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|
/*
* Copyright 2011-2021 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.
*/
#pragma once
#include "kernel/film/accumulate.h"
#include "kernel/film/passes.h"
#include "kernel/integrator/intersect_closest.h"
#include "kernel/integrator/path_state.h"
#include "kernel/integrator/shader_eval.h"
#include "kernel/integrator/volume_stack.h"
#include "kernel/light/light.h"
#include "kernel/light/sample.h"
CCL_NAMESPACE_BEGIN
#ifdef __VOLUME__
/* Events for probabilistic scattering. */
typedef enum VolumeIntegrateEvent {
VOLUME_PATH_SCATTERED = 0,
VOLUME_PATH_ATTENUATED = 1,
VOLUME_PATH_MISSED = 2
} VolumeIntegrateEvent;
typedef struct VolumeIntegrateResult {
/* Throughput and offset for direct light scattering. */
bool direct_scatter;
float3 direct_throughput;
float direct_t;
ShaderVolumePhases direct_phases;
/* Throughput and offset for indirect light scattering. */
bool indirect_scatter;
float3 indirect_throughput;
float indirect_t;
ShaderVolumePhases indirect_phases;
} VolumeIntegrateResult;
/* Ignore paths that have volume throughput below this value, to avoid unnecessary work
* and precision issues.
* todo: this value could be tweaked or turned into a probability to avoid unnecessary
* work in volumes and subsurface scattering. */
# define VOLUME_THROUGHPUT_EPSILON 1e-6f
/* Volume shader properties
*
* extinction coefficient = absorption coefficient + scattering coefficient
* sigma_t = sigma_a + sigma_s */
typedef struct VolumeShaderCoefficients {
float3 sigma_t;
float3 sigma_s;
float3 emission;
} VolumeShaderCoefficients;
/* Evaluate shader to get extinction coefficient at P. */
ccl_device_inline bool shadow_volume_shader_sample(KernelGlobals kg,
IntegratorShadowState state,
ccl_private ShaderData *ccl_restrict sd,
ccl_private float3 *ccl_restrict extinction)
{
VOLUME_READ_LAMBDA(integrator_state_read_shadow_volume_stack(state, i))
shader_eval_volume<true>(kg, state, sd, PATH_RAY_SHADOW, volume_read_lambda_pass);
if (!(sd->flag & SD_EXTINCTION)) {
return false;
}
const float density = object_volume_density(kg, sd->object);
*extinction = sd->closure_transparent_extinction * density;
return true;
}
/* Evaluate shader to get absorption, scattering and emission at P. */
ccl_device_inline bool volume_shader_sample(KernelGlobals kg,
IntegratorState state,
ccl_private ShaderData *ccl_restrict sd,
ccl_private VolumeShaderCoefficients *coeff)
{
const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
VOLUME_READ_LAMBDA(integrator_state_read_volume_stack(state, i))
shader_eval_volume<false>(kg, state, sd, path_flag, volume_read_lambda_pass);
if (!(sd->flag & (SD_EXTINCTION | SD_SCATTER | SD_EMISSION))) {
return false;
}
coeff->sigma_s = zero_float3();
coeff->sigma_t = (sd->flag & SD_EXTINCTION) ? sd->closure_transparent_extinction : zero_float3();
coeff->emission = (sd->flag & SD_EMISSION) ? sd->closure_emission_background : zero_float3();
if (sd->flag & SD_SCATTER) {
for (int i = 0; i < sd->num_closure; i++) {
ccl_private const ShaderClosure *sc = &sd->closure[i];
if (CLOSURE_IS_VOLUME(sc->type)) {
coeff->sigma_s += sc->weight;
}
}
}
const float density = object_volume_density(kg, sd->object);
coeff->sigma_s *= density;
coeff->sigma_t *= density;
coeff->emission *= density;
return true;
}
ccl_device_forceinline void volume_step_init(KernelGlobals kg,
ccl_private const RNGState *rng_state,
const float object_step_size,
float t,
ccl_private float *step_size,
ccl_private float *step_shade_offset,
ccl_private float *steps_offset,
ccl_private int *max_steps)
{
if (object_step_size == FLT_MAX) {
/* Homogeneous volume. */
*step_size = t;
*step_shade_offset = 0.0f;
*steps_offset = 1.0f;
*max_steps = 1;
}
else {
/* Heterogeneous volume. */
*max_steps = kernel_data.integrator.volume_max_steps;
float step = min(object_step_size, t);
/* compute exact steps in advance for malloc */
if (t > *max_steps * step) {
step = t / (float)*max_steps;
}
*step_size = step;
/* Perform shading at this offset within a step, to integrate over
* over the entire step segment. */
*step_shade_offset = path_state_rng_1D_hash(kg, rng_state, 0x1e31d8a4);
/* Shift starting point of all segment by this random amount to avoid
* banding artifacts from the volume bounding shape. */
*steps_offset = path_state_rng_1D_hash(kg, rng_state, 0x3d22c7b3);
}
}
/* Volume Shadows
*
* These functions are used to attenuate shadow rays to lights. Both absorption
* and scattering will block light, represented by the extinction coefficient. */
# if 0
/* homogeneous volume: assume shader evaluation at the starts gives
* the extinction coefficient for the entire line segment */
ccl_device void volume_shadow_homogeneous(KernelGlobals kg, IntegratorState state,
ccl_private Ray *ccl_restrict ray,
ccl_private ShaderData *ccl_restrict sd,
ccl_global float3 *ccl_restrict throughput)
{
float3 sigma_t = zero_float3();
if (shadow_volume_shader_sample(kg, state, sd, &sigma_t)) {
*throughput *= volume_color_transmittance(sigma_t, ray->t);
}
}
# endif
/* heterogeneous volume: integrate stepping through the volume until we
* reach the end, get absorbed entirely, or run out of iterations */
ccl_device void volume_shadow_heterogeneous(KernelGlobals kg,
IntegratorShadowState state,
ccl_private Ray *ccl_restrict ray,
ccl_private ShaderData *ccl_restrict sd,
ccl_private float3 *ccl_restrict throughput,
const float object_step_size)
{
/* Load random number state. */
RNGState rng_state;
shadow_path_state_rng_load(state, &rng_state);
float3 tp = *throughput;
/* Prepare for stepping.
* For shadows we do not offset all segments, since the starting point is
* already a random distance inside the volume. It also appears to create
* banding artifacts for unknown reasons. */
int max_steps;
float step_size, step_shade_offset, unused;
volume_step_init(kg,
&rng_state,
object_step_size,
ray->t,
&step_size,
&step_shade_offset,
&unused,
&max_steps);
const float steps_offset = 1.0f;
/* compute extinction at the start */
float t = 0.0f;
float3 sum = zero_float3();
for (int i = 0; i < max_steps; i++) {
/* advance to new position */
float new_t = min(ray->t, (i + steps_offset) * step_size);
float dt = new_t - t;
float3 new_P = ray->P + ray->D * (t + dt * step_shade_offset);
float3 sigma_t = zero_float3();
/* compute attenuation over segment */
sd->P = new_P;
if (shadow_volume_shader_sample(kg, state, sd, &sigma_t)) {
/* Compute `expf()` only for every Nth step, to save some calculations
* because `exp(a)*exp(b) = exp(a+b)`, also do a quick #VOLUME_THROUGHPUT_EPSILON
* check then. */
sum += (-sigma_t * dt);
if ((i & 0x07) == 0) { /* TODO: Other interval? */
tp = *throughput * exp3(sum);
/* stop if nearly all light is blocked */
if (tp.x < VOLUME_THROUGHPUT_EPSILON && tp.y < VOLUME_THROUGHPUT_EPSILON &&
tp.z < VOLUME_THROUGHPUT_EPSILON)
break;
}
}
/* stop if at the end of the volume */
t = new_t;
if (t == ray->t) {
/* Update throughput in case we haven't done it above */
tp = *throughput * exp3(sum);
break;
}
}
*throughput = tp;
}
/* Equi-angular sampling as in:
* "Importance Sampling Techniques for Path Tracing in Participating Media" */
/* Below this pdf we ignore samples, as they tend to lead to very long distances.
* This can cause performance issues with BVH traversal in OptiX, leading it to
* traverse many nodes. Since these contribute very little to the image, just ignore
* those samples. */
# define VOLUME_SAMPLE_PDF_CUTOFF 1e-8f
ccl_device float volume_equiangular_sample(ccl_private const Ray *ccl_restrict ray,
const float3 light_P,
const float xi,
ccl_private float *pdf)
{
const float t = ray->t;
const float delta = dot((light_P - ray->P), ray->D);
const float D = safe_sqrtf(len_squared(light_P - ray->P) - delta * delta);
if (UNLIKELY(D == 0.0f)) {
*pdf = 0.0f;
return 0.0f;
}
const float theta_a = -atan2f(delta, D);
const float theta_b = atan2f(t - delta, D);
const float t_ = D * tanf((xi * theta_b) + (1 - xi) * theta_a);
if (UNLIKELY(theta_b == theta_a)) {
*pdf = 0.0f;
return 0.0f;
}
*pdf = D / ((theta_b - theta_a) * (D * D + t_ * t_));
return min(t, delta + t_); /* min is only for float precision errors */
}
ccl_device float volume_equiangular_pdf(ccl_private const Ray *ccl_restrict ray,
const float3 light_P,
const float sample_t)
{
const float delta = dot((light_P - ray->P), ray->D);
const float D = safe_sqrtf(len_squared(light_P - ray->P) - delta * delta);
if (UNLIKELY(D == 0.0f)) {
return 0.0f;
}
const float t = ray->t;
const float t_ = sample_t - delta;
const float theta_a = -atan2f(delta, D);
const float theta_b = atan2f(t - delta, D);
if (UNLIKELY(theta_b == theta_a)) {
return 0.0f;
}
const float pdf = D / ((theta_b - theta_a) * (D * D + t_ * t_));
return pdf;
}
ccl_device float volume_equiangular_cdf(ccl_private const Ray *ccl_restrict ray,
const float3 light_P,
const float sample_t)
{
float delta = dot((light_P - ray->P), ray->D);
float D = safe_sqrtf(len_squared(light_P - ray->P) - delta * delta);
if (UNLIKELY(D == 0.0f)) {
return 0.0f;
}
const float t = ray->t;
const float t_ = sample_t - delta;
const float theta_a = -atan2f(delta, D);
const float theta_b = atan2f(t - delta, D);
if (UNLIKELY(theta_b == theta_a)) {
return 0.0f;
}
const float theta_sample = atan2f(t_, D);
const float cdf = (theta_sample - theta_a) / (theta_b - theta_a);
return cdf;
}
/* Distance sampling */
ccl_device float volume_distance_sample(float max_t,
float3 sigma_t,
int channel,
float xi,
ccl_private float3 *transmittance,
ccl_private float3 *pdf)
{
/* xi is [0, 1[ so log(0) should never happen, division by zero is
* avoided because sample_sigma_t > 0 when SD_SCATTER is set */
float sample_sigma_t = volume_channel_get(sigma_t, channel);
float3 full_transmittance = volume_color_transmittance(sigma_t, max_t);
float sample_transmittance = volume_channel_get(full_transmittance, channel);
float sample_t = min(max_t, -logf(1.0f - xi * (1.0f - sample_transmittance)) / sample_sigma_t);
*transmittance = volume_color_transmittance(sigma_t, sample_t);
*pdf = safe_divide_color(sigma_t * *transmittance, one_float3() - full_transmittance);
/* todo: optimization: when taken together with hit/miss decision,
* the full_transmittance cancels out drops out and xi does not
* need to be remapped */
return sample_t;
}
ccl_device float3 volume_distance_pdf(float max_t, float3 sigma_t, float sample_t)
{
float3 full_transmittance = volume_color_transmittance(sigma_t, max_t);
float3 transmittance = volume_color_transmittance(sigma_t, sample_t);
return safe_divide_color(sigma_t * transmittance, one_float3() - full_transmittance);
}
/* Emission */
ccl_device float3 volume_emission_integrate(ccl_private VolumeShaderCoefficients *coeff,
int closure_flag,
float3 transmittance,
float t)
{
/* integral E * exp(-sigma_t * t) from 0 to t = E * (1 - exp(-sigma_t * t))/sigma_t
* this goes to E * t as sigma_t goes to zero
*
* todo: we should use an epsilon to avoid precision issues near zero sigma_t */
float3 emission = coeff->emission;
if (closure_flag & SD_EXTINCTION) {
float3 sigma_t = coeff->sigma_t;
emission.x *= (sigma_t.x > 0.0f) ? (1.0f - transmittance.x) / sigma_t.x : t;
emission.y *= (sigma_t.y > 0.0f) ? (1.0f - transmittance.y) / sigma_t.y : t;
emission.z *= (sigma_t.z > 0.0f) ? (1.0f - transmittance.z) / sigma_t.z : t;
}
else
emission *= t;
return emission;
}
/* Volume Integration */
typedef struct VolumeIntegrateState {
/* Volume segment extents. */
float start_t;
float end_t;
/* If volume is absorption-only up to this point, and no probabilistic
* scattering or termination has been used yet. */
bool absorption_only;
/* Random numbers for scattering. */
float rscatter;
float rphase;
/* Multiple importance sampling. */
VolumeSampleMethod direct_sample_method;
bool use_mis;
float distance_pdf;
float equiangular_pdf;
} VolumeIntegrateState;
ccl_device_forceinline void volume_integrate_step_scattering(
ccl_private const ShaderData *sd,
ccl_private const Ray *ray,
const float3 equiangular_light_P,
ccl_private const VolumeShaderCoefficients &ccl_restrict coeff,
const float3 transmittance,
ccl_private VolumeIntegrateState &ccl_restrict vstate,
ccl_private VolumeIntegrateResult &ccl_restrict result)
{
/* Pick random color channel, we use the Veach one-sample
* model with balance heuristic for the channels. */
const float3 albedo = safe_divide_color(coeff.sigma_s, coeff.sigma_t);
float3 channel_pdf;
const int channel = volume_sample_channel(
albedo, result.indirect_throughput, vstate.rphase, &channel_pdf);
/* Equiangular sampling for direct lighting. */
if (vstate.direct_sample_method == VOLUME_SAMPLE_EQUIANGULAR && !result.direct_scatter) {
if (result.direct_t >= vstate.start_t && result.direct_t <= vstate.end_t &&
vstate.equiangular_pdf > VOLUME_SAMPLE_PDF_CUTOFF) {
const float new_dt = result.direct_t - vstate.start_t;
const float3 new_transmittance = volume_color_transmittance(coeff.sigma_t, new_dt);
result.direct_scatter = true;
result.direct_throughput *= coeff.sigma_s * new_transmittance / vstate.equiangular_pdf;
shader_copy_volume_phases(&result.direct_phases, sd);
/* Multiple importance sampling. */
if (vstate.use_mis) {
const float distance_pdf = vstate.distance_pdf *
dot(channel_pdf, coeff.sigma_t * new_transmittance);
const float mis_weight = 2.0f * power_heuristic(vstate.equiangular_pdf, distance_pdf);
result.direct_throughput *= mis_weight;
}
}
else {
result.direct_throughput *= transmittance;
vstate.distance_pdf *= dot(channel_pdf, transmittance);
}
}
/* Distance sampling for indirect and optional direct lighting. */
if (!result.indirect_scatter) {
/* decide if we will scatter or continue */
const float sample_transmittance = volume_channel_get(transmittance, channel);
if (1.0f - vstate.rscatter >= sample_transmittance) {
/* compute sampling distance */
const float sample_sigma_t = volume_channel_get(coeff.sigma_t, channel);
const float new_dt = -logf(1.0f - vstate.rscatter) / sample_sigma_t;
const float new_t = vstate.start_t + new_dt;
/* transmittance and pdf */
const float3 new_transmittance = volume_color_transmittance(coeff.sigma_t, new_dt);
const float distance_pdf = dot(channel_pdf, coeff.sigma_t * new_transmittance);
if (vstate.distance_pdf * distance_pdf > VOLUME_SAMPLE_PDF_CUTOFF) {
/* throughput */
result.indirect_scatter = true;
result.indirect_t = new_t;
result.indirect_throughput *= coeff.sigma_s * new_transmittance / distance_pdf;
shader_copy_volume_phases(&result.indirect_phases, sd);
if (vstate.direct_sample_method != VOLUME_SAMPLE_EQUIANGULAR) {
/* If using distance sampling for direct light, just copy parameters
* of indirect light since we scatter at the same point then. */
result.direct_scatter = true;
result.direct_t = result.indirect_t;
result.direct_throughput = result.indirect_throughput;
shader_copy_volume_phases(&result.direct_phases, sd);
/* Multiple importance sampling. */
if (vstate.use_mis) {
const float equiangular_pdf = volume_equiangular_pdf(ray, equiangular_light_P, new_t);
const float mis_weight = power_heuristic(vstate.distance_pdf * distance_pdf,
equiangular_pdf);
result.direct_throughput *= 2.0f * mis_weight;
}
}
}
}
else {
/* throughput */
const float pdf = dot(channel_pdf, transmittance);
result.indirect_throughput *= transmittance / pdf;
if (vstate.direct_sample_method != VOLUME_SAMPLE_EQUIANGULAR) {
vstate.distance_pdf *= pdf;
}
/* remap rscatter so we can reuse it and keep thing stratified */
vstate.rscatter = 1.0f - (1.0f - vstate.rscatter) / sample_transmittance;
}
}
}
/* heterogeneous volume distance sampling: integrate stepping through the
* volume until we reach the end, get absorbed entirely, or run out of
* iterations. this does probabilistically scatter or get transmitted through
* for path tracing where we don't want to branch. */
ccl_device_forceinline void volume_integrate_heterogeneous(
KernelGlobals kg,
IntegratorState state,
ccl_private Ray *ccl_restrict ray,
ccl_private ShaderData *ccl_restrict sd,
ccl_private const RNGState *rng_state,
ccl_global float *ccl_restrict render_buffer,
const float object_step_size,
const VolumeSampleMethod direct_sample_method,
const float3 equiangular_light_P,
ccl_private VolumeIntegrateResult &result)
{
PROFILING_INIT(kg, PROFILING_SHADE_VOLUME_INTEGRATE);
/* Prepare for stepping.
* Using a different step offset for the first step avoids banding artifacts. */
int max_steps;
float step_size, step_shade_offset, steps_offset;
volume_step_init(kg,
rng_state,
object_step_size,
ray->t,
&step_size,
&step_shade_offset,
&steps_offset,
&max_steps);
/* Initialize volume integration state. */
VolumeIntegrateState vstate ccl_optional_struct_init;
vstate.start_t = 0.0f;
vstate.end_t = 0.0f;
vstate.absorption_only = true;
vstate.rscatter = path_state_rng_1D(kg, rng_state, PRNG_SCATTER_DISTANCE);
vstate.rphase = path_state_rng_1D(kg, rng_state, PRNG_PHASE_CHANNEL);
/* Multiple importance sampling: pick between equiangular and distance sampling strategy. */
vstate.direct_sample_method = direct_sample_method;
vstate.use_mis = (direct_sample_method == VOLUME_SAMPLE_MIS);
if (vstate.use_mis) {
if (vstate.rscatter < 0.5f) {
vstate.rscatter *= 2.0f;
vstate.direct_sample_method = VOLUME_SAMPLE_DISTANCE;
}
else {
vstate.rscatter = (vstate.rscatter - 0.5f) * 2.0f;
vstate.direct_sample_method = VOLUME_SAMPLE_EQUIANGULAR;
}
}
vstate.equiangular_pdf = 0.0f;
vstate.distance_pdf = 1.0f;
/* Initialize volume integration result. */
const float3 throughput = INTEGRATOR_STATE(state, path, throughput);
result.direct_throughput = throughput;
result.indirect_throughput = throughput;
/* Equiangular sampling: compute distance and PDF in advance. */
if (vstate.direct_sample_method == VOLUME_SAMPLE_EQUIANGULAR) {
result.direct_t = volume_equiangular_sample(
ray, equiangular_light_P, vstate.rscatter, &vstate.equiangular_pdf);
}
# ifdef __DENOISING_FEATURES__
const bool write_denoising_features = (INTEGRATOR_STATE(state, path, flag) &
PATH_RAY_DENOISING_FEATURES);
float3 accum_albedo = zero_float3();
# endif
float3 accum_emission = zero_float3();
for (int i = 0; i < max_steps; i++) {
/* Advance to new position */
vstate.end_t = min(ray->t, (i + steps_offset) * step_size);
const float shade_t = vstate.start_t + (vstate.end_t - vstate.start_t) * step_shade_offset;
sd->P = ray->P + ray->D * shade_t;
/* compute segment */
VolumeShaderCoefficients coeff ccl_optional_struct_init;
if (volume_shader_sample(kg, state, sd, &coeff)) {
const int closure_flag = sd->flag;
/* Evaluate transmittance over segment. */
const float dt = (vstate.end_t - vstate.start_t);
const float3 transmittance = (closure_flag & SD_EXTINCTION) ?
volume_color_transmittance(coeff.sigma_t, dt) :
one_float3();
/* Emission. */
if (closure_flag & SD_EMISSION) {
/* Only write emission before indirect light scatter position, since we terminate
* stepping at that point if we have already found a direct light scatter position. */
if (!result.indirect_scatter) {
const float3 emission = volume_emission_integrate(
&coeff, closure_flag, transmittance, dt);
accum_emission += result.indirect_throughput * emission;
}
}
if (closure_flag & SD_EXTINCTION) {
if ((closure_flag & SD_SCATTER) || !vstate.absorption_only) {
# ifdef __DENOISING_FEATURES__
/* Accumulate albedo for denoising features. */
if (write_denoising_features && (closure_flag & SD_SCATTER)) {
const float3 albedo = safe_divide_color(coeff.sigma_s, coeff.sigma_t);
accum_albedo += result.indirect_throughput * albedo * (one_float3() - transmittance);
}
# endif
/* Scattering and absorption. */
volume_integrate_step_scattering(
sd, ray, equiangular_light_P, coeff, transmittance, vstate, result);
}
else {
/* Absorption only. */
result.indirect_throughput *= transmittance;
result.direct_throughput *= transmittance;
}
/* Stop if nearly all light blocked. */
if (!result.indirect_scatter) {
if (max3(result.indirect_throughput) < VOLUME_THROUGHPUT_EPSILON) {
result.indirect_throughput = zero_float3();
break;
}
}
else if (!result.direct_scatter) {
if (max3(result.direct_throughput) < VOLUME_THROUGHPUT_EPSILON) {
break;
}
}
}
/* If we have scattering data for both direct and indirect, we're done. */
if (result.direct_scatter && result.indirect_scatter) {
break;
}
}
/* Stop if at the end of the volume. */
vstate.start_t = vstate.end_t;
if (vstate.start_t == ray->t) {
break;
}
}
/* Write accumulated emission. */
if (!is_zero(accum_emission)) {
kernel_accum_emission(kg, state, accum_emission, render_buffer);
}
# ifdef __DENOISING_FEATURES__
/* Write denoising features. */
if (write_denoising_features) {
kernel_write_denoising_features_volume(
kg, state, accum_albedo, result.indirect_scatter, render_buffer);
}
# endif /* __DENOISING_FEATURES__ */
}
# ifdef __EMISSION__
/* Path tracing: sample point on light and evaluate light shader, then
* queue shadow ray to be traced. */
ccl_device_forceinline bool integrate_volume_sample_light(
KernelGlobals kg,
IntegratorState state,
ccl_private const ShaderData *ccl_restrict sd,
ccl_private const RNGState *ccl_restrict rng_state,
ccl_private LightSample *ccl_restrict ls)
{
/* Test if there is a light or BSDF that needs direct light. */
if (!kernel_data.integrator.use_direct_light) {
return false;
}
/* Sample position on a light. */
const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
const uint bounce = INTEGRATOR_STATE(state, path, bounce);
float light_u, light_v;
path_state_rng_2D(kg, rng_state, PRNG_LIGHT_U, &light_u, &light_v);
if (!light_distribution_sample_from_volume_segment(
kg, light_u, light_v, sd->time, sd->P, bounce, path_flag, ls)) {
return false;
}
if (ls->shader & SHADER_EXCLUDE_SCATTER) {
return false;
}
return true;
}
/* Path tracing: sample point on light and evaluate light shader, then
* queue shadow ray to be traced. */
ccl_device_forceinline void integrate_volume_direct_light(
KernelGlobals kg,
IntegratorState state,
ccl_private const ShaderData *ccl_restrict sd,
ccl_private const RNGState *ccl_restrict rng_state,
const float3 P,
ccl_private const ShaderVolumePhases *ccl_restrict phases,
ccl_private const float3 throughput,
ccl_private LightSample *ccl_restrict ls)
{
PROFILING_INIT(kg, PROFILING_SHADE_VOLUME_DIRECT_LIGHT);
if (!kernel_data.integrator.use_direct_light) {
return;
}
/* Sample position on the same light again, now from the shading
* point where we scattered.
*
* TODO: decorrelate random numbers and use light_sample_new_position to
* avoid resampling the CDF. */
{
const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
const uint bounce = INTEGRATOR_STATE(state, path, bounce);
float light_u, light_v;
path_state_rng_2D(kg, rng_state, PRNG_LIGHT_U, &light_u, &light_v);
if (!light_distribution_sample_from_position(
kg, light_u, light_v, sd->time, P, bounce, path_flag, ls)) {
return;
}
}
if (ls->shader & SHADER_EXCLUDE_SCATTER) {
return;
}
/* Evaluate light shader.
*
* TODO: can we reuse sd memory? In theory we can move this after
* integrate_surface_bounce, evaluate the BSDF, and only then evaluate
* the light shader. This could also move to its own kernel, for
* non-constant light sources. */
ShaderDataTinyStorage emission_sd_storage;
ccl_private ShaderData *emission_sd = AS_SHADER_DATA(&emission_sd_storage);
const float3 light_eval = light_sample_shader_eval(kg, state, emission_sd, ls, sd->time);
if (is_zero(light_eval)) {
return;
}
/* Evaluate BSDF. */
BsdfEval phase_eval ccl_optional_struct_init;
const float phase_pdf = shader_volume_phase_eval(kg, sd, phases, ls->D, &phase_eval);
if (ls->shader & SHADER_USE_MIS) {
float mis_weight = light_sample_mis_weight_nee(kg, ls->pdf, phase_pdf);
bsdf_eval_mul(&phase_eval, mis_weight);
}
bsdf_eval_mul3(&phase_eval, light_eval / ls->pdf);
/* Path termination. */
const float terminate = path_state_rng_light_termination(kg, rng_state);
if (light_sample_terminate(kg, ls, &phase_eval, terminate)) {
return;
}
/* Create shadow ray. */
Ray ray ccl_optional_struct_init;
light_sample_to_volume_shadow_ray(kg, sd, ls, P, &ray);
const bool is_light = light_sample_is_light(ls);
/* Branch off shadow kernel. */
INTEGRATOR_SHADOW_PATH_INIT(
shadow_state, state, DEVICE_KERNEL_INTEGRATOR_INTERSECT_SHADOW, shadow);
/* Write shadow ray and associated state to global memory. */
integrator_state_write_shadow_ray(kg, shadow_state, &ray);
INTEGRATOR_STATE_ARRAY_WRITE(shadow_state, shadow_isect, 0, object) = ray.self.object;
INTEGRATOR_STATE_ARRAY_WRITE(shadow_state, shadow_isect, 0, prim) = ray.self.prim;
INTEGRATOR_STATE_ARRAY_WRITE(shadow_state, shadow_isect, 1, object) = ray.self.light_object;
INTEGRATOR_STATE_ARRAY_WRITE(shadow_state, shadow_isect, 1, prim) = ray.self.light_prim;
/* Copy state from main path to shadow path. */
const uint16_t bounce = INTEGRATOR_STATE(state, path, bounce);
const uint16_t transparent_bounce = INTEGRATOR_STATE(state, path, transparent_bounce);
uint32_t shadow_flag = INTEGRATOR_STATE(state, path, flag);
shadow_flag |= (is_light) ? PATH_RAY_SHADOW_FOR_LIGHT : 0;
shadow_flag |= (shadow_flag & PATH_RAY_ANY_PASS) ? 0 : PATH_RAY_VOLUME_PASS;
const float3 throughput_phase = throughput * bsdf_eval_sum(&phase_eval);
if (kernel_data.kernel_features & KERNEL_FEATURE_LIGHT_PASSES) {
const packed_float3 pass_diffuse_weight = (bounce == 0) ?
packed_float3(one_float3()) :
INTEGRATOR_STATE(
state, path, pass_diffuse_weight);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, pass_diffuse_weight) = pass_diffuse_weight;
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, pass_glossy_weight) = zero_float3();
}
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, render_pixel_index) = INTEGRATOR_STATE(
state, path, render_pixel_index);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, rng_offset) = INTEGRATOR_STATE(
state, path, rng_offset);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, rng_hash) = INTEGRATOR_STATE(
state, path, rng_hash);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, sample) = INTEGRATOR_STATE(
state, path, sample);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, flag) = shadow_flag;
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, bounce) = bounce;
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, transparent_bounce) = transparent_bounce;
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, diffuse_bounce) = INTEGRATOR_STATE(
state, path, diffuse_bounce);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, glossy_bounce) = INTEGRATOR_STATE(
state, path, glossy_bounce);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, transmission_bounce) = INTEGRATOR_STATE(
state, path, transmission_bounce);
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, throughput) = throughput_phase;
if (kernel_data.kernel_features & KERNEL_FEATURE_SHADOW_PASS) {
INTEGRATOR_STATE_WRITE(shadow_state, shadow_path, unshadowed_throughput) = throughput;
}
integrator_state_copy_volume_stack_to_shadow(kg, shadow_state, state);
}
# endif
/* Path tracing: scatter in new direction using phase function */
ccl_device_forceinline bool integrate_volume_phase_scatter(
KernelGlobals kg,
IntegratorState state,
ccl_private ShaderData *sd,
ccl_private const RNGState *rng_state,
ccl_private const ShaderVolumePhases *phases)
{
PROFILING_INIT(kg, PROFILING_SHADE_VOLUME_INDIRECT_LIGHT);
float phase_u, phase_v;
path_state_rng_2D(kg, rng_state, PRNG_BSDF_U, &phase_u, &phase_v);
/* Phase closure, sample direction. */
float phase_pdf;
BsdfEval phase_eval ccl_optional_struct_init;
float3 phase_omega_in ccl_optional_struct_init;
differential3 phase_domega_in ccl_optional_struct_init;
const int label = shader_volume_phase_sample(kg,
sd,
phases,
phase_u,
phase_v,
&phase_eval,
&phase_omega_in,
&phase_domega_in,
&phase_pdf);
if (phase_pdf == 0.0f || bsdf_eval_is_zero(&phase_eval)) {
return false;
}
/* Setup ray. */
INTEGRATOR_STATE_WRITE(state, ray, P) = sd->P;
INTEGRATOR_STATE_WRITE(state, ray, D) = normalize(phase_omega_in);
INTEGRATOR_STATE_WRITE(state, ray, t) = FLT_MAX;
# ifdef __RAY_DIFFERENTIALS__
INTEGRATOR_STATE_WRITE(state, ray, dP) = differential_make_compact(sd->dP);
INTEGRATOR_STATE_WRITE(state, ray, dD) = differential_make_compact(phase_domega_in);
# endif
// Save memory by storing last hit prim and object in isect
INTEGRATOR_STATE_WRITE(state, isect, prim) = sd->prim;
INTEGRATOR_STATE_WRITE(state, isect, object) = sd->object;
/* Update throughput. */
const float3 throughput = INTEGRATOR_STATE(state, path, throughput);
const float3 throughput_phase = throughput * bsdf_eval_sum(&phase_eval) / phase_pdf;
INTEGRATOR_STATE_WRITE(state, path, throughput) = throughput_phase;
if (kernel_data.kernel_features & KERNEL_FEATURE_LIGHT_PASSES) {
INTEGRATOR_STATE_WRITE(state, path, pass_diffuse_weight) = one_float3();
INTEGRATOR_STATE_WRITE(state, path, pass_glossy_weight) = zero_float3();
}
/* Update path state */
INTEGRATOR_STATE_WRITE(state, path, mis_ray_pdf) = phase_pdf;
INTEGRATOR_STATE_WRITE(state, path, mis_ray_t) = 0.0f;
INTEGRATOR_STATE_WRITE(state, path, min_ray_pdf) = fminf(
phase_pdf, INTEGRATOR_STATE(state, path, min_ray_pdf));
path_state_next(kg, state, label);
return true;
}
/* get the volume attenuation and emission over line segment defined by
* ray, with the assumption that there are no surfaces blocking light
* between the endpoints. distance sampling is used to decide if we will
* scatter or not. */
ccl_device VolumeIntegrateEvent volume_integrate(KernelGlobals kg,
IntegratorState state,
ccl_private Ray *ccl_restrict ray,
ccl_global float *ccl_restrict render_buffer)
{
ShaderData sd;
shader_setup_from_volume(kg, &sd, ray);
/* Load random number state. */
RNGState rng_state;
path_state_rng_load(state, &rng_state);
/* Sample light ahead of volume stepping, for equiangular sampling. */
/* TODO: distant lights are ignored now, but could instead use even distribution. */
LightSample ls ccl_optional_struct_init;
const bool need_light_sample = !(INTEGRATOR_STATE(state, path, flag) & PATH_RAY_TERMINATE);
const bool have_equiangular_sample = need_light_sample &&
integrate_volume_sample_light(
kg, state, &sd, &rng_state, &ls) &&
(ls.t != FLT_MAX);
VolumeSampleMethod direct_sample_method = (have_equiangular_sample) ?
volume_stack_sample_method(kg, state) :
VOLUME_SAMPLE_DISTANCE;
/* Step through volume. */
VOLUME_READ_LAMBDA(integrator_state_read_volume_stack(state, i))
const float step_size = volume_stack_step_size(kg, volume_read_lambda_pass);
/* TODO: expensive to zero closures? */
VolumeIntegrateResult result = {};
volume_integrate_heterogeneous(kg,
state,
ray,
&sd,
&rng_state,
render_buffer,
step_size,
direct_sample_method,
ls.P,
result);
/* Perform path termination. The intersect_closest will have already marked this path
* to be terminated. That will shading evaluating to leave out any scattering closures,
* but emission and absorption are still handled for multiple importance sampling. */
const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
const float probability = (path_flag & PATH_RAY_TERMINATE_IN_NEXT_VOLUME) ?
0.0f :
INTEGRATOR_STATE(state, path, continuation_probability);
if (probability == 0.0f) {
return VOLUME_PATH_MISSED;
}
/* Direct light. */
if (result.direct_scatter) {
const float3 direct_P = ray->P + result.direct_t * ray->D;
result.direct_throughput /= probability;
integrate_volume_direct_light(kg,
state,
&sd,
&rng_state,
direct_P,
&result.direct_phases,
result.direct_throughput,
&ls);
}
/* Indirect light.
*
* Only divide throughput by probability if we scatter. For the attenuation
* case the next surface will already do this division. */
if (result.indirect_scatter) {
result.indirect_throughput /= probability;
}
INTEGRATOR_STATE_WRITE(state, path, throughput) = result.indirect_throughput;
if (result.indirect_scatter) {
sd.P = ray->P + result.indirect_t * ray->D;
if (integrate_volume_phase_scatter(kg, state, &sd, &rng_state, &result.indirect_phases)) {
return VOLUME_PATH_SCATTERED;
}
else {
return VOLUME_PATH_MISSED;
}
}
else {
return VOLUME_PATH_ATTENUATED;
}
}
#endif
ccl_device void integrator_shade_volume(KernelGlobals kg,
IntegratorState state,
ccl_global float *ccl_restrict render_buffer)
{
PROFILING_INIT(kg, PROFILING_SHADE_VOLUME_SETUP);
#ifdef __VOLUME__
/* Setup shader data. */
Ray ray ccl_optional_struct_init;
integrator_state_read_ray(kg, state, &ray);
Intersection isect ccl_optional_struct_init;
integrator_state_read_isect(kg, state, &isect);
/* Set ray length to current segment. */
ray.t = (isect.prim != PRIM_NONE) ? isect.t : FLT_MAX;
/* Clean volume stack for background rays. */
if (isect.prim == PRIM_NONE) {
volume_stack_clean(kg, state);
}
VolumeIntegrateEvent event = volume_integrate(kg, state, &ray, render_buffer);
if (event == VOLUME_PATH_SCATTERED) {
/* Queue intersect_closest kernel. */
INTEGRATOR_PATH_NEXT(DEVICE_KERNEL_INTEGRATOR_SHADE_VOLUME,
DEVICE_KERNEL_INTEGRATOR_INTERSECT_CLOSEST);
return;
}
else if (event == VOLUME_PATH_MISSED) {
/* End path. */
INTEGRATOR_PATH_TERMINATE(DEVICE_KERNEL_INTEGRATOR_SHADE_VOLUME);
return;
}
else {
/* Continue to background, light or surface. */
integrator_intersect_next_kernel_after_volume<DEVICE_KERNEL_INTEGRATOR_SHADE_VOLUME>(
kg, state, &isect, render_buffer);
return;
}
#endif /* __VOLUME__ */
}
CCL_NAMESPACE_END
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