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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
*/
#ifndef __BSDF_OREN_NAYAR_H__
#define __BSDF_OREN_NAYAR_H__
CCL_NAMESPACE_BEGIN
typedef struct BsdfOrenNayarClosure {
float m_a;
float m_b;
} BsdfOrenNayarClosure;
__device float3 bsdf_oren_nayar_get_intensity(const ShaderClosure *sc, float3 n, float3 v, float3 l)
{
float nl = max(dot(n, l), 0.0f);
float nv = max(dot(n, v), 0.0f);
float3 al = normalize(l - nl * n);
float3 av = normalize(v - nv * n);
float t = max(dot(al, 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);
float is = nl * (sc->data0 + sc->data1 * t * sin_a * tan_b);
return make_float3(is, is, is);
}
__device void bsdf_oren_nayar_setup(ShaderData *sd, ShaderClosure *sc, float sigma)
{
sc->type = CLOSURE_BSDF_OREN_NAYAR_ID;
sd->flag |= SD_BSDF | SD_BSDF_HAS_EVAL;
sigma = clamp(sigma, 0.0f, 1.0f);
sc->data0 = 1.0f / ((1.0f + 0.5f * sigma) * M_PI);
sc->data1 = sigma / ((1.0f + 0.5f * sigma) * M_PI);
}
__device void bsdf_oren_nayar_blur(ShaderClosure *sc, float roughness)
{
}
__device float3 bsdf_oren_nayar_eval_reflect(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
if (dot(sd->N, omega_in) > 0.0f) {
*pdf = 0.5f * M_1_PI_F;
return bsdf_oren_nayar_get_intensity(sc, sd->N, I, omega_in);
}
else {
*pdf = 0.0f;
return make_float3(0.0f, 0.0f, 0.0f);
}
}
__device float3 bsdf_oren_nayar_eval_transmit(const ShaderData *sd, const ShaderClosure *sc, const float3 I, const float3 omega_in, float *pdf)
{
return make_float3(0.0f, 0.0f, 0.0f);
}
__device float bsdf_oren_nayar_albedo(const ShaderData *sd, const ShaderClosure *sc, const float3 I)
{
return 1.0f;
}
__device int bsdf_oren_nayar_sample(const ShaderData *sd, const ShaderClosure *sc, float randu, float randv, float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
sample_uniform_hemisphere(sd->N, randu, randv, omega_in, pdf);
if (dot(sd->Ng, *omega_in) > 0.0f) {
*eval = bsdf_oren_nayar_get_intensity(sc, sd->N, sd->I, *omega_in);
#ifdef __RAY_DIFFERENTIALS__
// TODO: find a better approximation for the bounce
*domega_in_dx = (2.0f * dot(sd->N, sd->dI.dx)) * sd->N - sd->dI.dx;
*domega_in_dy = (2.0f * dot(sd->N, sd->dI.dy)) * sd->N - sd->dI.dy;
*domega_in_dx *= 125.0f;
*domega_in_dy *= 125.0f;
#endif
}
else {
*pdf = 0.0f;
*eval = make_float3(0.0f, 0.0f, 0.0f);
}
return LABEL_REFLECT | LABEL_DIFFUSE;
}
CCL_NAMESPACE_END
#endif /* __BSDF_OREN_NAYAR_H__ */
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