bsdf_westin.h

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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. 
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 *   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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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
*/

#ifndef __BSDF_WESTIN_H__
#define __BSDF_WESTIN_H__

CCL_NAMESPACE_BEGIN

/* WESTIN BACKSCATTER */

typedef struct BsdfWestinBackscatterClosure {
    //float3 m_N;
    float m_invroughness;
} BsdfWestinBackscatterClosure;

__device void bsdf_westin_backscatter_setup(ShaderData *sd, ShaderClosure *sc, float roughness)
{
    roughness = clamp(roughness, 1e-5f, 1.0f);
    float m_invroughness = 1.0f/roughness;

    sc->type = CLOSURE_BSDF_WESTIN_BACKSCATTER_ID;
    sd->flag |= SD_BSDF|SD_BSDF_HAS_EVAL|SD_BSDF_GLOSSY;
    sc->data0 = m_invroughness;
}

__device void bsdf_westin_backscatter_blur(ShaderClosure *sc, float roughness)
{
    float m_invroughness = sc->data0;
    m_invroughness = min(1.0f/roughness, m_invroughness);
    sc->data0 = m_invroughness;
}

__device float3 bsdf_westin_backscatter_eval_reflect(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
    float m_invroughness = sc->data0;
    float3 m_N = sd->N;

    // pdf is implicitly 0 (no indirect sampling)
    float cosNO = dot(m_N, I);
    float cosNI = dot(m_N, omega_in);
    if(cosNO > 0 && cosNI > 0) {
        float cosine = dot(I, omega_in);
        *pdf = cosine > 0 ? (m_invroughness + 1) * powf(cosine, m_invroughness) : 0;
        *pdf *= 0.5f * M_1_PI_F;
        return make_float3 (*pdf, *pdf, *pdf);
    }
    return make_float3 (0, 0, 0);
}

__device float3 bsdf_westin_backscatter_eval_transmit(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
    return make_float3(0.0f, 0.0f, 0.0f);
}

__device float bsdf_westin_backscatter_albedo(const ShaderData *sd, const ShaderClosure *sc, const float3 I)
{
    return 1.0f;
}

__device int bsdf_westin_backscatter_sample(const ShaderData *sd, const ShaderClosure *sc, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
    float m_invroughness = sc->data0;
    float3 m_N = sd->N;

    float cosNO = dot(m_N, sd->I);
    if(cosNO > 0) {
#ifdef __RAY_DIFFERENTIALS__
        *domega_in_dx = sd->dI.dx;
        *domega_in_dy = sd->dI.dy;
#endif
        float3 T, B;
        make_orthonormals (sd->I, &T, &B);
        float phi = 2 * M_PI_F * randu;
        float cosTheta = powf(randv, 1 / (m_invroughness + 1));
        float sinTheta2 = 1 - cosTheta * cosTheta;
        float sinTheta = sinTheta2 > 0 ? sqrtf(sinTheta2) : 0;
        *omega_in = (cosf(phi) * sinTheta) * T +
                   (sinf(phi) * sinTheta) * B +
                   (cosTheta) * sd->I;
        if(dot(sd->Ng, *omega_in) > 0)
        {
            // common terms for pdf and eval
            float cosNI = dot(m_N, *omega_in);
            // make sure the direction we chose is still in the right hemisphere
            if(cosNI > 0)
            {
                *pdf = 0.5f * M_1_PI_F * powf(cosTheta, m_invroughness);
                *pdf = (m_invroughness + 1) * (*pdf);
                *eval = make_float3(*pdf, *pdf, *pdf);
#ifdef __RAY_DIFFERENTIALS__
                // Since there is some blur to this reflection, make the
                // derivatives a bit bigger. In theory this varies with the
                // exponent but the exact relationship is complex and
                // requires more ops than are practical.
                *domega_in_dx *= 10.0f;
                *domega_in_dy *= 10.0f;
#endif
            }
        }
    }
    return LABEL_REFLECT|LABEL_GLOSSY;
}

/* WESTIN SHEEN */

typedef struct BsdfWestinSheenClosure {
    //float3 m_N;
    float m_edginess;
} BsdfWestinSheenClosure;

__device void bsdf_westin_sheen_setup(ShaderData *sd, ShaderClosure *sc, float edginess)
{
    sc->type = CLOSURE_BSDF_WESTIN_SHEEN_ID;
    sd->flag |= SD_BSDF|SD_BSDF_HAS_EVAL|SD_BSDF_GLOSSY;
    sc->data0 = edginess;
}

__device void bsdf_westin_sheen_blur(ShaderClosure *sc, float roughness)
{
}

__device float3 bsdf_westin_sheen_eval_reflect(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
    float m_edginess = sc->data0;
    float3 m_N = sd->N;

    // pdf is implicitly 0 (no indirect sampling)
    float cosNO = dot(m_N, I);
    float cosNI = dot(m_N, omega_in);
    if(cosNO > 0 && cosNI > 0) {
        float sinNO2 = 1 - cosNO * cosNO;
        *pdf = cosNI * M_1_PI_F;
        float westin = sinNO2 > 0 ? powf(sinNO2, 0.5f * m_edginess) * (*pdf) : 0;
        return make_float3 (westin, westin, westin);
    }
    return make_float3 (0, 0, 0);
}

__device float3 bsdf_westin_sheen_eval_transmit(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
    return make_float3(0.0f, 0.0f, 0.0f);
}

__device float bsdf_westin_sheen_albedo(const ShaderData *sd, const ShaderClosure *sc, const float3 I)
{
    return 1.0f;
}

__device int bsdf_westin_sheen_sample(const ShaderData *sd, const ShaderClosure *sc, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
    float m_edginess = sc->data0;
    float3 m_N = sd->N;

    // we are viewing the surface from the right side - send a ray out with cosine
    // distribution over the hemisphere
    sample_cos_hemisphere(m_N, randu, randv, omega_in, pdf);
    if(dot(sd->Ng, *omega_in) > 0) {
        // TODO: account for sheen when sampling
        float cosNO = dot(m_N, sd->I);
        float sinNO2 = 1 - cosNO * cosNO;
        float westin = sinNO2 > 0 ? powf(sinNO2, 0.5f * m_edginess) * (*pdf) : 0;
        *eval = make_float3(westin, westin, westin);
#ifdef __RAY_DIFFERENTIALS__
        // TODO: find a better approximation for the diffuse bounce
        *domega_in_dx = (2 * dot(m_N, sd->dI.dx)) * m_N - sd->dI.dx;
        *domega_in_dy = (2 * dot(m_N, sd->dI.dy)) * m_N - sd->dI.dy;
        *domega_in_dx *= 125.0f;
        *domega_in_dy *= 125.0f;
#endif
    } else
        pdf = 0;
    return LABEL_REFLECT|LABEL_DIFFUSE;
}

CCL_NAMESPACE_END

#endif /* __BSDF_WESTIN_H__ */