/* caustic.sl - Caustic shader by Stuart Ramsden
*  Sums brightness contributions to a surface, accounting for attenuation
*  induced by focusing.
*  The max and min values are highly dependant on the rendering geometry;
*  uncomment the printf line and inspect the numbers for appropriate values.
*/

surface
caustic(float brightness = 1.0;
	float maxval = 80.0;
	float minval = 10.0)
{
float lu,lv;

/*printf("du: %g dv: %g\n",length(dPdu), length(dPdv));
*/
lu = 1-smoothstep(minval,maxval,length(dPdu));
lv = 1-smoothstep(minval,maxval,length(dPdv));

Ci = 0.4*(lu*lu*lv*lv)*brightness;
Oi = 0;
}