// 判断一个点是否在多边形区域中

export const pointInPolygon = (point, vs, start, end) => {
  if (vs.length > 0 && Array.isArray(vs[0])) {
    return pointInPolygonNested(point, vs, start, end);
  } else {
    return pointInPolygonFlat(point, vs, start, end);
  }
};

export const pointInPolygonFlat = (point, vs, start, end) => {
  var x = point[0],
    y = point[1];
  var inside = false;
  if (start === undefined) start = 0;
  if (end === undefined) end = vs.length;
  var len = (end - start) / 2;
  for (var i = 0, j = len - 1; i < len; j = i++) {
    var xi = vs[start + i * 2 + 0],
      yi = vs[start + i * 2 + 1];
    var xj = vs[start + j * 2 + 0],
      yj = vs[start + j * 2 + 1];
    var intersect =
      yi > y !== yj > y && x < ((xj - xi) * (y - yi)) / (yj - yi) + xi;
    if (intersect) inside = !inside;
  }
  return inside;
};

export const pointInPolygonNested = (point, vs, start, end) => {
  var x = point[0],
    y = point[1];
  var inside = false;
  if (start === undefined) start = 0;
  if (end === undefined) end = vs.length;
  var len = end - start;
  for (var i = 0, j = len - 1; i < len; j = i++) {
    var xi = vs[i + start][0],
      yi = vs[i + start][1];
    var xj = vs[j + start][0],
      yj = vs[j + start][1];
    var intersect =
      yi > y !== yj > y && x < ((xj - xi) * (y - yi)) / (yj - yi) + xi;
    if (intersect) inside = !inside;
  }
  return inside;
};

```js