Cycles: improve sample stratification on area lights for path tracing.
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.
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@ -1013,20 +1013,21 @@ ccl_device_forceinline void triangle_light_sample(KernelGlobals *kg, int prim, i
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/* Light Distribution */
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ccl_device int light_distribution_sample(KernelGlobals *kg, float randt)
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ccl_device int light_distribution_sample(KernelGlobals *kg, float *randu)
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{
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/* this is basically std::upper_bound as used by pbrt, to find a point light or
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/* This is basically std::upper_bound as used by pbrt, to find a point light or
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* triangle to emit from, proportional to area. a good improvement would be to
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* also sample proportional to power, though it's not so well defined with
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* OSL shaders. */
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* arbitrary shaders. */
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int first = 0;
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int len = kernel_data.integrator.num_distribution + 1;
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float r = *randu;
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while(len > 0) {
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int half_len = len >> 1;
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int middle = first + half_len;
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if(randt < kernel_tex_fetch(__light_distribution, middle).x) {
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if(r < kernel_tex_fetch(__light_distribution, middle).x) {
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len = half_len;
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}
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else {
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@ -1035,9 +1036,17 @@ ccl_device int light_distribution_sample(KernelGlobals *kg, float randt)
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}
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}
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/* clamping should not be needed but float rounding errors seem to
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* make this fail on rare occasions */
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return clamp(first-1, 0, kernel_data.integrator.num_distribution-1);
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/* Clamping should not be needed but float rounding errors seem to
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* make this fail on rare occasions. */
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int index = clamp(first-1, 0, kernel_data.integrator.num_distribution-1);
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/* Rescale to reuse random number. this helps the 2D samples within
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* each area light be stratified as well. */
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float distr_min = kernel_tex_fetch(__light_distribution, index).x;
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float distr_max = kernel_tex_fetch(__light_distribution, index+1).x;
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*randu = (r - distr_min)/(distr_max - distr_min);
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return index;
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}
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/* Generic Light */
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@ -1049,7 +1058,6 @@ ccl_device bool light_select_reached_max_bounces(KernelGlobals *kg, int index, i
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}
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ccl_device_noinline bool light_sample(KernelGlobals *kg,
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float randt,
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float randu,
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float randv,
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float time,
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@ -1058,7 +1066,7 @@ ccl_device_noinline bool light_sample(KernelGlobals *kg,
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LightSample *ls)
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{
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/* sample index */
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int index = light_distribution_sample(kg, randt);
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int index = light_distribution_sample(kg, &randu);
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/* fetch light data */
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float4 l = kernel_tex_fetch(__light_distribution, index);
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@ -85,17 +85,16 @@ ccl_device_noinline void kernel_branched_path_surface_connect_light(
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float num_samples_inv = num_samples_adjust/num_samples;
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for(int j = 0; j < num_samples; j++) {
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float light_t = path_branched_rng_1D(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT);
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float light_u, light_v;
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path_branched_rng_2D(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT_U, &light_u, &light_v);
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float terminate = path_branched_rng_light_termination(kg, state->rng_hash, state, j, num_samples);
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/* only sample triangle lights */
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if(kernel_data.integrator.num_all_lights)
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light_t = 0.5f*light_t;
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light_u = 0.5f*light_u;
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LightSample ls;
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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/* Same as above, probability needs to be corrected since the sampling was forced to select a mesh light. */
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if(kernel_data.integrator.num_all_lights)
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ls.pdf *= 2.0f;
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@ -118,13 +117,12 @@ ccl_device_noinline void kernel_branched_path_surface_connect_light(
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}
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else {
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/* sample one light at random */
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float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
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float terminate = path_state_rng_light_termination(kg, state);
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LightSample ls;
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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/* sample random light */
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if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {
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/* trace shadow ray */
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@ -238,7 +236,6 @@ ccl_device_inline void kernel_path_surface_connect_light(KernelGlobals *kg,
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#endif
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/* sample illumination from lights to find path contribution */
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float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
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@ -251,7 +248,7 @@ ccl_device_inline void kernel_path_surface_connect_light(KernelGlobals *kg,
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#endif
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LightSample ls;
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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float terminate = path_state_rng_light_termination(kg, state);
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if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {
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/* trace shadow ray */
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@ -31,7 +31,6 @@ ccl_device_inline void kernel_path_volume_connect_light(
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return;
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/* sample illumination from lights to find path contribution */
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float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
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@ -45,7 +44,7 @@ ccl_device_inline void kernel_path_volume_connect_light(
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light_ray.time = sd->time;
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# endif
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls))
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls))
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{
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float terminate = path_state_rng_light_termination(kg, state);
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if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {
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@ -195,16 +194,15 @@ ccl_device void kernel_branched_path_volume_connect_light(
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for(int j = 0; j < num_samples; j++) {
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/* sample random position on random triangle */
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float light_t = path_branched_rng_1D_for_decision(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT);
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float light_u, light_v;
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path_branched_rng_2D(kg, state->rng_hash, state, j, num_samples, PRNG_LIGHT_U, &light_u, &light_v);
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/* only sample triangle lights */
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if(kernel_data.integrator.num_all_lights)
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light_t = 0.5f*light_t;
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light_u = 0.5f*light_u;
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LightSample ls;
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light_sample(kg, light_t, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
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light_sample(kg, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
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float3 tp = throughput;
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@ -219,7 +217,7 @@ ccl_device void kernel_branched_path_volume_connect_light(
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kernel_assert(result == VOLUME_PATH_SCATTERED);
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/* todo: split up light_sample so we don't have to call it again with new position */
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(kernel_data.integrator.num_all_lights)
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ls.pdf *= 2.0f;
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@ -239,12 +237,11 @@ ccl_device void kernel_branched_path_volume_connect_light(
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}
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else {
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/* sample random position on random light */
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float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
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LightSample ls;
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light_sample(kg, light_t, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
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light_sample(kg, light_u, light_v, sd->time, ray->P, state->bounce, &ls);
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float3 tp = throughput;
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@ -259,7 +256,7 @@ ccl_device void kernel_branched_path_volume_connect_light(
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kernel_assert(result == VOLUME_PATH_SCATTERED);
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/* todo: split up light_sample so we don't have to call it again with new position */
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if(light_sample(kg, light_t, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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if(light_sample(kg, light_u, light_v, sd->time, sd->P, state->bounce, &ls)) {
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/* sample random light */
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float terminate = path_state_rng_light_termination(kg, state);
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if(direct_emission(kg, sd, emission_sd, &ls, state, &light_ray, &L_light, &is_lamp, terminate)) {
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@ -292,7 +292,7 @@ enum PathTraceDimension {
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PRNG_BSDF_U = 0,
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PRNG_BSDF_V = 1,
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PRNG_BSDF = 2,
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PRNG_LIGHT = 3,
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PRNG_UNUSED3 = 3,
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PRNG_LIGHT_U = 4,
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PRNG_LIGHT_V = 5,
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PRNG_LIGHT_TERMINATE = 6,
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@ -81,14 +81,13 @@ ccl_device void kernel_direct_lighting(KernelGlobals *kg,
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if(flag) {
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/* Sample illumination from lights to find path contribution. */
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float light_t = path_state_rng_1D(kg, state, PRNG_LIGHT);
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float light_u, light_v;
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path_state_rng_2D(kg, state, PRNG_LIGHT_U, &light_u, &light_v);
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float terminate = path_state_rng_light_termination(kg, state);
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LightSample ls;
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if(light_sample(kg,
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light_t, light_u, light_v,
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light_u, light_v,
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sd->time,
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sd->P,
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state->bounce,
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