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Cycles: improve sample stratification on area lights for path tracing.

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Previously we used a 1D sequence to select a light, and another 2D sequence
to sample a point on the light. For multiple lights this meant each light
would get a random subset of a 2D stratified sequence, which is not
guaranteed to be stratified anymore.

Now we use only a 2D sequence, split into segments along the X axis, one for
each light. The samples that fall within a segment then each are a stratified
sequence, at least in the limit. So for example for two lights, we split up
the unit square into two segments [0,0.5[ x [0,1[ and [0.5,1[ x [0,1[.

This doesn't make much difference in most scenes, mainly helps if you have a
few large area lights or some types of HDR backgrounds.
This commit is contained in:
Brecht Van Lommel
2017-09-08 01:42:14 +02:00
parent d454a44e96
commit cd6c9e9e5f
5 changed files with 29 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
intern/cycles/kernel/kernel_path_volume.h
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@@ -31,7 +31,6 @@ ccl_device_inline void kernel_path_volume_connect_light(
return;
/* sample illumination from lights to find path contribution */
float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
float light_u, light_v;
path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
@@ -45,7 +44,7 @@ ccl_device_inline void kernel_path_volume_connect_light(
light_ray.time = sd->time;
# endif
if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls))
if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls))
{
float terminate = path_state_rng_light_termination(kg, state);
if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {
@@ -195,16 +194,15 @@ ccl_device void kernel_branched_path_volume_connect_light(
for(int j = 0; j < num_samples; j++) {
/* sample random position on random triangle */
float light_t = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT);
float light_u, light_v;
path_branched_rng_2D(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT_U, &light_u, &light_v);
/* only sample triangle lights */
if(kernel_data.integrator.num_all_lights)
light_t = 0.5f*light_t;
light_u = 0.5f*light_u;
LightSample ls;
light_sample(kg, light_t, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
light_sample(kg, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
float3 tp = throughput;
@@ -219,7 +217,7 @@ ccl_device void kernel_branched_path_volume_connect_light(
kernel_assert(result == VOLUME_PATH_SCATTERED);
/* todo: split up light_sample so we don't have to call it again with new position */
if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
if(kernel_data.integrator.num_all_lights)
ls.pdf *= 2.0f;
@@ -239,12 +237,11 @@ ccl_device void kernel_branched_path_volume_connect_light(
}
else {
/* sample random position on random light */
float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
float light_u, light_v;
path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
LightSample ls;
light_sample(kg, light_t, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
light_sample(kg, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
float3 tp = throughput;
@@ -259,7 +256,7 @@ ccl_device void kernel_branched_path_volume_connect_light(
kernel_assert(result == VOLUME_PATH_SCATTERED);
/* todo: split up light_sample so we don't have to call it again with new position */
if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
/* sample random light */
float terminate = path_state_rng_light_termination(kg, state);
if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {