surface placematsurf (
	float Ka = 1,
	      Kd = 1)
{
  float uthreads = 25;
  float vthreads = 25;

  vector Nf = faceforward(N,I);
  float kd = Kd;
  point P2;

  P2 = transform("shader", P);

  /* Black specs on cloth */
  float specfreq = 40;
  float spec = noise(P2*specfreq);
  /* sharpen peaks */
  spec = pow(spec, 25);
  float cutin = 0.003;
  kd *= 1-0.7*smoothstep(cutin, cutin + 0.00005, spec);

  /*
  float kd = float spline(min(mod(t*vthreads,1.0),mod(s*uthreads,1.0)), 
			  Kd*0.1, Kd*0.3, 
			  Kd, Kd, Kd, Kd, 
			  Kd*0.3, Kd*0.1);
  */

  /* fringe */
  float fringefreq = 30;
  float Omod = 0.5 *(sin((t+1.5*noise(t*fringefreq)/(fringefreq))*2*PI*fringefreq)+1);
  Omod *= Omod;
  Omod = 1-(smoothstep(0.984, 0.986, abs(s))*Omod);

  Oi = Os*Omod;
  Ci = Oi * Cs * (Ka*ambient() + kd*diffuse(normalize(Nf)));
}