#include "rmannotes.sl"

displacement rockfalls(float freq = 1, Km = 0.1, width = 0.1)
{
  float surface_mag, layer_mag;
  float ss, tt,half_width,d;
  float fuzz = 0.05;
  point p1,p2;
  float size = 1.0,
    magnitude =0.0,
    i;
  point P2;

  /* init */

  surface_mag = 0;

  /* rotate & repeat layers */
  ss = repeat(s, freq);
  tt = repeat(t, freq);

 
 
  /* layer 1 */
  p1 = (0.5, 0, 0);   
  p2 = (0.5, 1, 0);   
  d = ptlined(p1, p2, (ss, tt, 0)) + noise (ss * 10 , tt * 10)/20;
  layer_mag = 1 - smoothstep(width - fuzz, width, d);

  surface_mag += layer_mag;

  P2 = transform("shader",P);
  for (i= 0 ;i<10.0; i+=1.0)
    {
      magnitude += abs(.3 - snoise(P2*size))/(size-i);
      size *=2.0;
    }
  magnitude += udn2(ss,tt,.8,1.7);
  /* displace */
  N =faceforward(N,-I);
  P += -Km * (2 * magnitude * magnitude * normalize(N) * (1 - surface_mag) + 
	      surface_mag * normalize(N));
  N = calculatenormal(P);
}