Move Drawer to GestureDetector

This fixes an issue in the stocks app in horizontal mode where you could both
scroll and drag the drawer at the same time.

packages/flutter/lib/gestures/drag.dart

@@ -15,14 +15,14 @@ enum DragState {
 }
 
 typedef void GestureDragStartCallback();
-typedef void GestureDragUpdateCallback(double scrollDelta);
+typedef void GestureDragUpdateCallback(double delta);
 typedef void GestureDragEndCallback(sky.Offset velocity);
 
 typedef void GesturePanStartCallback();
-typedef void GesturePanUpdateCallback(sky.Offset scrollDelta);
+typedef void GesturePanUpdateCallback(sky.Offset delta);
 typedef void GesturePanEndCallback(sky.Offset velocity);
 
-typedef void _GesturePolymorphicUpdateCallback<T>(T scrollDelta);
+typedef void _GesturePolymorphicUpdateCallback<T>(T delta);
 
 int _eventTime(sky.PointerEvent event) => (event.timeStamp * 1000.0).toInt(); // microseconds
 
@@ -121,8 +121,7 @@ class VerticalDragGestureRecognizer extends _DragGestureRecognizer<double> {
   }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
 
   double get _initialPendingDragDelta => 0.0;
-  // Notice that we negate dy because scroll offsets go in the opposite direction.
-  double _getDragDelta(sky.PointerEvent event) => -event.dy;
+  double _getDragDelta(sky.PointerEvent event) => event.dy;
   bool get _hasSufficientPendingDragDeltaToAccept => _pendingDragDelta.abs() > kTouchSlop;
 }
 
@@ -135,7 +134,7 @@ class HorizontalDragGestureRecognizer extends _DragGestureRecognizer<double> {
   }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
 
   double get _initialPendingDragDelta => 0.0;
-  double _getDragDelta(sky.PointerEvent event) => -event.dx;
+  double _getDragDelta(sky.PointerEvent event) => event.dx;
   bool get _hasSufficientPendingDragDeltaToAccept => _pendingDragDelta.abs() > kTouchSlop;
 }
 
@@ -148,8 +147,7 @@ class PanGestureRecognizer extends _DragGestureRecognizer<sky.Offset> {
   }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
 
   sky.Offset get _initialPendingDragDelta => sky.Offset.zero;
-  // Notice that we negate dy because scroll offsets go in the opposite direction.
-  sky.Offset _getDragDelta(sky.PointerEvent event) => new sky.Offset(event.dx, -event.dy);
+  sky.Offset _getDragDelta(sky.PointerEvent event) => new sky.Offset(event.dx, event.dy);
   bool get _hasSufficientPendingDragDeltaToAccept {
     return _pendingDragDelta.dx.abs() > kTouchSlop || _pendingDragDelta.dy.abs() > kTouchSlop;
   }

packages/flutter/lib/src/widgets/dismissable.dart

@@ -119,7 +119,7 @@ class Dismissable extends StatefulComponent {
     });
   }
 
-  void _handleDragUpdate(double scrollOffset) {
+  void _handleDragUpdate(double delta) {
     if (!_isActive || _fadePerformance.isAnimating)
       return;
 
@@ -127,19 +127,19 @@ class Dismissable extends StatefulComponent {
     switch(direction) {
       case DismissDirection.horizontal:
       case DismissDirection.vertical:
-        _dragExtent -= scrollOffset;
+        _dragExtent += delta;
         break;
 
       case DismissDirection.up:
       case DismissDirection.left:
-        if (_dragExtent - scrollOffset < 0)
-          _dragExtent -= scrollOffset;
+        if (_dragExtent + delta < 0)
+          _dragExtent += delta;
         break;
 
       case DismissDirection.down:
       case DismissDirection.right:
-        if (_dragExtent - scrollOffset > 0)
-          _dragExtent -= scrollOffset;
+        if (_dragExtent + delta > 0)
+          _dragExtent += delta;
         break;
     }
 

packages/flutter/lib/src/widgets/drawer.dart

@@ -109,13 +109,11 @@ class Drawer extends StatefulComponent {
       )
     );
 
-    return new Listener(
-      child: new Stack([ mask, content ]),
-      onPointerDown: handlePointerDown,
-      onPointerMove: handlePointerMove,
-      onPointerUp: handlePointerUp,
-      onPointerCancel: handlePointerCancel,
-      onGestureFlingStart: handleFlingStart
+    return new GestureDetector(
+      onHorizontalDragStart: _performance.stop,
+      onHorizontalDragUpdate: _handleDragUpdate,
+      onHorizontalDragEnd: _handleDragEnd,
+      child: new Stack([ mask, content ])
     );
   }
 
@@ -132,41 +130,17 @@ class Drawer extends StatefulComponent {
 
   void _settle() { _isMostlyClosed ? _performance.reverse() : _performance.play(); }
 
-  // TODO(mpcomplete): Figure out how to generalize these handlers on a
-  // "PannableThingy" interface.
-  EventDisposition handlePointerDown(_) {
-    _performance.stop();
-    return EventDisposition.processed;
- }
-
-  EventDisposition handlePointerMove(sky.PointerEvent event) {
-    if (_performance.isAnimating)
-      return EventDisposition.ignored;
-    _performance.progress += event.dx / _kWidth;
-    return EventDisposition.processed;
+  void _handleDragUpdate(double delta) {
+    _performance.progress += delta / _kWidth;
   }
 
-  EventDisposition handlePointerUp(_) {
-    if (!_performance.isAnimating) {
+  void _handleDragEnd(Offset velocity) {
+    if (velocity.dx.abs() >= _kMinFlingVelocity) {
+      _performance.fling(velocity: velocity.dx * _kFlingVelocityScale);
+      return;
+    } else {
       _settle();
-      return EventDisposition.processed;
     }
-    return EventDisposition.ignored;
   }
 
-  EventDisposition handlePointerCancel(_) {
-    if (!_performance.isAnimating) {
-      _settle();
-      return EventDisposition.processed;
-    }
-    return EventDisposition.ignored;
-  }
-
-  EventDisposition handleFlingStart(event) {
-    if (event.velocityX.abs() >= _kMinFlingVelocity) {
-      _performance.fling(velocity: event.velocityX * _kFlingVelocityScale);
-      return EventDisposition.processed;
-    }
-    return EventDisposition.ignored;
-  }
 }

packages/flutter/lib/src/widgets/scrollable.dart

@@ -83,7 +83,7 @@ abstract class Scrollable extends StatefulComponent {
   GestureDragUpdateCallback _getDragUpdateHandler(ScrollDirection direction) {
     if (scrollDirection != direction || !scrollBehavior.isScrollable)
       return null;
-    return scrollBy;
+    return _handleDragUpdate;
   }
 
   GestureDragEndCallback _getDragEndHandler(ScrollDirection direction) {
@@ -181,6 +181,12 @@ abstract class Scrollable extends StatefulComponent {
     return EventDisposition.processed;
   }
 
+  void _handleDragUpdate(double delta) {
+    // We negate the delta here because a positive scroll offset moves the
+    // the content up (or to the left) rather than down (or the right).
+    scrollBy(-delta);
+  }
+
   void _handleDragEnd(Offset velocity) {
     if (velocity != Offset.zero) {
       _startToEndAnimation(velocity: _scrollVelocity(velocity));

packages/unit/test/gestures/scroll_test.dart

@@ -53,14 +53,14 @@ void main() {
     router.route(pointer.move(new Point(20.0, 20.0)));
     expect(didStartPan, isTrue);
     didStartPan = false;
-    expect(updatedScrollDelta, new sky.Offset(10.0, -10.0));
+    expect(updatedScrollDelta, new sky.Offset(10.0, 10.0));
     updatedScrollDelta = null;
     expect(didEndPan, isFalse);
     expect(didTap, isFalse);
 
     router.route(pointer.move(new Point(20.0, 25.0)));
     expect(didStartPan, isFalse);
-    expect(updatedScrollDelta, new sky.Offset(0.0, -5.0));
+    expect(updatedScrollDelta, new sky.Offset(0.0, 5.0));
     updatedScrollDelta = null;
     expect(didEndPan, isFalse);
     expect(didTap, isFalse);

packages/unit/test/widget/gesture_detector_test.dart

@@ -43,7 +43,7 @@ void main() {
     Point secondLocation = new Point(10.0, 9.0);
     tester.dispatchEvent(pointer.move(secondLocation), firstLocation);
     expect(didStartDrag, isFalse);
-    expect(updatedDragDelta, 1.0);
+    expect(updatedDragDelta, -1.0);
     updatedDragDelta = null;
     expect(didEndDrag, isFalse);
 
@@ -86,6 +86,6 @@ void main() {
     tester.dispatchEvent(pointer.up(), downLocation);
 
     expect(gestureCount, 2);
-    expect(dragDistance, -20.0);
+    expect(dragDistance, 20.0);
   });
 }