packages/flutter/lib/src/gestures/resampler.dart - external/github.com/flutter/flutter - Git at Google

 // Copyright 2014 The Flutter 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:collection';

 import 'events.dart';

 /// A callback used by [PointerEventResampler.sample] and
 /// [PointerEventResampler.stop] to process a resampled `event`.
 typedef HandleEventCallback = void Function(PointerEvent event);

 /// Class for pointer event resampling.
 ///
 /// An instance of this class can be used to resample one sequence
 /// of pointer events. Multiple instances are expected to be used for
 /// multi-touch support. The sampling frequency and the sampling
 /// offset is determined by the caller.
 ///
 /// This can be used to get smooth touch event processing at the cost
 /// of adding some latency. Devices with low frequency sensors or when
 /// the frequency is not a multiple of the display frequency
 /// (e.g., 120Hz input and 90Hz display) benefit from this.
 ///
 /// The following pointer event types are supported:
 /// [PointerAddedEvent], [PointerHoverEvent], [PointerDownEvent],
 /// [PointerMoveEvent], [PointerCancelEvent], [PointerUpEvent],
 /// [PointerRemovedEvent].
 ///
 /// Resampling is currently limited to event position and delta. All
 /// pointer event types except [PointerAddedEvent] will be resampled.
 /// [PointerHoverEvent] and [PointerMoveEvent] will only be generated
 /// when the position has changed.
 class PointerEventResampler {
   // Events queued for processing.
   final Queue<PointerEvent> _queuedEvents = Queue<PointerEvent>();

   // Pointer state required for resampling.
   PointerEvent? _last;
   PointerEvent? _next;
   Offset _position = Offset.zero;
   bool _isTracked = false;
   bool _isDown = false;
   int _pointerIdentifier = 0;
   int _hasButtons = 0;

   PointerEvent _toHoverEvent(
     PointerEvent event,
     Offset position,
     Offset delta,
     Duration timeStamp,
     int buttons,
   ) {
     return PointerHoverEvent(
       timeStamp: timeStamp,
       kind: event.kind,
       device: event.device,
       position: position,
       delta: delta,
       buttons: event.buttons,
       obscured: event.obscured,
       pressureMin: event.pressureMin,
       pressureMax: event.pressureMax,
       distance: event.distance,
       distanceMax: event.distanceMax,
       size: event.size,
       radiusMajor: event.radiusMajor,
       radiusMinor: event.radiusMinor,
       radiusMin: event.radiusMin,
       radiusMax: event.radiusMax,
       orientation: event.orientation,
       tilt: event.tilt,
       synthesized: event.synthesized,
       embedderId: event.embedderId,
     );
   }

   PointerEvent _toMoveEvent(
     PointerEvent event,
     Offset position,
     Offset delta,
     int pointerIdentifier,
     Duration timeStamp,
     int buttons,
   ) {
     return PointerMoveEvent(
       timeStamp: timeStamp,
       pointer: pointerIdentifier,
       kind: event.kind,
       device: event.device,
       position: position,
       delta: delta,
       buttons: buttons,
       obscured: event.obscured,
       pressure: event.pressure,
       pressureMin: event.pressureMin,
       pressureMax: event.pressureMax,
       distanceMax: event.distanceMax,
       size: event.size,
       radiusMajor: event.radiusMajor,
       radiusMinor: event.radiusMinor,
       radiusMin: event.radiusMin,
       radiusMax: event.radiusMax,
       orientation: event.orientation,
       tilt: event.tilt,
       platformData: event.platformData,
       synthesized: event.synthesized,
       embedderId: event.embedderId,
     );
   }

   PointerEvent _toMoveOrHoverEvent(
     PointerEvent event,
     Offset position,
     Offset delta,
     int pointerIdentifier,
     Duration timeStamp,
     bool isDown,
     int buttons,
   ) {
     return isDown
         ? _toMoveEvent(
             event, position, delta, pointerIdentifier, timeStamp, buttons)
         : _toHoverEvent(event, position, delta, timeStamp, buttons);
   }

   Offset _positionAt(Duration sampleTime) {
     // Use `next` position by default.
     double x = _next?.position.dx ?? 0.0;
     double y = _next?.position.dy ?? 0.0;

     final Duration nextTimeStamp = _next?.timeStamp ?? Duration.zero;
     final Duration lastTimeStamp = _last?.timeStamp ?? Duration.zero;

     // Resample if `next` time stamp is past `sampleTime`.
     if (nextTimeStamp > sampleTime && nextTimeStamp > lastTimeStamp) {
       final double interval = (nextTimeStamp - lastTimeStamp).inMicroseconds.toDouble();
       final double scalar = (sampleTime - lastTimeStamp).inMicroseconds.toDouble() / interval;
       final double lastX = _last?.position.dx ?? 0.0;
       final double lastY = _last?.position.dy ?? 0.0;
       x = lastX + (x - lastX) * scalar;
       y = lastY + (y - lastY) * scalar;
     }

     return Offset(x, y);
   }

   void _processPointerEvents(Duration sampleTime) {
     final Iterator<PointerEvent> it = _queuedEvents.iterator;
     while (it.moveNext()) {
       final PointerEvent event = it.current;

       // Update both `last` and `next` pointer event if time stamp is older
       // or equal to `sampleTime`.
       if (event.timeStamp <= sampleTime || _last == null) {
         _last = event;
         _next = event;
         continue;
       }

       // Update only `next` pointer event if time stamp is more recent than
       // `sampleTime` and next event is not already more recent.
       final Duration nextTimeStamp = _next?.timeStamp ?? Duration.zero;
       if (nextTimeStamp < sampleTime) {
         _next = event;
         break;
       }
     }
   }

   void _dequeueAndSampleNonHoverOrMovePointerEventsUntil(
     Duration sampleTime,
     Duration nextSampleTime,
     HandleEventCallback callback,
   ) {
     Duration endTime = sampleTime;
     // Scan queued events to determine end time.
     final Iterator<PointerEvent> it = _queuedEvents.iterator;
     while (it.moveNext()) {
       final PointerEvent event = it.current;

       // Potentially stop dispatching events if more recent than `sampleTime`.
       if (event.timeStamp > sampleTime) {
         // Definitely stop if more recent than `nextSampleTime`.
         if (event.timeStamp >= nextSampleTime) {
           break;
         }

         // Update `endTime` to allow early processing of up and removed
         // events as this improves resampling of these events, which is
         // important for fling animations.
         if (event is PointerUpEvent || event is PointerRemovedEvent) {
           endTime = event.timeStamp;
           continue;
         }

         // Stop if event is not move or hover.
         if (event is! PointerMoveEvent && event is! PointerHoverEvent) {
           break;
         }
       }
     }

     while (_queuedEvents.isNotEmpty) {
       final PointerEvent event = _queuedEvents.first;

       // Stop dispatching events if more recent than `endTime`.
       if (event.timeStamp > endTime) {
         break;
       }

       final bool wasTracked = _isTracked;
       final bool wasDown = _isDown;
       final int hadButtons = _hasButtons;

       // Update pointer state.
       _isTracked = event is! PointerRemovedEvent;
       _isDown = event.down;
       _hasButtons = event.buttons;

       // Position at `sampleTime`.
       final Offset position = _positionAt(sampleTime);

       // Initialize position if we are starting to track this pointer.
       if (_isTracked && !wasTracked) {
         _position = position;
       }

       // Current pointer identifier.
       final int pointerIdentifier = event.pointer;

       // Initialize pointer identifier for `move` events.
       // Identifier is expected to be the same while `down`.
       assert(!wasDown || _pointerIdentifier == pointerIdentifier);
       _pointerIdentifier = pointerIdentifier;

       // Skip `move` and `hover` events as they are automatically
       // generated when the position has changed.
       if (event is! PointerMoveEvent && event is! PointerHoverEvent) {
         // Add synthetics `move` or `hover` event if position has changed.
         // Note: Devices without `hover` events are expected to always have
         // `add` and `down` events with the same position and this logic will
         // therefore never produce `hover` events.
         if (position != _position) {
           final Offset delta = position - _position;
           callback(_toMoveOrHoverEvent(event, position, delta,
               _pointerIdentifier, sampleTime, wasDown, hadButtons));
           _position = position;
         }
         callback(event.copyWith(
           position: position,
           delta: Offset.zero,
           pointer: pointerIdentifier,
           timeStamp: sampleTime,
         ));
       }

       _queuedEvents.removeFirst();
     }
   }

   void _samplePointerPosition(
     Duration sampleTime,
     HandleEventCallback callback,
   ) {
     // Position at `sampleTime`.
     final Offset position = _positionAt(sampleTime);

     // Add `move` or `hover` events if position has changed.
     final PointerEvent? next = _next;
     if (position != _position && next != null) {
       final Offset delta = position - _position;
       callback(_toMoveOrHoverEvent(next, position, delta, _pointerIdentifier,
           sampleTime, _isDown, _hasButtons));
       _position = position;
     }
   }

   /// Enqueue pointer `event` for resampling.
   void addEvent(PointerEvent event) {
     _queuedEvents.add(event);
   }

   /// Dispatch resampled pointer events for the specified `sampleTime`
   /// by calling [callback].
   ///
   /// This may dispatch multiple events if position is not the only
   /// state that has changed since last sample.
   ///
   /// Calling [callback] must not add or sample events.
   ///
   /// Positive value for `nextSampleTime` allow early processing of
   /// up and removed events. This improves resampling of these events,
   /// which is important for fling animations.
   void sample(
     Duration sampleTime,
     Duration nextSampleTime,
     HandleEventCallback callback,
   ) {
     _processPointerEvents(sampleTime);

     // Dequeue and sample pointer events until `sampleTime`.
     _dequeueAndSampleNonHoverOrMovePointerEventsUntil(sampleTime, nextSampleTime, callback);

     // Dispatch resampled pointer location event if tracked.
     if (_isTracked) {
       _samplePointerPosition(sampleTime, callback);
     }
   }

   /// Stop resampling.
   ///
   /// This will dispatch pending events by calling [callback] and reset
   /// internal state.
   void stop(HandleEventCallback callback) {
     while (_queuedEvents.isNotEmpty) {
       callback(_queuedEvents.removeFirst());
     }
     _pointerIdentifier = 0;
     _isDown = false;
     _isTracked = false;
     _position = Offset.zero;
     _next = null;
     _last = null;
   }

   /// Returns `true` if a call to [sample] can dispatch more events.
   bool get hasPendingEvents => _queuedEvents.isNotEmpty;

   /// Returns `true` if pointer is currently tracked.
   bool get isTracked => _isTracked;

   /// Returns `true` if pointer is currently down.
   bool get isDown => _isDown;
 }
	// Copyright 2014 The Flutter 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:collection';

	import 'events.dart';

	/// A callback used by [PointerEventResampler.sample] and
	/// [PointerEventResampler.stop] to process a resampled `event`.
	typedef HandleEventCallback = void Function(PointerEvent event);

	/// Class for pointer event resampling.
	///
	/// An instance of this class can be used to resample one sequence
	/// of pointer events. Multiple instances are expected to be used for
	/// multi-touch support. The sampling frequency and the sampling
	/// offset is determined by the caller.
	///
	/// This can be used to get smooth touch event processing at the cost
	/// of adding some latency. Devices with low frequency sensors or when
	/// the frequency is not a multiple of the display frequency
	/// (e.g., 120Hz input and 90Hz display) benefit from this.
	///
	/// The following pointer event types are supported:
	/// [PointerAddedEvent], [PointerHoverEvent], [PointerDownEvent],
	/// [PointerMoveEvent], [PointerCancelEvent], [PointerUpEvent],
	/// [PointerRemovedEvent].
	///
	/// Resampling is currently limited to event position and delta. All
	/// pointer event types except [PointerAddedEvent] will be resampled.
	/// [PointerHoverEvent] and [PointerMoveEvent] will only be generated
	/// when the position has changed.
	class PointerEventResampler {
	// Events queued for processing.
	final Queue<PointerEvent> _queuedEvents = Queue<PointerEvent>();

	// Pointer state required for resampling.
	PointerEvent? _last;
	PointerEvent? _next;
	Offset _position = Offset.zero;
	bool _isTracked = false;
	bool _isDown = false;
	int _pointerIdentifier = 0;
	int _hasButtons = 0;

	PointerEvent _toHoverEvent(
	PointerEvent event,
	Offset position,
	Offset delta,
	Duration timeStamp,
	int buttons,
	) {
	return PointerHoverEvent(
	timeStamp: timeStamp,
	kind: event.kind,
	device: event.device,
	position: position,
	delta: delta,
	buttons: event.buttons,
	obscured: event.obscured,
	pressureMin: event.pressureMin,
	pressureMax: event.pressureMax,
	distance: event.distance,
	distanceMax: event.distanceMax,
	size: event.size,
	radiusMajor: event.radiusMajor,
	radiusMinor: event.radiusMinor,
	radiusMin: event.radiusMin,
	radiusMax: event.radiusMax,
	orientation: event.orientation,
	tilt: event.tilt,
	synthesized: event.synthesized,
	embedderId: event.embedderId,
	);
	}

	PointerEvent _toMoveEvent(
	PointerEvent event,
	Offset position,
	Offset delta,
	int pointerIdentifier,
	Duration timeStamp,
	int buttons,
	) {
	return PointerMoveEvent(
	timeStamp: timeStamp,
	pointer: pointerIdentifier,
	kind: event.kind,
	device: event.device,
	position: position,
	delta: delta,
	buttons: buttons,
	obscured: event.obscured,
	pressure: event.pressure,
	pressureMin: event.pressureMin,
	pressureMax: event.pressureMax,
	distanceMax: event.distanceMax,
	size: event.size,
	radiusMajor: event.radiusMajor,
	radiusMinor: event.radiusMinor,
	radiusMin: event.radiusMin,
	radiusMax: event.radiusMax,
	orientation: event.orientation,
	tilt: event.tilt,
	platformData: event.platformData,
	synthesized: event.synthesized,
	embedderId: event.embedderId,
	);
	}

	PointerEvent _toMoveOrHoverEvent(
	PointerEvent event,
	Offset position,
	Offset delta,
	int pointerIdentifier,
	Duration timeStamp,
	bool isDown,
	int buttons,
	) {
	return isDown
	? _toMoveEvent(
	event, position, delta, pointerIdentifier, timeStamp, buttons)
	: _toHoverEvent(event, position, delta, timeStamp, buttons);
	}

	Offset _positionAt(Duration sampleTime) {
	// Use `next` position by default.
	double x = _next?.position.dx ?? 0.0;
	double y = _next?.position.dy ?? 0.0;

	final Duration nextTimeStamp = _next?.timeStamp ?? Duration.zero;
	final Duration lastTimeStamp = _last?.timeStamp ?? Duration.zero;

	// Resample if `next` time stamp is past `sampleTime`.
	if (nextTimeStamp > sampleTime && nextTimeStamp > lastTimeStamp) {
	final double interval = (nextTimeStamp - lastTimeStamp).inMicroseconds.toDouble();
	final double scalar = (sampleTime - lastTimeStamp).inMicroseconds.toDouble() / interval;
	final double lastX = _last?.position.dx ?? 0.0;
	final double lastY = _last?.position.dy ?? 0.0;
	x = lastX + (x - lastX) * scalar;
	y = lastY + (y - lastY) * scalar;
	}

	return Offset(x, y);
	}

	void _processPointerEvents(Duration sampleTime) {
	final Iterator<PointerEvent> it = _queuedEvents.iterator;
	while (it.moveNext()) {
	final PointerEvent event = it.current;

	// Update both `last` and `next` pointer event if time stamp is older
	// or equal to `sampleTime`.
	if (event.timeStamp <= sampleTime \|\| _last == null) {
	_last = event;
	_next = event;
	continue;
	}

	// Update only `next` pointer event if time stamp is more recent than
	// `sampleTime` and next event is not already more recent.
	final Duration nextTimeStamp = _next?.timeStamp ?? Duration.zero;
	if (nextTimeStamp < sampleTime) {
	_next = event;
	break;
	}
	}
	}

	void _dequeueAndSampleNonHoverOrMovePointerEventsUntil(
	Duration sampleTime,
	Duration nextSampleTime,
	HandleEventCallback callback,
	) {
	Duration endTime = sampleTime;
	// Scan queued events to determine end time.
	final Iterator<PointerEvent> it = _queuedEvents.iterator;
	while (it.moveNext()) {
	final PointerEvent event = it.current;

	// Potentially stop dispatching events if more recent than `sampleTime`.
	if (event.timeStamp > sampleTime) {
	// Definitely stop if more recent than `nextSampleTime`.
	if (event.timeStamp >= nextSampleTime) {
	break;
	}

	// Update `endTime` to allow early processing of up and removed
	// events as this improves resampling of these events, which is
	// important for fling animations.
	if (event is PointerUpEvent \|\| event is PointerRemovedEvent) {
	endTime = event.timeStamp;
	continue;
	}

	// Stop if event is not move or hover.
	if (event is! PointerMoveEvent && event is! PointerHoverEvent) {
	break;
	}
	}
	}

	while (_queuedEvents.isNotEmpty) {
	final PointerEvent event = _queuedEvents.first;

	// Stop dispatching events if more recent than `endTime`.
	if (event.timeStamp > endTime) {
	break;
	}

	final bool wasTracked = _isTracked;
	final bool wasDown = _isDown;
	final int hadButtons = _hasButtons;

	// Update pointer state.
	_isTracked = event is! PointerRemovedEvent;
	_isDown = event.down;
	_hasButtons = event.buttons;

	// Position at `sampleTime`.
	final Offset position = _positionAt(sampleTime);

	// Initialize position if we are starting to track this pointer.
	if (_isTracked && !wasTracked) {
	_position = position;
	}

	// Current pointer identifier.
	final int pointerIdentifier = event.pointer;

	// Initialize pointer identifier for `move` events.
	// Identifier is expected to be the same while `down`.
	assert(!wasDown \|\| _pointerIdentifier == pointerIdentifier);
	_pointerIdentifier = pointerIdentifier;

	// Skip `move` and `hover` events as they are automatically
	// generated when the position has changed.
	if (event is! PointerMoveEvent && event is! PointerHoverEvent) {
	// Add synthetics `move` or `hover` event if position has changed.
	// Note: Devices without `hover` events are expected to always have
	// `add` and `down` events with the same position and this logic will
	// therefore never produce `hover` events.
	if (position != _position) {
	final Offset delta = position - _position;
	callback(_toMoveOrHoverEvent(event, position, delta,
	_pointerIdentifier, sampleTime, wasDown, hadButtons));
	_position = position;
	}
	callback(event.copyWith(
	position: position,
	delta: Offset.zero,
	pointer: pointerIdentifier,
	timeStamp: sampleTime,
	));
	}

	_queuedEvents.removeFirst();
	}
	}

	void _samplePointerPosition(
	Duration sampleTime,
	HandleEventCallback callback,
	) {
	// Position at `sampleTime`.
	final Offset position = _positionAt(sampleTime);

	// Add `move` or `hover` events if position has changed.
	final PointerEvent? next = _next;
	if (position != _position && next != null) {
	final Offset delta = position - _position;
	callback(_toMoveOrHoverEvent(next, position, delta, _pointerIdentifier,
	sampleTime, _isDown, _hasButtons));
	_position = position;
	}
	}

	/// Enqueue pointer `event` for resampling.
	void addEvent(PointerEvent event) {
	_queuedEvents.add(event);
	}

	/// Dispatch resampled pointer events for the specified `sampleTime`
	/// by calling [callback].
	///
	/// This may dispatch multiple events if position is not the only
	/// state that has changed since last sample.
	///
	/// Calling [callback] must not add or sample events.
	///
	/// Positive value for `nextSampleTime` allow early processing of
	/// up and removed events. This improves resampling of these events,
	/// which is important for fling animations.
	void sample(
	Duration sampleTime,
	Duration nextSampleTime,
	HandleEventCallback callback,
	) {
	_processPointerEvents(sampleTime);

	// Dequeue and sample pointer events until `sampleTime`.
	_dequeueAndSampleNonHoverOrMovePointerEventsUntil(sampleTime, nextSampleTime, callback);

	// Dispatch resampled pointer location event if tracked.
	if (_isTracked) {
	_samplePointerPosition(sampleTime, callback);
	}
	}

	/// Stop resampling.
	///
	/// This will dispatch pending events by calling [callback] and reset
	/// internal state.
	void stop(HandleEventCallback callback) {
	while (_queuedEvents.isNotEmpty) {
	callback(_queuedEvents.removeFirst());
	}
	_pointerIdentifier = 0;
	_isDown = false;
	_isTracked = false;
	_position = Offset.zero;
	_next = null;
	_last = null;
	}

	/// Returns `true` if a call to [sample] can dispatch more events.
	bool get hasPendingEvents => _queuedEvents.isNotEmpty;

	/// Returns `true` if pointer is currently tracked.
	bool get isTracked => _isTracked;

	/// Returns `true` if pointer is currently down.
	bool get isDown => _isDown;
	}