anchor.diff:  
       updateScaleStateFromNewScale(details.scale, newScale);
   
  +    print(details.focalPoint.dy);
  +
       updateMultiple(
         scale: newScale,
         position: clampPosition(delta * details.scale),
  
positive.code:             final matrix = Matrix4.identity()
                ..translate(value.position.dx, value.position.dy)
                ..scale(scale);
  
              final rotationMatrix = Matrix4.identity()..rotateZ(value.rotation);
              final Widget customChildLayout = CustomSingleChildLayout(
                delegate: _CenterWithOriginalSizeDelegate(
                  scaleBoundaries.childSize,
  
negative.code: import 'controller/photo_view_controller_delegate.dart';
  import 'photo_view_hero_attributes.dart';
  import 'photo_view_typedefs.dart';
  
  import 'dart:math' as math;
  
  typedef PhotoViewImageTapUpCallback = Function(BuildContext context,
      TapUpDetails details, PhotoViewControllerValue controllerValue);
  