internal static double Angle(D2 a, D2 b)
{
var p = new D2(-b.Y, b.X);
var angle = Math.Atan2(D2.Dot(a, p), D2.Dot(a, b));
return((angle < 0) ? 2.0 * Math.PI + angle : angle);
}
internal static bool InsideSquare(D2[] square, D2 p)
{
var ap = p - square[0];
var ab = square[1] - square[0];
var ad = square[3] - square[0];
var ap_dot_ab = D2.Dot(ap, ab);
var ap_dot_ad = D2.Dot(ap, ad);
return
((0 < ap_dot_ab) &&
(0 < ap_dot_ad) &&
(ap_dot_ab < D2.Dot(ab, ab)) &&
(ap_dot_ad < D2.Dot(ad, ad)));
}