ShapeInvariantMicrofacet.h

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#pragma once
 
#include "Core/SurfaceBehavior/Property/Microfacet.h"
#include "Core/SurfaceBehavior/Property/enums.h"
 
#include <Common/assertion.h>
 
namespace ph
{
 
class ShapeInvariantMicrofacet : public Microfacet
{
public:
    explicit ShapeInvariantMicrofacet(
        EMaskingShadowing maskingShadowingType);
 
    virtual std::array<real, 2> getAlphas(const SurfaceHit& X) const = 0;
 
    virtual real lambda(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H,
        const math::Vector3R& unitDir,
        const std::array<real, 2>& alphas) const = 0;
 
    real distribution(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H) const override = 0;
 
    void sampleH(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const std::array<real, 2>& sample,
        math::Vector3R* out_H) const override = 0;
 
    real geometry(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H,
        const math::Vector3R& L,
        const math::Vector3R& V) const override;
 
    lta::PDF pdfSampleH(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H) const override;
 
protected:
    real smithG1(real lambdaValue) const;
 
    real empiricalPhiCorrelation(
        const SurfaceHit& X,
        const math::Vector3R& L,
        const math::Vector3R& V) const;
 
    real projectedDistribution(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H) const;
 
    real visibleDistribution(
        const SurfaceHit& X,
        const math::Vector3R& N,
        const math::Vector3R& H,
        const math::Vector3R& V) const;
 
    EMaskingShadowing m_maskingShadowingType;
};
 
inline lta::PDF ShapeInvariantMicrofacet::pdfSampleH(
    const SurfaceHit& X,
    const math::Vector3R& N,
    const math::Vector3R& H) const
{
    return {
        .value = projectedDistribution(X, N, H),
        .domain = lta::EDomain::HalfSolidAngle};
}
 
inline real ShapeInvariantMicrofacet::smithG1(const real lambdaValue) const
{
    return 1.0_r / (1.0_r + lambdaValue);
}
 
inline real ShapeInvariantMicrofacet::projectedDistribution(
    const SurfaceHit& X,
    const math::Vector3R& N,
    const math::Vector3R& H) const
{
    PH_ASSERT_GE(N.dot(H), -1e-3_r);
 
    return distribution(X, N, H) * N.absDot(H);
}
 
inline real ShapeInvariantMicrofacet::visibleDistribution(
    const SurfaceHit& X,
    const math::Vector3R& N,
    const math::Vector3R& H,
    const math::Vector3R& V) const
{
    PH_ASSERT_GE(N.dot(H), -1e-3_r);
 
    const real lambdaV = lambda(X, N, H, V, getAlphas(X));
    const real g1V     = smithG1(lambdaV);
    const real ndf     = distribution(X, N, H);
    const real vndf    = g1V * ndf * std::abs(H.dot(V) / N.dot(V));
 
    return vndf;
}
 
}// end namespace ph