/* ------------------------------------------------------
 * polkadot.sl - a polka dot surface shader
 *
 * Parameters
 * Kd, Ka    : usual values for diffuse and ambient light
 * frequency : frequency of dots
 * radius    : size of each dot (ranges from 0.0 to 1.0)
 * backcolor : the background color
 *
 * the color of the polka dots is the current color
 *  - specify in .rib file with:  Color [r g b]
 *
 * author    : nima oreizy (cs184-aj)
 * date      : 11 Nov 1998
 * assignment: lab 7
 * ------------------------------------------------------ */

surface
polkadot ( float Kd = .5,
	         Ka = .4,
	         frequency=.9,
	         radius = 0.8;
	         color backcolor = color(0,0,0);)
{
  float length;
  float smod = mod(s * frequency, 1);
  float tmod = mod(t * frequency, 1);

  smod = smod - 0.5;
  tmod = tmod - 0.5;

  length = sqrt(smod*smod + tmod*tmod);
  if (length < (radius / 2))
    Ci = Cs;
  else
    Ci = backcolor;

  Oi = Os;
  Ci = Oi*Ci*(Ka*ambient() + Kd*diffuse(faceforward(normalize(N),I)));
}