windingLine.js

function windingLine(x0, y0, x1, y1, x, y) {
  if (y > y0 && y > y1 || y < y0 && y < y1) {
    return 0;
  } // Ignore horizontal line


  if (y1 === y0) {
    return 0;
  }

  var dir = y1 < y0 ? 1 : -1;
  var t = (y - y0) / (y1 - y0); // Avoid winding error when intersection point is the connect point of two line of polygon

  if (t === 1 || t === 0) {
    dir = y1 < y0 ? 0.5 : -0.5;
  }

  var x_ = t * (x1 - x0) + x0; // If (x, y) on the line, considered as "contain".

  return x_ === x ? Infinity : x_ > x ? dir : 0;
}

module.exports = windingLine;