Asserts if a given point is inside a polygon.

IsPointInPoly.js

//+   
//@ http://jsfromhell.com/math/is-point-in-poly [v1.0]
function isPointInPoly(poly, pt){
  for(var c = false, i = -1, l = poly.length, j = l - 1; ++i < l; j = i)
    ((poly[i].y <= pt.y && pt.y < poly[j].y) || (poly[j].y <= pt.y && pt.y < poly[i].y))
    && (pt.x < (poly[j].x - poly[i].x) * (pt.y - poly[i].y) / (poly[j].y - poly[i].y) + poly[i].x)
    && (c = !c);
  return c;
}