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blender/intern/cycles/kernel/kernel_emission.h
Lukas Stockner 23c276832b Cycles: Add multi-scattering, energy-conserving GGX as an option to the Glossy, Anisotropic and Glass BSDFs 
This commit adds a new distribution to the Glossy, Anisotropic and Glass BSDFs that implements the
multiple-scattering microfacet model described in the paper "Multiple-Scattering Microfacet BSDFs with the Smith Model".

Essentially, the improvement is that unlike classical GGX, which only models single scattering and assumes
the contribution of multiple bounces to be zero, this new model performs a random walk on the microsurface until
the ray leaves it again, which ensures perfect energy conservation.

In practise, this means that the "darkening problem" - GGX materials becoming darker with increasing
roughness - is solved in a physically correct and efficient way.

The downside of this model is that it has no (known) analytic expression for evalation. However, it can be
evaluated stochastically, and although the correct PDF isn't known either, the properties of MIS and the
balance heuristic guarantee an unbiased result at the cost of slightly higher noise.

Reviewers: dingto, #cycles, brecht

Reviewed By: dingto, #cycles, brecht

Subscribers: bliblubli, ace_dragon, gregzaal, brecht, harvester, dingto, marcog, swerner, jtheninja, Blendify, nutel

Differential Revision: https://developer.blender.org/D2002
2016-06-23 22:57:26 +02:00

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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.
*/
CCL_NAMESPACE_BEGIN
/* Direction Emission */
ccl_device_noinline float3 direct_emissive_eval(KernelGlobals *kg,
ShaderData *emission_sd,
LightSample *ls,
ccl_addr_space PathState *state,
float3 I,
differential3 dI,
float t,
float time)
{
/* setup shading at emitter */
float3 eval;
#ifdef __BACKGROUND_MIS__
if(ls->type == LIGHT_BACKGROUND) {
Ray ray;
ray.D = ls->D;
ray.P = ls->P;
ray.t = 1.0f;
# ifdef __OBJECT_MOTION__
ray.time = time;
# endif
ray.dP = differential3_zero();
ray.dD = dI;
shader_setup_from_background(kg, emission_sd, &ray);
path_state_modify_bounce(state, true);
eval = shader_eval_background(kg, emission_sd, state, 0, SHADER_CONTEXT_EMISSION);
path_state_modify_bounce(state, false);
}
else
#endif
{
shader_setup_from_sample(kg, emission_sd, ls->P, ls->Ng, I, ls->shader, ls->object, ls->prim, ls->u, ls->v, t, time);
ls->Ng = ccl_fetch(emission_sd, Ng);
/* no path flag, we're evaluating this for all closures. that's weak but
* we'd have to do multiple evaluations otherwise */
path_state_modify_bounce(state, true);
shader_eval_surface(kg, emission_sd, NULL, state, 0.0f, 0, SHADER_CONTEXT_EMISSION);
path_state_modify_bounce(state, false);
/* evaluate emissive closure */
if(ccl_fetch(emission_sd, flag) & SD_EMISSION)
eval = shader_emissive_eval(kg, emission_sd);
else
eval = make_float3(0.0f, 0.0f, 0.0f);
}
eval *= ls->eval_fac;
return eval;
}
ccl_device_noinline bool direct_emission(KernelGlobals *kg,
ShaderData *sd,
ShaderData *emission_sd,
LightSample *ls,
ccl_addr_space PathState *state,
Ray *ray,
BsdfEval *eval,
bool *is_lamp)
{
if(ls->pdf == 0.0f)
return false;
/* todo: implement */
differential3 dD = differential3_zero();
/* evaluate closure */
float3 light_eval = direct_emissive_eval(kg,
emission_sd,
ls,
state,
-ls->D,
dD,
ls->t,
ccl_fetch(sd, time));
if(is_zero(light_eval))
return false;
/* evaluate BSDF at shading point */
#ifdef __VOLUME__
if(ccl_fetch(sd, prim) != PRIM_NONE)
shader_bsdf_eval(kg, sd, ls->D, eval, ls->pdf, ls->shader & SHADER_USE_MIS);
else {
float bsdf_pdf;
shader_volume_phase_eval(kg, sd, ls->D, eval, &bsdf_pdf);
if(ls->shader & SHADER_USE_MIS) {
/* Multiple importance sampling. */
float mis_weight = power_heuristic(ls->pdf, bsdf_pdf);
light_eval *= mis_weight;
}
}
#else
shader_bsdf_eval(kg, sd, ls->D, eval, ls->pdf, ls->shader & SHADER_USE_MIS);
#endif
bsdf_eval_mul(eval, light_eval/ls->pdf);
#ifdef __PASSES__
/* use visibility flag to skip lights */
if(ls->shader & SHADER_EXCLUDE_ANY) {
if(ls->shader & SHADER_EXCLUDE_DIFFUSE) {
eval->diffuse = make_float3(0.0f, 0.0f, 0.0f);
eval->subsurface = make_float3(0.0f, 0.0f, 0.0f);
}
if(ls->shader & SHADER_EXCLUDE_GLOSSY)
eval->glossy = make_float3(0.0f, 0.0f, 0.0f);
if(ls->shader & SHADER_EXCLUDE_TRANSMIT)
eval->transmission = make_float3(0.0f, 0.0f, 0.0f);
if(ls->shader & SHADER_EXCLUDE_SCATTER)
eval->scatter = make_float3(0.0f, 0.0f, 0.0f);
}
#endif
if(bsdf_eval_is_zero(eval))
return false;
if(ls->shader & SHADER_CAST_SHADOW) {
/* setup ray */
bool transmit = (dot(ccl_fetch(sd, Ng), ls->D) < 0.0f);
ray->P = ray_offset(ccl_fetch(sd, P), (transmit)? -ccl_fetch(sd, Ng): ccl_fetch(sd, Ng));
if(ls->t == FLT_MAX) {
/* distant light */
ray->D = ls->D;
ray->t = ls->t;
}
else {
/* other lights, avoid self-intersection */
ray->D = ray_offset(ls->P, ls->Ng) - ray->P;
ray->D = normalize_len(ray->D, &ray->t);
}
ray->dP = ccl_fetch(sd, dP);
ray->dD = differential3_zero();
}
else {
/* signal to not cast shadow ray */
ray->t = 0.0f;
}
/* return if it's a lamp for shadow pass */
*is_lamp = (ls->prim == PRIM_NONE && ls->type != LIGHT_BACKGROUND);
return true;
}
/* Indirect Primitive Emission */
ccl_device_noinline float3 indirect_primitive_emission(KernelGlobals *kg, ShaderData *sd, float t, int path_flag, float bsdf_pdf)
{
/* evaluate emissive closure */
float3 L = shader_emissive_eval(kg, sd);
#ifdef __HAIR__
if(!(path_flag & PATH_RAY_MIS_SKIP) && (ccl_fetch(sd, flag) & SD_USE_MIS) && (ccl_fetch(sd, type) & PRIMITIVE_ALL_TRIANGLE))
#else
if(!(path_flag & PATH_RAY_MIS_SKIP) && (ccl_fetch(sd, flag) & SD_USE_MIS))
#endif
{
/* multiple importance sampling, get triangle light pdf,
* and compute weight with respect to BSDF pdf */
float pdf = triangle_light_pdf(kg, ccl_fetch(sd, Ng), ccl_fetch(sd, I), t);
float mis_weight = power_heuristic(bsdf_pdf, pdf);
return L*mis_weight;
}
return L;
}
/* Indirect Lamp Emission */
ccl_device_noinline bool indirect_lamp_emission(KernelGlobals *kg,
ShaderData *emission_sd,
ccl_addr_space PathState *state,
Ray *ray,
float3 *emission)
{
bool hit_lamp = false;
*emission = make_float3(0.0f, 0.0f, 0.0f);
for(int lamp = 0; lamp < kernel_data.integrator.num_all_lights; lamp++) {
LightSample ls;
if(!lamp_light_eval(kg, lamp, ray->P, ray->D, ray->t, &ls))
continue;
#ifdef __PASSES__
/* use visibility flag to skip lights */
if(ls.shader & SHADER_EXCLUDE_ANY) {
if(((ls.shader & SHADER_EXCLUDE_DIFFUSE) && (state->flag & PATH_RAY_DIFFUSE)) ||
((ls.shader & SHADER_EXCLUDE_GLOSSY) &&
((state->flag & (PATH_RAY_GLOSSY|PATH_RAY_REFLECT)) == (PATH_RAY_GLOSSY|PATH_RAY_REFLECT))) ||
((ls.shader & SHADER_EXCLUDE_TRANSMIT) && (state->flag & PATH_RAY_TRANSMIT)) ||
((ls.shader & SHADER_EXCLUDE_SCATTER) && (state->flag & PATH_RAY_VOLUME_SCATTER)))
continue;
}
#endif
float3 L = direct_emissive_eval(kg,
emission_sd,
&ls,
state,
-ray->D,
ray->dD,
ls.t,
ray->time);
#ifdef __VOLUME__
if(state->volume_stack[0].shader != SHADER_NONE) {
/* shadow attenuation */
Ray volume_ray = *ray;
volume_ray.t = ls.t;
float3 volume_tp = make_float3(1.0f, 1.0f, 1.0f);
kernel_volume_shadow(kg, emission_sd, state, &volume_ray, &volume_tp);
L *= volume_tp;
}
#endif
if(!(state->flag & PATH_RAY_MIS_SKIP)) {
/* multiple importance sampling, get regular light pdf,
* and compute weight with respect to BSDF pdf */
float mis_weight = power_heuristic(state->ray_pdf, ls.pdf);
L *= mis_weight;
}
*emission += L;
hit_lamp = true;
}
return hit_lamp;
}
/* Indirect Background */
ccl_device_noinline float3 indirect_background(KernelGlobals *kg,
ShaderData *emission_sd,
ccl_addr_space PathState *state,
ccl_addr_space Ray *ray)
{
#ifdef __BACKGROUND__
int shader = kernel_data.background.surface_shader;
/* use visibility flag to skip lights */
if(shader & SHADER_EXCLUDE_ANY) {
if(((shader & SHADER_EXCLUDE_DIFFUSE) && (state->flag & PATH_RAY_DIFFUSE)) ||
((shader & SHADER_EXCLUDE_GLOSSY) &&
((state->flag & (PATH_RAY_GLOSSY|PATH_RAY_REFLECT)) == (PATH_RAY_GLOSSY|PATH_RAY_REFLECT))) ||
((shader & SHADER_EXCLUDE_TRANSMIT) && (state->flag & PATH_RAY_TRANSMIT)) ||
((shader & SHADER_EXCLUDE_CAMERA) && (state->flag & PATH_RAY_CAMERA)) ||
((shader & SHADER_EXCLUDE_SCATTER) && (state->flag & PATH_RAY_VOLUME_SCATTER)))
return make_float3(0.0f, 0.0f, 0.0f);
}
/* evaluate background closure */
# ifdef __SPLIT_KERNEL__
Ray priv_ray = *ray;
shader_setup_from_background(kg, emission_sd, &priv_ray);
# else
shader_setup_from_background(kg, emission_sd, ray);
# endif
path_state_modify_bounce(state, true);
float3 L = shader_eval_background(kg, emission_sd, state, state->flag, SHADER_CONTEXT_EMISSION);
path_state_modify_bounce(state, false);
#ifdef __BACKGROUND_MIS__
/* check if background light exists or if we should skip pdf */
int res = kernel_data.integrator.pdf_background_res;
if(!(state->flag & PATH_RAY_MIS_SKIP) && res) {
/* multiple importance sampling, get background light pdf for ray
* direction, and compute weight with respect to BSDF pdf */
float pdf = background_light_pdf(kg, ray->P, ray->D);
float mis_weight = power_heuristic(state->ray_pdf, pdf);
return L*mis_weight;
}
#endif
return L;
#else
return make_float3(0.8f, 0.8f, 0.8f);
#endif
}
CCL_NAMESPACE_END
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