Disambiguate horizontal and vertical scrolling

We now have separate gestures for horizontal, vertical, and pan scrolling.

packages/flutter/lib/gestures/scroll.dart

@@ -15,43 +15,48 @@ enum ScrollState {
 }
 
 typedef void GestureScrollStartCallback();
-typedef void GestureScrollUpdateCallback(sky.Offset scrollDelta);
+typedef void GestureScrollUpdateCallback(double scrollDelta);
 typedef void GestureScrollEndCallback();
 
-sky.Offset _getScrollOffset(sky.PointerEvent event) {
-  // Notice that we negate dy because scroll offsets go in the opposite direction.
-  return new sky.Offset(event.dx, -event.dy);
-}
+typedef void GesturePanStartCallback();
+typedef void GesturePanUpdateCallback(sky.Offset scrollDelta);
+typedef void GesturePanEndCallback();
 
-class ScrollGestureRecognizer extends GestureRecognizer {
-  ScrollGestureRecognizer({ PointerRouter router, this.onScrollStart, this.onScrollUpdate, this.onScrollEnd })
+typedef void _GesturePolymorphicUpdateCallback<T>(T scrollDelta);
+
+abstract class _ScrollGestureRecognizer<T extends dynamic> extends GestureRecognizer {
+  _ScrollGestureRecognizer({ PointerRouter router, this.onStart, this.onUpdate, this.onEnd })
     : super(router: router);
 
-  GestureScrollStartCallback onScrollStart;
-  GestureScrollUpdateCallback onScrollUpdate;
-  GestureScrollEndCallback onScrollEnd;
+  GestureScrollStartCallback onStart;
+  _GesturePolymorphicUpdateCallback<T> onUpdate;
+  GestureScrollEndCallback onEnd;
+
+  ScrollState _state = ScrollState.ready;
+  T _pendingScrollDelta;
 
-  ScrollState state = ScrollState.ready;
-  sky.Offset pendingScrollOffset;
+  T get _initialPendingScrollDelta;
+  T _getScrollDelta(sky.PointerEvent event);
+  bool get _hasSufficientPendingScrollDeltaToAccept;
 
   void addPointer(sky.PointerEvent event) {
     startTrackingPointer(event.pointer);
-    if (state == ScrollState.ready) {
-      state = ScrollState.possible;
-      pendingScrollOffset = sky.Offset.zero;
+    if (_state == ScrollState.ready) {
+      _state = ScrollState.possible;
+      _pendingScrollDelta = _initialPendingScrollDelta;
     }
   }
 
   void handleEvent(sky.PointerEvent event) {
-    assert(state != ScrollState.ready);
+    assert(_state != ScrollState.ready);
     if (event.type == 'pointermove') {
-      sky.Offset offset = _getScrollOffset(event);
-      if (state == ScrollState.accepted) {
-        if (onScrollUpdate != null)
-          onScrollUpdate(offset);
+      T delta = _getScrollDelta(event);
+      if (_state == ScrollState.accepted) {
+        if (onUpdate != null)
+          onUpdate(delta);
       } else {
-        pendingScrollOffset += offset;
-        if (pendingScrollOffset.distance > kTouchSlop)
+        _pendingScrollDelta += delta;
+        if (_hasSufficientPendingScrollDeltaToAccept)
           resolve(GestureDisposition.accepted);
       }
     }
@@ -59,22 +64,64 @@ class ScrollGestureRecognizer extends GestureRecognizer {
   }
 
   void acceptGesture(int pointer) {
-    if (state != ScrollState.accepted) {
-      state = ScrollState.accepted;
-      sky.Offset offset = pendingScrollOffset;
-      pendingScrollOffset = null;
-      if (onScrollStart != null)
-        onScrollStart();
-      if (offset != sky.Offset.zero && onScrollUpdate != null)
-        onScrollUpdate(offset);
+    if (_state != ScrollState.accepted) {
+      _state = ScrollState.accepted;
+      T delta = _pendingScrollDelta;
+      _pendingScrollDelta = null;
+      if (onStart != null)
+        onStart();
+      if (delta != _initialPendingScrollDelta && onUpdate != null)
+        onUpdate(delta);
     }
   }
 
   void didStopTrackingLastPointer() {
-    bool wasAccepted = (state == ScrollState.accepted);
-    state = ScrollState.ready;
-    if (wasAccepted && onScrollEnd != null)
-      onScrollEnd();
+    bool wasAccepted = (_state == ScrollState.accepted);
+    _state = ScrollState.ready;
+    if (wasAccepted && onEnd != null)
+      onEnd();
   }
+}
+
+class VerticalScrollGestureRecognizer extends _ScrollGestureRecognizer<double> {
+  VerticalScrollGestureRecognizer({
+    PointerRouter router,
+    GestureScrollStartCallback onStart,
+    GestureScrollUpdateCallback onUpdate,
+    GestureScrollEndCallback onEnd
+  }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
 
+  double get _initialPendingScrollDelta => 0.0;
+  // Notice that we negate dy because scroll offsets go in the opposite direction.
+  double _getScrollDelta(sky.PointerEvent event) => -event.dy;
+  bool get _hasSufficientPendingScrollDeltaToAccept => _pendingScrollDelta.abs() > kTouchSlop;
+}
+
+class HorizontalScrollGestureRecognizer extends _ScrollGestureRecognizer<double> {
+  HorizontalScrollGestureRecognizer({
+    PointerRouter router,
+    GestureScrollStartCallback onStart,
+    GestureScrollUpdateCallback onUpdate,
+    GestureScrollEndCallback onEnd
+  }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
+
+  double get _initialPendingScrollDelta => 0.0;
+  double _getScrollDelta(sky.PointerEvent event) => -event.dx;
+  bool get _hasSufficientPendingScrollDeltaToAccept => _pendingScrollDelta.abs() > kTouchSlop;
+}
+
+class PanGestureRecognizer extends _ScrollGestureRecognizer<sky.Offset> {
+  PanGestureRecognizer({
+    PointerRouter router,
+    GesturePanStartCallback onStart,
+    GesturePanUpdateCallback onUpdate,
+    GesturePanEndCallback onEnd
+  }) : super(router: router, onStart: onStart, onUpdate: onUpdate, onEnd: onEnd);
+
+  sky.Offset get _initialPendingScrollDelta => sky.Offset.zero;
+  // Notice that we negate dy because scroll offsets go in the opposite direction.
+  sky.Offset _getScrollDelta(sky.PointerEvent event) => new sky.Offset(event.dx, -event.dy);
+  bool get _hasSufficientPendingScrollDeltaToAccept {
+    return _pendingScrollDelta.dx.abs() > kTouchSlop || _pendingScrollDelta.dy.abs() > kTouchSlop;
+  }
 }

packages/flutter/lib/widgets/gesture_detector.dart

@@ -19,27 +19,48 @@ class GestureDetector extends StatefulComponent {
     this.onTap,
     this.onShowPress,
     this.onLongPress,
-    this.onScrollStart,
-    this.onScrollUpdate,
-    this.onScrollEnd
+    this.onVerticalScrollStart,
+    this.onVerticalScrollUpdate,
+    this.onVerticalScrollEnd,
+    this.onHorizontalScrollStart,
+    this.onHorizontalScrollUpdate,
+    this.onHorizontalScrollEnd,
+    this.onPanStart,
+    this.onPanUpdate,
+    this.onPanEnd
   }) : super(key: key);
 
   Widget child;
   GestureTapListener onTap;
   GestureShowPressListener onShowPress;
   GestureLongPressListener onLongPress;
-  GestureScrollStartCallback onScrollStart;
-  GestureScrollUpdateCallback onScrollUpdate;
-  GestureScrollEndCallback onScrollEnd;
+
+  GestureScrollStartCallback onVerticalScrollStart;
+  GestureScrollUpdateCallback onVerticalScrollUpdate;
+  GestureScrollEndCallback onVerticalScrollEnd;
+
+  GestureScrollStartCallback onHorizontalScrollStart;
+  GestureScrollUpdateCallback onHorizontalScrollUpdate;
+  GestureScrollEndCallback onHorizontalScrollEnd;
+
+  GesturePanStartCallback onPanStart;
+  GesturePanUpdateCallback onPanUpdate;
+  GesturePanEndCallback onPanEnd;
 
   void syncConstructorArguments(GestureDetector source) {
     child = source.child;
     onTap = source.onTap;
     onShowPress = source.onShowPress;
     onLongPress = source.onLongPress;
-    onScrollStart = source.onScrollStart;
-    onScrollUpdate = source.onScrollUpdate;
-    onScrollEnd = source.onScrollEnd;
+    onVerticalScrollStart = onVerticalScrollStart;
+    onVerticalScrollUpdate = onVerticalScrollUpdate;
+    onVerticalScrollEnd = onVerticalScrollEnd;
+    onHorizontalScrollStart = onHorizontalScrollStart;
+    onHorizontalScrollUpdate = onHorizontalScrollUpdate;
+    onHorizontalScrollEnd = onHorizontalScrollEnd;
+    onPanStart = source.onPanStart;
+    onPanUpdate = source.onPanUpdate;
+    onPanEnd = source.onPanEnd;
     _syncGestureListeners();
   }
 
@@ -66,11 +87,25 @@ class GestureDetector extends StatefulComponent {
     return _longPress;
   }
 
-  ScrollGestureRecognizer _scroll;
-  ScrollGestureRecognizer _ensureScroll() {
-    if (_scroll == null)
-      _scroll = new ScrollGestureRecognizer(router: _router);
-    return _scroll;
+  VerticalScrollGestureRecognizer _verticalScroll;
+  VerticalScrollGestureRecognizer _ensureVerticalScroll() {
+    if (_verticalScroll == null)
+      _verticalScroll = new VerticalScrollGestureRecognizer(router: _router);
+    return _verticalScroll;
+  }
+
+  HorizontalScrollGestureRecognizer _horizontalScroll;
+  HorizontalScrollGestureRecognizer _ensureHorizontalScroll() {
+    if (_horizontalScroll == null)
+      _horizontalScroll = new HorizontalScrollGestureRecognizer(router: _router);
+    return _horizontalScroll;
+  }
+
+  PanGestureRecognizer _pan;
+  PanGestureRecognizer _ensurePan() {
+    if (_pan == null)
+      _pan = new PanGestureRecognizer(router: _router);
+    return _pan;
   }
 
   void didMount() {
@@ -83,14 +118,18 @@ class GestureDetector extends StatefulComponent {
     _tap = _ensureDisposed(_tap);
     _showPress = _ensureDisposed(_showPress);
     _longPress = _ensureDisposed(_longPress);
-    _scroll = _ensureDisposed(_scroll);
+    _verticalScroll = _ensureDisposed(_verticalScroll);
+    _horizontalScroll = _ensureDisposed(_horizontalScroll);
+    _pan = _ensureDisposed(_pan);
   }
 
   void _syncGestureListeners() {
     _syncTap();
     _syncShowPress();
     _syncLongPress();
-    _syncScroll();
+    _syncVerticalScroll();
+    _syncHorizontalScroll();
+    _syncPan();
   }
 
   void _syncTap() {
@@ -114,14 +153,36 @@ class GestureDetector extends StatefulComponent {
       _ensureLongPress().onLongPress = onLongPress;
   }
 
-  void _syncScroll() {
-    if (onScrollStart == null && onScrollUpdate == null && onScrollEnd == null) {
-      _scroll = _ensureDisposed(_scroll);
+  void _syncVerticalScroll() {
+    if (onVerticalScrollStart == null && onVerticalScrollUpdate == null && onVerticalScrollEnd == null) {
+      _verticalScroll = _ensureDisposed(_verticalScroll);
+    } else {
+      _ensureVerticalScroll()
+        ..onStart = onVerticalScrollStart
+        ..onUpdate = onVerticalScrollUpdate
+        ..onEnd = onVerticalScrollEnd;
+    }
+  }
+
+  void _syncHorizontalScroll() {
+    if (onHorizontalScrollStart == null && onHorizontalScrollUpdate == null && onHorizontalScrollEnd == null) {
+      _horizontalScroll = _ensureDisposed(_horizontalScroll);
+    } else {
+      _ensureHorizontalScroll()
+        ..onStart = onHorizontalScrollStart
+        ..onUpdate = onHorizontalScrollUpdate
+        ..onEnd = onHorizontalScrollEnd;
+    }
+  }
+
+  void _syncPan() {
+    if (onPanStart == null && onPanUpdate == null && onPanEnd == null) {
+      _pan = _ensureDisposed(_pan);
     } else {
-      _ensureScroll()
-        ..onScrollStart = onScrollStart
-        ..onScrollUpdate = onScrollUpdate
-        ..onScrollEnd = onScrollEnd;
+      _ensurePan()
+        ..onStart = onPanStart
+        ..onUpdate = onPanUpdate
+        ..onEnd = onPanEnd;
     }
   }
 
@@ -138,8 +199,12 @@ class GestureDetector extends StatefulComponent {
       _showPress.addPointer(event);
     if (_longPress != null)
       _longPress.addPointer(event);
-    if (_scroll != null)
-      _scroll.addPointer(event);
+    if (_verticalScroll != null)
+      _verticalScroll.addPointer(event);
+    if (_horizontalScroll != null)
+      _horizontalScroll.addPointer(event);
+    if (_pan != null)
+      _pan.addPointer(event);
     return EventDisposition.processed;
   }
 

packages/flutter/lib/widgets/scrollable.dart

@@ -84,8 +84,10 @@ abstract class Scrollable extends StatefulComponent {
 
   Widget build() {
     return new GestureDetector(
-      onScrollUpdate: _handleScrollUpdate,
-      onScrollEnd: _maybeSettleScrollOffset,
+      onVerticalScrollUpdate: scrollDirection == ScrollDirection.vertical ? scrollBy : null,
+      onVerticalScrollEnd: scrollDirection == ScrollDirection.vertical ? _maybeSettleScrollOffset : null,
+      onHorizontalScrollUpdate: scrollDirection == ScrollDirection.horizontal ? scrollBy : null,
+      onHorizontalScrollEnd: scrollDirection == ScrollDirection.horizontal ? _maybeSettleScrollOffset : null,
       child: new Listener(
         child: buildContent(),
         onPointerDown: _handlePointerDown,
@@ -172,10 +174,6 @@ abstract class Scrollable extends StatefulComponent {
     return EventDisposition.processed;
   }
 
-  void _handleScrollUpdate(Offset offset) {
-    scrollBy(scrollDirection == ScrollDirection.horizontal ? offset.dx : offset.dy);
-  }
-
   EventDisposition _handleFlingStart(sky.GestureEvent event) {
     _startToEndAnimation(velocity: _eventVelocity(event));
     return EventDisposition.processed;

packages/unit/test/gestures/scroll_test.dart

@@ -41,20 +41,20 @@ TestPointerEvent up = new TestPointerEvent(
 void main() {
   test('Should recognize scroll', () {
     PointerRouter router = new PointerRouter();
-    ScrollGestureRecognizer scroll = new ScrollGestureRecognizer(router: router);
+    PanGestureRecognizer scroll = new PanGestureRecognizer(router: router);
 
     bool didStartScroll = false;
-    scroll.onScrollStart = () {
+    scroll.onStart = () {
       didStartScroll = true;
     };
 
     sky.Offset updateOffset;
-    scroll.onScrollUpdate = (sky.Offset offset) {
+    scroll.onUpdate = (sky.Offset offset) {
       updateOffset = offset;
     };
 
     bool didEndScroll = false;
-    scroll.onScrollEnd = () {
+    scroll.onEnd = () {
       didEndScroll = true;
     };
 

packages/unit/test/widget/pageable_list_test.dart

@@ -43,7 +43,7 @@ void main() {
 
     expect(currentPage, isNull);
     new FakeAsync().run((async) {
-      tester.scroll(tester.findText('1'), new Offset(300.0, 0.0));
+      tester.scroll(tester.findText('1'), new Offset(-300.0, 0.0));
       // One frame to start the animation, a second to complete it.
       tester.pumpFrame(builder);
       tester.pumpFrame(builder, 5000.0);