Dielectric.h

#pragma once

class Dielectric: public ObjectMaterial {
public:
    Dielectric() = default;
    Dielectric( const float3& absorption, const float& n ): absorption( absorption ), n( n ) {}

    virtual MaterialType getFlag() const override {
        return MaterialType::DIELECTRIC;
    }

    virtual float3 GetColor( Ray& ray_in ) const override {
        float3 color = float3( 1 );
        if ( ray_in.inside ) {
            color.x = exp( -absorption.x * ray_in.t );
            color.y = exp( -absorption.y * ray_in.t );
            color.z = exp( -absorption.z * ray_in.t );
        }

        return color;
    }

    virtual bool scatter( Ray& ray_in, float3 I, float3 N, Ray& ray_out ) const override {
        float n1 = 1;
        float n2 = n;
        float n1Divn2 = n1 / n2;
        float cosi = dot( N, ray_in.D );
        if ( ray_in.inside ) n1Divn2 = 1 / n1Divn2;

        float k = 1 - ( n1Divn2 * n1Divn2 ) * ( 1 - ( cosi * cosi ) );
        // no choice when we TIR
        if ( k < 0 ) {
            ray_out = Ray( I, normalize( reflect( ray_in.D, N ) ) );
            ray_out.inside = true;
        } else {
            float Fr = 0;
            if ( !ray_in.inside ) {
                float sini = length( cross( N, ray_in.D ) );
                float cost = sqrtf( 1 - sqrf( n1Divn2 * sini ) );

                Fr = Fresnel( n1, n2, cost, -cosi );
            }

            if ( Fr > FLT_EPSILON && RandomFloat() < Fr ) {
                ray_out = Ray( I, normalize( reflect( ray_in.D, N ) ) );
            } else {
                float3 T = normalize( n1Divn2 * ray_in.D - ( n1Divn2 * cosi + sqrtf( k ) ) * N );
                ray_out = Ray( I, T );
                ray_out.inside = !ray_in.inside; // TODO: only when hitting object with volume, maybe material property?
            }
        }

        return true;
    }

    virtual float* getColorModifier( Ray& ray_in, float3 N ) const {
        float n1 = 1;
        float n2 = n;
        float n1Divn2 = n1 / n2;
        float cosi = dot( N, ray_in.D );
        float3 beers( 1 );
        if ( ray_in.inside ) {
            beers.x = exp( -absorption.x * ray_in.t );
            beers.y = exp( -absorption.y * ray_in.t );
            beers.z = exp( -absorption.z * ray_in.t );
            n1Divn2 = 1 / n1Divn2;
        }

        float k = 1 - ( n1Divn2 * n1Divn2 ) * ( 1 - ( cosi * cosi ) );
        // no choice when we TIR
        if ( k < 0 ) {
            return new float[7] { beers.x, beers.y, beers.z, - 1.0f };
        } else {
            float Fr = 0;
            if ( !( ray_in.inside ) ) {
                float sini = length( cross( N, ray_in.D ) );
                float cost = sqrtf( 1 - sqrf( n1Divn2 * sini ) );

                Fr = Fresnel( n1, n2, cost, -cosi );
            }

            float3 refractionD = normalize( n1Divn2 * ray_in.D - ( n1Divn2 * cosi + sqrtf( k ) ) * N );
            return new float[7] { beers.x, beers.y, beers.z, Fr, refractionD.x, refractionD.y, refractionD.z };
        }
    }

private:
    float3 absorption;
    float n;
};