blend.h

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#pragma once

#include <cugar/linalg/vector.h>
#include <cugar/basic/numbers.h>
#include <cugar/bsdf/differential_geometry.h>
#include <cugar/spherical/mappings.h>


namespace cugar {

template <
    typename TBsdf1,
    typename TBsdf2>
struct BlendBsdf
{
    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    BlendBsdf(
        const float  _w1    = 0.5f,
        const float  _w2    = 0.5f,
        const TBsdf1 _bsdf1 = TBsdf1(),
        const TBsdf2 _bsdf2 = TBsdf2()) :
        w1(_w1),
        w2(_w2),
        bsdf1(_bsdf1),
        bsdf2(_bsdf2)
    {}

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    Vector3f f(const DifferentialGeometry& geometry, const Vector3f V, const Vector3f L) const
    {
        return
            w1 * bsdf1.f(geometry,V,L) +
            w2 * bsdf2.f(geometry,V,L);
    }

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    Vector3f f_over_p(const DifferentialGeometry& geometry, const Vector3f V, const Vector3f L) const
    {
        return
            w1 * bsdf1.f_over_p(geometry,V,L) +
            w2 * bsdf2.f_over_p(geometry,V,L);
    }

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    void f_and_p(const DifferentialGeometry& geometry, const Vector3f V, const Vector3f L, Vector3f& f, float& p, const SphericalMeasure measure = kProjectedSolidAngle) const
    {
        Vector3f f1, f2;
        float    p1, p2;

        bsdf1.f_over_p( geometry, V, L, f1, p1, measure );
        bsdf2.f_over_p( geometry, V, L, f2, p2, measure );

        f = w1 * f1 + w2 * f2;
        p = w1 * p1 + w2 * p2;
    }

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    float p(const DifferentialGeometry& geometry, const Vector3f V, const Vector3f L, const SphericalMeasure measure = kProjectedSolidAngle) const
    {
        return
            w1 * bsdf1.p(geometry,V,L) +
            w2 * bsdf2.p(geometry,V,L);
    }

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    void sample(
        const Vector3f              u,
        const DifferentialGeometry& geometry, 
        const Vector3f              V,
              Vector3f&             L,
              Vector3f&             g,
              float&                p,
              float&                p_proj) const
    {
        if (u.z < w1)
        {
            // sample the first component
            bsdf1.sample( Vector3f(u.x,u.y,u.z/w1), geometry, V, L, g, p, p_proj );

            g      /= w1;
            p      *= w1;
            p_proj *= w1;
        }
        else if (u.z < w1 + w2)
        {
            // sample the second component
            bsdf2.sample( Vector3f(u.x,u.y,(u.z-w1)/w2), geometry, V, L, g, p, p_proj );

            g      /= w2;
            p      *= w2;
            p_proj *= w2;
        }
        else
        {
            // absorption
            g      = Vector3f(0.0f);
            p      = (1 - w1 - w2);
            p_proj = (1 - w1 - w2);
        }
    }

    template <typename RandomGeneratorT>
    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    bool invert(
        const DifferentialGeometry& geometry,
        const Vector3f              V,
        const Vector3f              L,
        RandomGeneratorT&           random,
        Vector3f&                   z,
        float&                      p,
        float&                      p_proj) const
    {
        // TODO
        return false;
    }

    CUGAR_FORCEINLINE CUGAR_HOST_DEVICE
    void inverse_pdf(
        const DifferentialGeometry& geometry,
        const Vector3f              V,
        const Vector3f              L,
        const Vector3f              u,
        float&                      p,
        float&                      p_proj) const
    {
        p_proj = 1.0f / this->p( geometry, V, L, u, kProjectedSolidAngle );
        p      = fabsf(dot(L, geometry.normal_s)) * p_proj;
    }

public:
    float   w1, w2;
    TBsdf1  bsdf1;
    TBsdf2  bsdf2;
};

} // namespace cugar