Consuming a touch move prevents only the next scroll update.

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/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/stl_util.h"
@@ skipping 274 matching lines @@
   // This is the list of the original events that were coalesced.
   WebTouchEventWithLatencyList events_;
 
   // If |ignore_ack_| is true, don't send this touch event to client
   // when the event is acked.
   bool ignore_ack_;
 
   DISALLOW_COPY_AND_ASSIGN(CoalescedWebTouchEvent);
 };
 
-TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client)
+TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
+                                 TouchScrollingMode mode)
     : client_(client),
       dispatching_touch_ack_(NULL),
       dispatching_touch_(false),
       touch_filtering_state_(TOUCH_FILTERING_STATE_DEFAULT),
-      ack_timeout_enabled_(false) {
+      ack_timeout_enabled_(false),
+      touch_scrolling_mode_(mode),
+      absorbing_touch_moves_(false) {
   DCHECK(client);
 }
 
 TouchEventQueue::~TouchEventQueue() {
   if (!touch_queue_.empty())
     STLDeleteElements(&touch_queue_);
 }
 
 void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
   TRACE_EVENT0("input", "TouchEventQueue::QueueEvent");
@@ skipping 83 matching lines @@
   TRACE_EVENT0("input", "TouchEventQueue::ForwardToRenderer");
 
   DCHECK(!dispatching_touch_);
   DCHECK_NE(touch_filtering_state_, DROP_ALL_TOUCHES);
 
   if (IsNewTouchSequence(touch.event)) {
     touch_filtering_state_ =
         ack_timeout_enabled_ ? FORWARD_TOUCHES_UNTIL_TIMEOUT
                              : FORWARD_ALL_TOUCHES;
     touch_ack_states_.clear();
+    absorbing_touch_moves_ = false;
   }
 
   // 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);
   client_->SendTouchEventImmediately(touch);
   if (dispatching_touch_ &&
       touch_filtering_state_ == FORWARD_TOUCHES_UNTIL_TIMEOUT &&
       ShouldTouchTypeTriggerTimeout(touch.event.type)) {
     DCHECK(timeout_handler_);
     timeout_handler_->Start(touch);
   }
 }
 
 void TouchEventQueue::OnGestureScrollEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
   if (gesture_event.event.type != blink::WebInputEvent::GestureScrollBegin)
     return;
 
+  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_TOUCHCANCEL)
+    return;
+
   // We assume that scroll events are generated synchronously from
   // dispatching a touch event ack. This allows us to generate a synthetic
   // cancel event that has the same touch ids as the touch event that
   // is being acked. Otherwise, we don't perform the touch-cancel optimization.
   if (!dispatching_touch_ack_)
     return;
 
   if (touch_filtering_state_ == DROP_TOUCHES_IN_SEQUENCE)
     return;
 
   touch_filtering_state_ = DROP_TOUCHES_IN_SEQUENCE;
 
   // Fake a TouchCancel to cancel the touch points of the touch event
   // that is currently being acked.
   // Note: |dispatching_touch_ack_| is non-null when we reach here, meaning we
   // are in the scope of PopTouchEventToClient() and that no touch event
   // in the queue is waiting for ack from renderer. So we can just insert
   // the touch cancel at the beginning of the queue.
   touch_queue_.push_front(new CoalescedWebTouchEvent(
       ObtainCancelEventForTouchEvent(
           dispatching_touch_ack_->coalesced_event()), true));
 }
 
+void TouchEventQueue::OnGestureEventAck(
+    const GestureEventWithLatencyInfo& event,
+    InputEventAckState ack_result) {
+  if (touch_scrolling_mode_ != TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE)
+    return;
+
+  if (event.event.type != blink::WebInputEvent::GestureScrollUpdate)
+    return;
+
+  // Suspend sending touchmove events as long as the scroll events are handled.
+  // Note that there's no guarantee that this ACK is for the most recent
+  // gesture event (or even part of the current sequence).  Worse case, the
+  // delay in updating the absorption state should onl result in minor UI
+  // glitches.
+  // TODO(rbyers): Define precise timing requirements and potentially implement
+  // mitigations for races.
+  absorbing_touch_moves_ = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED);
+}
+
 void TouchEventQueue::OnHasTouchEventHandlers(bool has_handlers) {
   DCHECK(!dispatching_touch_ack_);
   DCHECK(!dispatching_touch_);
 
   if (has_handlers) {
     if (touch_filtering_state_ == DROP_ALL_TOUCHES) {
       // If no touch handler was previously registered, ensure that we don't
       // send a partial touch sequence to the renderer.
       DCHECK(touch_queue_.empty());
       touch_filtering_state_ = DROP_TOUCHES_IN_SEQUENCE;
@@ skipping 105 matching lines @@
   if (touch_filtering_state_ == DROP_ALL_TOUCHES)
     return ACK_WITH_NO_CONSUMER_EXISTS;
 
   if (touch_filtering_state_ == DROP_TOUCHES_IN_SEQUENCE &&
       event.type != WebInputEvent::TouchCancel) {
     if (IsNewTouchSequence(event))
       return FORWARD_TO_RENDERER;
     return ACK_WITH_NOT_CONSUMED;
   }
 
+  if (absorbing_touch_moves_ && event.type == WebInputEvent::TouchMove)
+    return ACK_WITH_NOT_CONSUMED;
+
   // Touch press events should always be forwarded to the renderer.
   if (event.type == WebInputEvent::TouchStart)
     return FORWARD_TO_RENDERER;
 
   for (unsigned int i = 0; i < event.touchesLength; ++i) {
     const WebTouchPoint& point = event.touches[i];
     // If a point has been stationary, then don't take it into account.
     if (point.state == WebTouchPoint::StateStationary)
       continue;
 
@@ skipping 26 matching lines @@
   } else if (event.type == WebInputEvent::TouchStart) {
     for (unsigned i = 0; i < event.touchesLength; ++i) {
       const WebTouchPoint& point = event.touches[i];
       if (point.state == WebTouchPoint::StatePressed)
         touch_ack_states_[point.id] = ack_result;
     }
   }
 }
 
 }  // namespace content