Add onDrag Gestures

lib/photo_view.dart

@@ -1,7 +1,6 @@
 library photo_view;
 
 import 'package:flutter/material.dart';
-
 import 'package:photo_view/src/controller/photo_view_controller.dart';
 import 'package:photo_view/src/controller/photo_view_scalestate_controller.dart';
 import 'package:photo_view/src/core/photo_view_core.dart';
@@ -255,6 +254,7 @@ class PhotoView extends StatefulWidget {
     this.onTapUp,
     this.onTapDown,
     this.onScaleEnd,
+    this.onDragEnd,
     this.customSize,
     this.gestureDetectorBehavior,
     this.tightMode,
@@ -291,6 +291,7 @@ class PhotoView extends StatefulWidget {
     this.onTapUp,
     this.onTapDown,
     this.onScaleEnd,
+    this.onDragEnd,
     this.customSize,
     this.gestureDetectorBehavior,
     this.tightMode,
@@ -392,6 +393,10 @@ class PhotoView extends StatefulWidget {
   /// particular location.
   final PhotoViewImageScaleEndCallback? onScaleEnd;
 
+  /// A pointer that will trigger a drag has stopped contacting the screen at a
+  /// particular location.
+  final PhotoViewImageDragEndCallback? onDragEnd;
+
   /// [HitTestBehavior] to be passed to the internal gesture detector.
   final HitTestBehavior? gestureDetectorBehavior;
 
@@ -550,6 +555,7 @@ class _PhotoViewState extends State<PhotoView>
                 onTapUp: widget.onTapUp,
                 onTapDown: widget.onTapDown,
                 onScaleEnd: widget.onScaleEnd,
+                onDragEnd: widget.onDragEnd,
                 outerSize: computedOuterSize,
                 gestureDetectorBehavior: widget.gestureDetectorBehavior,
                 tightMode: widget.tightMode,
@@ -611,6 +617,13 @@ typedef PhotoViewImageScaleEndCallback = Function(
   PhotoViewControllerValue controllerValue,
 );
 
+/// A type definition for a callback when a user finished vertical drag
+typedef PhotoViewImageDragEndCallback = Function(
+  BuildContext context,
+  DragEndDetails details,
+  PhotoViewControllerValue controllerValue,
+);
+
 /// A type definition for a callback to show a widget while the image is loading, a [ImageChunkEvent] is passed to inform progress
 typedef LoadingBuilder = Widget Function(
   BuildContext context,

lib/src/core/photo_view_core.dart

@@ -1,11 +1,12 @@
 import 'package:flutter/widgets.dart';
 import 'package:photo_view/photo_view.dart'
     show
-        PhotoViewScaleState,
         PhotoViewHeroAttributes,
+        PhotoViewImageDragEndCallback,
+        PhotoViewImageScaleEndCallback,
         PhotoViewImageTapDownCallback,
         PhotoViewImageTapUpCallback,
-        PhotoViewImageScaleEndCallback,
+        PhotoViewScaleState,
         ScaleStateCycle;
 import 'package:photo_view/src/controller/photo_view_controller.dart';
 import 'package:photo_view/src/controller/photo_view_controller_delegate.dart';
@@ -32,6 +33,7 @@ class PhotoViewCore extends StatefulWidget {
     required this.onTapUp,
     required this.onTapDown,
     required this.onScaleEnd,
+    required this.onDragEnd,
     required this.gestureDetectorBehavior,
     required this.controller,
     required this.scaleBoundaries,
@@ -54,6 +56,7 @@ class PhotoViewCore extends StatefulWidget {
     this.onTapUp,
     this.onTapDown,
     this.onScaleEnd,
+    this.onDragEnd,
     this.gestureDetectorBehavior,
     required this.controller,
     required this.scaleBoundaries,
@@ -87,6 +90,8 @@ class PhotoViewCore extends StatefulWidget {
   final PhotoViewImageTapDownCallback? onTapDown;
   final PhotoViewImageScaleEndCallback? onScaleEnd;
 
+  final PhotoViewImageDragEndCallback? onDragEnd;
+
   final HitTestBehavior? gestureDetectorBehavior;
   final bool tightMode;
   final bool disableGestures;
@@ -146,6 +151,15 @@ class PhotoViewCoreState extends State<PhotoViewCore>
     _rotationAnimationController.stop();
   }
 
+  void onDragStart(DragStartDetails details) {
+    _rotationBefore = controller.rotation;
+    _scaleBefore = scale;
+    _normalizedPosition = details.globalPosition - controller.position;
+    _scaleAnimationController.stop();
+    _positionAnimationController.stop();
+    _rotationAnimationController.stop();
+  }
+
   void onScaleUpdate(ScaleUpdateDetails details) {
     final double newScale = _scaleBefore! * details.scale;
     final Offset delta = details.focalPoint - _normalizedPosition!;
@@ -163,6 +177,19 @@ class PhotoViewCoreState extends State<PhotoViewCore>
     );
   }
 
+  void onDragUpdate(DragUpdateDetails details) {
+    final double newScale = _scaleBefore! * 1;
+    final Offset delta = details.globalPosition - _normalizedPosition!;
+
+    updateScaleStateFromNewScale(newScale);
+
+    updateMultiple(
+      scale: newScale,
+      position:
+          widget.enablePanAlways ? delta : clampPosition(position: delta * 1),
+    );
+  }
+
   void onScaleEnd(ScaleEndDetails details) {
     final double _scale = scale;
     final Offset _position = controller.position;
@@ -209,6 +236,52 @@ class PhotoViewCoreState extends State<PhotoViewCore>
     }
   }
 
+  void onDragEnd(DragEndDetails details) {
+    final double _scale = scale;
+    final Offset _position = controller.position;
+    final double maxScale = scaleBoundaries.maxScale;
+    final double minScale = scaleBoundaries.minScale;
+
+    widget.onDragEnd?.call(context, details, controller.value);
+
+    //animate back to maxScale if gesture exceeded the maxScale specified
+    if (_scale > maxScale) {
+      final double scaleComebackRatio = maxScale / _scale;
+      animateScale(_scale, maxScale);
+      final Offset clampedPosition = clampPosition(
+        position: _position * scaleComebackRatio,
+        scale: maxScale,
+      );
+      animatePosition(_position, clampedPosition);
+      return;
+    }
+
+    //animate back to minScale if gesture fell smaller than the minScale specified
+    if (_scale < minScale) {
+      final double scaleComebackRatio = minScale / _scale;
+      animateScale(_scale, minScale);
+      animatePosition(
+        _position,
+        clampPosition(
+          position: _position * scaleComebackRatio,
+          scale: minScale,
+        ),
+      );
+      return;
+    }
+    // get magnitude from gesture velocity
+    final double magnitude = details.velocity.pixelsPerSecond.distance;
+
+    // animate velocity only if there is no scale change and a significant magnitude
+    if (_scaleBefore! / _scale == 1.0 && magnitude >= 400.0) {
+      final Offset direction = details.velocity.pixelsPerSecond / magnitude;
+      animatePosition(
+        _position,
+        clampPosition(position: _position + direction * 100.0),
+      );
+    }
+  }
+
   void onDoubleTap() {
     nextScaleState();
   }
@@ -350,6 +423,9 @@ class PhotoViewCoreState extends State<PhotoViewCore>
               onScaleStart: onScaleStart,
               onScaleUpdate: onScaleUpdate,
               onScaleEnd: onScaleEnd,
+              onDragStart: onDragStart,
+              onDragUpdate: onDragUpdate,
+              onDragEnd: onDragEnd,
               hitDetector: this,
               onTapUp: widget.onTapUp != null
                   ? (details) => widget.onTapUp!(context, details, value)

lib/src/core/photo_view_gesture_detector.dart

@@ -10,6 +10,9 @@ class PhotoViewGestureDetector extends StatelessWidget {
     this.onScaleStart,
     this.onScaleUpdate,
     this.onScaleEnd,
+    this.onDragStart,
+    this.onDragUpdate,
+    this.onDragEnd,
     this.onDoubleTap,
     this.child,
     this.onTapUp,
@@ -24,6 +27,10 @@ class PhotoViewGestureDetector extends StatelessWidget {
   final GestureScaleUpdateCallback? onScaleUpdate;
   final GestureScaleEndCallback? onScaleEnd;
 
+  final GestureDragStartCallback? onDragStart;
+  final GestureDragUpdateCallback? onDragUpdate;
+  final GestureDragEndCallback? onDragEnd;
+
   final GestureTapUpCallback? onTapUp;
   final GestureTapDownCallback? onTapDown;
 
@@ -59,6 +66,16 @@ class PhotoViewGestureDetector extends StatelessWidget {
         instance..onDoubleTap = onDoubleTap;
       },
     );
+    gestures[VerticalDragGestureRecognizer] =
+        GestureRecognizerFactoryWithHandlers<VerticalDragGestureRecognizer>(
+      () => VerticalDragGestureRecognizer(debugOwner: this),
+      (VerticalDragGestureRecognizer instance) {
+        instance
+          ..onStart = onDragStart
+          ..onUpdate = onDragUpdate
+          ..onEnd = onDragEnd;
+      },
+    );
 
     gestures[PhotoViewGestureRecognizer] =
         GestureRecognizerFactoryWithHandlers<PhotoViewGestureRecognizer>(

lib/src/photo_view_wrappers.dart

@@ -26,6 +26,7 @@ class ImageWrapper extends StatefulWidget {
     required this.onTapUp,
     required this.onTapDown,
     required this.onScaleEnd,
+    required this.onDragEnd,
     required this.outerSize,
     required this.gestureDetectorBehavior,
     required this.tightMode,
@@ -54,6 +55,7 @@ class ImageWrapper extends StatefulWidget {
   final PhotoViewImageTapUpCallback? onTapUp;
   final PhotoViewImageTapDownCallback? onTapDown;
   final PhotoViewImageScaleEndCallback? onScaleEnd;
+  final PhotoViewImageDragEndCallback? onDragEnd;
   final Size outerSize;
   final HitTestBehavior? gestureDetectorBehavior;
   final bool? tightMode;
@@ -196,6 +198,7 @@ class _ImageWrapperState extends State<ImageWrapper> {
       onTapUp: widget.onTapUp,
       onTapDown: widget.onTapDown,
       onScaleEnd: widget.onScaleEnd,
+      onDragEnd: widget.onDragEnd,
       gestureDetectorBehavior: widget.gestureDetectorBehavior,
       tightMode: widget.tightMode ?? false,
       filterQuality: widget.filterQuality ?? FilterQuality.none,