[Bf-blender-cvs] [47e7acf] master: Cycles code refactor: minor refactoring and comments for volume code.
Brecht Van Lommel
noreply at git.blender.org
Sat Mar 29 15:33:22 CET 2014
Commit: 47e7acf2313694460297ddfdac1d2a4a851b75ed
Author: Brecht Van Lommel
Date: Sat Mar 29 13:03:49 2014 +0100
https://developer.blender.org/rB47e7acf2313694460297ddfdac1d2a4a851b75ed
Cycles code refactor: minor refactoring and comments for volume code.
===================================================================
M intern/cycles/kernel/kernel_montecarlo.h
M intern/cycles/kernel/kernel_volume.h
===================================================================
diff --git a/intern/cycles/kernel/kernel_montecarlo.h b/intern/cycles/kernel/kernel_montecarlo.h
index 92f3420..af7b727 100644
--- a/intern/cycles/kernel/kernel_montecarlo.h
+++ b/intern/cycles/kernel/kernel_montecarlo.h
@@ -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)
diff --git a/intern/cycles/kernel/kernel_volume.h b/intern/cycles/kernel/kernel_volume.h
index 451d28b..e1682c9 100644
--- a/intern/cycles/kernel/kernel_volume.h
+++ b/intern/cycles/kernel/kernel_volume.h
@@ -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;
}
}
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