code: function isConvex(pts, righthanded){
    // 'pts' is an [x,y] pair
    // 'righthanded' is a boolean
    if (typeof(righthanded) === 'undefined') righthanded = true;
    if (pts.length != 3) throw new Error("This function requires an array of three points [x,y]");
    var d = (pts[1][0] - pts[0][0]) * (pts[2][1] - pts[0][1]) - (pts[1][1] - pts[0][1]) * (pts[2][0] - pts[0][0]);
    return (d >= 0) == righthanded;
  }
docs: Function to determine if three consecutive points of a simple, non-self-intersecting ring make up a convex vertex, assuming the ring is right- or lefthanded