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brdf.h
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// This file is distributed under the MIT license.
// See the LICENSE file for details.
#pragma once
#ifndef VSNRAY_BRDF_H
#define VSNRAY_BRDF_H 1
#include "detail/color_conversion.h"
#include "math/constants.h"
#include "math/vector.h"
#include "fresnel.h"
#include "mdf.h"
#include "sampling.h"
#include "spectrum.h"
#include "surface_interaction.h"
namespace visionaray
{
//-------------------------------------------------------------------------------------------------
// Lambertian reflection
//
template <typename T>
class lambertian
{
public:
using scalar_type = T;
public:
scalar_type kd;
spectrum<T> cd;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(n);
VSNRAY_UNUSED(wi);
VSNRAY_UNUSED(wo);
return spectrum<U>( cd * kd * constants::inv_pi<T>() );
}
template <typename U, typename Interaction, typename Generator>
VSNRAY_FUNC
spectrum<U> sample_f(
vector<3, T> const& n,
vector<3, U> const& wo,
vector<3, U>& wi,
U& pdf,
Interaction& inter,
Generator& gen
) const
{
auto w = n;
auto v = select(
abs(w.x) > abs(w.y),
normalize( vector<3, U>(-w.z, U(0.0), w.x) ),
normalize( vector<3, U>(U(0.0), w.z, -w.y) )
);
auto u = cross(v, w);
auto sp = cosine_sample_hemisphere(gen.next(), gen.next());
wi = normalize( sp.x * u + sp.y * v + sp.z * w );
pdf = this->pdf(n, wo, wi);
inter = Interaction(surface_interaction::Diffuse);
return f(n, wo, wi);
}
template <typename U>
VSNRAY_FUNC
U pdf(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(wo);
return dot(n, wi) * constants::inv_pi<U>();
}
};
//-------------------------------------------------------------------------------------------------
// Phong reflection
//
template <typename T>
class phong
{
public:
using scalar_type = T;
public:
spectrum<T> cs;
scalar_type ks;
scalar_type exp;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
auto r = reflect(wo, n);
auto rdotl = max( U(0.0), dot(r, wi) );
return spectrum<U>( cs * ks * ((exp + U(2.0)) / constants::two_pi<U>()) * pow(rdotl, exp) );
}
};
//-------------------------------------------------------------------------------------------------
// Blinn reflection
//
template <typename T>
class blinn
{
public:
using scalar_type = T;
public:
spectrum<T> cs;
scalar_type ks;
scalar_type exp;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
auto h = normalize(wo + wi);
auto hdotn = max( U(0.0), dot(h, n) );
auto spec = cs * ks;
auto schlick = spec + (U(1.0) - spec) * pow(U(1.0) - saturate(dot(wi, h)), U(5.0));
auto nfactor = ((exp + U(2.0)) / (U(8.0) * constants::pi<U>()));
return spectrum<U>(schlick * nfactor * pow(hdotn, exp) );
}
template <typename U, typename Interaction, typename Generator>
VSNRAY_FUNC
spectrum<U> sample_f(
vector<3, U> const& n,
vector<3, U> const& wo,
vector<3, U>& wi,
U& pdf,
Interaction& inter,
Generator& gen
) const
{
auto u1 = gen.next();
auto u2 = gen.next();
auto costheta = pow(u1, U(1.0) / (exp + U(1.0)));
auto sintheta = sqrt( max(U(0.0), U(1.0) - costheta * costheta) );
auto phi = u2 * constants::two_pi<U>();
auto w = n;
auto v = select(
abs(w.x) > abs(w.y),
normalize( vector<3, U>(-w.z, U(0.0), w.x) ),
normalize( vector<3, U>(U(0.0), w.z, -w.y) )
);
auto u = cross(v, w);
vector<3, U> h = normalize( sintheta * cos(phi) * u + sintheta * sin(phi) * v + costheta * w );
wi = reflect(wo, h);
auto vdoth = dot(wo, h);
pdf = ( ((exp + U(1.0)) * pow(costheta, exp)) / (U(2.0) * constants::pi<U>() * U(4.0) * vdoth) );
inter = Interaction(surface_interaction::GlossyReflection);
return f(n, wo, wi);
}
template <typename U>
VSNRAY_FUNC
U pdf(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
vector<3, U> h = normalize(wi + wo);
U costheta = dot(n, h);
U vdoth = dot(wo, h);
return ( ((exp + U(1.0)) * pow(costheta, exp)) / (U(2.0) * constants::pi<U>() * U(4.0) * vdoth) );
}
};
//-------------------------------------------------------------------------------------------------
// Cook Torrance reflection like in:
// Walter et al.: Microfacet Models for Refraction through Rough Surfaces
//
template <typename T, typename MDF>
class cook_torrance
{
public:
using scalar_type = T;
public:
spectrum<T> ior;
spectrum<T> absorption;
MDF mdf;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
// h is proportional to the microfacet normal
auto h = wi + wo;
auto ldotn = abs(dot(wi, n));
auto vdotn = abs(dot(wo, n));
auto active = length(h) != U(0.0) && ldotn != U(0.0) && vdotn != U(0.0);
h = normalize(h);
auto F = fresnel_reflectance(
conductor_tag{},
ior,
absorption,
dot(wi, h)
);
// "The Smith G approximates the bidirectional shadowing-masking as
// the separable product of two monodirectional shadowing terms G1:"
auto G = mdf.g1(n, h, wi) * mdf.g1(n, h, wo);
auto D = mdf.d(n, h);
auto denom = (U(4.0) * ldotn * vdotn);
auto fr = select(denom != U(0.0), (F * G * D) / denom, spectrum<U>(0.0));
return select(active, fr, spectrum<U>(0.0));
}
template <typename U, typename Interaction, typename Generator>
VSNRAY_FUNC
spectrum<U> sample_f(
vector<3, T> const& n,
vector<3, U> const& wo,
vector<3, U>& wi,
U& pdf,
Interaction& inter,
Generator& gen
) const
{
auto w = n;
auto v = select(
abs(w.x) > abs(w.y),
normalize( vector<3, U>(-w.z, U(0.0), w.x) ),
normalize( vector<3, U>(U(0.0), w.z, -w.y) )
);
auto u = cross(v, w);
auto sp = cosine_sample_hemisphere(gen.next(), gen.next());
wi = normalize( sp.x * u + sp.y * v + sp.z * w );
pdf = this->pdf(n, wo, wi);
inter = Interaction(surface_interaction::GlossyReflection);
return f(n, wo, wi);
}
template <typename U>
VSNRAY_FUNC
U pdf(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(wo);
return dot(n, wi) * constants::inv_pi<U>();
}
};
//-------------------------------------------------------------------------------------------------
// Perfect specular reflection
//
template <typename T>
class specular_reflection
{
public:
using scalar_type = T;
public:
spectrum<T> cr;
scalar_type kr;
spectrum<T> ior;
spectrum<T> absorption;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(n);
VSNRAY_UNUSED(wi);
VSNRAY_UNUSED(wo);
return spectrum<U>(0.0);
}
template <typename U, typename Interaction, typename Generator>
VSNRAY_FUNC
spectrum<U> sample_f(
vector<3, U> const& n,
vector<3, U> const& wo,
vector<3, U>& wi,
U& pdf,
Interaction& inter,
Generator& gen
) const
{
VSNRAY_UNUSED(gen);
wi = reflect(wo, n);
pdf = U(1.0);
inter = Interaction(surface_interaction::SpecularReflection);
return fresnel_reflectance(
conductor_tag(),
ior,
absorption,
abs( dot(n, wo) )
) * spectrum<U>(cr * kr) / abs( dot(n, wi) );
}
template <typename U>
VSNRAY_FUNC
U pdf(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(n);
VSNRAY_UNUSED(wo);
VSNRAY_UNUSED(wi);
return U(0.0);
}
};
//-------------------------------------------------------------------------------------------------
// Perfect specular transmission
//
template <typename T>
class specular_transmission
{
public:
using scalar_type = T;
public:
spectrum<T> ct;
scalar_type kt;
spectrum<T> cr;
scalar_type kr;
spectrum<T> ior;
template <typename U>
VSNRAY_FUNC
spectrum<U> f(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(n);
VSNRAY_UNUSED(wi);
VSNRAY_UNUSED(wo);
return spectrum<U>(0.0);
}
template <typename U, typename Interaction, typename Generator>
VSNRAY_FUNC
spectrum<U> sample_f(
vector<3, U> const& n,
vector<3, U> const& wo,
vector<3, U>& wi,
U& pdf,
Interaction& inter,
Generator& gen
) const
{
// IOR of material above normal direction
spectrum<U> ior1 = spectrum<U>(1.0);
// IOR of material below normal direction
spectrum<U> ior2 = spectrum<U>(ior);
U cosi = clamp(dot(n, wo), U(-1.0), U(1.0));
auto entering = cosi > U(0.0);
// If ray originates in 2nd medium, flip normal
// and swap refraction indices
vector<3, U> N = select(entering, n, -n);
spectrum<U> etai = select(entering, ior1, ior2);
spectrum<U> etat = select(entering, ior2, ior1);
cosi = select(!entering, abs(cosi), cosi);
U eta = etai[0] / etat[0]; // TODO: etaX are spectra!
// Snell's law
U sini = sqrt(max(U(0.0), U(1.0) - cosi * cosi));
U sint = eta * sini;
U cost = sqrt(max(U(0.0), U(1.0) - sint * sint));
spectrum<U> reflectance = fresnel_reflectance(
dielectric_tag(),
ior1,
ior2,
cosi,
cost
);
auto tir = sint >= U(1.0);
reflectance = select(tir, spectrum<U>(1.0), reflectance);
vector<3, U> refracted = refract(wo, N, eta); // NOTE: not normalized!
vector<3, U> reflected = reflect(wo, N);
auto u = gen.next();
wi = select(
u < reflectance[0],
reflected,
normalize(refracted)
);
pdf = select(
u < reflectance[0],
reflectance[0],
U(1.0) - reflectance[0]
);
inter = select(
u < reflectance[0],
Interaction(surface_interaction::SpecularReflection),
Interaction(surface_interaction::SpecularTransmission)
);
return select(
u < reflectance[0],
reflectance * spectrum<U>(cr * kr),
(spectrum<U>(1.0) - reflectance) * spectrum<U>(ct * kt)
) / dot(N, wi);
}
template <typename U>
VSNRAY_FUNC
U pdf(vector<3, U> const& n, vector<3, U> const& wo, vector<3, U> const& wi) const
{
VSNRAY_UNUSED(n);
VSNRAY_UNUSED(wo);
VSNRAY_UNUSED(wi);
return U(0.0);
}
};
} // visionaray
#endif // VSNRAY_BRDF_H