surface
blobby7(float	Kd = 1,
				iso   = 0.5;
		float	rad[3] = { 1, 1, 1 };
		float	polarity[3] = { 1, 1, 1 };
		point	pnt[3] = { 0, 0, 0 })
{
normal	nf, n;
color	diffusecolor,
		surfcolor = 1, surfopac = Os;
point	p;

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

/* STEP 2 - set the apparent surface opacity */
Oi = surfopac;

float 	totalfield = 0, dist;
uniform float j;
for(j = 0; j < 3; j = j + 1)
	{
	p = transform("current", pnt[j]);
	dist = distance(P, p);
	if(polarity[j] == 1)
		totalfield += 1 - smoothstep(0, rad[j], dist);
	else
		totalfield -= 1 - smoothstep(0, rad[j], dist);
	}

float blend = smoothstep(iso-0.07,iso,totalfield) *
				(1 - smoothstep(iso,iso+0.07,totalfield));
surfcolor = mix(Cs, color(1,0,0), blend);
		
/* STEP 3 - calculate the diffuse lighting component */
diffusecolor = Kd * diffuse(nf);

/* STEP 4 - calculate the apparent surface color */
Ci = Oi * Cs * surfcolor * diffusecolor;
}