forked from bartvdbraak/blender
138 lines
4.9 KiB
C++
138 lines
4.9 KiB
C++
/*
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* Adapted from Open Shading Language with this license:
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*
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* Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.
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* All Rights Reserved.
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*
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* Modifications Copyright 2011, Blender Foundation.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of Sony Pictures Imageworks nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <OpenImageIO/fmath.h>
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#include <OSL/genclosure.h>
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#include "osl_closures.h"
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CCL_NAMESPACE_BEGIN
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using namespace OSL;
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// Computes scattering properties based on Jensen's reparameterization
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// described in:
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// http://graphics.ucsd.edu/~henrik/papers/fast_bssrdf/
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class SubsurfaceClosure : public VolumeClosure {
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public:
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float m_g;
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float m_eta;
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Color3 m_mfp, m_albedo;
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static float root_find_Rd(const float Rd0, const float A) {
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// quick exit for trivial cases
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if (Rd0 <= 0) return 0;
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const float A43 = A * 4.0f / 3.0f;
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// Find alpha such that f(alpha) = Rd (see eq.15). A simple bisection
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// method can be used because this function is monotonicaly increasing.
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float lo = 0, hi = 1;
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for (int i = 0; i < 20; i++) { // 2^20 divisions should be sufficient
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// eval function at midpoint
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float alpha = 0.5f * (lo + hi);
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float a1 = sqrtf(3 * (1 - alpha));
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float e1 = expf(-a1);
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float e2 = expf(-A43 * a1);
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float Rd = 0.5f * alpha * (1 + e2) * e1 - Rd0;
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if (fabsf(Rd) < 1e-6f)
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return alpha; // close enough
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else if (Rd > 0)
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hi = alpha; // root is on left side
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else
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lo = alpha; // root is on right side
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}
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// didn't quite converge, pick result in the middle of remaining interval
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return 0.5f * (lo + hi);
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}
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SubsurfaceClosure() {
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}
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void setup()
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{
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ior(m_eta);
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if (m_g >= 0.99f) m_g = 0.99f;
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if (m_g <= -0.99f) m_g = -0.99f;
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// eq.10
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float inv_eta = 1 / m_eta;
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float Fdr = -1.440f * inv_eta * inv_eta + 0.710 * inv_eta + 0.668f + 0.0636 * m_eta;
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float A = (1 + Fdr) / (1 - Fdr);
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// compute sigma_s, sigma_a (eq.16)
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Color3 alpha_prime = Color3(root_find_Rd(m_albedo[0], A),
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root_find_Rd(m_albedo[1], A),
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root_find_Rd(m_albedo[2], A));
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Color3 sigma_t_prime = Color3(m_mfp.x > 0 ? 1.0f / (m_mfp[0] * sqrtf(3 * (1 - alpha_prime[0]))) : 0.0f,
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m_mfp.y > 0 ? 1.0f / (m_mfp[1] * sqrtf(3 * (1 - alpha_prime[1]))) : 0.0f,
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m_mfp.z > 0 ? 1.0f / (m_mfp[2] * sqrtf(3 * (1 - alpha_prime[2]))) : 0.0f);
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Color3 sigma_s_prime = alpha_prime * sigma_t_prime;
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sigma_s((1.0f / (1 - m_g)) * sigma_s_prime);
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sigma_a(sigma_t_prime - sigma_s_prime);
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}
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bool mergeable(const ClosurePrimitive *other) const {
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const SubsurfaceClosure *comp = (const SubsurfaceClosure *)other;
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return m_g == comp->m_g && VolumeClosure::mergeable(other);
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}
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size_t memsize() const { return sizeof(*this); }
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const char *name() const { return "subsurface"; }
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void print_on(std::ostream &out) const {
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out << name() << " ()";
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}
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virtual Color3 eval_phase(const Vec3 &omega_in, const Vec3 &omega_out) const {
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float costheta = omega_in.dot(omega_out);
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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));
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return Color3(ph, ph, ph);
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}
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};
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ClosureParam closure_subsurface_params[] = {
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CLOSURE_FLOAT_PARAM(SubsurfaceClosure, m_eta),
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CLOSURE_FLOAT_PARAM(SubsurfaceClosure, m_g),
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CLOSURE_COLOR_PARAM(SubsurfaceClosure, m_mfp),
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CLOSURE_COLOR_PARAM(SubsurfaceClosure, m_albedo),
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CLOSURE_STRING_KEYPARAM("label"),
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CLOSURE_FINISH_PARAM(SubsurfaceClosure)
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};
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CLOSURE_PREPARE(closure_subsurface_prepare, SubsurfaceClosure)
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CCL_NAMESPACE_END
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