forked from bartvdbraak/blender
Fix T39525: cycles volume render difference between branched/non-branched path.
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@ -322,7 +322,6 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
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int closure_flag = sd->flag;
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float t = ray->t;
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float3 new_tp;
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float3 transmittance;
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/* randomly scatter, and if we do t is shortened */
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if(closure_flag & SD_SCATTER) {
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@ -344,6 +343,7 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
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if(xi >= sample_transmittance) {
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/* scattering */
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float3 pdf;
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float3 transmittance;
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float sample_t;
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/* rescale random number so we can reuse it */
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@ -373,20 +373,22 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
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}
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else {
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/* no scattering */
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transmittance = volume_color_transmittance(sigma_t, t);
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float pdf = (transmittance.x + transmittance.y + transmittance.z) * (1.0f/3.0f);
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float3 transmittance = volume_color_transmittance(sigma_t, t);
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float pdf = average(transmittance);
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new_tp = *throughput * transmittance / pdf;
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}
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}
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else if(closure_flag & SD_ABSORPTION) {
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/* absorption only, no sampling needed */
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transmittance = volume_color_transmittance(coeff.sigma_a, t);
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float3 transmittance = volume_color_transmittance(coeff.sigma_a, t);
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new_tp = *throughput * transmittance;
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}
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/* integrate emission attenuated by extinction */
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if(closure_flag & SD_EMISSION) {
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float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, t);
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float3 sigma_t = coeff.sigma_a + coeff.sigma_s;
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float3 transmittance = volume_color_transmittance(sigma_t, ray->t);
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float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, ray->t);
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path_radiance_accum_emission(L, *throughput, emission, state->bounce);
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}
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@ -421,19 +423,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
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/* compute coefficients at the start */
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float t = 0.0f;
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/* accumulate these values so we can use a single stratified number to sample */
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float3 accum_transmittance = make_float3(1.0f, 1.0f, 1.0f);
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float3 accum_sigma_t = make_float3(0.0f, 0.0f, 0.0f);
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float3 accum_sigma_s = make_float3(0.0f, 0.0f, 0.0f);
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/* cache some constant variables */
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float nlogxi;
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float xi;
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int channel = -1;
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bool has_scatter = false;
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#if 0
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bool second_step = false;
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#endif
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for(int i = 0; i < max_steps; i++) {
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/* advance to new position */
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@ -441,12 +436,8 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
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float dt = new_t - t;
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/* use random position inside this segment to sample shader */
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if(new_t == ray->t) {
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if(new_t == ray->t)
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random_jitter_offset = lcg_step_float(&state->rng_congruential) * dt;
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#if 0
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second_step = true;
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#endif
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}
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float3 new_P = ray->P + ray->D * (t + random_jitter_offset);
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VolumeShaderCoefficients coeff;
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@ -468,60 +459,48 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
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/* lazily set up variables for sampling */
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if(channel == -1) {
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float xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
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nlogxi = -logf(1.0f - xi);
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/* pick random color channel, we use the Veach one-sample
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* model with balance heuristic for the channels */
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xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
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float rphase = path_state_rng_1D(kg, rng, state, PRNG_PHASE);
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channel = (int)(rphase*3.0f);
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sd->randb_closure = rphase*3.0f - channel;
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}
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/* pick random color channel, we use the Veach one-sample
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* model with balance heuristic for the channels */
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float sample_sigma_t = kernel_volume_channel_get(accum_sigma_t + dt*sigma_t, channel);
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/* compute transmittance over full step */
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transmittance = volume_color_transmittance(sigma_t, dt);
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if(nlogxi < sample_sigma_t) {
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/* decide if we will scatter or continue */
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float sample_transmittance = kernel_volume_channel_get(transmittance, channel);
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if(1.0f - xi >= sample_transmittance) {
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/* compute sampling distance */
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sample_sigma_t /= new_t;
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new_t = nlogxi/sample_sigma_t;
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dt = new_t - t; /* todo: apparently negative dt can happen */
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transmittance = volume_color_transmittance(sigma_t, dt);
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accum_transmittance *= transmittance;
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accum_sigma_t = (accum_sigma_t + dt*sigma_t)/new_t;
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accum_sigma_s = (accum_sigma_s + dt*sigma_s)/new_t;
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/* todo: it's not clear to me that this is correct if we move
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* through a color volume, needs verification */
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float pdf = dot(accum_sigma_t, accum_transmittance);
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new_tp = tp * accum_sigma_s * transmittance * (3.0f / pdf);
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float sample_sigma_t = kernel_volume_channel_get(sigma_t, channel);
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float new_dt = -logf(1.0f - xi)/sample_sigma_t;
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new_t = t + new_dt;
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/* transmittance, throughput */
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float3 new_transmittance = volume_color_transmittance(sigma_t, new_dt);
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float pdf = average(sigma_t * new_transmittance);
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new_tp = tp * sigma_s * new_transmittance / pdf;
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scatter = true;
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}
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else {
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transmittance = volume_color_transmittance(sigma_t, dt);
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/* throughput */
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float pdf = average(transmittance);
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new_tp = tp * transmittance / pdf;
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accum_transmittance *= transmittance;
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accum_sigma_t += dt*sigma_t;
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accum_sigma_s += dt*sigma_s;
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new_tp = tp * transmittance;
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/* remap xi so we can reuse it and keep thing stratified */
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xi = 1.0f - (1.0f - xi)/sample_transmittance;
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}
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}
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else if(closure_flag & SD_ABSORPTION) {
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/* absorption only, no sampling needed */
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float3 sigma_a = coeff.sigma_a;
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transmittance = volume_color_transmittance(sigma_a, dt);
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accum_transmittance *= transmittance;
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accum_sigma_t += dt*sigma_a;
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new_tp = tp * transmittance;
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/* todo: we could avoid computing expf() for each step by summing,
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* because exp(a)*exp(b) = exp(a+b), but we still want a quick
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* tp_eps check too */
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}
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/* integrate emission attenuated by absorption */
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@ -546,15 +525,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
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sd->P = ray->P + new_t*ray->D;
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*throughput = tp;
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#if 0
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/* debugging code to get exact same RNG samples to compare
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* homogeneous and heterogeneous sampling results */
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if(!second_step)
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lcg_step_float(&state->rng_congruential);
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#endif
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return VOLUME_PATH_SCATTERED;
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}
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else {
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/* accumulate transmittance */
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accum_transmittance *= transmittance;
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}
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}
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}
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@ -564,13 +540,6 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
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break;
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}
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/* include pdf for volumes with scattering */
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if(has_scatter) {
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float pdf = (accum_transmittance.x + accum_transmittance.y + accum_transmittance.z);
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if(pdf > 0.0f)
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tp *= (3.0f/pdf);
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}
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*throughput = tp;
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return VOLUME_PATH_ATTENUATED;
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@ -662,6 +631,13 @@ ccl_device void kernel_volume_decoupled_record(KernelGlobals *kg, PathState *sta
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/* compute accumulated transmittance */
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float3 transmittance = volume_color_transmittance(sigma_t, dt);
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/* compute emission attenuated by absorption */
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if(closure_flag & SD_EMISSION) {
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float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, dt);
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accum_emission += accum_transmittance * emission;
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}
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accum_transmittance *= transmittance;
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/* compute pdf for distance sampling */
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@ -674,12 +650,6 @@ ccl_device void kernel_volume_decoupled_record(KernelGlobals *kg, PathState *sta
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step->closure_flag = closure_flag;
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segment->closure_flag |= closure_flag;
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/* compute emission attenuated by absorption */
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if(closure_flag & SD_EMISSION) {
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float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, dt);
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accum_emission += accum_transmittance * emission;
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}
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}
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else {
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/* store empty step (todo: skip consecutive empty steps) */
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@ -788,7 +758,7 @@ ccl_device VolumeIntegrateResult kernel_volume_decoupled_scatter(
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/* sample distance and compute transmittance */
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float3 distance_pdf;
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sample_t = prev_t + kernel_volume_distance_sample(step_t, step->sigma_t, channel, xi, &transmittance, &distance_pdf);
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pdf = dot(distance_pdf, step_pdf) * (1.0f/3.0f);
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pdf = average(distance_pdf * step_pdf);
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}
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/* equi-angular sampling */
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else {
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