displacement
smoothbump3(float 	Km = 0.1,
					min_s = 0.1,
					max_s = 0.8,
					min_t = 0.1,
					max_t = 0.8,
					fuzz = 0.1)
{
float	hump = 0;
normal	n;

/* STEP 1 - make a copy of the surface normal one unit in length */
n = normalize(N);

/* STEP 2 - calculate an appropriate value for the displacement */
hump = 	smoothstep(min_s, min_s + fuzz, s) *
		(1 - smoothstep(max_s, max_s + fuzz, s)) *
 		smoothstep(min_t, min_t + fuzz, t) *
		(1 - smoothstep(max_t, max_t + fuzz, t));

/* STEP 3 - calculate the new position of the surface point */
/*			"P" based on the value of hump */
P = P - n * hump * Km;

/* STEP 4 - calculate the new orientation of the surface normal */
N = calculatenormal(P);
}