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 354 matching lines @@
 TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
                                  const Config& config)
     : client_(client),
       dispatching_touch_ack_(false),
       dispatching_touch_(false),
       has_handlers_(true),
       has_handler_for_current_sequence_(false),
       drop_remaining_touches_in_sequence_(false),
       touchmove_slop_suppressor_(new TouchMoveSlopSuppressor),
       send_touch_events_async_(false),
+      uncancelable_touch_moves_pending_ack_count_(0),
       last_sent_touch_timestamp_sec_(0) {
   DCHECK(client);
   if (config.touch_ack_timeout_supported) {
     timeout_handler_.reset(
         new TouchTimeoutHandler(this, config.touch_ack_timeout_delay));
   }
 }
 
 TouchEventQueue::~TouchEventQueue() {
   if (!touch_queue_.empty())
@@ skipping 46 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;
+
+  // Decrease the count once we receive the ack back from render for
+  // uncancelable touchmoves.
+  --uncancelable_touch_moves_pending_ack_count_;
+
+  // Send the next pending async touch move once we receive the ack.
+  if (pending_async_touchmove_ &&
+      uncancelable_touch_moves_pending_ack_count_ == 0) {
+    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 = !send_touch_events_async_;

[tdresser, 2015/03/31 14:44:07]

send_touch_events_async_ should never be false here, should it? It would be
strange to send the pending_async_touchmove synchronously.

[lanwei, 2015/04/01 13:14:21]

You are right, it will always be async, I thought we may coalesce a sync
touchmove, and in this case, we dispatch it right away, so
pending_async_touchmove is only async touchmove. 
Done.

+      pending_async_touchmove_.reset();
+      touch_queue_.push_front(new CoalescedWebTouchEvent(touch, true));
+      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 22 matching lines @@
     // 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;
 
-    if (!send_touchmove_now) {
+    if (!send_touchmove_now ||
+        uncancelable_touch_moves_pending_ack_count_ > 0) {
       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);
       // It's possible (though unlikely) that ack'ing the current touch will
       // trigger the queueing of another touch event (e.g., a touchcancel). As
       // forwarding of the queued event will be deferred while the ack is being
       // dispatched (see |OnTouchEvent()|), try forwarding it now.
       TryForwardNextEventToRenderer();
       return;
     }
   }
 
   last_sent_touch_timestamp_sec_ = touch.event.timeStampSeconds;
-
   // Flush any pending async touch move. If it can be combined with the current
   // (touchmove) event, great, otherwise send it immediately but separately. Its
   // ack will trigger forwarding of the original |touch| event.
   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 {
@@ skipping 128 matching lines @@
   touch_queue_.pop_front();
   return event.Pass();
 }
 
 void TouchEventQueue::SendTouchEventImmediately(
     TouchEventWithLatencyInfo* touch) {
   // For touchmove events, compare touch points position from current event
   // to last sent event and update touch points state.
   if (touch->event.type == WebInputEvent::TouchMove) {
     CHECK(last_sent_touchevent_);
+    // We increase the count when we send out a uncancelable touch move.
+    if (!touch->event.cancelable)
+      ++uncancelable_touch_moves_pending_ack_count_;
+
     for (unsigned int i = 0; i < last_sent_touchevent_->touchesLength; ++i) {
       const WebTouchPoint& last_touch_point =
           last_sent_touchevent_->touches[i];
       // Touches with same id may not have same index in Touches array.
       for (unsigned int j = 0; j < touch->event.touchesLength; ++j) {
         const WebTouchPoint& current_touchmove_point = touch->event.touches[j];
         if (current_touchmove_point.id != last_touch_point.id)
           continue;
 
         if (!HasPointChanged(last_touch_point, current_touchmove_point))
@@ skipping 89 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