1、 一个圆，裁剪出一段圆border

ClipOval(
  child: Container(
    width: 56,
    height: 56,
    alignment: Alignment.center,
    decoration: BoxDecoration(
      border: Border.all(color: Colors.red, width: 1),
      borderRadius: BorderRadius.all(Radius.circular(28)),
    ),
    child: Container(),
  ),
  clipper: MyClipper1(),
);


class MyClipper1 extends CustomClipper<Rect> {
  @override
  Rect getClip(Size size) {
    return new Rect.fromLTRB(60, 20, size.width - 15.0, size.height + 20.0);
  }

  @override
  bool shouldReclip(CustomClipper<Rect> oldClipper) {
    return true;
  }
}

效果图