Android Flutter绘制有趣的 loading加载动画

// 动画控制设置
controller =
  AnimationController(duration: const Duration(seconds: 3), vsync: this);
animation = Tween<double>(begin: 0, end: 1.0).animate(CurvedAnimation(
  parent: controller,
  curve: Curves.slowMiddle,
))
..addListener(() {
  setState(() {});
});

// 绘制和动画控制方法
_drawLoadinGCircle(canvas canvas, Size size) {
  var paint = Paint()..style = PaintingStyle.stroke
    ..color = Colors.blue[400]!
    ..strokeWidth = 2.0;
  var path = Path();
  final radius = 40.0;
  var center = Offset(size.width / 2, size.height / 2);
  path.addOval(Rect.fromCircle(center: center, radius: radius));
  canvas.drawPath(path, paint);
  
  var innerPath = Path();
  final ballRadius = 4.0;
  innerPath.addOval(Rect.fromCircle(center: center, radius: radius - ballRadius));
  var metrics = innerPath.computeMetrics();
  paint.color = Colors.red;
  paint.style = PaintingStyle.fill;
  for (var pathMetric in metrics) {
    var tangent = pathMetric.getTangentForOffset(pathMetric.length * animationValue);
    canvas.drawCircle(tangent!.position, ballRadius, paint);
  }
}

controller =
      AnimationController(duration: const Duration(seconds: 2), vsync: this);
  animation = Tween<double>(begin: 0, end: 1.0).animate(CurvedAnimation(
    parent: controller,
    curve: Curves.easeInOutSine,
  ))
    ..addListener(() {
      setState(() {});
    });

_drawTwinsCircle(Canvas canvas, Size size) {
  var paint = Paint()
    ..style = PaintingStyle.stroke
    ..color = Colors.blue[400]!
    ..strokeWidth = 2.0;

  final radius = 50.0;
  final ballRadius = 6.0;
  var center = Offset(size.width / 2, size.height / 2);
  var circlePath = Path()
    ..addOval(Rect.fromCircle(center: center, radius: radius));
  paint.style = PaintingStyle.stroke;
  paint.color = Colors.blue[400]!;
  canvas.drawPath(circlePath, paint);

  var circleMetrics = circlePath.computeMetrics();
  for (var pathMetric in circleMetrics) {
    var tangent = pathMetric
        .getTangentForOffset(pathMetric.length * animationValue);

    paint.style = PaintingStyle.fill;
    paint.color = Colors.blue;
    canvas.drawCircle(tangent!.position, ballRadius, paint);
  }

  paint.style = PaintingStyle.stroke;
  paint.color = Colors.green[600]!;
  var ovalPath = Path()
    ..addOval(Rect.fromCenter(center: center, width: 3 * radius, height: 40));
  canvas.drawPath(ovalPath, paint);
  var ovalMetrics = ovalPath.computeMetrics();

  for (var pathMetric in ovalMetrics) {
    var tangent =
        pathMetric.getTangentForOffset(pathMetric.length * animationValue);

    paint.style = PaintingStyle.fill;
    canvas.drawCircle(tangent!.position, ballRadius, paint);
  }
}

controller =
        AnimationController(duration: const Duration(seconds: 2), vsync: this);
animation = Tween<double>(begin: 0, end: 1.0).animate(CurvedAnimation(
  parent: controller,
  curve: Curves.easeInOutQuart,
))
  ..addListener(() {
    setState(() {});
  }
  ..addStatusListener((status) {
   if (status == AnimationStatus.completed) {
     controller.reverse();
   } else if (status == AnimationStatus.dismissed) {
     controller.forward();
   }
 });

_drawPendulum(Canvas canvas, Size size) {
  var paint = Paint()
    ..style = PaintingStyle.stroke
    ..color = Colors.blue[400]!
    ..strokeWidth = 2.0;

  final ceilWidth = 60.0;
  final pendulumHeight = 200.0;
  var ceilCenter =
      Offset(size.width / 2, size.height / 2 - pendulumHeight / 2);
  var ceilPath = Path()
    ..moveTo(ceilCenter.dx - ceilWidth / 2, ceilCenter.dy)
    ..lineTo(ceilCenter.dx + ceilWidth / 2, ceilCenter.dy);
  canvas.drawPath(ceilPath, paint);

  var pendulumArcPath = Path()
    ..addArc(Rect.fromCircle(center: ceilCenter, radius: pendulumHeight),
        3 * pi / 4, -pi / 2);

  paint.color = Colors.white70;
  var metrics = pendulumArcPath.computeMetrics();

  for (var pathMetric in metrics) {
    var tangent =
        pathMetric.getTangentForOffset(pathMetric.length * animationValue);

    canvas.drawLine(ceilCenter, tangent!.position, paint);
    paint.style = PaintingStyle.fill;
    paint.color = Colors.blue;
    paint.maskFilter = MaskFilter.blur(BlurStyle.solid, 4.0);
    canvas.drawCircle(tangent.position, 16.0, paint);
  }
}