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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,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
CCL_NAMESPACE_BEGIN
ccl_device float fresnel_dielectric(float eta,
const float3 N,
const float3 I,
ccl_private float3 *R,
ccl_private float3 *T,
#ifdef __RAY_DIFFERENTIALS__
const float3 dIdx,
const float3 dIdy,
ccl_private float3 *dRdx,
ccl_private float3 *dRdy,
ccl_private float3 *dTdx,
ccl_private float3 *dTdy,
#endif
ccl_private bool *is_inside)
{
float cos = dot(N, I), neta;
float3 Nn;
// 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;
}
// compute reflection
*R = (2 * cos) * Nn - I;
#ifdef __RAY_DIFFERENTIALS__
*dRdx = (2 * dot(Nn, dIdx)) * Nn - dIdx;
*dRdy = (2 * dot(Nn, dIdy)) * Nn - dIdy;
#endif
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 = max(sqrtf(arg), 1e-7f);
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);
}
}
ccl_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)
}
ccl_device float3 fresnel_conductor(float cosi, const float3 eta, const float3 k)
{
float3 cosi2 = make_float3(cosi * cosi, cosi * cosi, cosi * cosi);
float3 one = make_float3(1.0f, 1.0f, 1.0f);
float3 tmp_f = eta * eta + k * k;
float3 tmp = tmp_f * cosi2;
float3 Rparl2 = (tmp - (2.0f * eta * cosi) + one) / (tmp + (2.0f * eta * cosi) + one);
float3 Rperp2 = (tmp_f - (2.0f * eta * cosi) + cosi2) / (tmp_f + (2.0f * eta * cosi) + cosi2);
return (Rparl2 + Rperp2) * 0.5f;
}
ccl_device float schlick_fresnel(float u)
{
float m = clamp(1.0f - u, 0.0f, 1.0f);
float m2 = m * m;
return m2 * m2 * m; // pow(m, 5)
}
/* Calculate the fresnel color which is a blend between white and the F0 color (cspec0) */
ccl_device_forceinline float3
interpolate_fresnel_color(float3 L, float3 H, float ior, float F0, float3 cspec0)
{
/* Calculate the fresnel interpolation factor
* The value from fresnel_dielectric_cos(...) has to be normalized because
* the cspec0 keeps the F0 color
*/
float F0_norm = 1.0f / (1.0f - F0);
float FH = (fresnel_dielectric_cos(dot(L, H), ior) - F0) * F0_norm;
/* Blend between white and a specular color with respect to the fresnel */
return cspec0 * (1.0f - FH) + make_float3(1.0f, 1.0f, 1.0f) * FH;
}
CCL_NAMESPACE_END
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