Coalesce async touch move events until the ack back from render

content/browser/renderer_host/input/touch_event_queue.h

 // Copyright 2013 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 43 matching lines @@
 
   ~TouchEventQueue();
 
   // Adds an event to the queue. The event may be coalesced with previously
   // queued events (e.g. consecutive touch-move events can be coalesced into a
   // single touch-move event). The event may also be immediately forwarded to
   // the renderer (e.g. when there are no other queued touch event).
   void QueueEvent(const TouchEventWithLatencyInfo& event);
 
   // Notifies the queue that a touch-event has been processed by the renderer.
-  // At this point, the queue may send one or more gesture events and/or
-  // additional queued touch-events to the renderer.
+  // At this point, if the ack is for async touchmove, remove the uncancelable
+  // touchmove from the front of the queue and decide if it should dispatch the
+  // next pending async touch move event, otherwise the queue may send one or
+  // more gesture events and/or additional queued touch-events to the renderer.
   void ProcessTouchAck(InputEventAckState ack_result,
-                       const ui::LatencyInfo& latency_info);
+                       const ui::LatencyInfo& latency_info,
+                       const uint32 unique_touch_event_id);
 
   // When GestureScrollBegin is received, we send a touch cancel to renderer,
   // route all the following touch events directly to client, and ignore the
   // ack for the touch cancel. When Gesture{ScrollEnd,FlingStart} is received,
   // resume the normal flow of sending touch events to the renderer.
   void OnGestureScrollEvent(const GestureEventWithLatencyInfo& gesture_event);
 
   void OnGestureEventAck(
       const GestureEventWithLatencyInfo& event,
       InputEventAckState ack_result);
@@ skipping 17 matching lines @@
   bool empty() const WARN_UNUSED_RESULT {
     return touch_queue_.empty();
   }
 
   size_t size() const {
     return touch_queue_.size();
   }
 
   bool has_handlers() const { return has_handlers_; }
 
+  size_t uncancelable_touch_moves_pending_ack_count() const {
+    return ack_pending_async_touchmove_ids_.size();
+  }
+
  private:
   class TouchTimeoutHandler;
   class TouchMoveSlopSuppressor;
   friend class TouchTimeoutHandler;
   friend class TouchEventQueueTest;
 
   bool HasPendingAsyncTouchMoveForTesting() const;
   bool IsTimeoutRunningForTesting() const;
   const TouchEventWithLatencyInfo& GetLatestEventForTesting() const;
 
@@ skipping 34 matching lines @@
     ACK_WITH_NO_CONSUMER_EXISTS,
     ACK_WITH_NOT_CONSUMED,
     FORWARD_TO_RENDERER,
   };
   // Filter touches prior to forwarding to the renderer, e.g., if the renderer
   // has no touch handler.
   PreFilterResult FilterBeforeForwarding(const blink::WebTouchEvent& event);
   void ForwardToRenderer(const TouchEventWithLatencyInfo& event);
   void UpdateTouchConsumerStates(const blink::WebTouchEvent& event,
                                  InputEventAckState ack_result);
+  void FlushPendingAsyncTouchmove();
 
   // Handles touch event forwarding and ack'ed event dispatch.
   TouchEventQueueClient* client_;
 
   typedef std::deque<CoalescedWebTouchEvent*> TouchQueue;
   TouchQueue touch_queue_;
 
   // Position of the first touch in the most recent sequence forwarded to the
   // client.
   gfx::PointF touch_sequence_start_position_;
 
   // Used to defer touch forwarding when ack dispatch triggers |QueueEvent()|.
   // True within the scope of |AckTouchEventToClient()|.
   bool dispatching_touch_ack_;
 
-  // Used to prevent touch timeout scheduling if we receive a synchronous
-  // ack after forwarding a touch event to the client.
+  // Used to prevent touch timeout scheduling and increase the count for async
+  // touchmove if we receive a synchronous ack after forwarding a touch event
+  // to the client.
   bool dispatching_touch_;
 
   // Whether the renderer has at least one touch handler.
   bool has_handlers_;
 
   // Whether any pointer in the touch sequence reported having a consumer.
   bool has_handler_for_current_sequence_;
 
   // Whether to allow any remaining touches for the current sequence. Note that
   // this is a stricter condition than an empty |touch_consumer_states_|, as it
   // also prevents forwarding of touchstart events for new pointers in the
   // current sequence. This is only used when the event is synthetically
   // cancelled after a touch timeout.
   bool drop_remaining_touches_in_sequence_;
 
   // Optional handler for timed-out touch event acks.
   scoped_ptr<TouchTimeoutHandler> timeout_handler_;
 
   // Suppression of TouchMove's within a slop region when a sequence has not yet
   // been preventDefaulted.
   scoped_ptr<TouchMoveSlopSuppressor> touchmove_slop_suppressor_;
 
   // Whether touch events should remain buffered and dispatched asynchronously
   // while a scroll sequence is active.  In this mode, touchmove's are throttled
   // and ack'ed immediately, but remain buffered in |pending_async_touchmove_|
   // until a sufficient time period has elapsed since the last sent touch event.
   // For details see the design doc at http://goo.gl/lVyJAa.
   bool send_touch_events_async_;
   scoped_ptr<TouchEventWithLatencyInfo> pending_async_touchmove_;
+
+  // For uncancelable touch moves, not only we send a fake ack, but also a real
+  // ack from render, which we use to decide when to send the next async
+  // touchmove. This can help avoid the touch event queue keep growing when
+  // render handles touchmove slow. We use a queue
+  // ack_pending_async_touchmove_ids to store the recent dispatched
+  // uncancelable touchmoves which are still waiting for their acks back from
+  // render. We do not put them back to the front the touch_event_queue any
+  // more.
+  std::deque<uint32> ack_pending_async_touchmove_ids_;
+
   double last_sent_touch_timestamp_sec_;
 
   // Event is saved to compare pointer positions for new touchmove events.
   scoped_ptr<blink::WebTouchEvent> last_sent_touchevent_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_