画多角星函数：

1. function createStartPath(angles, r1, r2, offsetAngle = 0) {
2.     var a = 360 / angles, path = 'M';
3.     Array.from({length: angles}).forEach((_,k) => {
4.     var a1 = a * k + offsetAngle,
5.          a2 = a1 + a / 2,
6.         x1 = (r1 + r1 * Math.cos(Math.PI / 180 * a1)).toFixed(2),
7.         y1 = (r1 + r1 * Math.sin(Math.PI / 180 * a1)).toFixed(2),
8.         x2 = (r1 + r2 * Math.cos(Math.PI / 180 * a2)).toFixed(2),
9.         y2 = (r1 +  r2 * Math.sin(Math.PI / 180 * a2)).toFixed(2);
10.         path += `${x1} ${y1} ${x2} ${y2} `;
11.     );
12.     path += 'Z';
13.     return path;
14. }