packages/flutter/lib/src/gestures/multitap.dart - mirrors/flutter - Git at Google

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:async';
 import 'dart:ui' show Offset;
 import 'package:flutter/foundation.dart' show required;
 import 'package:vector_math/vector_math_64.dart';

 import 'arena.dart';
 import 'binding.dart';
 import 'constants.dart';
 import 'events.dart';
 import 'pointer_router.dart';
 import 'recognizer.dart';
 import 'tap.dart';

 /// Signature for callback when the user has tapped the screen at the same
 /// location twice in quick succession.
 ///
 /// See also:
 ///
 ///  * [GestureDetector.onDoubleTap], which matches this signature.
 typedef GestureDoubleTapCallback = void Function();

 /// Signature used by [MultiTapGestureRecognizer] for when a pointer that might
 /// cause a tap has contacted the screen at a particular location.
 typedef GestureMultiTapDownCallback = void Function(int pointer, TapDownDetails details);

 /// Signature used by [MultiTapGestureRecognizer] for when a pointer that will
 /// trigger a tap has stopped contacting the screen at a particular location.
 typedef GestureMultiTapUpCallback = void Function(int pointer, TapUpDetails details);

 /// Signature used by [MultiTapGestureRecognizer] for when a tap has occurred.
 typedef GestureMultiTapCallback = void Function(int pointer);

 /// Signature for when the pointer that previously triggered a
 /// [GestureMultiTapDownCallback] will not end up causing a tap.
 typedef GestureMultiTapCancelCallback = void Function(int pointer);

 /// CountdownZoned tracks whether the specified duration has elapsed since
 /// creation, honoring [Zone].
 class _CountdownZoned {
   _CountdownZoned({ @required Duration duration })
        : assert(duration != null) {
     Timer(duration, _onTimeout);
   }

   bool _timeout = false;

   bool get timeout => _timeout;

   void _onTimeout() {
     _timeout = true;
   }
 }

 /// TapTracker helps track individual tap sequences as part of a
 /// larger gesture.
 class _TapTracker {
   _TapTracker({
     @required PointerDownEvent event,
     this.entry,
     @required Duration doubleTapMinTime,
   }) : assert(doubleTapMinTime != null),
        assert(event != null),
        assert(event.buttons != null),
        pointer = event.pointer,
        _initialGlobalPosition = event.position,
        initialButtons = event.buttons,
        _doubleTapMinTimeCountdown = _CountdownZoned(duration: doubleTapMinTime);

   final int pointer;
   final GestureArenaEntry entry;
   final Offset _initialGlobalPosition;
   final int initialButtons;
   final _CountdownZoned _doubleTapMinTimeCountdown;

   bool _isTrackingPointer = false;

   void startTrackingPointer(PointerRoute route, Matrix4 transform) {
     if (!_isTrackingPointer) {
       _isTrackingPointer = true;
       GestureBinding.instance.pointerRouter.addRoute(pointer, route, transform);
     }
   }

   void stopTrackingPointer(PointerRoute route) {
     if (_isTrackingPointer) {
       _isTrackingPointer = false;
       GestureBinding.instance.pointerRouter.removeRoute(pointer, route);
     }
   }

   bool isWithinGlobalTolerance(PointerEvent event, double tolerance) {
     final Offset offset = event.position - _initialGlobalPosition;
     return offset.distance <= tolerance;
   }

   bool hasElapsedMinTime() {
     return _doubleTapMinTimeCountdown.timeout;
   }

   bool hasSameButton(PointerDownEvent event) {
     return event.buttons == initialButtons;
   }
 }

 /// Recognizes when the user has tapped the screen at the same location twice in
 /// quick succession.
 ///
 /// [DoubleTapGestureRecognizer] competes on pointer events of [kPrimaryButton]
 /// only when it has a non-null callback. If it has no callbacks, it is a no-op.
 ///
 class DoubleTapGestureRecognizer extends GestureRecognizer {
   /// Create a gesture recognizer for double taps.
   ///
   /// {@macro flutter.gestures.gestureRecognizer.kind}
   DoubleTapGestureRecognizer({
     Object debugOwner,
     PointerDeviceKind kind,
   }) : super(debugOwner: debugOwner, kind: kind);

   // Implementation notes:
   // The double tap recognizer can be in one of four states. There's no
   // explicit enum for the states, because they are already captured by
   // the state of existing fields. Specifically:
   // Waiting on first tap: In this state, the _trackers list is empty, and
   // _firstTap is null.
   // First tap in progress: In this state, the _trackers list contains all
   // the states for taps that have begun but not completed. This list can
   // have more than one entry if two pointers begin to tap.
   // Waiting on second tap: In this state, one of the in-progress taps has
   // completed successfully. The _trackers list is again empty, and
   // _firstTap records the successful tap.
   // Second tap in progress: Much like the "first tap in progress" state, but
   // _firstTap is non-null. If a tap completes successfully while in this
   // state, the callback is called and the state is reset.
   // There are various other scenarios that cause the state to reset:
   // - All in-progress taps are rejected (by time, distance, pointercancel, etc)
   // - The long timer between taps expires
   // - The gesture arena decides we have been rejected wholesale

   /// Called when the user has tapped the screen with a primary button at the
   /// same location twice in quick succession.
   ///
   /// This triggers when the pointer stops contacting the device after the 2nd tap,
   /// immediately after [onDoubleTapUp].
   ///
   /// See also:
   ///
   ///  * [kPrimaryButton], the button this callback responds to.
   GestureDoubleTapCallback onDoubleTap;

   Timer _doubleTapTimer;
   _TapTracker _firstTap;
   final Map<int, _TapTracker> _trackers = <int, _TapTracker>{};

   @override
   bool isPointerAllowed(PointerEvent event) {
     if (_firstTap == null) {
       switch (event.buttons) {
         case kPrimaryButton:
           if (onDoubleTap == null)
             return false;
           break;
         default:
           return false;
       }
     }
     return super.isPointerAllowed(event);
   }

   @override
   void addAllowedPointer(PointerEvent event) {
     if (_firstTap != null) {
       if (!_firstTap.isWithinGlobalTolerance(event, kDoubleTapSlop)) {
         // Ignore out-of-bounds second taps.
         return;
       } else if (!_firstTap.hasElapsedMinTime() || !_firstTap.hasSameButton(event)) {
         // Restart when the second tap is too close to the first, or when buttons
         // mismatch.
         _reset();
         return _trackFirstTap(event);
       }
     }
     _trackFirstTap(event);
   }

   void _trackFirstTap(PointerEvent event) {
     _stopDoubleTapTimer();
     final _TapTracker tracker = _TapTracker(
       event: event,
       entry: GestureBinding.instance.gestureArena.add(event.pointer, this),
       doubleTapMinTime: kDoubleTapMinTime,
     );
     _trackers[event.pointer] = tracker;
     tracker.startTrackingPointer(_handleEvent, event.transform);
   }

   void _handleEvent(PointerEvent event) {
     final _TapTracker tracker = _trackers[event.pointer];
     assert(tracker != null);
     if (event is PointerUpEvent) {
       if (_firstTap == null)
         _registerFirstTap(tracker);
       else
         _registerSecondTap(tracker);
     } else if (event is PointerMoveEvent) {
       if (!tracker.isWithinGlobalTolerance(event, kDoubleTapTouchSlop))
         _reject(tracker);
     } else if (event is PointerCancelEvent) {
       _reject(tracker);
     }
   }

   @override
   void acceptGesture(int pointer) { }

   @override
   void rejectGesture(int pointer) {
     _TapTracker tracker = _trackers[pointer];
     // If tracker isn't in the list, check if this is the first tap tracker
     if (tracker == null &&
         _firstTap != null &&
         _firstTap.pointer == pointer)
       tracker = _firstTap;
     // If tracker is still null, we rejected ourselves already
     if (tracker != null)
       _reject(tracker);
   }

   void _reject(_TapTracker tracker) {
     _trackers.remove(tracker.pointer);
     tracker.entry.resolve(GestureDisposition.rejected);
     _freezeTracker(tracker);
     // If the first tap is in progress, and we've run out of taps to track,
     // reset won't have any work to do. But if we're in the second tap, we need
     // to clear intermediate state.
     if (_firstTap != null &&
         (_trackers.isEmpty || tracker == _firstTap))
       _reset();
   }

   @override
   void dispose() {
     _reset();
     super.dispose();
   }

   void _reset() {
     _stopDoubleTapTimer();
     if (_firstTap != null) {
       // Note, order is important below in order for the resolve -> reject logic
       // to work properly.
       final _TapTracker tracker = _firstTap;
       _firstTap = null;
       _reject(tracker);
       GestureBinding.instance.gestureArena.release(tracker.pointer);
     }
     _clearTrackers();
   }

   void _registerFirstTap(_TapTracker tracker) {
     _startDoubleTapTimer();
     GestureBinding.instance.gestureArena.hold(tracker.pointer);
     // Note, order is important below in order for the clear -> reject logic to
     // work properly.
     _freezeTracker(tracker);
     _trackers.remove(tracker.pointer);
     _clearTrackers();
     _firstTap = tracker;
   }

   void _registerSecondTap(_TapTracker tracker) {
     _firstTap.entry.resolve(GestureDisposition.accepted);
     tracker.entry.resolve(GestureDisposition.accepted);
     _freezeTracker(tracker);
     _trackers.remove(tracker.pointer);
     _checkUp(tracker.initialButtons);
     _reset();
   }

   void _clearTrackers() {
     _trackers.values.toList().forEach(_reject);
     assert(_trackers.isEmpty);
   }

   void _freezeTracker(_TapTracker tracker) {
     tracker.stopTrackingPointer(_handleEvent);
   }

   void _startDoubleTapTimer() {
     _doubleTapTimer ??= Timer(kDoubleTapTimeout, _reset);
   }

   void _stopDoubleTapTimer() {
     if (_doubleTapTimer != null) {
       _doubleTapTimer.cancel();
       _doubleTapTimer = null;
     }
   }

   void _checkUp(int buttons) {
     assert(buttons == kPrimaryButton);
     if (onDoubleTap != null)
       invokeCallback<void>('onDoubleTap', onDoubleTap);
   }

   @override
   String get debugDescription => 'double tap';
 }

 /// TapGesture represents a full gesture resulting from a single tap sequence,
 /// as part of a [MultiTapGestureRecognizer]. Tap gestures are passive, meaning
 /// that they will not preempt any other arena member in play.
 class _TapGesture extends _TapTracker {

   _TapGesture({
     this.gestureRecognizer,
     PointerEvent event,
     Duration longTapDelay,
   }) : _lastPosition = OffsetPair.fromEventPosition(event),
        super(
     event: event,
     entry: GestureBinding.instance.gestureArena.add(event.pointer, gestureRecognizer),
     doubleTapMinTime: kDoubleTapMinTime,
   ) {
     startTrackingPointer(handleEvent, event.transform);
     if (longTapDelay > Duration.zero) {
       _timer = Timer(longTapDelay, () {
         _timer = null;
         gestureRecognizer._dispatchLongTap(event.pointer, _lastPosition);
       });
     }
   }

   final MultiTapGestureRecognizer gestureRecognizer;

   bool _wonArena = false;
   Timer _timer;

   OffsetPair _lastPosition;
   OffsetPair _finalPosition;

   void handleEvent(PointerEvent event) {
     assert(event.pointer == pointer);
     if (event is PointerMoveEvent) {
       if (!isWithinGlobalTolerance(event, kTouchSlop))
         cancel();
       else
         _lastPosition = OffsetPair.fromEventPosition(event);
     } else if (event is PointerCancelEvent) {
       cancel();
     } else if (event is PointerUpEvent) {
       stopTrackingPointer(handleEvent);
       _finalPosition = OffsetPair.fromEventPosition(event);
       _check();
     }
   }

   @override
   void stopTrackingPointer(PointerRoute route) {
     _timer?.cancel();
     _timer = null;
     super.stopTrackingPointer(route);
   }

   void accept() {
     _wonArena = true;
     _check();
   }

   void reject() {
     stopTrackingPointer(handleEvent);
     gestureRecognizer._dispatchCancel(pointer);
   }

   void cancel() {
     // If we won the arena already, then entry is resolved, so resolving
     // again is a no-op. But we still need to clean up our own state.
     if (_wonArena)
       reject();
     else
       entry.resolve(GestureDisposition.rejected); // eventually calls reject()
   }

   void _check() {
     if (_wonArena && _finalPosition != null)
       gestureRecognizer._dispatchTap(pointer, _finalPosition);
   }
 }

 /// Recognizes taps on a per-pointer basis.
 ///
 /// [MultiTapGestureRecognizer] considers each sequence of pointer events that
 /// could constitute a tap independently of other pointers: For example, down-1,
 /// down-2, up-1, up-2 produces two taps, on up-1 and up-2.
 ///
 /// See also:
 ///
 ///  * [TapGestureRecognizer]
 class MultiTapGestureRecognizer extends GestureRecognizer {
   /// Creates a multi-tap gesture recognizer.
   ///
   /// The [longTapDelay] defaults to [Duration.zero], which means
   /// [onLongTapDown] is called immediately after [onTapDown].
   MultiTapGestureRecognizer({
     this.longTapDelay = Duration.zero,
     Object debugOwner,
     PointerDeviceKind kind,
   }) : super(debugOwner: debugOwner, kind: kind);

   /// A pointer that might cause a tap has contacted the screen at a particular
   /// location.
   GestureMultiTapDownCallback onTapDown;

   /// A pointer that will trigger a tap has stopped contacting the screen at a
   /// particular location.
   GestureMultiTapUpCallback onTapUp;

   /// A tap has occurred.
   GestureMultiTapCallback onTap;

   /// The pointer that previously triggered [onTapDown] will not end up causing
   /// a tap.
   GestureMultiTapCancelCallback onTapCancel;

   /// The amount of time between [onTapDown] and [onLongTapDown].
   Duration longTapDelay;

   /// A pointer that might cause a tap is still in contact with the screen at a
   /// particular location after [longTapDelay].
   GestureMultiTapDownCallback onLongTapDown;

   final Map<int, _TapGesture> _gestureMap = <int, _TapGesture>{};

   @override
   void addAllowedPointer(PointerEvent event) {
     assert(!_gestureMap.containsKey(event.pointer));
     _gestureMap[event.pointer] = _TapGesture(
       gestureRecognizer: this,
       event: event,
       longTapDelay: longTapDelay,
     );
     if (onTapDown != null)
       invokeCallback<void>('onTapDown', () {
         onTapDown(event.pointer, TapDownDetails(
           globalPosition: event.position,
           localPosition: event.localPosition,
           kind: event.kind,
         ));
       });
   }

   @override
   void acceptGesture(int pointer) {
     assert(_gestureMap.containsKey(pointer));
     _gestureMap[pointer].accept();
   }

   @override
   void rejectGesture(int pointer) {
     assert(_gestureMap.containsKey(pointer));
     _gestureMap[pointer].reject();
     assert(!_gestureMap.containsKey(pointer));
   }

   void _dispatchCancel(int pointer) {
     assert(_gestureMap.containsKey(pointer));
     _gestureMap.remove(pointer);
     if (onTapCancel != null)
       invokeCallback<void>('onTapCancel', () => onTapCancel(pointer));
   }

   void _dispatchTap(int pointer, OffsetPair position) {
     assert(_gestureMap.containsKey(pointer));
     _gestureMap.remove(pointer);
     if (onTapUp != null)
       invokeCallback<void>('onTapUp', () {
         onTapUp(pointer, TapUpDetails(
           localPosition: position.local,
           globalPosition: position.global,
         ));
       });
     if (onTap != null)
       invokeCallback<void>('onTap', () => onTap(pointer));
   }

   void _dispatchLongTap(int pointer, OffsetPair lastPosition) {
     assert(_gestureMap.containsKey(pointer));
     if (onLongTapDown != null)
       invokeCallback<void>('onLongTapDown', () {
         onLongTapDown(
           pointer,
           TapDownDetails(
             globalPosition: lastPosition.global,
             localPosition: lastPosition.local,
             kind: getKindForPointer(pointer),
           ),
         );
       });
   }

   @override
   void dispose() {
     final List<_TapGesture> localGestures = List<_TapGesture>.from(_gestureMap.values);
     for (_TapGesture gesture in localGestures)
       gesture.cancel();
     // Rejection of each gesture should cause it to be removed from our map
     assert(_gestureMap.isEmpty);
     super.dispose();
   }

   @override
   String get debugDescription => 'multitap';
 }
	// Copyright 2015 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:async';
	import 'dart:ui' show Offset;
	import 'package:flutter/foundation.dart' show required;
	import 'package:vector_math/vector_math_64.dart';

	import 'arena.dart';
	import 'binding.dart';
	import 'constants.dart';
	import 'events.dart';
	import 'pointer_router.dart';
	import 'recognizer.dart';
	import 'tap.dart';

	/// Signature for callback when the user has tapped the screen at the same
	/// location twice in quick succession.
	///
	/// See also:
	///
	/// * [GestureDetector.onDoubleTap], which matches this signature.
	typedef GestureDoubleTapCallback = void Function();

	/// Signature used by [MultiTapGestureRecognizer] for when a pointer that might
	/// cause a tap has contacted the screen at a particular location.
	typedef GestureMultiTapDownCallback = void Function(int pointer, TapDownDetails details);

	/// Signature used by [MultiTapGestureRecognizer] for when a pointer that will
	/// trigger a tap has stopped contacting the screen at a particular location.
	typedef GestureMultiTapUpCallback = void Function(int pointer, TapUpDetails details);

	/// Signature used by [MultiTapGestureRecognizer] for when a tap has occurred.
	typedef GestureMultiTapCallback = void Function(int pointer);

	/// Signature for when the pointer that previously triggered a
	/// [GestureMultiTapDownCallback] will not end up causing a tap.
	typedef GestureMultiTapCancelCallback = void Function(int pointer);

	/// CountdownZoned tracks whether the specified duration has elapsed since
	/// creation, honoring [Zone].
	class _CountdownZoned {
	_CountdownZoned({ @required Duration duration })
	: assert(duration != null) {
	Timer(duration, _onTimeout);
	}

	bool _timeout = false;

	bool get timeout => _timeout;

	void _onTimeout() {
	_timeout = true;
	}
	}

	/// TapTracker helps track individual tap sequences as part of a
	/// larger gesture.
	class _TapTracker {
	_TapTracker({
	@required PointerDownEvent event,
	this.entry,
	@required Duration doubleTapMinTime,
	}) : assert(doubleTapMinTime != null),
	assert(event != null),
	assert(event.buttons != null),
	pointer = event.pointer,
	_initialGlobalPosition = event.position,
	initialButtons = event.buttons,
	_doubleTapMinTimeCountdown = _CountdownZoned(duration: doubleTapMinTime);

	final int pointer;
	final GestureArenaEntry entry;
	final Offset _initialGlobalPosition;
	final int initialButtons;
	final _CountdownZoned _doubleTapMinTimeCountdown;

	bool _isTrackingPointer = false;

	void startTrackingPointer(PointerRoute route, Matrix4 transform) {
	if (!_isTrackingPointer) {
	_isTrackingPointer = true;
	GestureBinding.instance.pointerRouter.addRoute(pointer, route, transform);
	}
	}

	void stopTrackingPointer(PointerRoute route) {
	if (_isTrackingPointer) {
	_isTrackingPointer = false;
	GestureBinding.instance.pointerRouter.removeRoute(pointer, route);
	}
	}

	bool isWithinGlobalTolerance(PointerEvent event, double tolerance) {
	final Offset offset = event.position - _initialGlobalPosition;
	return offset.distance <= tolerance;
	}

	bool hasElapsedMinTime() {
	return _doubleTapMinTimeCountdown.timeout;
	}

	bool hasSameButton(PointerDownEvent event) {
	return event.buttons == initialButtons;
	}
	}

	/// Recognizes when the user has tapped the screen at the same location twice in
	/// quick succession.
	///
	/// [DoubleTapGestureRecognizer] competes on pointer events of [kPrimaryButton]
	/// only when it has a non-null callback. If it has no callbacks, it is a no-op.
	///
	class DoubleTapGestureRecognizer extends GestureRecognizer {
	/// Create a gesture recognizer for double taps.
	///
	/// {@macro flutter.gestures.gestureRecognizer.kind}
	DoubleTapGestureRecognizer({
	Object debugOwner,
	PointerDeviceKind kind,
	}) : super(debugOwner: debugOwner, kind: kind);

	// Implementation notes:
	// The double tap recognizer can be in one of four states. There's no
	// explicit enum for the states, because they are already captured by
	// the state of existing fields. Specifically:
	// Waiting on first tap: In this state, the _trackers list is empty, and
	// _firstTap is null.
	// First tap in progress: In this state, the _trackers list contains all
	// the states for taps that have begun but not completed. This list can
	// have more than one entry if two pointers begin to tap.
	// Waiting on second tap: In this state, one of the in-progress taps has
	// completed successfully. The _trackers list is again empty, and
	// _firstTap records the successful tap.
	// Second tap in progress: Much like the "first tap in progress" state, but
	// _firstTap is non-null. If a tap completes successfully while in this
	// state, the callback is called and the state is reset.
	// There are various other scenarios that cause the state to reset:
	// - All in-progress taps are rejected (by time, distance, pointercancel, etc)
	// - The long timer between taps expires
	// - The gesture arena decides we have been rejected wholesale

	/// Called when the user has tapped the screen with a primary button at the
	/// same location twice in quick succession.
	///
	/// This triggers when the pointer stops contacting the device after the 2nd tap,
	/// immediately after [onDoubleTapUp].
	///
	/// See also:
	///
	/// * [kPrimaryButton], the button this callback responds to.
	GestureDoubleTapCallback onDoubleTap;

	Timer _doubleTapTimer;
	_TapTracker _firstTap;
	final Map<int, _TapTracker> _trackers = <int, _TapTracker>{};

	@override
	bool isPointerAllowed(PointerEvent event) {
	if (_firstTap == null) {
	switch (event.buttons) {
	case kPrimaryButton:
	if (onDoubleTap == null)
	return false;
	break;
	default:
	return false;
	}
	}
	return super.isPointerAllowed(event);
	}

	@override
	void addAllowedPointer(PointerEvent event) {
	if (_firstTap != null) {
	if (!_firstTap.isWithinGlobalTolerance(event, kDoubleTapSlop)) {
	// Ignore out-of-bounds second taps.
	return;
	} else if (!_firstTap.hasElapsedMinTime() \|\| !_firstTap.hasSameButton(event)) {
	// Restart when the second tap is too close to the first, or when buttons
	// mismatch.
	_reset();
	return _trackFirstTap(event);
	}
	}
	_trackFirstTap(event);
	}

	void _trackFirstTap(PointerEvent event) {
	_stopDoubleTapTimer();
	final _TapTracker tracker = _TapTracker(
	event: event,
	entry: GestureBinding.instance.gestureArena.add(event.pointer, this),
	doubleTapMinTime: kDoubleTapMinTime,
	);
	_trackers[event.pointer] = tracker;
	tracker.startTrackingPointer(_handleEvent, event.transform);
	}

	void _handleEvent(PointerEvent event) {
	final _TapTracker tracker = _trackers[event.pointer];
	assert(tracker != null);
	if (event is PointerUpEvent) {
	if (_firstTap == null)
	_registerFirstTap(tracker);
	else
	_registerSecondTap(tracker);
	} else if (event is PointerMoveEvent) {
	if (!tracker.isWithinGlobalTolerance(event, kDoubleTapTouchSlop))
	_reject(tracker);
	} else if (event is PointerCancelEvent) {
	_reject(tracker);
	}
	}

	@override
	void acceptGesture(int pointer) { }

	@override
	void rejectGesture(int pointer) {
	_TapTracker tracker = _trackers[pointer];
	// If tracker isn't in the list, check if this is the first tap tracker
	if (tracker == null &&
	_firstTap != null &&
	_firstTap.pointer == pointer)
	tracker = _firstTap;
	// If tracker is still null, we rejected ourselves already
	if (tracker != null)
	_reject(tracker);
	}

	void _reject(_TapTracker tracker) {
	_trackers.remove(tracker.pointer);
	tracker.entry.resolve(GestureDisposition.rejected);
	_freezeTracker(tracker);
	// If the first tap is in progress, and we've run out of taps to track,
	// reset won't have any work to do. But if we're in the second tap, we need
	// to clear intermediate state.
	if (_firstTap != null &&
	(_trackers.isEmpty \|\| tracker == _firstTap))
	_reset();
	}

	@override
	void dispose() {
	_reset();
	super.dispose();
	}

	void _reset() {
	_stopDoubleTapTimer();
	if (_firstTap != null) {
	// Note, order is important below in order for the resolve -> reject logic
	// to work properly.
	final _TapTracker tracker = _firstTap;
	_firstTap = null;
	_reject(tracker);
	GestureBinding.instance.gestureArena.release(tracker.pointer);
	}
	_clearTrackers();
	}

	void _registerFirstTap(_TapTracker tracker) {
	_startDoubleTapTimer();
	GestureBinding.instance.gestureArena.hold(tracker.pointer);
	// Note, order is important below in order for the clear -> reject logic to
	// work properly.
	_freezeTracker(tracker);
	_trackers.remove(tracker.pointer);
	_clearTrackers();
	_firstTap = tracker;
	}

	void _registerSecondTap(_TapTracker tracker) {
	_firstTap.entry.resolve(GestureDisposition.accepted);
	tracker.entry.resolve(GestureDisposition.accepted);
	_freezeTracker(tracker);
	_trackers.remove(tracker.pointer);
	_checkUp(tracker.initialButtons);
	_reset();
	}

	void _clearTrackers() {
	_trackers.values.toList().forEach(_reject);
	assert(_trackers.isEmpty);
	}

	void _freezeTracker(_TapTracker tracker) {
	tracker.stopTrackingPointer(_handleEvent);
	}

	void _startDoubleTapTimer() {
	_doubleTapTimer ??= Timer(kDoubleTapTimeout, _reset);
	}

	void _stopDoubleTapTimer() {
	if (_doubleTapTimer != null) {
	_doubleTapTimer.cancel();
	_doubleTapTimer = null;
	}
	}

	void _checkUp(int buttons) {
	assert(buttons == kPrimaryButton);
	if (onDoubleTap != null)
	invokeCallback<void>('onDoubleTap', onDoubleTap);
	}

	@override
	String get debugDescription => 'double tap';
	}

	/// TapGesture represents a full gesture resulting from a single tap sequence,
	/// as part of a [MultiTapGestureRecognizer]. Tap gestures are passive, meaning
	/// that they will not preempt any other arena member in play.
	class _TapGesture extends _TapTracker {

	_TapGesture({
	this.gestureRecognizer,
	PointerEvent event,
	Duration longTapDelay,
	}) : _lastPosition = OffsetPair.fromEventPosition(event),
	super(
	event: event,
	entry: GestureBinding.instance.gestureArena.add(event.pointer, gestureRecognizer),
	doubleTapMinTime: kDoubleTapMinTime,
	) {
	startTrackingPointer(handleEvent, event.transform);
	if (longTapDelay > Duration.zero) {
	_timer = Timer(longTapDelay, () {
	_timer = null;
	gestureRecognizer._dispatchLongTap(event.pointer, _lastPosition);
	});
	}
	}

	final MultiTapGestureRecognizer gestureRecognizer;

	bool _wonArena = false;
	Timer _timer;

	OffsetPair _lastPosition;
	OffsetPair _finalPosition;

	void handleEvent(PointerEvent event) {
	assert(event.pointer == pointer);
	if (event is PointerMoveEvent) {
	if (!isWithinGlobalTolerance(event, kTouchSlop))
	cancel();
	else
	_lastPosition = OffsetPair.fromEventPosition(event);
	} else if (event is PointerCancelEvent) {
	cancel();
	} else if (event is PointerUpEvent) {
	stopTrackingPointer(handleEvent);
	_finalPosition = OffsetPair.fromEventPosition(event);
	_check();
	}
	}

	@override
	void stopTrackingPointer(PointerRoute route) {
	_timer?.cancel();
	_timer = null;
	super.stopTrackingPointer(route);
	}

	void accept() {
	_wonArena = true;
	_check();
	}

	void reject() {
	stopTrackingPointer(handleEvent);
	gestureRecognizer._dispatchCancel(pointer);
	}

	void cancel() {
	// If we won the arena already, then entry is resolved, so resolving
	// again is a no-op. But we still need to clean up our own state.
	if (_wonArena)
	reject();
	else
	entry.resolve(GestureDisposition.rejected); // eventually calls reject()
	}

	void _check() {
	if (_wonArena && _finalPosition != null)
	gestureRecognizer._dispatchTap(pointer, _finalPosition);
	}
	}

	/// Recognizes taps on a per-pointer basis.
	///
	/// [MultiTapGestureRecognizer] considers each sequence of pointer events that
	/// could constitute a tap independently of other pointers: For example, down-1,
	/// down-2, up-1, up-2 produces two taps, on up-1 and up-2.
	///
	/// See also:
	///
	/// * [TapGestureRecognizer]
	class MultiTapGestureRecognizer extends GestureRecognizer {
	/// Creates a multi-tap gesture recognizer.
	///
	/// The [longTapDelay] defaults to [Duration.zero], which means
	/// [onLongTapDown] is called immediately after [onTapDown].
	MultiTapGestureRecognizer({
	this.longTapDelay = Duration.zero,
	Object debugOwner,
	PointerDeviceKind kind,
	}) : super(debugOwner: debugOwner, kind: kind);

	/// A pointer that might cause a tap has contacted the screen at a particular
	/// location.
	GestureMultiTapDownCallback onTapDown;

	/// A pointer that will trigger a tap has stopped contacting the screen at a
	/// particular location.
	GestureMultiTapUpCallback onTapUp;

	/// A tap has occurred.
	GestureMultiTapCallback onTap;

	/// The pointer that previously triggered [onTapDown] will not end up causing
	/// a tap.
	GestureMultiTapCancelCallback onTapCancel;

	/// The amount of time between [onTapDown] and [onLongTapDown].
	Duration longTapDelay;

	/// A pointer that might cause a tap is still in contact with the screen at a
	/// particular location after [longTapDelay].
	GestureMultiTapDownCallback onLongTapDown;

	final Map<int, _TapGesture> _gestureMap = <int, _TapGesture>{};

	@override
	void addAllowedPointer(PointerEvent event) {
	assert(!_gestureMap.containsKey(event.pointer));
	_gestureMap[event.pointer] = _TapGesture(
	gestureRecognizer: this,
	event: event,
	longTapDelay: longTapDelay,
	);
	if (onTapDown != null)
	invokeCallback<void>('onTapDown', () {
	onTapDown(event.pointer, TapDownDetails(
	globalPosition: event.position,
	localPosition: event.localPosition,
	kind: event.kind,
	));
	});
	}

	@override
	void acceptGesture(int pointer) {
	assert(_gestureMap.containsKey(pointer));
	_gestureMap[pointer].accept();
	}

	@override
	void rejectGesture(int pointer) {
	assert(_gestureMap.containsKey(pointer));
	_gestureMap[pointer].reject();
	assert(!_gestureMap.containsKey(pointer));
	}

	void _dispatchCancel(int pointer) {
	assert(_gestureMap.containsKey(pointer));
	_gestureMap.remove(pointer);
	if (onTapCancel != null)
	invokeCallback<void>('onTapCancel', () => onTapCancel(pointer));
	}

	void _dispatchTap(int pointer, OffsetPair position) {
	assert(_gestureMap.containsKey(pointer));
	_gestureMap.remove(pointer);
	if (onTapUp != null)
	invokeCallback<void>('onTapUp', () {
	onTapUp(pointer, TapUpDetails(
	localPosition: position.local,
	globalPosition: position.global,
	));
	});
	if (onTap != null)
	invokeCallback<void>('onTap', () => onTap(pointer));
	}

	void _dispatchLongTap(int pointer, OffsetPair lastPosition) {
	assert(_gestureMap.containsKey(pointer));
	if (onLongTapDown != null)
	invokeCallback<void>('onLongTapDown', () {
	onLongTapDown(
	pointer,
	TapDownDetails(
	globalPosition: lastPosition.global,
	localPosition: lastPosition.local,
	kind: getKindForPointer(pointer),
	),
	);
	});
	}

	@override
	void dispose() {
	final List<_TapGesture> localGestures = List<_TapGesture>.from(_gestureMap.values);
	for (_TapGesture gesture in localGestures)
	gesture.cancel();
	// Rejection of each gesture should cause it to be removed from our map
	assert(_gestureMap.isEmpty);
	super.dispose();
	}

	@override
	String get debugDescription => 'multitap';
	}