bsdf.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. 
 * * 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 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
*/

#ifndef __OSL_BSDF_H__
#define __OSL_BSDF_H__

CCL_NAMESPACE_BEGIN

__device float fresnel_dielectric(float eta, const float3 N,
        const float3 I, float3 *R, float3 *T,
#ifdef __RAY_DIFFERENTIALS__
        const float3 dIdx, const float3 dIdy,
        float3 *dRdx, float3 *dRdy,
        float3 *dTdx, float3 *dTdy, 
#endif
        bool *is_inside)
{
    float cos = dot(N, I), neta;
    float3 Nn;
    // compute reflection
    *R =(2 * cos)* N - I;
#ifdef __RAY_DIFFERENTIALS__
    *dRdx = (2 * dot(N, dIdx)) * N - dIdx;
    *dRdy = (2 * dot(N, dIdy)) * N - dIdy;
#endif
    // check which side of the surface we are on
    if(cos > 0) {
        // we are on the outside of the surface, going in
        neta = 1 / eta;
        Nn   = N;
        *is_inside = false;
    } else {
        // we are inside the surface, 
        cos  = -cos;
        neta = eta;
        Nn   = -N;
        *is_inside = true;
    }
    *R =(2 * cos)* Nn - I;
    float arg = 1 -(neta * neta *(1 -(cos * cos)));
    if(arg < 0) {
        *T= make_float3(0.0f, 0.0f, 0.0f);
#ifdef __RAY_DIFFERENTIALS__
        *dTdx= make_float3(0.0f, 0.0f, 0.0f);
        *dTdy= make_float3(0.0f, 0.0f, 0.0f);
#endif
        return 1; // total internal reflection
    } else {
        float dnp = sqrtf(arg);
        float nK =(neta * cos)- dnp;
        *T = -(neta * I)+(nK * Nn);
#ifdef __RAY_DIFFERENTIALS__
        *dTdx = -(neta * dIdx) + ((neta - neta * neta * cos / dnp) * dot(dIdx, Nn)) * Nn;
        *dTdy = -(neta * dIdy) + ((neta - neta * neta * cos / dnp) * dot(dIdy, Nn)) * Nn;
#endif
        // compute Fresnel terms
        float cosTheta1 = cos; // N.R
        float cosTheta2 = -dot(Nn, *T);
        float pPara =(cosTheta1 - eta * cosTheta2)/(cosTheta1 + eta * cosTheta2);
        float pPerp =(eta * cosTheta1 - cosTheta2)/(eta * cosTheta1 + cosTheta2);
        return 0.5f * (pPara * pPara + pPerp * pPerp);
    }
}

__device float fresnel_dielectric_cos(float cosi, float eta)
{
    // compute fresnel reflectance without explicitly computing
    // the refracted direction
    float c = fabsf(cosi);
    float g = eta * eta - 1 + c * c;
    if(g > 0) {
        g = sqrtf(g);
        float A =(g - c)/(g + c);
        float B =(c *(g + c)- 1)/(c *(g - c)+ 1);
        return 0.5f * A * A *(1 + B * B);
    }
    return 1.0f; // TIR(no refracted component)
}

__device float fresnel_conductor(float cosi, float eta, float k)
{
    float tmp_f = eta * eta + k * k;
    float tmp = tmp_f * cosi * cosi;
    float Rparl2 =(tmp -(2.0f * eta * cosi)+ 1)/
                 (tmp +(2.0f * eta * cosi)+ 1);
    float Rperp2 =(tmp_f -(2.0f * eta * cosi)+ cosi * cosi)/
                 (tmp_f +(2.0f * eta * cosi)+ cosi * cosi);
    return(Rparl2 + Rperp2) * 0.5f;
}

__device float smooth_step(float edge0, float edge1, float x)
{
    float result;
    if(x < edge0) result = 0.0f;
    else if(x >= edge1) result = 1.0f;
    else {
        float t = (x - edge0)/(edge1 - edge0);
        result = (3.0f-2.0f*t)*(t*t);
    }
    return result;
}

CCL_NAMESPACE_END

#endif /* __OSL_BSDF_H__ */