blender/intern/cycles/kernel/kernel_subsurface.h

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/*
* Copyright 2013, 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.
*/
CCL_NAMESPACE_BEGIN
#define BSSRDF_MULTI_EVAL
#define BSSRDF_SKIP_NO_HIT
__device float bssrdf_sample_distance(KernelGlobals *kg, float radius, float refl, float u)
{
int table_offset = kernel_data.bssrdf.table_offset;
float r = lookup_table_read_2D(kg, u, refl, table_offset, BSSRDF_RADIUS_TABLE_SIZE, BSSRDF_REFL_TABLE_SIZE);
return r*radius;
}
#ifdef BSSRDF_MULTI_EVAL
__device float bssrdf_pdf(KernelGlobals *kg, float radius, float refl, float r)
{
if(r >= radius)
return 0.0f;
/* todo: when we use the real BSSRDF this will need to be divided by the maximum
* radius instead of the average radius */
float t = r/radius;
int table_offset = kernel_data.bssrdf.table_offset + BSSRDF_PDF_TABLE_OFFSET;
float pdf = lookup_table_read_2D(kg, t, refl, table_offset, BSSRDF_RADIUS_TABLE_SIZE, BSSRDF_REFL_TABLE_SIZE);
pdf /= radius;
return pdf;
}
#endif
__device ShaderClosure *subsurface_scatter_pick_closure(KernelGlobals *kg, ShaderData *sd, float *probability)
{
/* sum sample weights of bssrdf and bsdf */
float bsdf_sum = 0.0f;
float bssrdf_sum = 0.0f;
for(int i = 0; i < sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
if(CLOSURE_IS_BSDF(sc->type))
bsdf_sum += sc->sample_weight;
else if(CLOSURE_IS_BSSRDF(sc->type))
bssrdf_sum += sc->sample_weight;
}
/* use bsdf or bssrdf? */
float r = sd->randb_closure*(bsdf_sum + bssrdf_sum);
if(r < bsdf_sum) {
/* use bsdf, and adjust randb so we can reuse it for picking a bsdf */
sd->randb_closure = r/bsdf_sum;
*probability = (bsdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/bsdf_sum: 1.0f;
return NULL;
}
/* use bssrdf */
r -= bsdf_sum;
sd->randb_closure = 0.0f; /* not needed anymore */
float sum = 0.0f;
for(int i = 0; i < sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
if(CLOSURE_IS_BSSRDF(sc->type)) {
sum += sc->sample_weight;
if(r <= sum) {
#ifdef BSSRDF_MULTI_EVAL
*probability = (bssrdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/bssrdf_sum: 1.0f;
#else
*probability = (bssrdf_sum > 0.0f)? (bsdf_sum + bssrdf_sum)/sc->sample_weight: 1.0f;
#endif
return sc;
}
}
}
/* should never happen */
*probability = 1.0f;
return NULL;
}
#ifdef BSSRDF_MULTI_EVAL
__device float3 subsurface_scatter_multi_eval(KernelGlobals *kg, ShaderData *sd, bool hit, float refl, float *r, int num_r, bool all)
{
/* compute pdf */
float3 eval_sum = make_float3(0.0f, 0.0f, 0.0f);
float pdf_sum = 0.0f;
float sample_weight_sum = 0.0f;
int num_bssrdf = 0;
for(int i = 0; i < sd->num_closure; i++) {
ShaderClosure *sc = &sd->closure[i];
if(CLOSURE_IS_BSSRDF(sc->type)) {
float sample_weight = (all)? 1.0f: sc->sample_weight;
/* compute pdf */
float pdf = 1.0f;
for(int i = 0; i < num_r; i++)
pdf *= bssrdf_pdf(kg, sc->data0, refl, r[i]);
eval_sum += sc->weight*pdf;
pdf_sum += sample_weight*pdf;
sample_weight_sum += sample_weight;
num_bssrdf++;
}
}
float inv_pdf_sum;
if(pdf_sum > 0.0f) {
/* in case of non-progressive integrate we sample all bssrdf's once,
* for progressive we pick one, so adjust pdf for that */
if(all)
inv_pdf_sum = 1.0f/pdf_sum;
else
inv_pdf_sum = sample_weight_sum/pdf_sum;
}
else
inv_pdf_sum = 0.0f;
float3 weight = eval_sum * inv_pdf_sum;
return weight;
}
#endif
/* replace closures with a single diffuse bsdf closure after scatter step */
__device void subsurface_scatter_setup_diffuse_bsdf(ShaderData *sd, float3 weight)
{
ShaderClosure *sc = &sd->closure[0];
sd->num_closure = 1;
sc->weight = weight;
sc->sample_weight = 1.0f;
sc->data0 = 0.0f;
sc->data1 = 0.0f;
sc->N = sd->N;
sd->flag &= ~SD_CLOSURE_FLAGS;
sd->flag |= bsdf_diffuse_setup(sc);
sd->randb_closure = 0.0f;
/* todo: evaluate shading to get blurred textures and bump mapping */
/* shader_eval_surface(kg, sd, 0.0f, state_flag, SHADER_CONTEXT_SSS); */
}
/* subsurface scattering step, from a point on the surface to another nearby point on the same object */
__device void subsurface_scatter_step(KernelGlobals *kg, ShaderData *sd, int state_flag, ShaderClosure *sc, uint *lcg_state, bool all)
{
float radius = sc->data0;
float refl = max(average(sc->weight)*3.0f, 0.0f);
float r = 0.0f;
bool hit = false;
float3 weight = make_float3(1.0f, 1.0f, 1.0f);
#ifdef BSSRDF_MULTI_EVAL
float r_attempts[BSSRDF_MAX_ATTEMPTS];
#endif
int num_attempts;
/* attempt to find a hit a given number of times before giving up */
for(num_attempts = 0; num_attempts < kernel_data.bssrdf.num_attempts; num_attempts++) {
/* random numbers for sampling */
float u1 = lcg_step(lcg_state);
float u2 = lcg_step(lcg_state);
float u3 = lcg_step(lcg_state);
float u4 = lcg_step(lcg_state);
float u5 = lcg_step(lcg_state);
float u6 = lcg_step(lcg_state);
r = bssrdf_sample_distance(kg, radius, refl, u5);
#ifdef BSSRDF_MULTI_EVAL
r_attempts[num_attempts] = r;
#endif
float3 p1 = sd->P + sample_uniform_sphere(u1, u2)*r;
float3 p2 = sd->P + sample_uniform_sphere(u3, u4)*r;
/* create ray */
Ray ray;
ray.P = p1;
ray.D = normalize_len(p2 - p1, &ray.t);
ray.dP = sd->dP;
ray.dD = differential3_zero();
ray.time = sd->time;
/* intersect with the same object. if multiple intersections are
* found it will randomly pick one of them */
Intersection isect;
if(!scene_intersect_subsurface(kg, &ray, &isect, sd->object, u6))
continue;
/* setup new shading point */
shader_setup_from_subsurface(kg, sd, &isect, &ray);
hit = true;
num_attempts++;
break;
}
/* evaluate subsurface scattering closures */
#ifdef BSSRDF_MULTI_EVAL
weight *= subsurface_scatter_multi_eval(kg, sd, hit, refl, r_attempts, num_attempts, all);
#else
weight *= sc->weight;
#endif
#ifdef BSSRDF_SKIP_NO_HIT
if(!hit)
weight = make_float3(0.0f, 0.0f, 0.0f);
#endif
/* replace closures with a single diffuse BSDF */
subsurface_scatter_setup_diffuse_bsdf(sd, weight);
}
CCL_NAMESPACE_END