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Cycles code refactor: minor refactoring and comments for volume code.

This commit is contained in:
Brecht Van Lommel 2014-03-29 13:03:49 +01:00
parent 7cb28f41f9
commit 47e7acf231
2 changed files with 54 additions and 16 deletions
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5
intern/cycles/kernel/kernel_montecarlo.h
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@ -131,6 +131,11 @@ ccl_device float power_heuristic_3(float a, float b, float c)
return (a*a)/(a*a + b*b + c*c);
}
ccl_device float max_heuristic(float a, float b)
{
return (a > b)? 1.0f: 0.0f;
}
/* distribute uniform xy on [0,1] over unit disk [-1,1], with concentric mapping
* to better preserve stratification for some RNG sequences */
ccl_device float2 concentric_sample_disk(float u1, float u2)

65
intern/cycles/kernel/kernel_volume.h
View File

@ -16,6 +16,8 @@
CCL_NAMESPACE_BEGIN
/* Events for probalistic scattering */
typedef enum VolumeIntegrateResult {
VOLUME_PATH_SCATTERED = 0,
VOLUME_PATH_ATTENUATED = 1,
@ -193,7 +195,7 @@ ccl_device_noinline void kernel_volume_shadow(KernelGlobals *kg, PathState *stat
/* Equi-angular sampling as in:
* "Importance Sampling Techniques for Path Tracing in Participating Media" */
ccl_device float kernel_volume_equiangular_sample(Ray *ray, float3 sigma_t, float3 light_P, float xi, float3 *transmittance, float *pdf)
ccl_device float kernel_volume_equiangular_sample(Ray *ray, float3 light_P, float xi, float *pdf)
{
float t = ray->t;
@ -205,10 +207,7 @@ ccl_device float kernel_volume_equiangular_sample(Ray *ray, float3 sigma_t, floa
*pdf = D / ((theta_b - theta_a) * (D * D + t_ * t_));
float sample_t = min(t, delta + t_); /* min is only for float precision errors */
*transmittance = volume_color_transmittance(sigma_t, sample_t);
return sample_t;
return min(t, delta + t_); /* min is only for float precision errors */
}
ccl_device float kernel_volume_equiangular_pdf(Ray *ray, float3 light_P, float sample_t)
@ -244,17 +243,27 @@ ccl_device bool kernel_volume_equiangular_light_position(KernelGlobals *kg, Path
return true;
}
ccl_device float kernel_volume_decoupled_equiangular_pdf(KernelGlobals *kg, PathState *state, Ray *ray, RNG *rng, float sample_t)
{
float3 light_P;
if(!kernel_volume_equiangular_light_position(kg, state, ray, rng, &light_P))
return 0.0f;
return kernel_volume_equiangular_pdf(ray, light_P, sample_t);
}
/* Distance sampling */
ccl_device float kernel_volume_distance_sample(Ray *ray, float3 sigma_t, int channel, float xi, float3 *transmittance, float3 *pdf)
ccl_device float kernel_volume_distance_sample(float max_t, float3 sigma_t, int channel, float xi, float3 *transmittance, 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 = kernel_volume_channel_get(sigma_t, channel);
float3 full_transmittance = volume_color_transmittance(sigma_t, ray->t);
float3 full_transmittance = volume_color_transmittance(sigma_t, max_t);
float sample_transmittance = kernel_volume_channel_get(full_transmittance, channel);
float sample_t = min(ray->t, -logf(1.0f - xi*(1.0f - sample_transmittance))/sample_sigma_t);
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 = (sigma_t * *transmittance)/(make_float3(1.0f, 1.0f, 1.0f) - full_transmittance);
@ -266,6 +275,14 @@ ccl_device float kernel_volume_distance_sample(Ray *ray, float3 sigma_t, int cha
return sample_t;
}
ccl_device float3 kernel_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 (sigma_t * transmittance)/(make_float3(1.0f, 1.0f, 1.0f) - full_transmittance);
}
/* Emission */
ccl_device float3 kernel_volume_emission_integrate(VolumeShaderCoefficients *coeff, int closure_flag, float3 transmittance, float t)
@ -328,7 +345,7 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
/* scattering */
if(kernel_data.integrator.volume_homogeneous_sampling == 0 || !kernel_data.integrator.num_all_lights) {
/* distance sampling */
sample_t = kernel_volume_distance_sample(ray, sigma_t, channel, xi, &transmittance, &pdf);
sample_t = kernel_volume_distance_sample(ray->t, sigma_t, channel, xi, &transmittance, &pdf);
}
else {
/* equiangular sampling */
@ -337,11 +354,12 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
if(!kernel_volume_equiangular_light_position(kg, state, ray, rng, &light_P))
return VOLUME_PATH_MISSED;
sample_t = kernel_volume_equiangular_sample(ray, sigma_t, light_P, xi, &transmittance, &equi_pdf);
sample_t = kernel_volume_equiangular_sample(ray, light_P, xi, &equi_pdf);
transmittance = volume_color_transmittance(sigma_t, sample_t);
pdf = make_float3(equi_pdf, equi_pdf, equi_pdf);
}
new_tp = *throughput * coeff.sigma_s * transmittance / ((pdf.x + pdf.y + pdf.z) * (1.0f/3.0f));
new_tp = *throughput * coeff.sigma_s * transmittance / average(pdf);
t = sample_t;
}
else {
@ -362,7 +380,7 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
if(kernel_data.integrator.volume_homogeneous_sampling == 0 || !kernel_data.integrator.num_all_lights) {
/* distance sampling */
sample_t = kernel_volume_distance_sample(ray, sigma_t, channel, xi, &transmittance, &pdf);
sample_t = kernel_volume_distance_sample(ray->t, sigma_t, channel, xi, &transmittance, &pdf);
}
else {
/* equiangular sampling */
@ -371,14 +389,15 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_homogeneous(KernelGloba
if(!kernel_volume_equiangular_light_position(kg, state, ray, rng, &light_P))
return VOLUME_PATH_MISSED;
sample_t = kernel_volume_equiangular_sample(ray, sigma_t, light_P, xi, &transmittance, &equi_pdf);
sample_t = kernel_volume_equiangular_sample(ray, light_P, xi, &equi_pdf);
transmittance = volume_color_transmittance(sigma_t, sample_t);
pdf = make_float3(equi_pdf, equi_pdf, equi_pdf);
}
/* modifiy pdf for hit/miss decision */
pdf *= make_float3(1.0f, 1.0f, 1.0f) - volume_color_transmittance(sigma_t, t);
new_tp = *throughput * coeff.sigma_s * transmittance / ((pdf.x + pdf.y + pdf.z) * (1.0f/3.0f));
new_tp = *throughput * coeff.sigma_s * transmittance / average(pdf);
t = sample_t;
}
else {
@ -442,6 +461,9 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
float nlogxi;
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 */
@ -449,8 +471,12 @@ 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;
@ -488,7 +514,7 @@ ccl_device VolumeIntegrateResult kernel_volume_integrate_heterogeneous(KernelGlo
/* compute sampling distance */
sample_sigma_t /= new_t;
new_t = nlogxi/sample_sigma_t;
dt = new_t - t;
dt = new_t - t; /* todo: apparently negative dt can happen */
transmittance = volume_color_transmittance(sigma_t, dt);
@ -550,6 +576,13 @@ 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;
}
}