Apple's Breathe Animation in Flutter

main.dart

// MIT License
//
// Copyright (c) 2020 Neevash Ramdial
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

import 'dart:math' as math;

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: Home(),
    ),
  );
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> with SingleTickerProviderStateMixin {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: SizedBox.expand(child: CupertinoBreathe()),
    );
  }
}

class CupertinoBreathe extends StatefulWidget {
  @override
  _CupertinoBreatheState createState() => _CupertinoBreatheState();
}

class _CupertinoBreatheState extends State<CupertinoBreathe>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 3),
      vsync: this,
    )..repeat(reverse: true);
  }

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

  @override
  Widget build(BuildContext context) {
    return Center(
      child: AspectRatio(
        aspectRatio: 1.0,
        child: CustomPaint(
          painter: _BreathePainter(
            CurvedAnimation(parent: _controller, curve: Curves.ease),
           ),
          size: Size.infinite,
        ),
      ),
    );
  }
}

class _BreathePainter extends CustomPainter {
  _BreathePainter(
    this.animation, {
    this.count = 6,
    Color color = const Color(0xFF61bea2),
  })  : circlePaint = Paint()
          ..color = color
          ..blendMode = BlendMode.screen,
        super(repaint: animation);

  final Animation<double> animation;
  final int count;
  final Paint circlePaint;

  @override
  void paint(Canvas canvas, Size size) {
    final center = size.center(Offset.zero);
    final radius = (size.shortestSide * 0.25) * animation.value;
    for (int index = 0; index < count; index++) {
      final indexAngle = (index * math.pi / count * 2);
      final angle = indexAngle + (math.pi * 1.5 * animation.value);
      final offset = Offset(math.sin(angle), math.cos(angle)) * radius * 0.985;
      canvas.drawCircle(center + offset * animation.value, radius, circlePaint);
    }
  }

  @override
  bool shouldRepaint(_BreathePainter oldDelegate) =>
      animation != oldDelegate.animation;
}