bsdf_ashikhmin_velvet.cpp

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/*
 * Adapted from Open Shading Language with this license:
 *
 * Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
 * All Rights Reserved.
 *
 * Modifications Copyright 2011, Blender Foundation.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * * Neither the name of Sony Pictures Imageworks nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 */

#include <OpenImageIO/fmath.h>

#include <OSL/genclosure.h>

#include "osl_closures.h"

CCL_NAMESPACE_BEGIN

using namespace OSL;

class AshikhminVelvetClosure : public BSDFClosure {
public:
    Vec3 m_N;
    float m_sigma;
    float m_invsigma2;

    AshikhminVelvetClosure() : BSDFClosure(Labels::DIFFUSE) { }

    void setup()
    {
        m_sigma = std::max(m_sigma, 0.01f);
        m_invsigma2 = 1.0f/(m_sigma * m_sigma);
    }

    bool mergeable (const ClosurePrimitive *other) const {
        const AshikhminVelvetClosure *comp = (const AshikhminVelvetClosure *)other;
        return m_N == comp->m_N && m_sigma == comp->m_sigma &&
            BSDFClosure::mergeable(other);
    }

    size_t memsize () const { return sizeof(*this); }

    const char *name () const { return "ashikhmin_velvet"; }

    void print_on (std::ostream &out) const
    {
        out << name() << " (";
        out << "(" << m_N[0] << ", " << m_N[1] << ", " << m_N[2] << "), ";
        out << m_sigma;
        out << ")";
    }

    float albedo (const Vec3 &omega_out) const
    {
        return 1.0f;
    }

    Color3 eval_reflect (const Vec3 &omega_out, const Vec3 &omega_in, float& pdf) const
    {
        float cosNO = m_N.dot(omega_out);
        float cosNI = m_N.dot(omega_in);
        if (cosNO > 0 && cosNI > 0) {
            Vec3 H = omega_in + omega_out;
            H.normalize();

            float cosNH = m_N.dot(H);
            float cosHO = fabsf(omega_out.dot(H));

            float cosNHdivHO = cosNH / cosHO;
            cosNHdivHO = std::max(cosNHdivHO, 0.00001f);

            float fac1 = 2 * fabsf(cosNHdivHO * cosNO);
            float fac2 = 2 * fabsf(cosNHdivHO * cosNI);

            float sinNH2 = 1 - cosNH * cosNH;
            float sinNH4 = sinNH2 * sinNH2;
            float cotangent2 =  (cosNH * cosNH) / sinNH2; 

            float D = expf(-cotangent2 * m_invsigma2) * m_invsigma2 * float(M_1_PI) / sinNH4;
            float G = std::min(1.0f, std::min(fac1, fac2)); // TODO: derive G from D analytically

            float out = 0.25f * (D * G) / cosNO;

            pdf = 0.5f * (float) M_1_PI;
            return Color3 (out, out, out);
        }
        return Color3 (0, 0, 0);
    }

    Color3 eval_transmit (const Vec3 &omega_out, const Vec3 &omega_in, float& pdf) const
    {
        return Color3 (0, 0, 0);
    }

    ustring sample (const Vec3 &Ng,
                 const Vec3 &omega_out, const Vec3 &domega_out_dx, const Vec3 &domega_out_dy,
                 float randu, float randv,
                 Vec3 &omega_in, Vec3 &domega_in_dx, Vec3 &domega_in_dy,
                 float &pdf, Color3 &eval) const
    {
        // we are viewing the surface from above - send a ray out with uniform
        // distribution over the hemisphere
        sample_uniform_hemisphere (m_N, omega_out, randu, randv, omega_in, pdf);
        if (Ng.dot(omega_in) > 0) {
            Vec3 H = omega_in + omega_out;
            H.normalize();

            float cosNI = m_N.dot(omega_in);
            float cosNO = m_N.dot(omega_out);
            float cosNH = m_N.dot(H);
            float cosHO = fabsf(omega_out.dot(H));

            float cosNHdivHO = cosNH / cosHO;
            cosNHdivHO = std::max(cosNHdivHO, 0.00001f);

            float fac1 = 2 * fabsf(cosNHdivHO * cosNO);
            float fac2 = 2 * fabsf(cosNHdivHO * cosNI);

            float sinNH2 = 1 - cosNH * cosNH;
            float sinNH4 = sinNH2 * sinNH2;
            float cotangent2 =  (cosNH * cosNH) / sinNH2; 

            float D = expf(-cotangent2 * m_invsigma2) * m_invsigma2 * float(M_1_PI) / sinNH4;
            float G = std::min(1.0f, std::min(fac1, fac2)); // TODO: derive G from D analytically

            float power = 0.25f * (D * G) / cosNO;

            eval.setValue(power, power, power);

            // TODO: find a better approximation for the retroreflective bounce
            domega_in_dx = (2 * m_N.dot(domega_out_dx)) * m_N - domega_out_dx;
            domega_in_dy = (2 * m_N.dot(domega_out_dy)) * m_N - domega_out_dy;
            domega_in_dx *= 125;
            domega_in_dy *= 125;
        } else
            pdf = 0;
        return Labels::REFLECT;
    }

};



ClosureParam bsdf_ashikhmin_velvet_params[] = {
    CLOSURE_VECTOR_PARAM(AshikhminVelvetClosure, m_N),
    CLOSURE_FLOAT_PARAM (AshikhminVelvetClosure, m_sigma),
    CLOSURE_STRING_KEYPARAM("label"),
    CLOSURE_FINISH_PARAM(AshikhminVelvetClosure) };

CLOSURE_PREPARE(bsdf_ashikhmin_velvet_prepare, AshikhminVelvetClosure)

CCL_NAMESPACE_END