point in polygon

gistfile1.txt

    pointInside: function(pt) {
        var i, j, a, b, xpi, ypi, xpj, ypj;
        var x = pt.x;
        var y = pt.y;
        var c = false;
        for (i = 0; i < this.points.length; i++) {
            j = (i+1) % this.points.length;
            a = this.points[i];
            b = this.points[j];
            xpi = a.x;
            ypi = a.y;
            xpj = b.x;
            ypj = b.y;
            if ((((ypi<=y) && (y<ypj)) || ((ypj<=y) && (y<ypi))) && 
                (x < (xpj-xpi)*(y-ypi)/(ypj-ypi)+xpi)) {
                c = !c;    
            }
        }
        return c;
    }