Refactor to move conversion into the binding class

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

@@ -2,25 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui;
-
 /// Base class for input events.
 class InputEvent {
 
   const InputEvent({ this.type, this.timeStamp: 0.0 });
 
-  factory InputEvent.fromUiEvent(ui.Event event) {
-    if (event is ui.PointerEvent)
-      return new PointerInputEvent.fromUiEvent(event);
-
-    // Default event
-    return new InputEvent(
-      type: event.type,
-      timeStamp: event.timeStamp
-    );
-  }
-
   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;
 
 }
@@ -55,53 +44,6 @@ class PointerInputEvent extends InputEvent {
     this.tilt
   }) : super(type: type, timeStamp: timeStamp);
 
-  factory PointerInputEvent.fromUiEvent(ui.PointerEvent event) {
-     PointerInputEvent result = new PointerInputEvent(
-        type: event.type,
-        timeStamp: event.timeStamp,
-        pointer: _getPointerValue(event.type, event.pointer),
-        kind: event.kind,
-        x: event.x,
-        y: event.y,
-        dx: event.dx,
-        dy: event.dy,
-        buttons: event.buttons,
-        down: event.down,
-        primary: event.primary,
-        obscured: event.obscured,
-        pressure: event.pressure,
-        pressureMin: event.pressureMin,
-        pressureMax: event.pressureMax,
-        distance: event.distance,
-        distanceMin: event.distanceMin,
-        distanceMax: event.distanceMax,
-        radiusMajor: event.radiusMajor,
-        radiusMinor: event.radiusMinor,
-        radiusMin: event.radiusMin,
-        radiusMax: event.radiusMax,
-        orientation: event.orientation,
-        tilt: event.tilt
-      );
-      return result;
-  }
-
-  // Map actual input pointer value to a unique value
-  // Since events are serialized we can just use a counter
-  static Map<int, int> _pointerMap = new Map<int, int>();
-  static int _pointerCount = 0;
-
-  static int _getPointerValue(String eventType, int pointer) {
-    int result;
-    if (eventType == 'pointerdown') {
-      result = pointer;
-      _pointerMap[pointer] = _pointerCount;
-      _pointerCount++;
-    } else {
-      result = _pointerMap[pointer];
-    }
-    return result;
-  }
-
   final int pointer;
   final String kind;
   final double x;

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

@@ -23,12 +23,6 @@ int _hammingWeight(int value) {
   return weight;
 }
 
-class _PointerState {
-  _PointerState({ this.result, this.lastPosition });
-  HitTestResult result;
-  Point lastPosition;
-}
-
 typedef void EventListener(InputEvent event);
 
 /// A hit test entry used by [FlutterBinding]
@@ -39,6 +33,93 @@ class BindingHitTestEntry extends HitTestEntry {
   final HitTestResult result;
 }
 
+/// State used in converting ui.Event to InputEvent
+class _PointerState {
+  _PointerState({ this.pointer, this.lastPosition });
+  int pointer;
+  Point lastPosition;
+}
+
+class _UiEventConverter {
+  static InputEvent convert(ui.Event event) {
+    if (event is ui.PointerEvent)
+      return convertPointerEvent(event);
+
+    // Default event
+    return new InputEvent(
+      type: event.type,
+      timeStamp: event.timeStamp
+    );
+  }
+
+  // Map actual input pointer value to a unique value
+  // Since events are serialized we can just use a counter
+  static Map<int, _PointerState> _stateForPointer = new Map<int, _PointerState>();
+  static int _pointerCount = 0;
+
+  static PointerInputEvent convertPointerEvent(ui.PointerEvent event) {
+    Point position = new Point(event.x, event.y);
+
+    _PointerState state = _stateForPointer[event.pointer];
+    double dx, dy;
+    switch (event.type) {
+      case 'pointerdown':
+        if (state == null) {
+          state = new _PointerState(lastPosition: position);
+          _stateForPointer[event.pointer] = state;
+        }
+        state.pointer = _pointerCount;
+        _pointerCount++;
+        break;
+      case 'pointermove':
+        // state == null means the pointer is hovering
+        if (state != null) {
+          dx = position.x - state.lastPosition.x;
+          dy = position.y - state.lastPosition.y;
+          state.lastPosition = position;
+        }
+        break;
+      case 'pointerup':
+      case 'pointercancel':
+        // state == null indicates spurious events
+        if (state != null) {
+          // Only remove the pointer state when the last button has been released.
+          if (_hammingWeight(event.buttons) <= 1)
+            _stateForPointer.remove(event.pointer);
+        }
+        break;
+    }
+
+    return new PointerInputEvent(
+       type: event.type,
+       timeStamp: event.timeStamp,
+       pointer: state.pointer,
+       kind: event.kind,
+       x: event.x,
+       y: event.y,
+       dx: dx,
+       dy: dy,
+       buttons: event.buttons,
+       down: event.down,
+       primary: event.primary,
+       obscured: event.obscured,
+       pressure: event.pressure,
+       pressureMin: event.pressureMin,
+       pressureMax: event.pressureMax,
+       distance: event.distance,
+       distanceMin: event.distanceMin,
+       distanceMax: event.distanceMax,
+       radiusMajor: event.radiusMajor,
+       radiusMinor: event.radiusMinor,
+       radiusMin: event.radiusMin,
+       radiusMax: event.radiusMax,
+       orientation: event.orientation,
+       tilt: event.tilt
+     );
+  }
+
+}
+
 /// The glue between the render tree and the Flutter engine
 class FlutterBinding extends HitTestTarget {
 
@@ -95,7 +176,7 @@ class FlutterBinding extends HitTestTarget {
   bool removeEventListener(EventListener listener) => _eventListeners.remove(listener);
 
   void _handleEvent(ui.Event event) {
-    InputEvent ourEvent = new InputEvent.fromUiEvent(event);
+    InputEvent ourEvent = _UiEventConverter.convert(event);
     if (ourEvent is PointerInputEvent) {
       _handlePointerInputEvent(ourEvent);
     } else {
@@ -110,41 +191,36 @@ class FlutterBinding extends HitTestTarget {
   /// State for all pointers which are currently down.
   /// We do not track the state of hovering pointers because we need
   /// to hit-test them on each movement.
-  Map<int, _PointerState> _stateForPointer = new Map<int, _PointerState>();
+  Map<int, HitTestResult> _resultForPointer = new Map<int, HitTestResult>();
 
   void _handlePointerInputEvent(PointerInputEvent event) {
-    Point position = new Point(event.x, event.y);
-
-    _PointerState state = _stateForPointer[event.pointer];
+    HitTestResult result = _resultForPointer[event.pointer];
     switch (event.type) {
       case 'pointerdown':
-        if (state == null) {
-          state = new _PointerState(result: hitTest(position), lastPosition: position);
-          _stateForPointer[event.pointer] = state;
+        if (result == null) {
+          result = hitTest(new Point(event.x, event.y));
+          _resultForPointer[event.pointer] = result;
         }
         break;
       case 'pointermove':
-        if (state == null) {
+        if (result == null) {
           // The pointer is hovering, ignore it for now since we don't
           // know what to do with it yet.
           return;
         }
-        event.dx = position.x - state.lastPosition.x;
-        event.dy = position.y - state.lastPosition.y;
-        state.lastPosition = position;
         break;
       case 'pointerup':
       case 'pointercancel':
-        if (state == null) {
+        if (result == null) {
           // This seems to be a spurious event.  Ignore it.
           return;
         }
-        // Only remove the pointer state when the last button has been released.
+        // Only remove the hit test result when the last button has been released.
         if (_hammingWeight(event.buttons) <= 1)
-          _stateForPointer.remove(event.pointer);
+          _resultForPointer.remove(event.pointer);
         break;
     }
-    dispatchEvent(event, state.result);
+    dispatchEvent(event, result);
   }
 
   /// Determine which [HitTestTarget] objects are located at a given position