/*perturb.sl by wooksang*/

#include "rmannotes.sl"
surface 
perturb( float Ks=.5, Kd=.5, Ka=1, roughness=.1; color specularcolor=1;
	 string image="grid.tx";)
{
    normal Nf;
    vector V;
    float ss,tt;
    point PP;
    color surface_color;

    PP = transform("shader",P);
    ss = s+snoise(PP*8)*0.2;
    tt = t+snoise(PP*10)*0.2;
    
    surface_color = texture(image,ss,tt);

    Nf = faceforward( normalize(N), I );
    V = normalize(I);

    Oi = Os;
    Ci = Os * ( surface_color * (Ka*ambient() + Kd*diffuse(Nf)) + 
	 	specularcolor * Ks * specular(Nf,-V,roughness) );
}