#include "rmannotes.sl"
surface experiment(float tile = 4, radius = 0.35, width = 0.25, pivot = 0.5;
		   float Ka = 0.5, Kd = 0.5;
		   float Ks = 0.5, roughness = 0.009; color specularcolor = 1.0)
     {
	color paper, ink, ink1;
	float ss, tt,w, x, ink_opac, paper_opac;
	float fuzz = 0.01;
	float c1, c2, c3, c4, d;
	point center, Nf, V;


/* init */


paper = color (t, s, .6);
paper_opac = 0.2;

Nf = faceforward(normalize(N), I);
V = -normalize(I);

center = (.6, .4, 0);
ss = s; tt = t;
s = repeat(s, tile); t = repeat(t, tile);
d = distance(center, (s, t, 0));

/* layer 1 */

ink_opac = pulse(radius - width /2, radius + width / 2, fuzz, d);
ink = color (s, t, 1);
paper = mix(paper, ink, ink_opac);
s = ss; t = tt;

ink1 =  color (s, t, 0); 
rotate2d(s, t, radians(90), pivot, pivot, ss,tt);
ss = repeat(ss, tile);
tt = repeat(tt, tile);
s = repeat(s, tile);
t = repeat(t, tile);

c3 = smoothstep(ss-fuzz, ss+fuzz, tt);
c4 = smoothstep(w-fuzz, w+fuzz, x); /* w and x work by magic! */

c1 = smoothstep(t + 0.2-fuzz, t + 0.2 + fuzz,s);
c2 = smoothstep(tt + 0.2-fuzz, tt + 0.2 + fuzz,ss);

/* layer 2 */

ink_opac =  union(intersection(c1,c2),intersection(c3,c4));
paper_opac = union(paper_opac, ink_opac);


paper = paper * Ka * ambient() +
        paper * Kd * diffuse(Nf) +
	specularcolor * Ks * specular(Nf, V, roughness);
Ci = paper * mix(ink, ink1, ink_opac) * paper_opac; 
    }