Test whether a point lies inside a polygon

pointInPolygonTest.js

// borrowd from http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html
function pnpoly (points, test) {
  var i, j, c = false;
  for( i = 0, j = points.length-1; i < points.length; j = i++ ) {
    if( ( ( points[i].y > test.y ) != ( points[j].y > test.y ) ) &&
      ( test.x < ( points[j].x - points[i].x ) * ( test.y - points[i].y ) / ( points[j].y - points[i].y ) + points[i].x ) ) {
      c = !c;
    }
  }
  return c;
}

// input:
//  - pnpoly([{x: 0, y: 0}, {x: 10, y: 0}, {x: 10, y: 10}, {x: 0, y: 10}], {x: 5, y: 5});
// output:
//  - true