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/* Listing 16.16 Displacement shader to dent a surface*/
/*
* dented(): Create a worn surface.
*/
displacement
dented (float Km = 1.0 )
{
float size = 1.0,
magnitude = 0.0,
i;
point P2;
normal Ndiff;
P2 = transform("shader", P);
for (i = 0; i < 6.0; i += 1.0) {
/* Calculate a simple fractal 1/f noise function */
magnitude += abs(.5 - noise(P2 * size)) / size;
size *= 2.0;
}
Ndiff = normalize(N) - normalize(Ng);
P2 = P - normalize(N) * (magnitude * magnitude * magnitude) * Km;
/* correct the normal */
N = normalize(calculatenormal (P2)) + Ndiff;
}
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