#include "rmannotes.sl"
displacement
datol(
          float   Km = .3, roughness = .2,
                  txtscale = 1;)
{
    point PP;            /* scaled point in shader space */
    float csp;           /* color spline parameter */
    float pixelsize, twice, scale, weight, turbulence;

   
    PP = transform("shader", P) * txtscale;
    pixelsize = sqrt(area(PP));
    twice = 2 * pixelsize;
    turbulence = 0;
    csp = 0.0;
    for (scale = 1; scale > twice; scale /= 2)
        turbulence += scale * noise(PP/scale);

    /* Gradual fade out of highest-frequency component near limit */
    if (scale > pixelsize) {
        weight = (scale / pixelsize) - 1;
        weight = clamp(weight, 0, 1);
        turbulence += weight * scale * noise(PP/scale);
    }

   
    csp = clamp(3 * turbulence - 3, 0, 1);

     
  P -= Km * csp * normalize(N);
  N = calculatenormal(P);

}