CookTorrance.cpp

#include "math.h"

vector Schlick (float cosT; vector Fi)
{
    return (Fi + (1-Fi) * pow(1-cosT, 5));
}

vector cookTorrance(vector nN; string category; vector Fi; float roughness)
{
    vector out = {0,0,0};
    
    vector nV = normalize(-I);   //normalized I
    float r2 = roughness * roughness;
    
    illuminance(P, nN, M_PI, bouncemask("reflect"), "category", category)
    {
    
        vector nL = normalize(L);   //normalized dir to light
        
        vector H = normalize(nV + nL); // half vector
        
        float NdotH = dot(nN, H);
        float NdotL = dot(nN, nL);
        float VdotH = dot(nV, H);
        float NdotV = dot(nN, nV);
        
        //fresnel
        vector kr = Schlick(NdotV, Fi);
    
        // Geometry function
        float G = min(1, (2*NdotH*NdotV/VdotH), (2*NdotH*NdotL/VdotH));
        
        // beckman
        float roughness_a = 1.0f / ( 4.0f * r2 * pow( NdotH, 4 ) );
        float roughness_b = NdotH * NdotH - 1.0f;
        float roughness_c = r2 * NdotH * NdotH;
        
        float D = roughness_a * exp( roughness_b / roughness_c );
        
        out += shadow(Cl) * (kr * D * G) / (M_PI * NdotV);
    }

return out;
}