Testing 3 ways to animate a transform on a widget: Transform(), FilteredWidget(), and Transform(cacheTransform: ...)

main.dart

import 'dart:math';
import 'dart:ui';

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Animating Widget Demo',
      home: MyHomePage(title: 'Animating Widget'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

enum FilterType {
  OPACITY, ROTATE_TRANSFORM, ROTATE_FILTER,
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  bool _useRepaintBoundary = false;
  bool _cacheTransformChild = false;
  bool _complexChild = false;
  double _cacheScale = 1.0;
  double _cacheRotate = 0.0;
  FilterType _filterType;
  GlobalKey _childKey = GlobalKey(debugLabel: 'child to animate');
  Offset _childCenter = Offset.zero;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
      RenderBox childBox = _childKey.currentContext.findRenderObject();
      _childCenter = childBox.paintBounds.center;
    });
    _controller = AnimationController(vsync: this, duration: Duration(seconds: 2));
    _controller.repeat();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  void _setFilterType(FilterType type, bool selected) {
    setState(() => _filterType = selected ? type : null);
  }

  Matrix4 get _cacheMatrix {
    if (_cacheTransformChild) {
      // ?: operator is apparently confused by .. operator?
      return Matrix4.identity()
        ..scale(_cacheScale)
        ..rotateZ(_cacheRotate);
    }
    return null;
  }

  List<Widget> makeComplexChildList(int rows, int cols, double w, double h) {
    List<Widget> children = <Widget>[];
    double sx = w / cols;
    double sy = h / rows;
    double tx = - sx * cols / 2.0;
    double ty = - sy * rows / 2.0;
    for (int r = 0; r < rows; r++) {
      for (int c = 0; c < cols; c++) {
        children.add(RepaintBoundary(child: Transform(
          child: Text('text'),
          transform: Matrix4.translationValues(c * sx + tx, r * sy + ty, 0.0),
        )));
      }
    }
    return children;
  }

  static Widget _makeChild(int rows, int cols, double fontSize, bool complex) {
    BoxDecoration decoration = BoxDecoration(
      color: Colors.green,
      boxShadow: complex ? <BoxShadow>[
        BoxShadow(
          color: Colors.black,
          blurRadius: 10.0,
        ),
      ] : null,
      borderRadius: BorderRadius.circular(10.0),
    );
    return Stack(
      alignment: Alignment.center,
      children: <Widget>[
        Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: List<Widget>.generate(rows, (r) => Row(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: List<Widget>.generate(cols, (c) => Container(
              child: Text('text', style: TextStyle(fontSize: fontSize)),
              decoration: decoration,
            )),
          )),
        ),
        Text('child',
          style: TextStyle(
            color: Colors.white,
            fontSize: 36,
          ),
        ),
      ],
    );
  }

  static Widget _protectChild({Widget child, bool protect}) {
    if (protect) {
      child = RepaintBoundary(child: child,);
    }
    return child;
  }

  Widget buildOpacity(BuildContext context, Widget child) {
    return Opacity(
      opacity: (_controller.value * 2.0 - 1.0).abs(),
      child: child,
    );
  }

  Widget _animate(Widget child) {
    if (_filterType == null) {
      _controller.reset();
      return child;
    }
    _controller.repeat();
    Function builder;
    switch (_filterType) {
      case FilterType.OPACITY:
        builder = (context, child) => Opacity(
          opacity: (_controller.value * 2.0 - 1.0).abs(),
          child: child,
        );
        break;
      case FilterType.ROTATE_TRANSFORM:
        builder = (center, child) => Transform(
          transform: Matrix4.rotationZ(_controller.value * 2.0 * pi),
          cacheTransform: _cacheMatrix,
          alignment: Alignment.center,
          child: child,
        );
        break;
      case FilterType.ROTATE_FILTER:
        builder = (center, child) => ImageFiltered(
          imageFilter: ImageFilter.matrix((
              Matrix4.identity()
                ..translate(_childCenter.dx, _childCenter.dy)
                ..rotateZ(_controller.value * 2.0 * pi)
                ..translate(- _childCenter.dx, - _childCenter.dy)
          ).storage),
          child: child,
        );
        break;
    }
    return RepaintBoundary(
      child: AnimatedBuilder(
        animation: _controller,
        child: child,
        builder: builder,
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _animate(_protectChild(
            child: Container(
              key: _childKey,
              color: Colors.yellow,
              width: 300,
              height: 300,
              child: Center(
                child: _makeChild(4, 3, 24.0, _complexChild),
              ),
            ),
            protect: _useRepaintBoundary,
          ),
        ),
      ),
      bottomNavigationBar: BottomAppBar(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                Text('Opacity:'),
                Checkbox(
                  value: _filterType == FilterType.OPACITY,
                  onChanged: (b) => _setFilterType(FilterType.OPACITY, b),
                ),
                Text('Tx Rotate:'),
                Checkbox(
                  value: _filterType == FilterType.ROTATE_TRANSFORM,
                  onChanged: (b) => _setFilterType(FilterType.ROTATE_TRANSFORM, b),
                ),
                Text('IF Rotate:'),
                Checkbox(
                  value: _filterType == FilterType.ROTATE_FILTER,
                  onChanged: (b) => _setFilterType(FilterType.ROTATE_FILTER, b),
                ),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              mainAxisSize: MainAxisSize.min,
              children: <Widget>[
                Text('Complex child:'),
                Checkbox(
                  value: _complexChild,
                  onChanged: (b) => setState(() => _complexChild = b),
                ),
                Text('Child RPB:'),
                Checkbox(
                  value: _useRepaintBoundary,
                  onChanged: (b) => setState(() => _useRepaintBoundary = b),
                ),
                Text('cache tx:'),
                Checkbox(
                  value: _cacheTransformChild,
                  onChanged: (b) => setState(() => _cacheTransformChild = b),
                ),
              ],
            ),
            Slider(
              value: _cacheScale,
              onChanged: (value) => setState(() => _cacheScale = value),
              max: 2.0,
              min: 0.05,
            ),
            Slider(
              value: _cacheRotate,
              onChanged: (value) => setState(() => _cacheRotate = value),
              max: pi * 2.0,
            ),
          ],
        ),
      ),
    );
  }
}