#101 adapted ScaleGestureRecognizer to eagerly accept multiple pointer gestures

lib/model/entry.dart

@@ -454,7 +454,7 @@ class AvesEntry {
     _catalogMetadata = newMetadata;
     _bestTitle = null;
     _tags = null;
-    metadataChangeNotifier.notifyListeners();
+    metadataChangeNotifier.notify();
 
     _onVisualFieldChanged(oldDateModifiedSecs, oldRotationDegrees, oldIsFlipped);
   }
@@ -496,7 +496,7 @@ class AvesEntry {
 
   set addressDetails(AddressDetails? newAddress) {
     _addressDetails = newAddress;
-    addressChangeNotifier.notifyListeners();
+    addressChangeNotifier.notify();
   }
 
   Future<void> locate({required bool background, required bool force, required Locale geocoderLocale}) async {
@@ -620,7 +620,7 @@ class AvesEntry {
     }
 
     await _onVisualFieldChanged(oldDateModifiedSecs, oldRotationDegrees, oldIsFlipped);
-    metadataChangeNotifier.notifyListeners();
+    metadataChangeNotifier.notify();
   }
 
   Future<void> refresh({
@@ -717,7 +717,7 @@ class AvesEntry {
   Future<void> _onVisualFieldChanged(int? oldDateModifiedSecs, int oldRotationDegrees, bool oldIsFlipped) async {
     if (oldDateModifiedSecs != dateModifiedSecs || oldRotationDegrees != rotationDegrees || oldIsFlipped != isFlipped) {
       await EntryCache.evict(uri, mimeType, oldDateModifiedSecs, oldRotationDegrees, oldIsFlipped);
-      imageChangeNotifier.notifyListeners();
+      imageChangeNotifier.notify();
     }
   }
 

lib/model/source/collection_lens.dart

@@ -10,6 +10,7 @@ import 'package:aves/model/filters/location.dart';
 import 'package:aves/model/filters/query.dart';
 import 'package:aves/model/settings/settings.dart';
 import 'package:aves/model/source/collection_source.dart';
+import 'package:aves/model/source/events.dart';
 import 'package:aves/model/source/location.dart';
 import 'package:aves/model/source/section_keys.dart';
 import 'package:aves/model/source/tag.dart';

lib/model/source/collection_source.dart

@@ -11,6 +11,7 @@ import 'package:aves/model/settings/settings.dart';
 import 'package:aves/model/source/album.dart';
 import 'package:aves/model/source/analysis_controller.dart';
 import 'package:aves/model/source/enums.dart';
+import 'package:aves/model/source/events.dart';
 import 'package:aves/model/source/location.dart';
 import 'package:aves/model/source/tag.dart';
 import 'package:aves/services/analysis_service.dart';
@@ -183,7 +184,7 @@ abstract class CollectionSource with SourceBase, AlbumMixin, LocationMixin, TagM
           return;
         }
         await _moveEntry(entry, newFields, persist: persist);
-        entry.metadataChangeNotifier.notifyListeners();
+        entry.metadataChangeNotifier.notify();
         eventBus.fire(EntryMovedEvent({entry}));
         completer.complete(true);
       },
@@ -381,46 +382,3 @@ abstract class CollectionSource with SourceBase, AlbumMixin, LocationMixin, TagM
     }
   }
 }
-
-@immutable
-class EntryAddedEvent {
-  final Set<AvesEntry>? entries;
-
-  const EntryAddedEvent([this.entries]);
-}
-
-@immutable
-class EntryRemovedEvent {
-  final Set<AvesEntry> entries;
-
-  const EntryRemovedEvent(this.entries);
-}
-
-@immutable
-class EntryMovedEvent {
-  final Set<AvesEntry> entries;
-
-  const EntryMovedEvent(this.entries);
-}
-
-@immutable
-class EntryRefreshedEvent {
-  final Set<AvesEntry> entries;
-
-  const EntryRefreshedEvent(this.entries);
-}
-
-@immutable
-class FilterVisibilityChangedEvent {
-  final Set<CollectionFilter> filters;
-  final bool visible;
-
-  const FilterVisibilityChangedEvent(this.filters, this.visible);
-}
-
-@immutable
-class ProgressEvent {
-  final int done, total;
-
-  const ProgressEvent({required this.done, required this.total});
-}

lib/model/source/events.dart

@@ -0,0 +1,46 @@
+import 'package:aves/model/entry.dart';
+import 'package:aves/model/filters/filters.dart';
+import 'package:flutter/foundation.dart';
+
+@immutable
+class EntryAddedEvent {
+  final Set<AvesEntry>? entries;
+
+  const EntryAddedEvent([this.entries]);
+}
+
+@immutable
+class EntryRemovedEvent {
+  final Set<AvesEntry> entries;
+
+  const EntryRemovedEvent(this.entries);
+}
+
+@immutable
+class EntryMovedEvent {
+  final Set<AvesEntry> entries;
+
+  const EntryMovedEvent(this.entries);
+}
+
+@immutable
+class EntryRefreshedEvent {
+  final Set<AvesEntry> entries;
+
+  const EntryRefreshedEvent(this.entries);
+}
+
+@immutable
+class FilterVisibilityChangedEvent {
+  final Set<CollectionFilter> filters;
+  final bool visible;
+
+  const FilterVisibilityChangedEvent(this.filters, this.visible);
+}
+
+@immutable
+class ProgressEvent {
+  final int done, total;
+
+  const ProgressEvent({required this.done, required this.total});
+}

lib/services/common/output_buffer.dart

@@ -1,7 +1,7 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
-// cf flutter/foundation `consolidateHttpClientResponseBytes`
+// adapted from Flutter `_OutputBuffer` in `/foundation/consolidate_response.dart`
 class OutputBuffer extends ByteConversionSinkBase {
   List<List<int>>? _chunks = <List<int>>[];
   int _contentLength = 0;
@@ -21,8 +21,8 @@ class OutputBuffer extends ByteConversionSinkBase {
       return;
     }
     _bytes = Uint8List(_contentLength);
-    var offset = 0;
-    for (final chunk in _chunks!) {
+    int offset = 0;
+    for (final List<int> chunk in _chunks!) {
       _bytes!.setRange(offset, offset + chunk.length, chunk);
       offset += chunk.length;
     }

lib/utils/android_file_utils.dart

@@ -32,10 +32,10 @@ class AndroidFileUtils {
     downloadPath = pContext.join(primaryStorage, 'Download');
     moviesPath = pContext.join(primaryStorage, 'Movies');
     picturesPath = pContext.join(primaryStorage, 'Pictures');
-    avesVideoCapturesPath = pContext.join(dcimPath, 'Videocaptures');
+    avesVideoCapturesPath = pContext.join(dcimPath, 'Video Captures');
     videoCapturesPaths = {
       // from Samsung
-      pContext.join(dcimPath, 'Video Captures'),
+      pContext.join(dcimPath, 'Videocaptures'),
       // from Aves
       avesVideoCapturesPath,
     };

lib/utils/change_notifier.dart

@@ -1,26 +1,9 @@
 import 'package:flutter/foundation.dart';
 
-// reimplemented ChangeNotifier so that it can be used anywhere, not just as a mixin
-class AChangeNotifier implements Listenable {
-  ObserverList<VoidCallback>? _listeners = ObserverList<VoidCallback>();
-
-  @override
-  void addListener(VoidCallback listener) => _listeners!.add(listener);
-
-  @override
-  void removeListener(VoidCallback listener) => _listeners!.remove(listener);
-
-  void dispose() => _listeners = null;
-
-  void notifyListeners() {
-    if (_listeners == null) return;
-    final localListeners = List<VoidCallback>.from(_listeners!);
-    for (final listener in localListeners) {
-      try {
-        if (_listeners!.contains(listener)) listener();
-      } catch (error, stack) {
-        debugPrint('$runtimeType failed to notify listeners with error=$error\n$stack');
-      }
-    }
+// `ChangeNotifier` wrapper so that it can be used anywhere, not just as a mixin
+class AChangeNotifier extends ChangeNotifier {
+  void notify() {
+    // why is this protected?
+    super.notifyListeners();
   }
 }

lib/widgets/collection/query_bar.dart

@@ -42,8 +42,6 @@ class _EntryQueryBarState extends State<EntryQueryBar> {
     super.dispose();
   }
 
-  // TODO TLAD focus on text field when enabled (`autofocus` is unusable)
-  // TODO TLAD lose focus on navigation to viewer?
   void _registerWidget(EntryQueryBar widget) {
     widget.queryNotifier.addListener(_onQueryChanged);
   }

lib/widgets/common/app_bar_subtitle.dart

@@ -1,5 +1,6 @@
 import 'package:aves/model/source/collection_source.dart';
 import 'package:aves/model/source/enums.dart';
+import 'package:aves/model/source/events.dart';
 import 'package:aves/model/source/source_state.dart';
 import 'package:aves/theme/durations.dart';
 import 'package:aves/widgets/common/extensions/build_context.dart';

lib/widgets/common/aves_highlight.dart

@@ -2,7 +2,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:highlight/highlight.dart' show highlight, Node;
 
-// TODO TLAD use the TextSpan getter instead of this modified `HighlightView` when this is fixed: https://github.com/git-touch/highlight/issues/6
+// adapted from package `flutter_highlight` v0.7.0 `HighlightView`
+// TODO TLAD use the TextSpan getter when this is fixed: https://github.com/git-touch/highlight/issues/6
 
 /// Highlight Flutter Widget
 class AvesHighlightView extends StatelessWidget {

lib/widgets/common/basic/draggable_scrollbar.dart

@@ -4,7 +4,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 /*
-  This is derived from `draggable_scrollbar` package v0.0.4:
+  adapted from package `draggable_scrollbar` v0.0.4:
   - removed default thumb builders
   - allow any `ScrollView` as child
   - allow any `Widget` as label content

lib/widgets/common/behaviour/eager_scale_gesture_recognizer.dart

@@ -0,0 +1,395 @@
+import 'dart:math' as math;
+
+import 'package:flutter/gestures.dart';
+import 'package:vector_math/vector_math_64.dart';
+
+// adapted from Flutter `ScaleGestureRecognizer` in `/gestures/scale.dart`
+// ignore_for_file: curly_braces_in_flow_control_structures, deprecated_member_use, unnecessary_null_comparison
+
+/// The possible states of a [ScaleGestureRecognizer].
+enum _ScaleState {
+  /// The recognizer is ready to start recognizing a gesture.
+  ready,
+
+  /// The sequence of pointer events seen thus far is consistent with a scale
+  /// gesture but the gesture has not been accepted definitively.
+  possible,
+
+  /// The sequence of pointer events seen thus far has been accepted
+  /// definitively as a scale gesture.
+  accepted,
+
+  /// The sequence of pointer events seen thus far has been accepted
+  /// definitively as a scale gesture and the pointers established a focal point
+  /// and initial scale.
+  started,
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+bool _isFlingGesture(Velocity velocity) {
+  assert(velocity != null);
+  final double speedSquared = velocity.pixelsPerSecond.distanceSquared;
+  return speedSquared > kMinFlingVelocity * kMinFlingVelocity;
+}
+
+/// Defines a line between two pointers on screen.
+///
+/// [_LineBetweenPointers] is an abstraction of a line between two pointers in
+/// contact with the screen. Used to track the rotation of a scale gesture.
+class _LineBetweenPointers {
+  /// Creates a [_LineBetweenPointers]. None of the [pointerStartLocation], [pointerStartId]
+  /// [pointerEndLocation] and [pointerEndId] must be null. [pointerStartId] and [pointerEndId]
+  /// should be different.
+  _LineBetweenPointers({
+    this.pointerStartLocation = Offset.zero,
+    this.pointerStartId = 0,
+    this.pointerEndLocation = Offset.zero,
+    this.pointerEndId = 1,
+  })  : assert(pointerStartLocation != null && pointerEndLocation != null),
+        assert(pointerStartId != null && pointerEndId != null),
+        assert(pointerStartId != pointerEndId);
+
+  // The location and the id of the pointer that marks the start of the line.
+  final Offset pointerStartLocation;
+  final int pointerStartId;
+
+  // The location and the id of the pointer that marks the end of the line.
+  final Offset pointerEndLocation;
+  final int pointerEndId;
+}
+
+/// Recognizes a scale gesture.
+///
+/// [ScaleGestureRecognizer] tracks the pointers in contact with the screen and
+/// calculates their focal point, indicated scale, and rotation. When a focal
+/// pointer is established, the recognizer calls [onStart]. As the focal point,
+/// scale, rotation change, the recognizer calls [onUpdate]. When the pointers
+/// are no longer in contact with the screen, the recognizer calls [onEnd].
+class EagerScaleGestureRecognizer extends OneSequenceGestureRecognizer {
+  /// Create a gesture recognizer for interactions intended for scaling content.
+  ///
+  /// {@macro flutter.gestures.GestureRecognizer.supportedDevices}
+  EagerScaleGestureRecognizer({
+    Object? debugOwner,
+    @Deprecated(
+      'Migrate to supportedDevices. '
+      'This feature was deprecated after v2.3.0-1.0.pre.',
+    )
+        PointerDeviceKind? kind,
+    Set<PointerDeviceKind>? supportedDevices,
+    this.dragStartBehavior = DragStartBehavior.down,
+  })  : assert(dragStartBehavior != null),
+        super(
+          debugOwner: debugOwner,
+          kind: kind,
+          supportedDevices: supportedDevices,
+        );
+
+  /// Determines what point is used as the starting point in all calculations
+  /// involving this gesture.
+  ///
+  /// When set to [DragStartBehavior.down], the scale is calculated starting
+  /// from the position where the pointer first contacted the screen.
+  ///
+  /// When set to [DragStartBehavior.start], the scale is calculated starting
+  /// from the position where the scale gesture began. The scale gesture may
+  /// begin after the time that the pointer first contacted the screen if there
+  /// are multiple listeners competing for the gesture. In that case, the
+  /// gesture arena waits to determine whether or not the gesture is a scale
+  /// gesture before giving the gesture to this GestureRecognizer. This happens
+  /// in the case of nested GestureDetectors, for example.
+  ///
+  /// Defaults to [DragStartBehavior.down].
+  ///
+  /// See also:
+  ///
+  /// * https://flutter.dev/docs/development/ui/advanced/gestures#gesture-disambiguation,
+  ///   which provides more information about the gesture arena.
+  DragStartBehavior dragStartBehavior;
+
+  /// The pointers in contact with the screen have established a focal point and
+  /// initial scale of 1.0.
+  ///
+  /// This won't be called until the gesture arena has determined that this
+  /// GestureRecognizer has won the gesture.
+  ///
+  /// See also:
+  ///
+  /// * https://flutter.dev/docs/development/ui/advanced/gestures#gesture-disambiguation,
+  ///   which provides more information about the gesture arena.
+  GestureScaleStartCallback? onStart;
+
+  /// The pointers in contact with the screen have indicated a new focal point
+  /// and/or scale.
+  GestureScaleUpdateCallback? onUpdate;
+
+  /// The pointers are no longer in contact with the screen.
+  GestureScaleEndCallback? onEnd;
+
+  _ScaleState _state = _ScaleState.ready;
+
+  Matrix4? _lastTransform;
+
+  late Offset _initialFocalPoint;
+  late Offset _currentFocalPoint;
+  late double _initialSpan;
+  late double _currentSpan;
+  late double _initialHorizontalSpan;
+  late double _currentHorizontalSpan;
+  late double _initialVerticalSpan;
+  late double _currentVerticalSpan;
+  _LineBetweenPointers? _initialLine;
+  _LineBetweenPointers? _currentLine;
+  late Map<int, Offset> _pointerLocations;
+  late List<int> _pointerQueue; // A queue to sort pointers in order of entrance
+  final Map<int, VelocityTracker> _velocityTrackers = <int, VelocityTracker>{};
+
+  double get _scaleFactor => _initialSpan > 0.0 ? _currentSpan / _initialSpan : 1.0;
+
+  double get _horizontalScaleFactor => _initialHorizontalSpan > 0.0 ? _currentHorizontalSpan / _initialHorizontalSpan : 1.0;
+
+  double get _verticalScaleFactor => _initialVerticalSpan > 0.0 ? _currentVerticalSpan / _initialVerticalSpan : 1.0;
+
+  double _computeRotationFactor() {
+    if (_initialLine == null || _currentLine == null) {
+      return 0.0;
+    }
+    final double fx = _initialLine!.pointerStartLocation.dx;
+    final double fy = _initialLine!.pointerStartLocation.dy;
+    final double sx = _initialLine!.pointerEndLocation.dx;
+    final double sy = _initialLine!.pointerEndLocation.dy;
+
+    final double nfx = _currentLine!.pointerStartLocation.dx;
+    final double nfy = _currentLine!.pointerStartLocation.dy;
+    final double nsx = _currentLine!.pointerEndLocation.dx;
+    final double nsy = _currentLine!.pointerEndLocation.dy;
+
+    final double angle1 = math.atan2(fy - sy, fx - sx);
+    final double angle2 = math.atan2(nfy - nsy, nfx - nsx);
+
+    return angle2 - angle1;
+  }
+
+  @override
+  void addAllowedPointer(PointerDownEvent event) {
+    super.addAllowedPointer(event);
+    _velocityTrackers[event.pointer] = VelocityTracker.withKind(event.kind);
+    if (_state == _ScaleState.ready) {
+      _state = _ScaleState.possible;
+      _initialSpan = 0.0;
+      _currentSpan = 0.0;
+      _initialHorizontalSpan = 0.0;
+      _currentHorizontalSpan = 0.0;
+      _initialVerticalSpan = 0.0;
+      _currentVerticalSpan = 0.0;
+      _pointerLocations = <int, Offset>{};
+      _pointerQueue = <int>[];
+    }
+  }
+
+  @override
+  void handleEvent(PointerEvent event) {
+    assert(_state != _ScaleState.ready);
+    bool didChangeConfiguration = false;
+    bool shouldStartIfAccepted = false;
+    if (event is PointerMoveEvent) {
+      final VelocityTracker tracker = _velocityTrackers[event.pointer]!;
+      if (!event.synthesized) tracker.addPosition(event.timeStamp, event.position);
+      _pointerLocations[event.pointer] = event.position;
+      shouldStartIfAccepted = true;
+      _lastTransform = event.transform;
+    } else if (event is PointerDownEvent) {
+      _pointerLocations[event.pointer] = event.position;
+      _pointerQueue.add(event.pointer);
+      didChangeConfiguration = true;
+      shouldStartIfAccepted = true;
+      _lastTransform = event.transform;
+    } else if (event is PointerUpEvent || event is PointerCancelEvent) {
+      _pointerLocations.remove(event.pointer);
+      _pointerQueue.remove(event.pointer);
+      didChangeConfiguration = true;
+      _lastTransform = event.transform;
+    }
+
+    _updateLines();
+    _update();
+
+    if (!didChangeConfiguration || _reconfigure(event.pointer)) _advanceStateMachine(shouldStartIfAccepted, event.kind);
+    stopTrackingIfPointerNoLongerDown(event);
+  }
+
+  void _update() {
+    final int count = _pointerLocations.keys.length;
+
+    // Compute the focal point
+    Offset focalPoint = Offset.zero;
+    for (final int pointer in _pointerLocations.keys) focalPoint += _pointerLocations[pointer]!;
+    _currentFocalPoint = count > 0 ? focalPoint / count.toDouble() : Offset.zero;
+
+    // Span is the average deviation from focal point. Horizontal and vertical
+    // spans are the average deviations from the focal point's horizontal and
+    // vertical coordinates, respectively.
+    double totalDeviation = 0.0;
+    double totalHorizontalDeviation = 0.0;
+    double totalVerticalDeviation = 0.0;
+    for (final int pointer in _pointerLocations.keys) {
+      totalDeviation += (_currentFocalPoint - _pointerLocations[pointer]!).distance;
+      totalHorizontalDeviation += (_currentFocalPoint.dx - _pointerLocations[pointer]!.dx).abs();
+      totalVerticalDeviation += (_currentFocalPoint.dy - _pointerLocations[pointer]!.dy).abs();
+    }
+    _currentSpan = count > 0 ? totalDeviation / count : 0.0;
+    _currentHorizontalSpan = count > 0 ? totalHorizontalDeviation / count : 0.0;
+    _currentVerticalSpan = count > 0 ? totalVerticalDeviation / count : 0.0;
+  }
+
+  /// Updates [_initialLine] and [_currentLine] accordingly to the situation of
+  /// the registered pointers.
+  void _updateLines() {
+    final int count = _pointerLocations.keys.length;
+    assert(_pointerQueue.length >= count);
+
+    /// In case of just one pointer registered, reconfigure [_initialLine]
+    if (count < 2) {
+      _initialLine = _currentLine;
+    } else if (_initialLine != null && _initialLine!.pointerStartId == _pointerQueue[0] && _initialLine!.pointerEndId == _pointerQueue[1]) {
+      /// Rotation updated, set the [_currentLine]
+      _currentLine = _LineBetweenPointers(
+        pointerStartId: _pointerQueue[0],
+        pointerStartLocation: _pointerLocations[_pointerQueue[0]]!,
+        pointerEndId: _pointerQueue[1],
+        pointerEndLocation: _pointerLocations[_pointerQueue[1]]!,
+      );
+    } else {
+      /// A new rotation process is on the way, set the [_initialLine]
+      _initialLine = _LineBetweenPointers(
+        pointerStartId: _pointerQueue[0],
+        pointerStartLocation: _pointerLocations[_pointerQueue[0]]!,
+        pointerEndId: _pointerQueue[1],
+        pointerEndLocation: _pointerLocations[_pointerQueue[1]]!,
+      );
+      _currentLine = _initialLine;
+    }
+  }
+
+  bool _reconfigure(int pointer) {
+    _initialFocalPoint = _currentFocalPoint;
+    _initialSpan = _currentSpan;
+    _initialLine = _currentLine;
+    _initialHorizontalSpan = _currentHorizontalSpan;
+    _initialVerticalSpan = _currentVerticalSpan;
+    if (_state == _ScaleState.started) {
+      if (onEnd != null) {
+        final VelocityTracker tracker = _velocityTrackers[pointer]!;
+
+        Velocity velocity = tracker.getVelocity();
+        if (_isFlingGesture(velocity)) {
+          final Offset pixelsPerSecond = velocity.pixelsPerSecond;
+          if (pixelsPerSecond.distanceSquared > kMaxFlingVelocity * kMaxFlingVelocity) velocity = Velocity(pixelsPerSecond: (pixelsPerSecond / pixelsPerSecond.distance) * kMaxFlingVelocity);
+          invokeCallback<void>('onEnd', () => onEnd!(ScaleEndDetails(velocity: velocity, pointerCount: _pointerQueue.length)));
+        } else {
+          invokeCallback<void>('onEnd', () => onEnd!(ScaleEndDetails(velocity: Velocity.zero, pointerCount: _pointerQueue.length)));
+        }
+      }
+      _state = _ScaleState.accepted;
+      return false;
+    }
+    return true;
+  }
+
+  void _advanceStateMachine(bool shouldStartIfAccepted, PointerDeviceKind pointerDeviceKind) {
+    if (_state == _ScaleState.ready) _state = _ScaleState.possible;
+
+    // TLAD insert start
+    if (_pointerQueue.length == 2) {
+      resolve(GestureDisposition.accepted);
+    }
+    // TLAD insert end
+
+    if (_state == _ScaleState.possible) {
+      final double spanDelta = (_currentSpan - _initialSpan).abs();
+      final double focalPointDelta = (_currentFocalPoint - _initialFocalPoint).distance;
+      if (spanDelta > computeScaleSlop(pointerDeviceKind) || focalPointDelta > computePanSlop(pointerDeviceKind)) resolve(GestureDisposition.accepted);
+    } else if (_state.index >= _ScaleState.accepted.index) {
+      resolve(GestureDisposition.accepted);
+    }
+
+    if (_state == _ScaleState.accepted && shouldStartIfAccepted) {
+      _state = _ScaleState.started;
+      _dispatchOnStartCallbackIfNeeded();
+    }
+
+    if (_state == _ScaleState.started && onUpdate != null)
+      invokeCallback<void>('onUpdate', () {
+        onUpdate!(ScaleUpdateDetails(
+          scale: _scaleFactor,
+          horizontalScale: _horizontalScaleFactor,
+          verticalScale: _verticalScaleFactor,
+          focalPoint: _currentFocalPoint,
+          localFocalPoint: PointerEvent.transformPosition(_lastTransform, _currentFocalPoint),
+          rotation: _computeRotationFactor(),
+          pointerCount: _pointerQueue.length,
+          delta: _currentFocalPoint - _initialFocalPoint,
+        ));
+      });
+  }
+
+  void _dispatchOnStartCallbackIfNeeded() {
+    assert(_state == _ScaleState.started);
+    if (onStart != null)
+      invokeCallback<void>('onStart', () {
+        onStart!(ScaleStartDetails(
+          focalPoint: _currentFocalPoint,
+          localFocalPoint: PointerEvent.transformPosition(_lastTransform, _currentFocalPoint),
+          pointerCount: _pointerQueue.length,
+        ));
+      });
+  }
+
+  @override
+  void acceptGesture(int pointer) {
+    if (_state == _ScaleState.possible) {
+      _state = _ScaleState.started;
+      _dispatchOnStartCallbackIfNeeded();
+      if (dragStartBehavior == DragStartBehavior.start) {
+        _initialFocalPoint = _currentFocalPoint;
+        _initialSpan = _currentSpan;
+        _initialLine = _currentLine;
+        _initialHorizontalSpan = _currentHorizontalSpan;
+        _initialVerticalSpan = _currentVerticalSpan;
+      }
+    }
+  }
+
+  @override
+  void rejectGesture(int pointer) {
+    stopTrackingPointer(pointer);
+  }
+
+  @override
+  void didStopTrackingLastPointer(int pointer) {
+    switch (_state) {
+      case _ScaleState.possible:
+        resolve(GestureDisposition.rejected);
+        break;
+      case _ScaleState.ready:
+        assert(false); // We should have not seen a pointer yet
+        break;
+      case _ScaleState.accepted:
+        break;
+      case _ScaleState.started:
+        assert(false); // We should be in the accepted state when user is done
+        break;
+    }
+    _state = _ScaleState.ready;
+  }
+
+  @override
+  void dispose() {
+    _velocityTrackers.clear();
+    super.dispose();
+  }
+
+  @override
+  String get debugDescription => 'scale';
+}

lib/widgets/common/fx/transition_image.dart

@@ -3,7 +3,7 @@ import 'dart:ui' as ui;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
-// adapted from `RawImage`, `paintImage()` from `DecorationImagePainter`, etc.
+// adapted from Flutter `RawImage`, `paintImage()` from `DecorationImagePainter`, etc.
 // to transition between 2 different fits during hero animation:
 // - BoxFit.cover at t=0
 // - BoxFit.contain at t=1

lib/widgets/common/grid/sliver.dart

@@ -12,7 +12,7 @@ import 'package:provider/provider.dart';
 // With the multiple `SliverGrid` solution, thumbnails at the beginning of each sections are built even though they are offscreen
 // because of `RenderSliverMultiBoxAdaptor.addInitialChild` called by `RenderSliverGrid.performLayout` (line 547), as of Flutter v1.17.0.
 // cf https://github.com/flutter/flutter/issues/49027
-// adapted from `RenderSliverFixedExtentBoxAdaptor`
+// adapted from Flutter `RenderSliverFixedExtentBoxAdaptor` in `/rendering/sliver_fixed_extent_list.dart`
 class SectionedListSliver<T> extends StatelessWidget {
   const SectionedListSliver({Key? key}) : super(key: key);
 

lib/widgets/common/magnifier/magnifier.dart

@@ -7,7 +7,7 @@ import 'package:aves/widgets/common/magnifier/scale/state.dart';
 import 'package:flutter/material.dart';
 
 /*
-  `Magnifier` is derived from `photo_view` package v0.9.2:
+  adapted from package `photo_view` v0.9.2:
   - removed image related aspects to focus on a general purpose pan/scale viewer (à la `InteractiveViewer`)
   - removed rotation and many customization parameters
   - removed ignorable/ignoring partial notifiers

lib/widgets/common/map/geo_map.dart

@@ -268,7 +268,7 @@ class _GeoMapState extends State<GeoMap> {
   void _onCollectionChanged() {
     _defaultMarkerCluster = _buildFluster();
     _slowMarkerCluster = null;
-    _clusterChangeNotifier.notifyListeners();
+    _clusterChangeNotifier.notify();
   }
 
   Fluster<GeoEntry> _buildFluster({int nodeSize = 64}) {

lib/widgets/common/map/google/map.dart

@@ -134,7 +134,7 @@ class _EntryGoogleMapState extends State<EntryGoogleMap> with WidgetsBindingObse
           isReadyToRender: (key) => key.entry.isThumbnailReady(extent: GeoMap.markerImageExtent),
           onRendered: (key, bitmap) {
             _markerBitmaps[key] = bitmap;
-            _markerBitmapChangeNotifier.notifyListeners();
+            _markerBitmapChangeNotifier.notify();
           },
         ),
         MapDecorator(

lib/widgets/common/scaling.dart

@@ -2,10 +2,12 @@ import 'dart:ui' as ui;
 
 import 'package:aves/model/highlight.dart';
 import 'package:aves/theme/durations.dart';
+import 'package:aves/widgets/common/behaviour/eager_scale_gesture_recognizer.dart';
 import 'package:aves/widgets/common/grid/theme.dart';
 import 'package:aves/widgets/common/providers/media_query_data_provider.dart';
 import 'package:aves/widgets/common/tile_extent_controller.dart';
 import 'package:collection/collection.dart';
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:provider/provider.dart';
@@ -49,95 +51,116 @@ class _GridScaleGestureDetectorState<T> extends State<GridScaleGestureDetector<T
 
   @override
   Widget build(BuildContext context) {
-    return GestureDetector(
-      onScaleStart: (details) {
-        // the gesture detector wrongly detects a new scaling gesture
-        // when scaling ends and we apply the new extent, so we prevent this
-        // until we scaled and scrolled to the tile in the new grid
-        if (_applyingScale) return;
+    final child = GestureDetector(
+      // Horizontal/vertical drag gestures are interpreted as scaling
+      // if they are not handled by `onHorizontalDragStart`/`onVerticalDragStart`
+      // at the scaling `GestureDetector` level, or handled beforehand down the widget tree.
+      // Setting `onHorizontalDragStart`, `onVerticalDragStart`, and `onScaleStart`
+      // all at once is not allowed, so we use another `GestureDetector` for that.
+      onVerticalDragStart: (details) {},
+      onHorizontalDragStart: (details) {},
+      child: widget.child,
+    );
 
-        final tileExtentController = context.read<TileExtentController>();
+    // as of Flutter v2.5.3, `ScaleGestureRecognizer` does not work well
+    // when combined with the `VerticalDragGestureRecognizer` inside a `GridView`,
+    // so it is modified to eagerly accept the gesture
+    // when multiple pointers are involved, and take priority over drag gestures.
+    return RawGestureDetector(
+      gestures: <Type, GestureRecognizerFactory>{
+        EagerScaleGestureRecognizer: GestureRecognizerFactoryWithHandlers<EagerScaleGestureRecognizer>(
+          () => EagerScaleGestureRecognizer(debugOwner: this),
+          (instance) {
+            instance
+              ..onStart = _onScaleStart
+              ..onUpdate = _onScaleUpdate
+              ..onEnd = _onScaleEnd
+              ..dragStartBehavior = DragStartBehavior.start;
+          },
+        ),
+      },
+      child: child,
+    );
+  }
 
-        final scrollableContext = widget.scrollableKey.currentContext!;
-        final scrollableBox = scrollableContext.findRenderObject() as RenderBox;
-        final renderMetaData = _getClosestRenderMetadata(
-          box: scrollableBox,
-          localFocalPoint: details.localFocalPoint,
-          spacing: tileExtentController.spacing,
-        );
-        // abort if we cannot find an image to show on overlay
-        if (renderMetaData == null) return;
-        _metadata = renderMetaData.metaData;
-        _startSize = renderMetaData.size;
-        _scaledSizeNotifier = ValueNotifier(_startSize!);
+  void _onScaleStart(ScaleStartDetails details) {
+    // the gesture detector wrongly detects a new scaling gesture
+    // when scaling ends and we apply the new extent, so we prevent this
+    // until we scaled and scrolled to the tile in the new grid
+    if (_applyingScale) return;
 
-        // not the same as `MediaQuery.size.width`, because of screen insets/padding
-        final gridWidth = scrollableBox.size.width;
+    final tileExtentController = context.read<TileExtentController>();
 
-        _extentMin = tileExtentController.effectiveExtentMin;
-        _extentMax = tileExtentController.effectiveExtentMax;
+    final scrollableContext = widget.scrollableKey.currentContext!;
+    final scrollableBox = scrollableContext.findRenderObject() as RenderBox;
+    final renderMetaData = _getClosestRenderMetadata(
+      box: scrollableBox,
+      localFocalPoint: details.localFocalPoint,
+      spacing: tileExtentController.spacing,
+    );
+    // abort if we cannot find an image to show on overlay
+    if (renderMetaData == null) return;
+    _metadata = renderMetaData.metaData;
+    _startSize = renderMetaData.size;
+    _scaledSizeNotifier = ValueNotifier(_startSize!);
 
-        final halfSize = _startSize! / 2;
-        final thumbnailCenter = renderMetaData.localToGlobal(Offset(halfSize.width, halfSize.height));
-        _overlayEntry = OverlayEntry(
-          builder: (context) => ScaleOverlay(
-            builder: (scaledTileSize) => SizedBox.fromSize(
-              size: scaledTileSize,
-              child: GridTheme(
-                extent: scaledTileSize.width,
-                child: widget.scaledBuilder(_metadata!.item, scaledTileSize),
-              ),
-            ),
-            center: thumbnailCenter,
-            viewportWidth: gridWidth,
-            gridBuilder: widget.gridBuilder,
-            scaledSizeNotifier: _scaledSizeNotifier!,
+    // not the same as `MediaQuery.size.width`, because of screen insets/padding
+    final gridWidth = scrollableBox.size.width;
+
+    _extentMin = tileExtentController.effectiveExtentMin;
+    _extentMax = tileExtentController.effectiveExtentMax;
+
+    final halfSize = _startSize! / 2;
+    final thumbnailCenter = renderMetaData.localToGlobal(Offset(halfSize.width, halfSize.height));
+    _overlayEntry = OverlayEntry(
+      builder: (context) => ScaleOverlay(
+        builder: (scaledTileSize) => SizedBox.fromSize(
+          size: scaledTileSize,
+          child: GridTheme(
+            extent: scaledTileSize.width,
+            child: widget.scaledBuilder(_metadata!.item, scaledTileSize),
           ),
-        );
-        Overlay.of(scrollableContext)!.insert(_overlayEntry!);
-      },
-      onScaleUpdate: (details) {
-        if (_scaledSizeNotifier == null) return;
-        final s = details.scale;
-        final scaledWidth = (_startSize!.width * s).clamp(_extentMin!, _extentMax!);
-        _scaledSizeNotifier!.value = Size(scaledWidth, widget.heightForWidth(scaledWidth));
-      },
-      onScaleEnd: (details) {
-        if (_scaledSizeNotifier == null) return;
-        if (_overlayEntry != null) {
-          _overlayEntry!.remove();
-          _overlayEntry = null;
-        }
-
-        _applyingScale = true;
-        final tileExtentController = context.read<TileExtentController>();
-        final oldExtent = tileExtentController.extentNotifier.value;
-        // sanitize and update grid layout if necessary
-        final newExtent = tileExtentController.setUserPreferredExtent(_scaledSizeNotifier!.value.width);
-        _scaledSizeNotifier = null;
-        if (newExtent == oldExtent) {
-          _applyingScale = false;
-        } else {
-          // scroll to show the focal point thumbnail at its new position
-          WidgetsBinding.instance!.addPostFrameCallback((_) {
-            final trackItem = _metadata!.item;
-            final highlightItem = widget.highlightItem?.call(trackItem) ?? trackItem;
-            context.read<HighlightInfo>().trackItem(trackItem, animate: false, highlightItem: highlightItem);
-            _applyingScale = false;
-          });
-        }
-      },
-      child: GestureDetector(
-        // Horizontal/vertical drag gestures are interpreted as scaling
-        // if they are not handled by `onHorizontalDragStart`/`onVerticalDragStart`
-        // at the scaling `GestureDetector` level, or handled beforehand down the widget tree.
-        // Setting `onHorizontalDragStart`, `onVerticalDragStart`, and `onScaleStart`
-        // all at once is not allowed, so we use another `GestureDetector` for that.
-        onVerticalDragStart: (details) {},
-        onHorizontalDragStart: (details) {},
-        child: widget.child,
+        ),
+        center: thumbnailCenter,
+        viewportWidth: gridWidth,
+        gridBuilder: widget.gridBuilder,
+        scaledSizeNotifier: _scaledSizeNotifier!,
       ),
     );
+    Overlay.of(scrollableContext)!.insert(_overlayEntry!);
+  }
+
+  void _onScaleUpdate(ScaleUpdateDetails details) {
+    if (_scaledSizeNotifier == null) return;
+    final s = details.scale;
+    final scaledWidth = (_startSize!.width * s).clamp(_extentMin!, _extentMax!);
+    _scaledSizeNotifier!.value = Size(scaledWidth, widget.heightForWidth(scaledWidth));
+  }
+
+  void _onScaleEnd(ScaleEndDetails details) {
+    if (_scaledSizeNotifier == null) return;
+    if (_overlayEntry != null) {
+      _overlayEntry!.remove();
+      _overlayEntry = null;
+    }
+
+    _applyingScale = true;
+    final tileExtentController = context.read<TileExtentController>();
+    final oldExtent = tileExtentController.extentNotifier.value;
+    // sanitize and update grid layout if necessary
+    final newExtent = tileExtentController.setUserPreferredExtent(_scaledSizeNotifier!.value.width);
+    _scaledSizeNotifier = null;
+    if (newExtent == oldExtent) {
+      _applyingScale = false;
+    } else {
+      // scroll to show the focal point thumbnail at its new position
+      WidgetsBinding.instance!.addPostFrameCallback((_) {
+        final trackItem = _metadata!.item;
+        final highlightItem = widget.highlightItem?.call(trackItem) ?? trackItem;
+        context.read<HighlightInfo>().trackItem(trackItem, animate: false, highlightItem: highlightItem);
+        _applyingScale = false;
+      });
+    }
   }
 
   RenderMetaData? _getClosestRenderMetadata({

lib/widgets/dialogs/entry_editors/edit_entry_tags_dialog.dart

@@ -5,10 +5,10 @@ import 'package:aves/model/filters/tag.dart';
 import 'package:aves/model/source/collection_source.dart';
 import 'package:aves/theme/durations.dart';
 import 'package:aves/theme/icons.dart';
+import 'package:aves/widgets/common/expandable_filter_row.dart';
 import 'package:aves/widgets/common/extensions/build_context.dart';
 import 'package:aves/widgets/common/identity/aves_filter_chip.dart';
 import 'package:aves/widgets/common/providers/media_query_data_provider.dart';
-import 'package:aves/widgets/search/expandable_filter_row.dart';
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';

lib/widgets/search/search_delegate.dart

@@ -15,9 +15,9 @@ import 'package:aves/model/source/tag.dart';
 import 'package:aves/ref/mime_types.dart';
 import 'package:aves/theme/icons.dart';
 import 'package:aves/widgets/collection/collection_page.dart';
+import 'package:aves/widgets/common/expandable_filter_row.dart';
 import 'package:aves/widgets/common/extensions/build_context.dart';
 import 'package:aves/widgets/common/identity/aves_filter_chip.dart';
-import 'package:aves/widgets/search/expandable_filter_row.dart';
 import 'package:aves/widgets/search/search_page.dart';
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
@@ -273,7 +273,7 @@ class CollectionSearchDelegate {
     focusNode?.unfocus();
   }
 
-  // adapted from `SearchDelegate`
+  // adapted from Flutter `SearchDelegate` in `/material/search.dart`
 
   void showResults(BuildContext context) {
     focusNode?.unfocus();
@@ -311,10 +311,10 @@ class CollectionSearchDelegate {
   SearchPageRoute? route;
 }
 
-// adapted from `SearchDelegate`
+// adapted from Flutter `_SearchBody` in `/material/search.dart`
 enum SearchBody { suggestions, results }
 
-// adapted from `SearchDelegate`
+// adapted from Flutter `_SearchPageRoute` in `/material/search.dart`
 class SearchPageRoute<T> extends PageRoute<T> {
   SearchPageRoute({
     required this.delegate,

lib/widgets/settings/common/quick_actions/editor_page.dart

@@ -290,7 +290,7 @@ class _QuickActionEditorBodyState<T extends Object> extends State<QuickActionEdi
       targetIndex,
       duration: Durations.quickActionListAnimation,
     );
-    _quickActionsChangeNotifier.notifyListeners();
+    _quickActionsChangeNotifier.notify();
     Future.delayed(Durations.quickActionListAnimation).then((value) => _reordering = false);
     return true;
   }
@@ -305,7 +305,7 @@ class _QuickActionEditorBodyState<T extends Object> extends State<QuickActionEdi
       (context, animation) => DraggedPlaceholder(child: _buildQuickActionButton(action, animation)),
       duration: Durations.quickActionListAnimation,
     );
-    _quickActionsChangeNotifier.notifyListeners();
+    _quickActionsChangeNotifier.notify();
     return true;
   }
 

lib/widgets/viewer/entry_viewer_stack.dart

@@ -390,7 +390,7 @@ class _EntryViewerStackState extends State<EntryViewerStack> with FeedbackMixin,
     if (!_isEntryTracked && _verticalPager.page?.floor() == transitionPage) {
       _trackEntry();
     }
-    _verticalScrollNotifier.notifyListeners();
+    _verticalScrollNotifier.notify();
   }
 
   void _goToCollection(CollectionFilter filter) {

lib/widgets/viewer/info/metadata/xmp_ns/photoshop.dart

@@ -1,9 +1,8 @@
-// cf photoshop:ColorMode
-// cf https://github.com/adobe/xmp-docs/blob/master/XMPNamespaces/photoshop.md
 import 'package:aves/widgets/viewer/info/metadata/xmp_namespaces.dart';
 import 'package:aves/widgets/viewer/info/metadata/xmp_structs.dart';
 import 'package:flutter/widgets.dart';
 
+// cf https://github.com/adobe/xmp-docs/blob/master/XMPNamespaces/photoshop.md
 class XmpPhotoshopNamespace extends XmpNamespace {
   static const ns = 'photoshop';
 

lib/widgets/viewer/overlay/common.dart

@@ -75,7 +75,6 @@ class OverlayTextButton extends StatelessWidget {
             shape: MaterialStateProperty.all<OutlinedBorder>(const RoundedRectangleBorder(
               borderRadius: BorderRadius.all(Radius.circular(_borderRadius)),
             )),
-            // shape: MaterialStateProperty.all<OutlinedBorder>(CircleBorder()),
           ),
           child: Text(buttonLabel),
         ),

lib/widgets/viewer/video/fijkplayer.dart

@@ -86,7 +86,7 @@ class IjkPlayerAvesVideoController extends AvesVideoController {
 
   void _startListening() {
     _instance.addListener(_onValueChanged);
-    _subscriptions.add(_valueStream.where((value) => value.state == FijkState.completed).listen((_) => _completedNotifier.notifyListeners()));
+    _subscriptions.add(_valueStream.where((value) => value.state == FijkState.completed).listen((_) => _completedNotifier.notify()));
     _subscriptions.add(_instance.onTimedText.listen(_timedTextStreamController.add));
   }
 

pubspec.yaml

@@ -117,3 +117,30 @@ flutter:
 
 # capture shaders in profile mode (real device only):
 # % flutter drive --flavor play -t test_driver/driver_play.dart --profile --cache-sksl --write-sksl-on-exit shaders.sksl.json
+
+################################################################################
+# Adaptations
+
+#  `DraggableScrollbar` in `/widgets/common/basic/draggable_scrollbar.dart`
+#  adapts from package `draggable_scrollbar` v0.0.4
+#
+#  `Magnifier` in `/widgets/common/magnifier/magnifier.dart`
+#  adapts from package `photo_view` v0.9.2
+#
+#  `AvesHighlightView` in `/widgets/common/aves_highlight.dart`
+#  adapts from package `flutter_highlight` v0.7.0
+#
+#  `OutputBuffer` in `/services/common/output_buffer.dart`
+#  adapts from Flutter `_OutputBuffer` in `/foundation/consolidate_response.dart`
+#
+#  `EagerScaleGestureRecognizer` in `/widgets/common/behaviour/eager_scale_gesture_recognizer.dart`
+#  adapts from Flutter `ScaleGestureRecognizer` in `/gestures/scale.dart`
+#
+#  `TransitionImage` in `/widgets/common/fx/transition_image.dart`
+#  adapts from Flutter `RawImage` in `/widgets/basic.dart` and `DecorationImagePainter` in `/painting/decoration_image.dart`
+#
+#  `_RenderSliverKnownExtentBoxAdaptor` in `/widgets/common/grid/sliver.dart`
+#  adapts from Flutter `RenderSliverFixedExtentBoxAdaptor` in `/rendering/sliver_fixed_extent_list.dart`
+#
+#  `CollectionSearchDelegate`, `SearchPageRoute` in `/widgets/search/search_delegate.dart`
+#  adapts from Flutter `SearchDelegate`, `_SearchPageRoute` in `/material/search.dart`