[Aura] Reduce frequency of PinchUpdate events.

ui/events/gesture_detection/scale_gesture_detector.cc

 // Copyright 2014 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 "ui/events/gesture_detection/scale_gesture_detector.h"
 
 #include <limits.h>
 #include <cmath>
 
 #include "base/float_util.h"
@@ skipping 15 matching lines @@
 
 const float kScaleFactor = .5f;
 
 }  // namespace
 
 // Note: These constants were taken directly from the default (unscaled)
 // versions found in Android's ViewConfiguration.
 ScaleGestureDetector::Config::Config()
     : min_scaling_touch_major(48),
       min_scaling_span(200),
-      quick_scale_enabled(true) {}
+      quick_scale_enabled(true),
+      min_pinch_update_distance(0) {}
 
 ScaleGestureDetector::Config::~Config() {}
 
 bool ScaleGestureDetector::SimpleScaleGestureListener::OnScale(
     const ScaleGestureDetector&, const MotionEvent&) {
   return false;
 }
 
 bool ScaleGestureDetector::SimpleScaleGestureListener::OnScaleBegin(
     const ScaleGestureDetector&, const MotionEvent&) {
@@ skipping 26 matching lines @@
       touch_history_direction_(0),
       touch_min_major_(0),
       double_tap_focus_x_(0),
       double_tap_focus_y_(0),
       double_tap_mode_(DOUBLE_TAP_MODE_NONE),
       event_before_or_above_starting_gesture_event_(false) {
   DCHECK(listener_);
   span_slop_ =
       (config.gesture_detector_config.touch_slop + kSlopEpsilon) * 2;
   touch_min_major_ = config.min_scaling_touch_major;
+  min_pinch_update_distance_ = config.min_pinch_update_distance;
   min_span_ = config.min_scaling_span + kSlopEpsilon;
   SetQuickScaleEnabled(config.quick_scale_enabled);
 }
 
 ScaleGestureDetector::~ScaleGestureDetector() {}
 
 bool ScaleGestureDetector::OnTouchEvent(const MotionEvent& event) {
   curr_time_ = event.GetEventTime();
 
   const int action = event.GetAction();
@@ skipping 105 matching lines @@
     in_progress_ = false;
     initial_span_ = span;
     double_tap_mode_ = DOUBLE_TAP_MODE_NONE;
   }
   if (config_changed) {
     prev_span_x_ = curr_span_x_ = span_x;
     prev_span_y_ = curr_span_y_ = span_y;
     initial_span_ = prev_span_ = curr_span_ = span;
   }
 
+  bool pinch_occured =
+        std::abs(span - prev_span_) >= min_pinch_update_distance_;

[jdduke (slow), 2014/05/21 19:30:37]

Can we move this check into the ACTION_MOVE portion below?

[tdresser, 2014/05/22 12:31:44]

We need to read prev_span_ before it is modified below.

+
   const float min_span = InDoubleTapMode() ? span_slop_ : min_span_;
   if (!in_progress_ && span >= min_span &&
       (was_in_progress || std::abs(span - initial_span_) > span_slop_)) {
     prev_span_x_ = curr_span_x_ = span_x;
     prev_span_y_ = curr_span_y_ = span_y;
     prev_span_ = curr_span_ = span;

[tdresser, 2014/05/22 12:31:44]

Need to read prev_span_ before this line.

     prev_time_ = curr_time_;
     in_progress_ = listener_->OnScaleBegin(*this, event);
   }
 
   // Handle motion; focal point and span/scale factor are changing.
   if (action == MotionEvent::ACTION_MOVE) {
+    if (!pinch_occured)
+      return true;
+
     curr_span_x_ = span_x;
     curr_span_y_ = span_y;
     curr_span_ = span;
 
     bool update_prev = true;
 
     if (in_progress_) {
       update_prev = listener_->OnScale(*this, event);
     }
 
@@ skipping 135 matching lines @@
 
 void ScaleGestureDetector::ClearTouchHistory() {
   touch_upper_ = std::numeric_limits<float>::quiet_NaN();
   touch_lower_ = std::numeric_limits<float>::quiet_NaN();
   touch_history_last_accepted_ = std::numeric_limits<float>::quiet_NaN();
   touch_history_direction_ = 0;
   touch_history_last_accepted_time_ = base::TimeTicks();
 }
 
 }  // namespace ui