/*
 * Aurora.sl 
 *
 *  Description:
 *     Shader that generates lightwave-like pattern using turbulence technique.
 *
 *  Parameters: turbfreq : use for increasing or decreasing the size and 
 *                         the number of wave, working like zoom in, zoom out.
 *                  frame: use for changing the light wave pattern in order
 *                         to make different pattern.    
 *             lightcolor: color of light.
 *
 *  Author: Akanee  Mahasith
 */

#include "rmannotes.sl"

surface Aurora(float Ka = .2, Kd = .8;
               float frame = 1;
               float turbfreq = 2;
               color lightcolor = color (0.051, 0.530, 1))
{
    point PP;
    float turb, f;
    float freq;
    color surface_color, layer_color;
    color surface_opac, layer_opac;
     
     surface_color = lightcolor;
     surface_opac  = 1  ;

  
     PP = transform("shader", P) * turbfreq;


     turb = 0; 
     freq = frame / 20;
     turb += abs(snoise(PP + freq * PI));

     turb = pow((1 - turb), 8);

     layer_color = lightcolor;
     layer_opac = turb;
     surface_color = blend(surface_color, layer_color, layer_opac);
                                                                            
     Oi = surface_opac * turb;
     Ci = surface_color * turb * surface_opac;
}