gabrielbull/react-aim

/**
 * @license MIT
 * @url https://github.com/substack/point-in-polygon
 */

export default function (point, vs) {
  // ray-casting algorithm based on
  // http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html

  var x = point[0], y = point[1];

  var inside = false;
  for (var i = 0, j = vs.length - 1; i < vs.length; j = i++) {
    var xi = vs[i][0], yi = vs[i][1];
    var xj = vs[j][0], yj = vs[j][1];

    var intersect = ((yi > y) != (yj > y))
      && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
    if (intersect) inside = !inside;
  }

  return inside;
};