Don't send touch move to renderer while scrolling

content/browser/renderer_host/touch_event_queue.cc

 // Copyright (c) 2012 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/touch_event_queue.h"
 
 #include "base/debug/trace_event.h"
 #include "base/stl_util.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/public/browser/render_widget_host_view.h"
@@ skipping 81 matching lines @@
 TouchEventQueue::TouchEventQueue(RenderWidgetHostImpl* host)
     : render_widget_host_(host) {
 }
 
 TouchEventQueue::~TouchEventQueue() {
   if (!touch_queue_.empty())
     STLDeleteElements(&touch_queue_);
 }
 
 void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
+  latest_event_ = event;
   if (touch_queue_.empty()) {
     // There is no touch event in the queue. Forward it to the renderer
     // immediately.
     touch_queue_.push_back(new CoalescedWebTouchEvent(event));
     if (ShouldForwardToRenderer(event.event))
       render_widget_host_->ForwardTouchEventImmediately(event);
     else
       PopTouchEventToView(INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS);
     return;
   }
 
   // If the last queued touch-event was a touch-move, and the current event is
   // also a touch-move, then the events can be coalesced into a single event.
   if (touch_queue_.size() > 1) {
     CoalescedWebTouchEvent* last_event = touch_queue_.back();
-    if (last_event->CoalesceEventIfPossible(event))
+    if (last_event->CoalesceEventIfPossible(event)) {
+      latest_event_ = last_event->coalesced_event();
       return;
+    }
   }
   touch_queue_.push_back(new CoalescedWebTouchEvent(event));
 }
 
 void TouchEventQueue::ProcessTouchAck(InputEventAckState ack_result) {
   if (touch_queue_.empty())
     return;
 
+  // If scroll update is in progress, we should have cleared the touch
+  // event queue.
+  DCHECK(!render_widget_host_->is_scroll_update_in_progress());
+
   // Update the ACK status for each touch point in the ACKed event.
   const WebKit::WebTouchEvent& event =
       touch_queue_.front()->coalesced_event().event;
   if (event.type == WebKit::WebInputEvent::TouchEnd ||
       event.type == WebKit::WebInputEvent::TouchCancel) {
     // The points have been released. Erase the ACK states.
     for (unsigned i = 0; i < event.touchesLength; ++i) {
       const WebKit::WebTouchPoint& point = event.touches[i];
       if (point.state == WebKit::WebTouchPoint::StateReleased ||
           point.state == WebKit::WebTouchPoint::StateCancelled)
@@ skipping 15 matching lines @@
     const TouchEventWithLatencyInfo& touch =
         touch_queue_.front()->coalesced_event();
     if (ShouldForwardToRenderer(touch.event)) {
       render_widget_host_->ForwardTouchEventImmediately(touch);
       break;
     }
     PopTouchEventToView(INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS);
   }
 }
 
+void TouchEventQueue::OnGestureScrollStart() {
+  TouchEventWithLatencyInfo cancel_event = GetLatestEvent();
+  FlushQueue();
+  cancel_event.event.type = WebKit::WebInputEvent::TouchCancel;
+  for (size_t i = 0; i < cancel_event.event.touchesLength; i++)
+    cancel_event.event.touches[i].state = WebKit::WebTouchPoint::StateCancelled;
+  render_widget_host_->ForwardTouchEventImmediately(cancel_event);
+  // We only want to send the touch cancel to the renderer, but don't want
+  // it gets processed in view. So clear the touch event queue here and the
+  // ack for the cancel event will just be ignored.
+  Reset();
+}
+
 void TouchEventQueue::FlushQueue() {
   while (!touch_queue_.empty())
     PopTouchEventToView(INPUT_EVENT_ACK_STATE_NOT_CONSUMED);
 }
 
 void TouchEventQueue::Reset() {
   if (!touch_queue_.empty())
     STLDeleteElements(&touch_queue_);
 }
 
 size_t TouchEventQueue::GetQueueSize() const {
   return touch_queue_.size();
 }
 
 const TouchEventWithLatencyInfo& TouchEventQueue::GetLatestEvent() const {
-  return touch_queue_.back()->coalesced_event();

[sadrul, 2013/06/20 08:51:27]

When is touch_queue_ empty here?

[Yufeng Shen (Slow to review), 2013/06/20 17:56:45]

The PopTouchEventToView() below first pops the touch event in the queue, which
can make the queue empty. Then the popped touch event is sent to View, which can
result in a gesture event (e.g. ScrollUpdate). Then on receiving
GestureScrollUpdate, we want to make a cancel event from the latest event from
touch event queue, which could be empty.

+  return latest_event_;
 }
 
 void TouchEventQueue::PopTouchEventToView(InputEventAckState ack_result) {
   if (touch_queue_.empty())
     return;
   scoped_ptr<CoalescedWebTouchEvent> acked_event(touch_queue_.front());
   touch_queue_.pop_front();
 
   // Note that acking the touch-event may result in multiple gestures being sent
   // to the renderer.
@@ skipping 26 matching lines @@
       // If the ACK status of a point is unknown, then the event should be
       // forwarded to the renderer.
       return true;
     }
   }
 
   return false;
 }
 
 }  // namespace content