Fresnel.h

Go to the documentation of this file.

#ifndef FRESNEL_H
#define FRESNEL_H FRESNEL_H

#include "StdDefs.h"

class Fresnel {
    public:
        virtual float Evaluate (float cosi) { 
            return 0; 
        }

        virtual ~Fresnel () {};
};

class FresnelDielectric : public Fresnel {
    private:
    
        float eta_i;

        float eta_t;
    
        float FrDielectric (float cosi, float cost, float etai, float etat) {
            float r_par = (etat*cosi - etai*cost) / (etat*cosi + etai*cost);
            float r_per = (etai*cosi - etat*cost) / (etai*cosi + etat*cost);
            //  Assumption: The light is unpolarised and therefore the Fresnel reflectance is the average
            //  of the squares of the parallel and perpendicular polarization term.
            return  0.5 * (r_par*r_par + r_per*r_per);
        }

    public:
        
        FresnelDielectric (float ei, float et) : eta_i(ei), eta_t(et) {};
        
        ~FresnelDielectric() {};    
        
        float Evaluate (float cosi) {
            bool entering = cosi > 0;
            float ei = entering ? eta_i : eta_t;
            float et = entering ? eta_t : eta_i;
            // Compute sint using Snell's law
            float sint = ei/et * sqrtf(MAX(0, 1 - cosi*cosi));
            if (sint > 1) {
                // Total internal reflection!
                return 1;
            } else {
                float cost = sqrtf(MAX(0.f, 1.f - sint*sint));
                return FrDielectric(fabs(cosi), cost, ei, et);
            }
        }
};

class FresnelConductor : public Fresnel {
    private:
    
        float eta;

        float kappa;
    
    public:
        FresnelConductor (float e, float k) : eta(e), kappa(k) {};
        
        ~FresnelConductor () {};    
        
        float Evaluate (float cosi) {
            cosi = fabsf(cosi);
            float tmp1 = eta*eta + kappa*kappa;
            float tmp2 = cosi * cosi;
            float tmp3 = 2.f * eta *cosi;
            float rparl2 = (tmp1 * tmp2 - tmp3  + 1) / (tmp1 * tmp2 + tmp3 +1);
            float rperp2 = (tmp1 - tmp3 + tmp2) / (tmp1 + tmp3 + tmp2);
            return (rparl2 + rperp2) / 2.f;
        }
};

#endif

---