Flutter Canvas animation example with CustomPainter

flutter-canvas-animation-example.dart

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter/semantics.dart';
import 'dart:ui';

void main() => runApp(new MyApp());

class Sky extends CustomPainter {
  final double value;

  const Sky(this.value);

  @override
  void paint(Canvas canvas, Size size) {
    canvas.scale(value + 1.0, value + 1.0);
    canvas.rotate(value * 3.0);

    print("SIZE${size.width}");
    var rect = Offset.zero & size;
    var gradient = new RadialGradient(
      center: new Alignment(value, value),
      radius: 0.6,
      colors: [const Color(0xffFF0000), const Color(0xFF0000FF)],
      stops: [0.4, 1.0],
    );
    canvas.drawRect(
      rect,
      new Paint()..shader = gradient.createShader(rect),
    );
  }

  @override
  SemanticsBuilderCallback get semanticsBuilder {
    return (Size size) {
      // Annotate a rectangle containing the picture of the sun
      // with the label "Sun". When text to speech feature is enabled on the
      // device, a user will be able to locate the sun on this picture by
      // touch.
      var rect = Offset.zero & size;
      var width = size.shortestSide * 0.4;
      rect = const Alignment(0.8, -0.9).inscribe(new Size(width, width), rect);
      return [
        new CustomPainterSemantics(
          rect: rect,
          properties: new SemanticsProperties(
            label: 'Sun',
            textDirection: TextDirection.ltr,
          ),
        ),
      ];
    };
  }

  // Since this Sky painter has no fields, it always paints
  // the same thing and semantics information is the same.
  // Therefore we return false here. If we had fields (set
  // from the constructor) then we would return true if any
  // of them differed from the same fields on the oldDelegate.
  @override
  bool shouldRepaint(Sky oldDelegate) => true;

  @override
  bool shouldRebuildSemantics(Sky oldDelegate) => false;
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or press Run > Flutter Hot Reload in IntelliJ). Notice that the
        // counter didn't reset back to zero; the application is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  int _counter = 0;
  Animation<double> animation;
  AnimationController controller;

  initState() {
    super.initState();
    controller = AnimationController(
        duration: const Duration(milliseconds: 1000), vsync: this);
    animation = Tween(begin: -1.0, end: 1.0).animate(controller);

    controller.repeat();
  }

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return new Scaffold(
      appBar: new AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: new Text(widget.title),
      ),
      body: new Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: new Column(
          // Column is also layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug paint" (press "p" in the console where you ran
          // "flutter run", or select "Toggle Debug Paint" from the Flutter tool
          // window in IntelliJ) to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            AnimatedBuilder(
                animation: animation,
                builder: (BuildContext context, Widget child) {
                  return Container(
                      color: Colors.red,
                      width: 400.0,
                      height: 400.0,
                      margin: const EdgeInsets.symmetric(horizontal: 5.0),
                      child: ClipRect(
                          child: CustomPaint(painter: Sky(animation.value))));
                })
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}