Convert PointerInputEvent to Duration for timestamp

To make the units clear.

packages/flutter/lib/src/gestures/events.dart

@@ -8,14 +8,9 @@ export 'dart:ui' show Point;
 
 /// Base class for input events.
 class InputEvent {
-
-  const InputEvent({ this.type, this.timeStamp: 0.0 });
-
+  const InputEvent({ this.type, this.timeStamp: const Duration() });
   final String type;
-  // TODO: Should timeStamp be a DateTime object instead of double?
-  // Some client code (e.g. drag.dart) does math on the time stamp.
-  final double timeStamp;
-
+  final Duration timeStamp;
 }
 
 /// Input event representing a touch or button.
@@ -23,7 +18,7 @@ class PointerInputEvent extends InputEvent {
 
   const PointerInputEvent({
     String type,
-    double timeStamp: 0.0,
+    Duration timeStamp: const Duration(),
     this.pointer: 0,
     this.kind,
     this.x: 0.0,

packages/flutter/lib/src/gestures/velocity_tracker.dart

@@ -16,7 +16,7 @@ class GestureVelocity {
 
 class _Estimator {
   int degree;
-  double time;
+  Duration time;
   List<double> xCoefficients;
   List<double> yCoefficients;
   double confidence;
@@ -32,7 +32,7 @@ class _Estimator {
 }
 
 abstract class _VelocityTrackerStrategy {
-  void addMovement(double timeStamp, double x, double y);
+  void addMovement(Duration timeStamp, double x, double y);
   bool getEstimator(_Estimator estimator);
   void clear();
 }
@@ -45,7 +45,7 @@ enum _Weighting {
 }
 
 class _Movement {
-  double eventTime = 0.0;
+  Duration eventTime = const Duration();
   ui.Point position = ui.Point.origin;
 }
 
@@ -61,7 +61,7 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
   final List<_Movement> _movements;
   int _index;
 
-  void addMovement(double timeStamp, double x, double y) {
+  void addMovement(Duration timeStamp, double x, double y) {
     if (++_index == kHistorySize)
       _index = 0;
     _Movement movement = _getMovement(_index);
@@ -81,7 +81,7 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
     do {
       _Movement movement = _getMovement(index);
 
-      double age = newestMovement.eventTime - movement.eventTime;
+      double age = (newestMovement.eventTime - movement.eventTime).inMilliseconds.toDouble();
       if (age > kHorizonMilliseconds)
         break;
 
@@ -143,8 +143,7 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
           return 1.0;
         }
         int nextIndex = (index + 1) % kHistorySize;
-        double deltaMilliseconds = _movements[nextIndex].eventTime -
-          _movements[index].eventTime;
+        int deltaMilliseconds = (_movements[nextIndex].eventTime - _movements[index].eventTime).inMilliseconds;
         if (deltaMilliseconds < 0)
           return 0.5;
         if (deltaMilliseconds < 10)
@@ -159,8 +158,7 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
         //   age 10ms: 1.0
         //   age 50ms: 1.0
         //   age 60ms: 0.5
-        double ageMilliseconds = _movements[_index].eventTime -
-          _movements[index].eventTime;
+        int ageMilliseconds = (_movements[_index].eventTime - _movements[index].eventTime).inMilliseconds;
         if (ageMilliseconds < 0)
           return 0.5;
         if (ageMilliseconds < 10)
@@ -177,8 +175,7 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
         //   age   0ms: 1.0
         //   age  50ms: 1.0
         //   age 100ms: 0.5
-        double ageMilliseconds = _movements[_index].eventTime -
-          _movements[index].eventTime;
+        int ageMilliseconds = (_movements[_index].eventTime - _movements[index].eventTime).inMilliseconds;
         if (ageMilliseconds < 50) {
           return 1.0;
         }
@@ -207,13 +204,13 @@ class _LeastSquaresVelocityTrackerStrategy extends _VelocityTrackerStrategy {
 class VelocityTracker {
   static const int kAssumePointerMoveStoppedTimeMs = 40;
 
-  VelocityTracker() : _lastTimeStamp = 0.0, _strategy = _createStrategy();
+  VelocityTracker() : _strategy = _createStrategy();
 
-  double _lastTimeStamp;
+  Duration _lastTimeStamp = const Duration();
   _VelocityTrackerStrategy _strategy;
 
-  void addPosition(double timeStamp, double x, double y) {
-    if ((timeStamp - _lastTimeStamp) >= kAssumePointerMoveStoppedTimeMs)
+  void addPosition(Duration timeStamp, double x, double y) {
+    if ((timeStamp - _lastTimeStamp).inMilliseconds >= kAssumePointerMoveStoppedTimeMs)
       _strategy.clear();
     _lastTimeStamp = timeStamp;
     _strategy.addMovement(timeStamp, x, y);

packages/flutter/lib/src/rendering/binding.dart

@@ -90,7 +90,7 @@ class _PointerEventConverter {
 
     return new PointerInputEvent(
        type: eventType,
-       timeStamp: pointer.timeStamp.toDouble(),
+       timeStamp: new Duration(microseconds: pointer.timeStamp),
        pointer: pointerIndex,
        kind: _mapPointerKindToString(pointer.kind),
        x: pointer.x,
@@ -200,11 +200,12 @@ class FlutterBinding extends HitTestTarget {
   /// Stops calling listener for every event that isn't localized to a given view coordinate
   bool removeEventListener(EventListener listener) => _eventListeners.remove(listener);
 
+  // TODO(abarth): The engine should give us the timeStamp in Durations.
   void _handleEvent(String eventType, double timeStamp) {
     assert(eventType == 'back');
     InputEvent ourEvent = new InputEvent(
       type: eventType,
-      timeStamp: timeStamp
+      timeStamp: new Duration(microseconds: timeStamp.round())
     );
     for (EventListener listener in _eventListeners)
       listener(ourEvent);

packages/unit/test/engine/mock_events.dart

@@ -11,7 +11,7 @@ class TestPointer {
   bool isDown = false;
   ui.Point location;
 
-  PointerInputEvent down(ui.Point newLocation, { double timeStamp: 0.0 }) {
+  PointerInputEvent down(ui.Point newLocation, { Duration timeStamp: const Duration() }) {
     assert(!isDown);
     isDown = true;
     location = newLocation;
@@ -24,7 +24,7 @@ class TestPointer {
     );
   }
 
-  PointerInputEvent move(ui.Point newLocation, { double timeStamp: 0.0 }) {
+  PointerInputEvent move(ui.Point newLocation, { Duration timeStamp: const Duration() }) {
     assert(isDown);
     ui.Offset delta = newLocation - location;
     location = newLocation;
@@ -39,7 +39,7 @@ class TestPointer {
     );
   }
 
-  PointerInputEvent up({ double timeStamp: 0.0 }) {
+  PointerInputEvent up({ Duration timeStamp: const Duration() }) {
     assert(isDown);
     isDown = false;
     return new PointerInputEvent(
@@ -51,7 +51,7 @@ class TestPointer {
     );
   }
 
-  PointerInputEvent cancel({ double timeStamp: 0.0 }) {
+  PointerInputEvent cancel({ Duration timeStamp: const Duration() }) {
     assert(isDown);
     isDown = false;
     return new PointerInputEvent(

packages/unit/test/gestures/velocity_tracker_test.dart

@@ -24,7 +24,7 @@ List<PointerInputEvent> _eventFromMap(List<Map> intermediate) {
 PointerInputEvent _eventFor(Map entry) {
   PointerInputEvent result = new PointerInputEvent(
     type: entry['type'],
-    timeStamp: entry['timeStamp'],
+    timeStamp: new Duration(milliseconds: entry['timeStamp'].round()),
     pointer: entry['pointer'],
     x: entry['x'],
     y: entry['y']

packages/unit/test/widget/widget_tester.dart

@@ -165,13 +165,13 @@ class WidgetTester {
     final kMoveCount = 50; // Needs to be >= kHistorySize, see _LeastSquaresVelocityTrackerStrategy
     final double timeStampDelta = 1000.0 * offset.distance / (kMoveCount * velocity);
     double timeStamp = 0.0;
-    _dispatchEvent(p.down(startLocation, timeStamp: timeStamp), result);
+    _dispatchEvent(p.down(startLocation, timeStamp: new Duration(milliseconds: timeStamp.round())), result);
     for(int i = 0; i < kMoveCount; i++) {
       final Point location = startLocation + Offset.lerp(Offset.zero, offset, i / kMoveCount);
-      _dispatchEvent(p.move(location, timeStamp: timeStamp), result);
+      _dispatchEvent(p.move(location, timeStamp: new Duration(milliseconds: timeStamp.round())), result);
       timeStamp += timeStampDelta;
     }
-    _dispatchEvent(p.up(timeStamp: timeStamp), result);
+    _dispatchEvent(p.up(timeStamp: new Duration(milliseconds: timeStamp.round())), result);
   }
 
   void scroll(Element element, Offset offset, { int pointer: 1 }) {