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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
/* VOLUME EXTINCTION */
ccl_device void volume_extinction_setup(ShaderData *sd, float3 weight)
{
if (sd->flag & SD_EXTINCTION) {
sd->closure_transparent_extinction += weight;
}
else {
sd->flag |= SD_EXTINCTION;
sd->closure_transparent_extinction = weight;
}
}
/* HENYEY-GREENSTEIN CLOSURE */
typedef ccl_addr_space struct HenyeyGreensteinVolume {
SHADER_CLOSURE_BASE;
float g;
} HenyeyGreensteinVolume;
static_assert(sizeof(ShaderClosure) >= sizeof(HenyeyGreensteinVolume),
"HenyeyGreensteinVolume is too large!");
/* 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(HenyeyGreensteinVolume *volume)
{
volume->type = CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID;
/* clamp anisotropy to avoid delta function */
volume->g = signf(volume->g) * min(fabsf(volume->g), 1.0f - 1e-3f);
return SD_SCATTER;
}
ccl_device bool volume_henyey_greenstein_merge(const ShaderClosure *a, const ShaderClosure *b)
{
const HenyeyGreensteinVolume *volume_a = (const HenyeyGreensteinVolume *)a;
const HenyeyGreensteinVolume *volume_b = (const HenyeyGreensteinVolume *)b;
return (volume_a->g == volume_b->g);
}
ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc,
const float3 I,
float3 omega_in,
float *pdf)
{
const HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume *)sc;
float g = volume->g;
/* 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 float3
henyey_greenstrein_sample(float3 D, float g, float randu, float randv, float *pdf)
{
/* match pdf for small g */
float cos_theta;
bool isotropic = fabsf(g) < 1e-3f;
if (isotropic) {
cos_theta = (1.0f - 2.0f * randu);
if (pdf) {
*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);
if (pdf) {
*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;
float3 dir = make_float3(sin_theta * cosf(phi), sin_theta * sinf(phi), cos_theta);
float3 T, B;
make_orthonormals(D, &T, &B);
dir = dir.x * T + dir.y * B + dir.z * D;
return dir;
}
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)
{
const HenyeyGreensteinVolume *volume = (const HenyeyGreensteinVolume *)sc;
float g = volume->g;
/* note that I points towards the viewer and so is used negated */
*omega_in = henyey_greenstrein_sample(-I, g, randu, randv, pdf);
*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;
}
/* 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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