#include "rmannotes.sl"

#define circle(cx, cy, fuzz, x, y) \
(1-smoothstep(0.5-fuzz, 0.5+fuzz, distance((x, y, 0), (cx, cy ,0))))

surface ass32(float Ka = 1, Kd = 1)
{
  color paper, ink;
  float tile_s, tile_t;
  float opac, fuzz, o1, o2, o3, o4;
  float left, right;

  point Nf;

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

  paper = color(.545, .270, .504);
  fuzz = 0.01;

  Oi = .5;

  tile_s = repeat(s, 3);
  tile_t = repeat(t, 3);

  ink = color(1, 1, 1);


  o1 = circle(0.5, 0, fuzz, tile_s, tile_t);
  o2 = circle(0, 0.5, fuzz, tile_s, tile_t);
  o3 = circle(0.5, 1, fuzz, tile_s, tile_t);
  o4 = circle(1, 0.5, fuzz, tile_s, tile_t);

  left = union(intersection(o1, o2), intersection(o2, o3));
  right = union(intersection(o3, o4), intersection(o4, o1));
  opac = union(left, right);
  paper = mix(paper, ink, opac);

  ink = color(.803, .4, 0);
  opac = circle(0.5, 0.5, fuzz, tile_s, tile_t);
  opac *= .5;
  paper = mix(paper, ink, opac);
  
  Ci = Oi * paper * (Ka * ambient() + Kd * diffuse(Nf));
}