[Aura] Reduce frequency of PinchUpdate events.

ui/events/gesture_detection/scale_gesture_detector.cc

Index: ui/events/gesture_detection/scale_gesture_detector.cc
diff --git a/ui/events/gesture_detection/scale_gesture_detector.cc b/ui/events/gesture_detection/scale_gesture_detector.cc
index f9e091bc6ce55204704cf144593c114f7050ca51..5ac30d3e6f89fa50e200aad94c326d5970cd6dfd 100644
--- a/ui/events/gesture_detection/scale_gesture_detector.cc
+++ b/ui/events/gesture_detection/scale_gesture_detector.cc
@@ -33,7 +33,8 @@ const float kScaleFactor = .5f;
 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() {}
 
@@ -80,6 +81,7 @@ ScaleGestureDetector::ScaleGestureDetector(const Config& config,
   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);
 }
@@ -205,6 +207,9 @@ bool ScaleGestureDetector::OnTouchEvent(const MotionEvent& event) {
     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_)) {
@@ -217,6 +222,9 @@ bool ScaleGestureDetector::OnTouchEvent(const MotionEvent& 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;