Coalesce async touch move events until the ack back from render

content/browser/renderer_host/input/touch_event_queue.cc

 // 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.
 
 #include "content/browser/renderer_host/input/touch_event_queue.h"
 
 #include "base/auto_reset.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/renderer_host/input/timeout_monitor.h"
@@ skipping 23 matching lines @@
   WebTouchEventTraits::ResetTypeAndTouchStates(
       WebInputEvent::TouchCancel,
       // TODO(rbyers): Shouldn't we use a fresh timestamp?
       event.event.timeStampSeconds,
       &event.event);
   return event;
 }
 
 bool ShouldTouchTriggerTimeout(const WebTouchEvent& event) {
   return (event.type == WebInputEvent::TouchStart ||
-          event.type == WebInputEvent::TouchMove) &&
-         !WebInputEventTraits::IgnoresAckDisposition(event);
+          event.type == WebInputEvent::TouchMove) && event.cancelable;
 }
 
 // Compare all properties of touch points to determine the state.
 bool HasPointChanged(const WebTouchPoint& point_1,
     const WebTouchPoint& point_2) {
   DCHECK_EQ(point_1.id, point_2.id);
   if (point_1.screenPosition != point_2.screenPosition ||
       point_1.position != point_2.position ||
       point_1.radiusX != point_2.radiusX ||
       point_1.radiusY != point_2.radiusY ||
@@ skipping 375 matching lines @@
 
   touchmove_slop_suppressor_->ConfirmTouchEvent(ack_result);
 
   if (touch_queue_.empty())
     return;
 
   PopTouchEventToClient(ack_result, latency_info);
   TryForwardNextEventToRenderer();
 }
 
+void TouchEventQueue::ProcessUncancelableTouchMoveAck() {
+  TRACE_EVENT0("input", "TouchEventQueue::ProcessUncancelableTouchMoveAck");
+
+  DCHECK(!dispatching_touch_ack_);
+  dispatching_touch_ = false;
+
+  // Remove it from the queue once we receive the ack back from render for
+  // uncancelable touchmoves.
+  DCHECK(!ack_pending_async_touchmove_.empty());
+  ack_pending_async_touchmove_.pop_back();
+
+  // Send the next pending async touch move once we receive the ack.
+  if (pending_async_touchmove_ && ack_pending_async_touchmove_.empty()) {
+    TouchEventWithLatencyInfo touch = *pending_async_touchmove_;
+
+    // Dispatch the next pending async touch move when time expires.
+    if (touch.event.timeStampSeconds >=
+        last_sent_touch_timestamp_sec_ + kAsyncTouchMoveIntervalSec) {
+      touch.event.cancelable = false;
+      pending_async_touchmove_.reset();
+      SendTouchEventImmediately(&touch);
+    }
+  }
+}
+
 void TouchEventQueue::TryForwardNextEventToRenderer() {
   DCHECK(!dispatching_touch_ack_);
   // If there are queued touch events, then try to forward them to the renderer
   // immediately, or ACK the events back to the client if appropriate.
   while (!touch_queue_.empty()) {
     PreFilterResult filter_result =
         FilterBeforeForwarding(touch_queue_.front()->coalesced_event().event);
     switch (filter_result) {
       case ACK_WITH_NO_CONSUMER_EXISTS:
         PopTouchEventToClient(INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS);
@@ skipping 21 matching lines @@
     // reduces the risk of jank. However, it's still important that the web
     // application be sent touches at key points in the gesture stream,
     // e.g., when the application slop region is exceeded or touchmove
     // coalescing fails because of different modifiers.
     bool send_touchmove_now = size() > 1;
     send_touchmove_now |= pending_async_touchmove_ &&
                           !pending_async_touchmove_->CanCoalesceWith(touch);
     send_touchmove_now |=
         touch.event.timeStampSeconds >=
         last_sent_touch_timestamp_sec_ + kAsyncTouchMoveIntervalSec;
+    send_touchmove_now &= ack_pending_async_touchmove_.empty();

[jdduke (slow), 2015/04/15 17:14:53]

So, I think we have to send the touchmove if we can't coalesce or there are
events already in the queue. I think this condition should be:

send_touchmove_now |=
    !pending_async_touchmove_ack_count &&
    (touch.event.timeStampSeconds >=
     last_sent_touch_timestamp_sec_ + kAsyncTouchMoveIntervalSec);

[lanwei, 2015/04/17 20:49:00]

Done.

 
     if (!send_touchmove_now) {
       if (!pending_async_touchmove_) {
         pending_async_touchmove_.reset(new TouchEventWithLatencyInfo(touch));
       } else {
         DCHECK(pending_async_touchmove_->CanCoalesceWith(touch));
         pending_async_touchmove_->CoalesceWith(touch);
       }
       DCHECK_EQ(1U, size());
       PopTouchEventToClient(INPUT_EVENT_ACK_STATE_NOT_CONSUMED);
@@ skipping 14 matching lines @@
   if (pending_async_touchmove_) {
     if (pending_async_touchmove_->CanCoalesceWith(touch)) {
       pending_async_touchmove_->CoalesceWith(touch);
       pending_async_touchmove_->event.cancelable = !send_touch_events_async_;
       touch = *pending_async_touchmove_;
       pending_async_touchmove_.reset();
     } else {
       scoped_ptr<TouchEventWithLatencyInfo> async_move =
           pending_async_touchmove_.Pass();
       async_move->event.cancelable = false;
-      touch_queue_.push_front(new CoalescedWebTouchEvent(*async_move, true));
       SendTouchEventImmediately(async_move.get());
       return;
     }
   }
 
   // Note: Touchstart events are marked cancelable to allow transitions between
   // platform scrolling and JS pinching. Touchend events, however, remain
   // uncancelable, mitigating the risk of jank when transitioning to a fling.
   if (send_touch_events_async_ && touch.event.type != WebInputEvent::TouchStart)
     touch.event.cancelable = false;
 
+  // For the async touchmove, when we dispatch it, we will remove it from the
+  // front of the queue and keep it in a separate queue.
+  if (touch.event.type == WebInputEvent::TouchMove && !touch.event.cancelable) {
+    PopTouchEvent();

[jdduke (slow), 2015/04/15 17:14:53]

Why can't we move this code next to the other async touchmove code we have in 
SendTouchEventImmediately?

[lanwei, 2015/04/17 20:49:00]

When pending_async_touchmove_ is not null and we have a no-async-touchmove at
the front of the queue, we need to flush the pending_async_touchmove_, and we
cannot PopTouchEvent (in this case, it is no-async-touchmove).

+  }
   // A synchronous ack will reset |dispatching_touch_|, in which case
   // the touch timeout should not be started.
   base::AutoReset<bool> dispatching_touch(&dispatching_touch_, true);
   SendTouchEventImmediately(&touch);
   if (dispatching_touch_ && timeout_handler_)
     timeout_handler_->StartIfNecessary(touch);
 }
 
 void TouchEventQueue::OnGestureScrollEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
@@ skipping 126 matching lines @@
       }
     }
   }
 
   if (last_sent_touchevent_)
     *last_sent_touchevent_ = touch->event;
   else
     last_sent_touchevent_.reset(new WebTouchEvent(touch->event));
 
   client_->SendTouchEventImmediately(*touch);
+
+  if (touch->event.type == WebInputEvent::TouchMove &&

[jdduke (slow), 2015/04/15 17:14:53]

I think we may need a guard here in the event that we get a synchronous ack for
whatever reason (e.g., the touch is filtered by WebView).

Right now we have a |base::AutoReset<bool>
dispatching_touch(&dispatching_touch_, true);| call to guard against that case.
We might need to move that guard into this function, and then we only do this
logic if we haven't yet received an ack.

[lanwei, 2015/04/17 20:49:00]

Done.

+      !touch->event.cancelable) {
+    // We push it into the queue when we send out a uncancelable touch move.
+    // For the async touchmove, we do not process input event ack any more, we
+    // will ack to client and wait for the ack from render.
+    ack_pending_async_touchmove_.push_front(*touch);

[jdduke (slow), 2015/04/15 17:14:53]

A count should be sufficient.

[lanwei, 2015/04/17 20:49:00]

Done.

+    client_->OnTouchEventAck(*touch, INPUT_EVENT_ACK_STATE_IGNORED);
+    TryForwardNextEventToRenderer();
+  }
 }
 
 TouchEventQueue::PreFilterResult
 TouchEventQueue::FilterBeforeForwarding(const WebTouchEvent& event) {
   if (WebTouchEventTraits::IsTouchSequenceStart(event)) {
     has_handler_for_current_sequence_ = false;
     send_touch_events_async_ = false;
     pending_async_touchmove_.reset();
     last_sent_touchevent_.reset();
 
@@ skipping 66 matching lines @@
     if (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED)
       send_touch_events_async_ = false;
     has_handler_for_current_sequence_ |=
         ack_result != INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS;
   } else if (WebTouchEventTraits::IsTouchSequenceEnd(event)) {
     has_handler_for_current_sequence_ = false;
   }
 }
 
 }  // namespace content