star-phor

commit aba7e50b586998d548fa314d6b90188361a22f4f
parent 430ae867b63ad4aaaf3535edd76d6e6359fb4992
Author: Eduardo Fontana Lazzari <edufonlaz@gmail.com>
Date:   Wed,  9 Jul 2025 14:20:09 +0200

Attach a hit filter function to the global scene view

During path sampling, the hit function is responsible for discarding
ray-geometry intersections that should not be considered valid.

Currently, only self-intersections are discarded. A hit is considered
a self-intersection when the primitive from which the ray originates
is the same as the one it intersects. Self-intersections are usually
detected by comparing the IDs of the primitives, assuming they belong
to the same scene_view.

However, in star-phor, there are multiple scene_views: one containing
all primitives, and one scene_view per source used in sampling.
Therefore, ID comparison is not sufficient. Instead, self-intersections
are detected by comparing the coordinates of the three vertices of the
departing and intersected primitives, which allows filtering out
self-intersections even across different scene_view contexts.

Diffstat:
M
src/sphor_config.c
 | 
67
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 67 insertions(+), 0 deletions(-)
diff --git a/src/sphor_config.c b/src/sphor_config.c
@@ -25,6 +25,7 @@
 #include "sphor.h"
 #include "sphor_c.h"
 
+#include <rsys/float3.h>
 #include <star/sphin.h>
 #include <star/s3d.h>
 #include <star/suniq.h>
@@ -511,6 +512,69 @@ error:
   goto exit;
 }
 
+/* Check if two primitives are geometrically identical by comparing the coordinates
+ * of their vertices. If all vertices have the same positions, return 1; otherwise,
+ * return 0. This function is particularly useful when dealing with configurations
+ * composed of multiple scenes, where primitive IDs may not be reliable.
+ * In cases where primitives are known to belong to the same scene, it is simpler
+ * and more efficient to compare their IDs directly. */
+static int
+are_primitives_coordinates_identical(
+  const struct s3d_primitive* prim0,
+  const struct s3d_primitive* prim1)
+{
+  struct s3d_attrib prim0_pos;
+  struct s3d_attrib prim1_pos;
+  int i, j; /* Iterators */
+  /* Barycentric coordinates corresponding to each one of the vertices in the
+   * primitive */
+  float st[3][2] = {{0,0}, {0,1}, {1,0}};
+
+  ASSERT(NULL != prim0);
+  ASSERT(NULL != prim1);
+
+  FOR_EACH(i, 0, 3) {
+    int equal = 0;
+    s3d_primitive_get_attrib(prim0, S3D_POSITION, st[i], &prim0_pos);
+    FOR_EACH(j, 0, 3) {
+      s3d_primitive_get_attrib(prim1, S3D_POSITION, st[j], &prim1_pos);
+      if (1 == f3_eq(prim0_pos.value, prim1_pos.value)) {
+        equal = 1;
+        break;
+      }
+    }
+    if (1 != equal) {
+      /* vertex i of prim0 does not match any vertex in prim1 -> primitives
+       * vertices are not the same */
+      return 0;
+    }
+  }
+  /* All vertices in prim0 match exactly one vertex in prim1 -> primitives are
+   * the same */
+  return 1;
+}
+
+/* Function attached to the scene view that determines whether a hit is valid.
+ * Returns 0 if the hit is valid, 1 otherwise. */
+static int
+hit_filter_function
+  (const struct s3d_hit* hit,
+   const float pos[3],
+   const float dir[3],
+   const float range[2],
+   void* primitive,
+   void* interface)
+{
+  (void)pos;
+  (void)dir;
+  (void)range;
+  (void)interface;
+
+  struct s3d_primitive* prim = primitive;
+
+  return are_primitives_coordinates_identical(prim, &hit->prim);
+}
+
 /*******************************************************************************
  * Local functions
  ******************************************************************************/
@@ -652,6 +716,9 @@ setup_geometry_accel_struct
   res = s3d_scene_create(device, &scene);
   if (RES_OK != res) { goto error; }
 
+  res = s3d_mesh_set_hit_filter_function(shape, hit_filter_function, NULL);
+  if (RES_OK != res) { goto error; }
+
   res = s3d_scene_attach_shape(scene, shape);
   if (RES_OK != res) { goto error; }