#include "rmannotes.sl"
 
surface
aliasnoise (
	float	MINFREQ		= 0.50;
	float	MAXFREQ		= 0.50;
	float 	brightness	= 0.20;
	float 	contrast	= 1.50)
{
	
	float value = 0.0;
	float f, fade, cutoff;
	float fwidth;
	      
	point P2= transform("shader", P);
	float x = xcomp(P2);
	float y = ycomp(P2);
	float z = zcomp(P2);
	
	fwidth	= abs(Du(x)*du) + abs(Dv(x)*dv) +
		  abs(Du(y)*du) + abs(Dv(y)*dv) +
		  abs(Du(z)*du) + abs(Dv(z)*dv);



	value	= 0;
	cutoff	= clamp(0.5/fwidth, 0, MAXFREQ);

	for (f = MINFREQ; f < 0.5*cutoff; f *= 2)
	    value += snoise(f*P2)/f;

	fade 	= clamp(2*(cutoff-f)/cutoff, 0, 1);
	value  += fade * snoise(f*P2)/f;


	Oi	= Os;
	Ci	= Oi * color( value * contrast + brightness);

}