Avoid sending touchmove events where all pointers are stationary

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 28 matching lines @@
   return event;
 }
 
 bool ShouldTouchTriggerTimeout(const WebTouchEvent& event) {
   return (event.type == WebInputEvent::TouchStart ||
           event.type == WebInputEvent::TouchMove) &&
          !WebInputEventTraits::IgnoresAckDisposition(event);
 }
 
 // Compare all properties of touch points to determine the state.
-bool HasPointChanged(const WebTouchPoint& last_point,
-    const WebTouchPoint& current_point) {
-  if (last_point.screenPosition != current_point.screenPosition ||
-      last_point.position != current_point.position ||
-      last_point.radiusX != current_point.radiusX ||
-      last_point.radiusY != current_point.radiusY ||
-      last_point.rotationAngle != current_point.rotationAngle ||
-      last_point.force != current_point.force) {
+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 ||
+      point_1.rotationAngle != point_2.rotationAngle ||
+      point_1.force != point_2.force) {
     return true;
   }
   return false;
 }
 
 }  // namespace
 
 
 // Cancels a touch sequence if a touchstart or touchmove ack response is
 // sufficiently delayed.
@@ skipping 655 matching lines @@
       const WebTouchPoint& point = event.touches[i];
       if (point.state == WebTouchPoint::StateStationary)
         continue;
 
       // |last_sent_touchevent_| will be non-null as long as there is an
       // active touch sequence being forwarded to the renderer.
       if (!last_sent_touchevent_)
         continue;
 
       for (size_t j = 0; j < last_sent_touchevent_->touchesLength; ++j) {
-        if (point.id == last_sent_touchevent_->touches[j].id)
+        if (point.id != last_sent_touchevent_->touches[j].id)
+          continue;
+
+        if (event.type != WebInputEvent::TouchMove)
           return FORWARD_TO_RENDERER;
+
+        // All pointers in TouchMove events may have state as StateMoved,
+        // even though none of the pointers have not changed in real.
+        // Forward these events when at least one pointer has changed.
+        if (HasPointChanged(last_sent_touchevent_->touches[j], point))
+          return FORWARD_TO_RENDERER;
+
+        // This is a TouchMove event and not forwarded yet.

[jdduke (slow), 2015/02/13 16:37:37]

Nit: Maybe reword this like:

// This is a TouchMove event for which we have yet to find a non-stationary
pointer. Continue checking the next pointers in the |event|.

[USE s.singapati at gmail.com, 2015/02/16 10:52:01]

Done.

+        // Continue checking the next pointers in the |event|.
+        break;
       }

[jdduke (slow), 2015/02/13 16:37:37]

It's a shame we can't "clean up" the pointer state here while we're at it, but
that would involve making the argument a pointer and maybe it's not worth it.

[USE s.singapati at gmail.com, 2015/02/16 10:52:01]

Acknowledged. Lets see if this can be done may be after this patch.

+
     }
   }
 
+  if (event.type == WebInputEvent::TouchMove)

[jdduke (slow), 2015/02/13 16:37:37]

This isn't always correct. Let's just go ahead and stick with NO_CONSUMER_EXISTS
for now.

[USE s.singapati at gmail.com, 2015/02/16 10:52:01]

Done.

+    return ACK_WITH_NOT_CONSUMED;
+
   return ACK_WITH_NO_CONSUMER_EXISTS;
 }
 
 void TouchEventQueue::UpdateTouchConsumerStates(const WebTouchEvent& event,
                                                 InputEventAckState ack_result) {
   if (event.type == WebInputEvent::TouchStart) {
     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