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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.
*/
#include <OpenImageIO/fmath.h>
#include <OSL/genclosure.h>
#include "osl_closures.h"
CCL_NAMESPACE_BEGIN
using namespace OSL;
// Computes scattering properties based on Jensen's reparameterization
// described in:
// http://graphics.ucsd.edu/~henrik/papers/fast_bssrdf/
class SubsurfaceClosure : public VolumeClosure {
public:
float m_g;
float m_eta;
Color3 m_mfp, m_albedo;
static float root_find_Rd(const float Rd0, const float A) {
// quick exit for trivial cases
if (Rd0 <= 0) return 0;
const float A43 = A * 4.0f / 3.0f;
// Find alpha such that f(alpha) = Rd (see eq.15). A simple bisection
// method can be used because this function is monotonicaly increasing.
float lo = 0, hi = 1;
for (int i = 0; i < 20; i++) { // 2^20 divisions should be sufficient
// eval function at midpoint
float alpha = 0.5f * (lo + hi);
float a1 = sqrtf(3 * (1 - alpha));
float e1 = expf(-a1);
float e2 = expf(-A43 * a1);
float Rd = 0.5f * alpha * (1 + e2) * e1 - Rd0;
if (fabsf(Rd) < 1e-6f)
return alpha; // close enough
else if (Rd > 0)
hi = alpha; // root is on left side
else
lo = alpha; // root is on right side
}
// didn't quite converge, pick result in the middle of remaining interval
return 0.5f * (lo + hi);
}
SubsurfaceClosure() { }
void setup()
{
ior(m_eta);
if (m_g >= 0.99f) m_g = 0.99f;
if (m_g <= -0.99f) m_g = -0.99f;
// eq.10
float inv_eta = 1 / m_eta;
float Fdr = -1.440f * inv_eta * inv_eta + 0.710 * inv_eta + 0.668f + 0.0636 * m_eta;
float A = (1 + Fdr) / (1 - Fdr);
// compute sigma_s, sigma_a (eq.16)
Color3 alpha_prime = Color3 (root_find_Rd(m_albedo[0], A),
root_find_Rd(m_albedo[1], A),
root_find_Rd(m_albedo[2], A));
Color3 sigma_t_prime = Color3 (m_mfp.x > 0 ? 1.0f / (m_mfp[0] * sqrtf(3 * (1 - alpha_prime[0]))) : 0.0f,
m_mfp.y > 0 ? 1.0f / (m_mfp[1] * sqrtf(3 * (1 - alpha_prime[1]))) : 0.0f,
m_mfp.z > 0 ? 1.0f / (m_mfp[2] * sqrtf(3 * (1 - alpha_prime[2]))) : 0.0f);
Color3 sigma_s_prime = alpha_prime * sigma_t_prime;
sigma_s((1.0f / (1 - m_g)) * sigma_s_prime);
sigma_a(sigma_t_prime - sigma_s_prime);
}
bool mergeable (const ClosurePrimitive *other) const {
const SubsurfaceClosure *comp = (const SubsurfaceClosure *)other;
return m_g == comp->m_g && VolumeClosure::mergeable(other);
}
size_t memsize () const { return sizeof(*this); }
const char *name () const { return "subsurface"; }
void print_on (std::ostream &out) const {
out << name() << " ()";
}
virtual Color3 eval_phase(const Vec3 &omega_in, const Vec3 &omega_out) const {
float costheta = omega_in.dot(omega_out);
float ph = 0.25f * float(M_1_PI) * ((1 - m_g * m_g) / powf(1 + m_g * m_g - 2.0f * m_g * costheta, 1.5f));
return Color3 (ph, ph, ph);
}
};
ClosureParam closure_subsurface_params[] = {
CLOSURE_FLOAT_PARAM (SubsurfaceClosure, m_eta),
CLOSURE_FLOAT_PARAM (SubsurfaceClosure, m_g),
CLOSURE_COLOR_PARAM (SubsurfaceClosure, m_mfp),
CLOSURE_COLOR_PARAM (SubsurfaceClosure, m_albedo),
CLOSURE_STRING_KEYPARAM("label"),
CLOSURE_FINISH_PARAM(SubsurfaceClosure) };
CLOSURE_PREPARE(closure_subsurface_prepare, SubsurfaceClosure)
CCL_NAMESPACE_END
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