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Fix T39525: cycles volume render difference between branched/non-branched path.

This commit is contained in:
Brecht Van Lommel 2014-04-02 15:41:45 +02:00
parent 7ed9d1b402
commit a58814acf5
Notes: blender-bot 2023-02-14 11:34:30 +01:00 
Referenced by issue #39567, Simple Deform modifier error
Referenced by issue #39525, Cycles: Volume looks different (Path / Branched Path)
1 changed files with 43 additions and 73 deletions
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116
intern/cycles/kernel/kernel_volume.h
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@ -322,7 +322,6 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
int closure_flag = sd->flag;
float t = ray->t;
float3 new_tp;
float3 transmittance;
/* randomly scatter, and if we do t is shortened */
if(closure_flag & SD_SCATTER) {
@ -344,6 +343,7 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
if(xi >= sample_transmittance) {
/* scattering */
float3 pdf;
float3 transmittance;
float sample_t;
/* rescale random number so we can reuse it */
@ -373,20 +373,22 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
}
else {
/* no scattering */
transmittance = volume_color_transmittance(sigma_t, t);
float pdf = (transmittance.x + transmittance.y + transmittance.z) * (1.0f/3.0f);
float3 transmittance = volume_color_transmittance(sigma_t, t);
float pdf = average(transmittance);
new_tp = *throughput * transmittance / pdf;
}
}
else if(closure_flag & SD_ABSORPTION) {
/* absorption only, no sampling needed */
transmittance = volume_color_transmittance(coeff.sigma_a, t);
float3 transmittance = volume_color_transmittance(coeff.sigma_a, t);
new_tp = *throughput * transmittance;
}
/* integrate emission attenuated by extinction */
if(closure_flag & SD_EMISSION) {
float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, t);
float3 sigma_t = coeff.sigma_a + coeff.sigma_s;
float3 transmittance = volume_color_transmittance(sigma_t, ray->t);
float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, ray->t);
path_radiance_accum_emission(L, *throughput, emission, state->bounce);
}
@ -421,19 +423,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
/* compute coefficients at the start */
float t = 0.0f;
/* accumulate these values so we can use a single stratified number to sample */
float3 accum_transmittance = make_float3(1.0f, 1.0f, 1.0f);
float3 accum_sigma_t = make_float3(0.0f, 0.0f, 0.0f);
float3 accum_sigma_s = make_float3(0.0f, 0.0f, 0.0f);
/* cache some constant variables */
float nlogxi;
float xi;
int channel = -1;
bool has_scatter = false;
#if 0
bool second_step = false;
#endif
for(int i = 0; i < max_steps; i++) {
/* advance to new position */
@ -441,12 +436,8 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
float dt = new_t - t;
/* use random position inside this segment to sample shader */
if(new_t == ray->t) {
if(new_t == ray->t)
random_jitter_offset = lcg_step_float(&state->rng_congruential) * dt;
#if 0
second_step = true;
#endif
}
float3 new_P = ray->P + ray->D * (t + random_jitter_offset);
VolumeShaderCoefficients coeff;
@ -468,60 +459,48 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
/* lazily set up variables for sampling */
if(channel == -1) {
float xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
nlogxi = -logf(1.0f - xi);
/* pick random color channel, we use the Veach one-sample
* model with balance heuristic for the channels */
xi = path_state_rng_1D(kg, rng, state, PRNG_SCATTER_DISTANCE);
float rphase = path_state_rng_1D(kg, rng, state, PRNG_PHASE);
channel = (int)(rphase*3.0f);
sd->randb_closure = rphase*3.0f - channel;
}
/* pick random color channel, we use the Veach one-sample
* model with balance heuristic for the channels */
float sample_sigma_t = kernel_volume_channel_get(accum_sigma_t + dt*sigma_t, channel);
/* compute transmittance over full step */
transmittance = volume_color_transmittance(sigma_t, dt);
if(nlogxi < sample_sigma_t) {
/* decide if we will scatter or continue */
float sample_transmittance = kernel_volume_channel_get(transmittance, channel);
if(1.0f - xi >= sample_transmittance) {
/* compute sampling distance */
sample_sigma_t /= new_t;
new_t = nlogxi/sample_sigma_t;
dt = new_t - t; /* todo: apparently negative dt can happen */
transmittance = volume_color_transmittance(sigma_t, dt);
accum_transmittance *= transmittance;
accum_sigma_t = (accum_sigma_t + dt*sigma_t)/new_t;
accum_sigma_s = (accum_sigma_s + dt*sigma_s)/new_t;
/* todo: it's not clear to me that this is correct if we move
* through a color volume, needs verification */
float pdf = dot(accum_sigma_t, accum_transmittance);
new_tp = tp * accum_sigma_s * transmittance * (3.0f / pdf);
float sample_sigma_t = kernel_volume_channel_get(sigma_t, channel);
float new_dt = -logf(1.0f - xi)/sample_sigma_t;
new_t = t + new_dt;
/* transmittance, throughput */
float3 new_transmittance = volume_color_transmittance(sigma_t, new_dt);
float pdf = average(sigma_t * new_transmittance);
new_tp = tp * sigma_s * new_transmittance / pdf;
scatter = true;
}
else {
transmittance = volume_color_transmittance(sigma_t, dt);
/* throughput */
float pdf = average(transmittance);
new_tp = tp * transmittance / pdf;
accum_transmittance *= transmittance;
accum_sigma_t += dt*sigma_t;
accum_sigma_s += dt*sigma_s;
new_tp = tp * transmittance;
/* remap xi so we can reuse it and keep thing stratified */
xi = 1.0f - (1.0f - xi)/sample_transmittance;
}
}
else if(closure_flag & SD_ABSORPTION) {
/* absorption only, no sampling needed */
float3 sigma_a = coeff.sigma_a;
transmittance = volume_color_transmittance(sigma_a, dt);
accum_transmittance *= transmittance;
accum_sigma_t += dt*sigma_a;
new_tp = tp * transmittance;
/* todo: we could avoid computing expf() for each step by summing,
* because exp(a)*exp(b) = exp(a+b), but we still want a quick
* tp_eps check too */
}
/* integrate emission attenuated by absorption */
@ -546,15 +525,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
sd->P = ray->P + new_t*ray->D;
*throughput = tp;
#if 0
/* debugging code to get exact same RNG samples to compare
* homogeneous and heterogeneous sampling results */
if(!second_step)
lcg_step_float(&state->rng_congruential);
#endif
return VOLUME_PATH_SCATTERED;
}
else {
/* accumulate transmittance */
accum_transmittance *= transmittance;
}
}
}
@ -564,13 +540,6 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
break;
}
/* include pdf for volumes with scattering */
if(has_scatter) {
float pdf = (accum_transmittance.x + accum_transmittance.y + accum_transmittance.z);
if(pdf > 0.0f)
tp *= (3.0f/pdf);
}
*throughput = tp;
return VOLUME_PATH_ATTENUATED;
@ -662,6 +631,13 @@ ccl_device void kernel_volume_decoupled_record(KernelGlobals *kg, PathState *sta
/* compute accumulated transmittance */
float3 transmittance = volume_color_transmittance(sigma_t, dt);
/* compute emission attenuated by absorption */
if(closure_flag & SD_EMISSION) {
float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, dt);
accum_emission += accum_transmittance * emission;
}
accum_transmittance *= transmittance;
/* compute pdf for distance sampling */
@ -674,12 +650,6 @@ ccl_device void kernel_volume_decoupled_record(KernelGlobals *kg, PathState *sta
step->closure_flag = closure_flag;
segment->closure_flag |= closure_flag;
/* compute emission attenuated by absorption */
if(closure_flag & SD_EMISSION) {
float3 emission = kernel_volume_emission_integrate(&coeff, closure_flag, transmittance, dt);
accum_emission += accum_transmittance * emission;
}
}
else {
/* store empty step (todo: skip consecutive empty steps) */
@ -788,7 +758,7 @@ ccl_device VolumeIntegrateResult kernel_volume_decoupled_scatter(
/* sample distance and compute transmittance */
float3 distance_pdf;
sample_t = prev_t + kernel_volume_distance_sample(step_t, step->sigma_t, channel, xi, &transmittance, &distance_pdf);
pdf = dot(distance_pdf, step_pdf) * (1.0f/3.0f);
pdf = average(distance_pdf * step_pdf);
}
/* equi-angular sampling */
else {