// shadow intersect functie

public bool Intersects(Ray r, float d)
        {
            foreach (Primitive p in primitives)
            {
                Intersection q = p.Intersect(r);

                if (q != null)
                {
                    if(q.distance < d && q.distance>0)
                    {
                        return true;
                    }
                }
            }
            return false;
        }

// shadow ray functie

Vector3 l = Vector3.Normalize(s.Location - i.Location);
float dotnl = Vector3.Dot(Vector3.Normalize(i.Normal), l);


//shadow ray
if(dotnl >= 0)
    {

                    Vector3 direction = s.Location - i.Location;
                    float shadow_length = direction.Length - 2 * epsilon.X;

                    Ray shadow_ray = new Ray(i.Location + epsilon, Vector3.Normalize(direction));

                    if (!Intersects(shadow_ray, shadow_length))
                    {

                        // lambertian
                        Vector3 result_lambertian = (Vector3.Multiply(s.Intensity * i.primitive.material.color, Math.Max(0, dotnl)));

                        // blinn-phong
                        Vector3 v = Vector3.Normalize(c.Position - i.Location);
                        Vector3 h = Vector3.Normalize(v + l);

                        float dotnh = Vector3.Dot(Vector3.Normalize(i.Normal), h);
                        Vector3 result_blinnphong = Vector3.Multiply(s.Intensity * i.primitive.material.ambient_color,                  (float)Math.Pow(Math.Max(0, dotnh), p));

                        total += Vector3.Multiply((result_blinnphong + result_lambertian), 0.7f);
                    }
                }