commit b9bdd278372b200207ee9de1d61c1fceabcbea9f
parent 59b76e8ff5019cafa97baf2eeb4c65c604cb3712
Author: Eduardo Fontana Lazzari <edufonlaz@gmail.com>
Date: Mon, 8 Sep 2025 11:48:51 +0200
Implement spectral computations
The spectral properties implemented in star-phor-input provide the
foundation for wavelength-dependent computations in star-phor. This
commit introduces the structures and functions required for this type of
computation, as well as their integration with some of the functions
exposed by star-phor-input, in order to retrieve spectral properties
during path tracing.
For the data processing required by these computations, the normalized
discrete source emission spectrum provided by sphin is transformed into
a probability density function (PDF) using star-sampling. Each spectrum
is modeled as a piecewise linear function, and the resulting PDF is
included as part of the source_view structure.
Diffstat:
3 files changed, 113 insertions(+), 13 deletions(-)
diff --git a/src/sphor_compute_mvrea.c b/src/sphor_compute_mvrea.c
@@ -44,13 +44,16 @@ compute_MVREA_realization
double* weight/* TODO make this a list in sphor, since we can have multiple
sensors. Each sensor should have its own weight */)
{
+ double concentration = 0;
double ka = 0; /* Absorption coefficient of current volume */
+ double reflectivity = 0; /* Surface reflectivity */
+ double response_function = 0;
+ double sigma_a = 0;
+ double wavelength = 0;
double normal[3] = {0}; /* Geometry normal */
double dir[3] = {0}; /* Current direction in path sampling */
double pos[3] = {0}; /* Current position in path sampling */
double sample[3] = {0};
- double reflectivity = 0; /* Surface reflectivity */
- double response_function = 0;
double s = 0; /* Random number */
enum sphin_brdf_type brdf_type = SPHIN_BRDF_NONE__;
enum sphin_side side_id = SPHIN_SIDE_NONE__;
@@ -61,8 +64,10 @@ compute_MVREA_realization
float range[2] = {0.f, FLT_MAX};
float st[2] = {0}; /* Parametric coordinates of a point in a s3d_primitive */
int i = 0; /* Iterator */
+ size_t j = 0;
size_t triangle_id;
size_t scn_prim_id;
+ size_t prop_rad_count;
struct interface interface = INTERFACE_NULL;
struct s3d_attrib attrib;
struct s3d_hit hit = S3D_HIT_NULL;
@@ -70,10 +75,15 @@ compute_MVREA_realization
struct s3d_primitive src_prim = S3D_PRIMITIVE_NULL;
struct source_view* source_view = NULL;
struct sphin_brdf* brdf = NULL;
+ struct sphin_prop_rad* prop_rad = NULL;
+ struct sphin_scatterer* scatterer = NULL;
struct sphin_sensor_volume* sensor_volume = NULL;
struct sphin_source_surface* source = NULL;
+ struct sphin_spectral_property* abs_cross_sec = NULL;
struct sphin_surface* surface = NULL;
struct sphin_volume* volume = NULL;
+ struct sphin_source_surface_flux_density flux_density
+ = SPHIN_SOURCE_SURFACE_FLUX_DENSITY_NULL;
res_T res = RES_OK;
ASSERT(NULL != sphor);
@@ -94,8 +104,6 @@ compute_MVREA_realization
d3_set_f3(pos, attrib.value);
- /* TODO Sample a wavelength when spectral information available in sphin */
-
res = sphin_config_get_surface
(sphor->config, source_view->sphin_id, &surface);
if (RES_OK != res){ goto error; }
@@ -108,6 +116,15 @@ compute_MVREA_realization
if (RES_OK != res){ goto error; }
d3_normalize(normal, d3_minus(normal, d3_set_f3(normal, attrib.value)));
+ /* Sample a wavelength according to the source emission spectrum */
+ res = sphin_source_surface_get_flux_density(source, &flux_density);
+ if (RES_OK != res){ goto error; }
+
+ if (NULL != flux_density.emission_spectrum) {
+ wavelength = ssp_ranst_piecewise_linear_get
+ (source_view->emission_spectrum_pdf, rng);
+ }
+
/* Sample a direction according to the source direction distribution */
res = source_surface_sample_direction(source, rng, &src_prim, dir);
if (RES_OK != res){ goto error; }
@@ -157,10 +174,33 @@ compute_MVREA_realization
(sphor->config, interface.volumes[side_id], &volume);
if (RES_OK != res){ goto error; }
- res = sphin_volume_get_ka(volume, &ka);
+ /* Get ka corresponding to the current wavelength */
+ res = sphin_volume_get_prop_rad_count(volume, &prop_rad_count);
if (RES_OK != res){ goto error; }
- /* Sample free path length according to the volume absorption coefficent */
+ ka = 0.;
+
+ FOR_EACH(j, 0, prop_rad_count) {
+ res = sphin_volume_get_prop_rad(volume, j, &prop_rad);
+ if (RES_OK != res){ goto error; }
+
+ res = sphin_prop_rad_get_scatterer(prop_rad, &scatterer);
+ if (RES_OK != res){ goto error; }
+
+ res = sphin_scatterer_get_concentration(scatterer, &concentration);
+ if (RES_OK != res){ goto error; }
+
+ res = sphin_scatterer_get_abs_cross_sec(scatterer, &abs_cross_sec);
+ if (RES_OK != res){ goto error; }
+
+ res = sphin_spectral_property_interpolate_at_wavelength
+ (abs_cross_sec, wavelength, SPHIN_INTERPOLATION_LINEAR, &sigma_a);
+ if (RES_OK != res){ goto error; }
+
+ ka += concentration * sigma_a;
+ }
+
+ /* Sample free path length according to volume absorption coefficent */
s = ssp_ran_exp(rng, ka);}
else {
s = FLT_MAX;
diff --git a/src/sphor_sources.c b/src/sphor_sources.c
@@ -100,6 +100,53 @@ error:
}
static res_T
+setup_emission_spectrum_pdf
+ (struct sphor* sphor,
+ struct sphin_surface* surface,
+ struct source_view* source)
+{
+ struct sphin_source_surface* sphin_source = NULL;
+ struct sphin_spectral_property_descriptor spectrum =
+ SPHIN_SPECTRAL_PROPERTY_DESCRIPTOR_NULL;
+ struct sphin_source_surface_flux_density density =
+ SPHIN_SOURCE_SURFACE_FLUX_DENSITY_NULL;
+ res_T res = RES_OK;
+
+ ASSERT(NULL != sphor);
+ ASSERT(NULL != surface);
+ ASSERT(NULL != source);
+
+ SPHIN(surface_get_source(surface, &sphin_source));
+ if(NULL == sphin_source) { res = RES_BAD_ARG; goto error; }
+
+ SPHIN(source_surface_get_flux_density(sphin_source, &density));
+
+ /* TODO Discuss what to do if the spectrum is not given in the config file */
+ if (NULL == density.emission_spectrum) { goto exit; } /* Nothing to do */
+
+ SPHIN(spectral_property_get_desc(density.emission_spectrum, &spectrum));
+
+ res = ssp_ranst_piecewise_linear_create
+ (sphor->allocator, &source->emission_spectrum_pdf);
+ if(RES_OK != res) { goto error; }
+
+ res = ssp_ranst_piecewise_linear_setup
+ (source->emission_spectrum_pdf,
+ spectrum.wavelengths,
+ spectrum.values,
+ spectrum.data_count);
+ if(RES_OK != res) { goto error; }
+
+exit:
+ return res;
+error:
+ if(source->emission_spectrum_pdf != NULL) {
+ SSP(ranst_piecewise_linear_ref_put(source->emission_spectrum_pdf));
+ }
+ goto exit;
+}
+
+static res_T
setup_source_view
(struct sphor* sphor,
const struct sphor_create_args* args,
@@ -132,6 +179,9 @@ setup_source_view
res = setup_geometry_accel_struct(sphor, suniq, S3D_SAMPLE, &source->view);
if (RES_OK != res) { goto error; }
+ res = setup_emission_spectrum_pdf(sphor, surface, source);
+ if (RES_OK != res) { goto error; }
+
exit:
if (NULL != suniq) { SUNIQ(ref_put(suniq)); }
return res;
@@ -149,7 +199,6 @@ register_source_view
struct sphin_surface* surface = NULL;
struct sphin_source_surface* source_surface = NULL;
struct source_view source = SOURCE_VIEW_NULL;
- double power = 0;
res_T res = RES_OK;
ASSERT(NULL != sphor);
@@ -161,9 +210,6 @@ register_source_view
SPHIN(surface_get_source(surface, &source_surface));
ASSERT(NULL != source_surface);
- res = sphin_surface_source_get_power(surface, &power);
- if (RES_OK != res) { goto error; }
-
source.sphin_id = isurface;
res = setup_source_view(sphor, args, surface, suniq_scene, &source);
@@ -225,6 +271,7 @@ setup_source_distrib_power
(struct sphor* sphor,
const struct sphor_create_args* args)
{
+ double power = 0;
size_t i_surface = 0;
size_t surface_count = 0;
struct darray_double powers;
@@ -250,7 +297,6 @@ setup_source_distrib_power
if (RES_OK != res) { goto error; }
if (NULL != source_surface) {
- double power = 0;
res = sphin_surface_source_get_power(surface, &power);
if (RES_OK != res) { goto error; }
res = darray_double_push_back(&powers, &power);
diff --git a/src/sphor_sources.h b/src/sphor_sources.h
@@ -25,6 +25,7 @@
#define SPHOR_SOURCES_H
#include <star/s3d.h>
+#include <star/ssp.h>
#include <rsys/dynamic_array.h>
#include <rsys/dynamic_array_size_t.h>
@@ -37,8 +38,11 @@ struct ssp_rng;
struct source_view {
struct s3d_scene_view* view; /* View of the source */
- struct darray_size_t src2scn; /* Map the prim id of a source to its prim in
- the scene */
+ /* Map the prim id of a source to its prim in the scene */
+ struct darray_size_t src2scn;
+ /* Normalized probability density function derived from emission spectrum */
+ struct ssp_ranst_piecewise_linear* emission_spectrum_pdf;
+
size_t sphin_id; /* Surface identifier in star-phor-input */
};
@@ -67,6 +71,10 @@ source_release
S3D(scene_view_ref_put(source->view));
source->view = NULL;
}
+ if(NULL != source->emission_spectrum_pdf) {
+ SSP(ranst_piecewise_linear_ref_put(source->emission_spectrum_pdf));
+ source->emission_spectrum_pdf = NULL;
+ }
darray_size_t_release(&source->src2scn);
}
@@ -81,6 +89,10 @@ source_copy
dst->sphin_id = src->sphin_id;
S3D(scene_view_ref_get(src->view));
dst->view = src->view;
+ if(src->emission_spectrum_pdf != NULL) {
+ SSP(ranst_piecewise_linear_ref_get(src->emission_spectrum_pdf));
+ dst->emission_spectrum_pdf = src->emission_spectrum_pdf;
+ }
return darray_size_t_copy(&dst->src2scn, &src->src2scn);
}
@@ -94,8 +106,10 @@ source_copy_and_release
dst->sphin_id = src->sphin_id;
dst->view = src->view;
+ dst->emission_spectrum_pdf = src->emission_spectrum_pdf;
src->view = NULL;
+ src->emission_spectrum_pdf = NULL;
return darray_size_t_copy_and_release(&dst->src2scn, &src->src2scn);
}
