/*nightsky surface shader
 * Final Assignment: Shader with turbulence, perturbed patterns, bombing.
 * Tom Suchan
 * This shader generates a night sky with a wash from blue to black 
   and a randomized star field. It also includes an optional gas nebula 
   to simulate other planetary environments. The user has the option 
   to input "Venus" which creates a bluish space cloud, "Mercury" to 
   create a volatile fire like backdrop, or space fans can create their 
   own by changing colors--good luck spacecadets.
*/
#include "rmannotes.sl"

surface nightsky(float Ka = 2, Kd = 2, Ks = 1, roughness = 0.8; 
         color specularcolor = 1; float starfreq = .5; string location  ="")
{
   color paper,  ink;
   float  paper_opac = 1, ink_opac;
   point center;
   float radius, ss, tt;
   float col, row, noi,noi2;
   float freq = 6;
   float d;
   float fuzz = .1;  
   float circle1, circle2;
   point Nf, V; 
   float noifreq = 5;
   float noiscale = 0.8;
   float scale, turb = 0;
   float turbfreq = 2;
   point PP;
   float pixelsize, twice;
 
  /*layer one horizon: creates a color wash*/
   paper_opac = 1;
   paper = color(0, 0, 0);
   ink_opac = 1;
     
   ink =spline(t,color(0,0,0),color(0,0,0),color(0,0,0),
                 color(.5 ,0,.5), color(0, 0,1), color(0, 0, 1));
   paper= mix(paper, ink, ink_opac);

   /* Optional layer two: cloud nebulas */
  
  if(location  == "venus"){
  noi2 = noise(s * noifreq, t * noifreq);

  /* perturb y */

   t  = t + snoise(noi2 + 3752) * noiscale;

  ink = spline(t,color(1,1,1),color(1,1,1),color(0,1,.2),
                 color(1,1,1), color(0, 0,1), color(0, 0, 1));
  ink_opac = pulse(0.85, 0.95, fuzz, t);
  paper = mix(paper, ink, ink_opac);
  }
  if(location  == "mercury"){
  PP = transform("shader", P) * turbfreq; /* creates trubulence based on P */
  pixelsize = sqrt(area(PP));
  twice = pixelsize * 2;
  for(scale = 1; scale > twice; scale /= 2)
  turb += abs(noise(PP/scale) - 0.5) * scale;
  turb = turb * 2;
  

  ink =  spline(turb, color(1,1,0), color(1,1,0), color(1,0,0), 
                 color(1,1,1), color(1,1,1)); 
  ink_opac = pulse(.6, 1, .25, t);
  paper = mix(paper, ink, ink_opac);
  }
  
   /*layer three  star field base-seed to udn on current row and column*/

   col = whichtile(s, freq);
   row = whichtile(t, freq);
   noi = noise(col * 10 + 0.5, row * 10 + 0.5);

  /* repeat texture coords, jitter tiles by plus or minus 0.35, 
     and rotate by 45 */

  tt = repeat(s, freq) + udn(noi * 1183, .1, 0.6);
  ss  = repeat(t, freq) + udn(noi * 999, .1, 0.6);

  /* generates star-filed tiles, sets radius, creates % of stars */

   ink = color(1, 1, 1);
   center = (0.5, 0.5, 0); 
   radius =  udn(noi * 4362, .005,.05);
   d = distance(center, (ss, tt, 0)); 
  
  if(udn(noi * 314, 0,1) > starfreq) {
  freq = 8;
  fuzz = .05;
  ink_opac = 1 - smoothstep(radius - fuzz, radius + fuzz, d);
  paper = mix(paper, ink, ink_opac);
  }

  /* illumination */

        paper = paper * Ka * ambient() +
        paper * Kd * diffuse(Nf) +
        specularcolor * Ks * specular(Nf, V, roughness);

/*output*/


   Oi=paper_opac;
   Ci=paper_opac * paper;
}