Should go in flutter/lib/src/widgets/implicit_animations.dart

animated_transform.dart

import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';

class AnimatedTransform extends ImplicitlyAnimatedWidget {
  const AnimatedTransform({
    Key? key,
    this.child,
    required this.transform,
    this.alignment = Alignment.center,
    this.filterQuality,
    Curve curve = Curves.linear,
    required Duration duration,
    VoidCallback? onEnd,
    this.alwaysIncludeSemantics = false,
  }) : super(key: key, curve: curve, duration: duration, onEnd: onEnd);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.ProxyWidget.child}
  final Widget? child;

  final Matrix4? transform;

  /// The alignment of the origin of the coordinate system in which the scale
  /// takes place, relative to the size of the box.
  ///
  /// For example, to set the origin of the scale to bottom middle, you can use
  /// an alignment of (0.0, 1.0).
  final Alignment alignment;

  /// The filter quality with which to apply the transform as a bitmap operation.
  ///
  /// {@macro flutter.widgets.Transform.optional.FilterQuality}
  final FilterQuality? filterQuality;

  /// Whether the semantic information of the children is always included.
  ///
  /// Defaults to false.
  final bool alwaysIncludeSemantics;

  @override
  ImplicitlyAnimatedWidgetState<AnimatedTransform> createState() =>
      _AnimatedTransformState();

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty('transform', transform,
        defaultValue: Matrix4.identity()));
    properties.add(DiagnosticsProperty<Alignment>('alignment', alignment,
        defaultValue: Alignment.center));
    properties.add(EnumProperty<FilterQuality>('filterQuality', filterQuality,
        defaultValue: null));
  }
}

class _AnimatedTransformState
    extends ImplicitlyAnimatedWidgetState<AnimatedTransform> {
  Tween<Matrix4>? _transform;
  late Animation<Matrix4> _animationTransform;

  @override
  void forEachTween(TweenVisitor<dynamic> visitor) {
    _transform = visitor(_transform, widget.transform,
            (dynamic value) => Tween<Matrix4>(begin: value as Matrix4))
        as Tween<Matrix4>?;
  }

  @override
  void didUpdateTweens() {
    _animationTransform = animation.drive(_transform!);
  }

  @override
  Widget build(BuildContext context) {
    return TransformTransition(
      transform: _animationTransform,
      alignment: widget.alignment,
      child: widget.child,
    );
  }
}

class TransformTransition extends AnimatedWidget {
  const TransformTransition({
    Key? key,
    required Animation<Matrix4> transform,
    this.alignment = Alignment.center,
    this.filterQuality,
    this.child,
  }) : super(key: key, listenable: transform);

  Animation<Matrix4> get transform => listenable as Animation<Matrix4>;

  /// The alignment of the origin of the coordinate system in which the scale
  /// takes place, relative to the size of the box.
  ///
  /// For example, to set the origin of the scale to bottom middle, you can use
  /// an alignment of (0.0, 1.0).
  final Alignment alignment;

  /// The filter quality with which to apply the transform as a bitmap operation.
  ///
  /// {@macro flutter.widgets.Transform.optional.FilterQuality}
  final FilterQuality? filterQuality;

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.ProxyWidget.child}
  final Widget? child;

  @override
  Widget build(BuildContext context) {
    return Transform(
      transform: transform.value,
      alignment: alignment,
      filterQuality: filterQuality,
      child: child,
    );
  }
}