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/*
* Copyright 2011, Blender Foundation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
/*
* An implementation of Oren-Nayar reflectance model, public domain
* http://www1.cs.columbia.edu/CAVE/publications/pdfs/Oren_SIGGRAPH94.pdf
*
* NOTE:
* BSDF = A + B * cos() * sin() * tan()
*
* The parameter sigma means different from original.
* A and B are calculated by the following formula:
* 0 <= sigma <= 1
* A = 1 / ((1 + sigma / 2) * pi);
* B = sigma / ((1 + sigma / 2) * pi);
*
* This formula is derived as following:
*
* 0. Normalize A-term and B-term of BSDF *individually*.
* B-term is normalized at maximum point: dot(L, N) = 0.
* A = (1/pi) * A'
* B = (2/pi) * B'
*
* 1. Solve the following equation:
* A' + B' = 1
* B / A = sigma
*/
#include <OpenImageIO/fmath.h>
#include <OSL/genclosure.h>
#include "osl_closures.h"
CCL_NAMESPACE_BEGIN
using namespace OSL;
class OrenNayarClosure: public BSDFClosure {
public:
Vec3 m_N;
float m_sigma;
float m_a, m_b;
OrenNayarClosure(): BSDFClosure(Labels::DIFFUSE) {}
void setup() {
m_sigma = clamp(m_sigma, 0.0f, 1.0f);
m_a = 1.0f / ((1.0f + 0.5f * m_sigma) * M_PI);
m_b = m_sigma / ((1.0f + 0.5f * m_sigma) * M_PI);
}
bool mergeable(const ClosurePrimitive* other) const {
const OrenNayarClosure* comp = static_cast<const OrenNayarClosure*>(other);
return
m_N == comp->m_N &&
m_sigma == comp->m_sigma &&
BSDFClosure::mergeable(other);
}
size_t memsize() const {
return sizeof(*this);
}
const char* name() const {
return "oren_nayar";
}
void print_on(std::ostream& out) const {
out << name() << " (";
out << "(" << m_N[0] << ", " << m_N[1] << ", " << m_N[2] << "), ";
out << m_sigma;
out << ")";
}
float albedo(const Vec3& omega_out) const {
return 1.0f;
}
Color3 eval_reflect(const Vec3& omega_out, const Vec3& omega_in, float& pdf) const {
if (m_N.dot(omega_in) > 0.0f) {
pdf = float(0.5 * M_1_PI);
float is = get_intensity(m_N, omega_out, omega_in);
return Color3(is, is, is);
}
else {
pdf = 0.0f;
return Color3(0.0f, 0.0f, 0.0f);
}
}
Color3 eval_transmit(const Vec3& omega_out, const Vec3& omega_in, float& pdf) const {
return Color3(0.0f, 0.0f, 0.0f);
}
ustring sample(
const Vec3& Ng,
const Vec3& omega_out, const Vec3& domega_out_dx, const Vec3& domega_out_dy,
float randu, float randv,
Vec3& omega_in, Vec3& domega_in_dx, Vec3& domega_in_dy,
float& pdf, Color3& eval
) const {
sample_uniform_hemisphere (m_N, omega_out, randu, randv, omega_in, pdf);
if (Ng.dot(omega_in) > 0.0f) {
float is = get_intensity(m_N, omega_out, omega_in);
eval.setValue(is, is, is);
// TODO: find a better approximation for the bounce
domega_in_dx = (2.0f * m_N.dot(domega_out_dx)) * m_N - domega_out_dx;
domega_in_dy = (2.0f * m_N.dot(domega_out_dy)) * m_N - domega_out_dy;
domega_in_dx *= 125.0f;
domega_in_dy *= 125.0f;
}
else {
pdf = 0.0f;
}
return Labels::REFLECT;
}
private:
float get_intensity(Vec3 const& n, Vec3 const& v, Vec3 const& l) const {
float nl = max(n.dot(l), 0.0f);
float nv = max(n.dot(v), 0.0f);
Vec3 al = l - nl * n;
al.normalize();
Vec3 av = v - nv * n;
av.normalize();
float t = max(al.dot(av), 0.0f);
float cos_a, cos_b;
if (nl < nv) {
cos_a = nl;
cos_b = nv;
}
else {
cos_a = nv;
cos_b = nl;
}
float sin_a = sqrtf(1.0f - cos_a * cos_a);
float tan_b = sqrtf(1.0f - cos_b * cos_b) / (cos_b + FLT_MIN);
return nl * (m_a + m_b * t * sin_a * tan_b);
}
};
ClosureParam bsdf_oren_nayar_params[] = {
CLOSURE_VECTOR_PARAM (OrenNayarClosure, m_N),
CLOSURE_FLOAT_PARAM (OrenNayarClosure, m_sigma),
CLOSURE_STRING_KEYPARAM ("label"),
CLOSURE_FINISH_PARAM (OrenNayarClosure)
};
CLOSURE_PREPARE(bsdf_oren_nayar_prepare, OrenNayarClosure)
CCL_NAMESPACE_END
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