k3d/share/shaders/k3d_rustymetal.sl:53:  point Nrust;                 /* perturbed normal for the rusty areas */
k3d/share/shaders/k3d_rustymetal.sl:72:  Nrust = calculatenormal (P + rustbump * snoise(PP) * normalize(N));
k3d/share/shaders/k3d_rustymetal.sl:85:      Nf = faceforward (normalize(Nrust),I);
