LDEVICE float BeckmannDistribution::G(
float3 N,
float3 H,
float3 w_in,
float3 w_out
) const
{
return smithG1( N, H, w_in ) * smithG1( N, H, w_out );
}
Float microfacet(Float mu_o, Float mu_i, std::complex<Float> eta_,
Float alpha, Float phi_d) {
Float sinThetaI = math::safe_sqrt(1-mu_i*mu_i),
sinThetaO = math::safe_sqrt(1-mu_o*mu_o),
cosPhi = std::cos(phi_d),
sinPhi = std::sin(phi_d);
Vector wi(-sinThetaI, 0, -mu_i);
Vector wo(sinThetaO*cosPhi, sinThetaO*sinPhi, mu_o);
bool reflect = -mu_i*mu_o > 0;
if (mu_o == 0 || mu_i == 0)
return 0.f;
bool conductor = eta_.imag() != 0.0f;
if (conductor && !reflect)
return 0.0f;
std::complex<Float> eta =
(-mu_i > 0 || conductor) ? eta_ : std::complex<Float>(1) / eta_;
Vector H = (wi + wo * (reflect ? 1.0f : eta.real())).normalized();
H *= math::signum(Frame::cosTheta(H));
Float cosThetaH2 = Frame::cosTheta2(H),
exponent = -Frame::tanTheta2(H) / (alpha*alpha),
D = std::exp(exponent) / (math::Pi * alpha*alpha * cosThetaH2*cosThetaH2),
F = !conductor ? fresnelDielectric(wi.dot(H), eta_.real())
: fresnelConductor(std::abs(wi.dot(H)), eta),
G = smithG1(wi, H, alpha) * smithG1(wo, H, alpha);
if (reflect) {
return F * D * G / (4.0f * std::abs(mu_i*mu_o));
} else {
Float sqrtDenom = wi.dot(H) + eta.real() * wo.dot(H);
return std::abs(((1 - F) * D * G * eta.real() * eta.real() * wi.dot(H)
* wo.dot(H)) / (mu_i*mu_o * sqrtDenom * sqrtDenom));
}
}
