anisotropic.cpp

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/***************************************************************************
 *   Copyright (C) 1998-2008 by authors (see AUTHORS.txt )                 *
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 *   This file is part of LuxRender.                                       *
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 *   Lux Renderer is free software; you can redistribute it and/or modify  *
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// anisotropic.cpp*
#include "anisotropic.h"
#include "color.h"
#include "spectrum.h"
#include "mc.h"
#include "sampling.h"
#include <stdarg.h>

using namespace lux;

void Anisotropic::Sample_f(const Vector &wo, Vector *wi,
                float u1, float u2, float *pdf) const {
        // Sample from first quadrant and remap to hemisphere to sample \wh
        float phi, costheta;
        if (u1 < .25f) {
                sampleFirstQuadrant(4.f * u1, u2, &phi, &costheta);
        } else if (u1 < .5f) {
                u1 = 4.f * (.5f - u1);
                sampleFirstQuadrant(u1, u2, &phi, &costheta);
                phi = M_PI - phi;
        } else if (u1 < .75f) {
                u1 = 4.f * (u1 - .5f);
                sampleFirstQuadrant(u1, u2, &phi, &costheta);
                phi += M_PI;
        } else {
                u1 = 4.f * (1.f - u1);
                sampleFirstQuadrant(u1, u2, &phi, &costheta);
                phi = 2.f * M_PI - phi;
        }
        float sintheta = sqrtf(max(0.f, 1.f - costheta*costheta));
        Vector H = SphericalDirection(sintheta, costheta, phi);
        if (Dot(wo, H) < 0.f) H = -H;
        // Compute incident direction by reflecting about $\wh$
        *wi = -wo + 2.f * Dot(wo, H) * H;
        // Compute PDF for \wi from Anisotropic distribution
        float anisotropic_pdf = D(H) / (4.f * Dot(wo, H));
        *pdf = anisotropic_pdf;
}
void Anisotropic::sampleFirstQuadrant(float u1, float u2,
                float *phi, float *costheta) const {
        if (ex == ey)
                *phi = M_PI * u1 * 0.5f;
        else
                *phi = atanf(sqrtf((ex+1)/(ey+1)) *
                        tanf(M_PI * u1 * 0.5f));
        float cosphi = cosf(*phi), sinphi = sinf(*phi);
        *costheta = powf(u2, 1.f/(ex * cosphi * cosphi +
                ey * sinphi * sinphi + 1));
}
float Anisotropic::Pdf(const Vector &wo,
                const Vector &wi) const {
        Vector H = Normalize(wo + wi);
        // Compute PDF for \wi from Anisotropic distribution
        float anisotropic_pdf = D(H) / (4.f * Dot(wo, H));
        return anisotropic_pdf;
}

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