anchor.diff:      // 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 + direction * 100.0), magnitude);
  +      animatePosition( _position, clampPosition(_position + direction * 100.0));
       }
   
     }
  
positive.code:       ..fling(velocity: 0.4);
    }
  
    TickerFuture animatePosition(Offset from, Offset to, [double magnitude = 1.0]) {
      _positionAnimation = Tween<Offset>(begin: from, end: to)
          .animate(_positionAnimationController);
      _positionAnimationController
        ..value = 0.0;
      return _positionAnimationController.fling(velocity: 0.4);
    }
  
    @override
  
negative.code: class _PhotoViewImageWrapperState extends State<PhotoViewImageWrapper>
      with TickerProviderStateMixin {
    Offset _position;
    Offset _normalizedPosition;
    double _scale;
    double _scaleBefore;
  