+    root_scroll_elasticity_helper_.reset(
         ScrollElasticityHelper::CreateForLayerTreeHostImpl(this));
   }
-  return scroll_elasticity_helper_.get();
+  return root_scroll_elasticity_helper_.get();
+}
+
+base::WeakPtr<ScrollElasticityHelper>
+LayerTreeHostImpl::ScrollElasticityHelperForScrollingLayer() {
+  LayerImpl* scrolling_layer_impl = CurrentlyScrollingLayer();
+  if (!scrolling_layer_impl)
+    return nullptr;
+
+  return ScrollElasticityHelperForId(scrolling_layer_impl->id())->GetWeakPtr();
 }
 
 bool LayerTreeHostImpl::GetScrollOffsetForLayer(int layer_id,
                                                 gfx::ScrollOffset* offset) {
   LayerImpl* layer = active_tree()->FindActiveTreeLayerById(layer_id);
   if (!layer)
     return false;
 
   *offset = layer->CurrentScrollOffset();
   return true;
@@ skipping 1976 matching lines @@
   scroll_status.thread = SCROLL_ON_IMPL_THREAD;
   ScrollAnimationAbort(scrolling_layer_impl);
 
   top_controls_manager_->ScrollBegin();
 
   active_tree_->SetCurrentlyScrollingLayer(scrolling_layer_impl);
   // TODO(majidvp): get rid of wheel_scrolling_ and set is_direct_manipulation
   // in input_handler_proxy instead.
   wheel_scrolling_ = IsWheelBasedScroll(type);
   scroll_state->set_is_direct_manipulation(!wheel_scrolling_);
-  // Invoke |DistributeScrollDelta| even with zero delta and velocity to ensure
-  // scroll customization callbacks are invoked.
+  // Invoke |DistributeScrollDelta| even with zero delta and velocity to process
+  // overscroll and ensure scroll customization callbacks are invoked.
   DistributeScrollDelta(scroll_state);
 
   client_->RenewTreePriority();
   RecordCompositorSlowScrollMetric(type, CC_THREAD);
 
   return scroll_status;
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::RootScrollBegin(
     ScrollState* scroll_state,
@@ skipping 887 matching lines @@
   // is registered with the outer viewport.
   if (InnerViewportScrollLayer() && OuterViewportScrollLayer() &&
       scroll_layer_id == InnerViewportScrollLayer()->id())
     scroll_layer_id = OuterViewportScrollLayer()->id();
   auto i = scrollbar_animation_controllers_.find(scroll_layer_id);
   if (i == scrollbar_animation_controllers_.end())
     return nullptr;
   return i->second.get();
 }
 
+void LayerTreeHostImpl::RegisterScrollElasticityHelper(int scroll_layer_id) {
+  DCHECK(!InnerViewportScrollLayer() ||
+         scroll_layer_id != InnerViewportScrollLayer()->id());
+  DCHECK(!OuterViewportScrollLayer() ||
+         scroll_layer_id != OuterViewportScrollLayer()->id());
+  DCHECK(settings().enable_elastic_overscroll);
+
+  auto& helper = scroll_elasticity_helpers_[scroll_layer_id];
+  if (!helper)
+    helper = active_tree_->CreateScrollElasticityHelper(scroll_layer_id);
+}
+
+void LayerTreeHostImpl::UnregisterScrollElasticityHelper(int scroll_layer_id) {
+  scroll_elasticity_helpers_.erase(scroll_layer_id);
+}
+
+ScrollElasticityHelper* LayerTreeHostImpl::ScrollElasticityHelperForId(
+    int scroll_layer_id) {
+  if (!settings().enable_elastic_overscroll)
+    return nullptr;
+
+  auto i = scroll_elasticity_helpers_.find(scroll_layer_id);
+  if (i != scroll_elasticity_helpers_.end())
+    return i->second.get();
+
+  if (!root_scroll_elasticity_helper_) {
+    root_scroll_elasticity_helper_.reset(
+        ScrollElasticityHelper::CreateForLayerTreeHostImpl(this));
+  }
+  return root_scroll_elasticity_helper_.get();
+}
+
 void LayerTreeHostImpl::PostDelayedScrollbarAnimationTask(
     const base::Closure& task,
     base::TimeDelta delay) {
   client_->PostDelayedAnimationTaskOnImplThread(task, delay);
 }
 
 // TODO(danakj): Make this a return value from the Animate() call instead of an
 // interface on LTHI. (Also, crbug.com/551138.)
 void LayerTreeHostImpl::SetNeedsAnimateForScrollbarAnimation() {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::SetNeedsAnimateForScrollbarAnimation");
@@ skipping 563 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc