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/*
* Copyright 2011-2013 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef __VOLUME_H__
#define __VOLUME_H__
CCL_NAMESPACE_BEGIN
/* HENYEY-GREENSTEIN CLOSURE */
/* Given cosine between rays, return probability density that a photon bounces
* to that direction. The g parameter controls how different it is from the
* uniform sphere. g=0 uniform diffuse-like, g=1 close to sharp single ray. */
ccl_device float single_peaked_henyey_greenstein(float cos_theta, float g)
{
return ((1.0f - g * g) / safe_powf(1.0f + g * g - 2.0f * g * cos_theta, 1.5f)) * (M_1_PI_F * 0.25f);
};
ccl_device int volume_henyey_greenstein_setup(ShaderClosure *sc)
{
sc->type = CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID;
/* clamp anisotropy to avoid delta function */
sc->data0 = signf(sc->data0) * min(fabsf(sc->data0), 1.0f - 1e-3f);
return SD_SCATTER;
}
ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc, const float3 I, float3 omega_in, float *pdf)
{
float g = sc->data0;
/* note that I points towards the viewer */
if(fabsf(g) < 1e-3f) {
*pdf = M_1_PI_F * 0.25f;
}
else {
float cos_theta = dot(-I, omega_in);
*pdf = single_peaked_henyey_greenstein(cos_theta, g);
}
return make_float3(*pdf, *pdf, *pdf);
}
ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc, float3 I, float3 dIdx, float3 dIdy, float randu, float randv,
float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
{
float g = sc->data0;
float cos_phi, sin_phi, cos_theta;
/* match pdf for small g */
if(fabsf(g) < 1e-3f) {
cos_theta = (1.0f - 2.0f * randu);
*pdf = M_1_PI_F * 0.25f;
}
else {
float k = (1.0f - g * g) / (1.0f - g + 2.0f * g * randu);
cos_theta = (1.0f + g * g - k * k) / (2.0f * g);
*pdf = single_peaked_henyey_greenstein(cos_theta, g);
}
float sin_theta = safe_sqrtf(1.0f - cos_theta * cos_theta);
float phi = M_2PI_F * randv;
cos_phi = cosf(phi);
sin_phi = sinf(phi);
/* note that I points towards the viewer and so is used negated */
float3 T, B;
make_orthonormals(-I, &T, &B);
*omega_in = sin_theta * cos_phi * T + sin_theta * sin_phi * B + cos_theta * (-I);
*eval = make_float3(*pdf, *pdf, *pdf); /* perfect importance sampling */
#ifdef __RAY_DIFFERENTIALS__
/* todo: implement ray differential estimation */
*domega_in_dx = make_float3(0.0f, 0.0f, 0.0f);
*domega_in_dy = make_float3(0.0f, 0.0f, 0.0f);
#endif
return LABEL_VOLUME_SCATTER;
}
/* ABSORPTION VOLUME CLOSURE */
ccl_device int volume_absorption_setup(ShaderClosure *sc)
{
sc->type = CLOSURE_VOLUME_ABSORPTION_ID;
return SD_ABSORPTION;
}
/* VOLUME CLOSURE */
ccl_device float3 volume_phase_eval(const ShaderData *sd, const ShaderClosure *sc, float3 omega_in, float *pdf)
{
kernel_assert(sc->type == CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID);
return volume_henyey_greenstein_eval_phase(sc, sd->I, omega_in, pdf);
}
ccl_device int volume_phase_sample(const ShaderData *sd, const ShaderClosure *sc, float randu,
float randv, float3 *eval, float3 *omega_in, differential3 *domega_in, float *pdf)
{
int label;
switch(sc->type) {
case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
label = volume_henyey_greenstein_sample(sc, sd->I, sd->dI.dx, sd->dI.dy, randu, randv, eval, omega_in, &domega_in->dx, &domega_in->dy, pdf);
break;
default:
*eval = make_float3(0.0f, 0.0f, 0.0f);
label = LABEL_NONE;
break;
}
return label;
}
CCL_NAMESPACE_END
#endif
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