public bool Scatter(ref Ray r, ref Hit_record rec, ref Vector3 attenuation, ref Ray scattered)
        {
            Vector3 target = rec.normal.normalized * 0.5f +
                             new Vector3(Chapter11.RandomFloat11(), Chapter11.RandomFloat11(), Chapter11.RandomFloat11()).normalized;

            scattered.origin    = rec.hitpoint;
            scattered.direction = target;
            attenuation         = albedo;
            return(true);
        }
 private Vector3 Random_in_unit_sphere()
 {
     return(new Vector3(Chapter11.RandomFloat11(), Chapter11.RandomFloat11(), Chapter11.RandomFloat11()).normalized);
 }