Add MESH geometric object type for arbitrary triangulated 3D surfaces

Implement a new MESH primitive alongside SPHERE, CYLINDER, BLOCK, and
PRISM. A mesh is defined by a vertex array and triangle index array,
with a BVH (bounding volume hierarchy) for O(log N) queries.

Core operations implemented:
- point_in_mesh: ray casting with parity counting and deduplication
- normal_to_mesh: BVH-accelerated closest-face search
- get_mesh_bounding_box: from BVH root node
- get_mesh_volume: divergence theorem (signed tetrahedron volumes)
- intersect_line_segment_with_mesh: for subpixel smoothing integration
- init_mesh: validates geometry, computes normals, fixes winding, builds BVH

BVH uses SAH (surface area heuristic) binned construction with flat
array layout. Ray-triangle intersection uses Moller-Trumbore algorithm.
Closest-point queries use Eberly's algorithm with BVH pruning.

Also adds make_mesh/make_mesh_with_center constructors, mesh
copy/equal/destroy in geom-ctl-io.c, and 11 unit tests covering
point-in, volume, bbox, normals, line-segment intersection, and
comparison against the Block primitive.

Author: Luochenghuang

utils/Makefile.am

@@ -20,13 +20,17 @@ geomtst_SOURCES = geomtst.c
 geomtst_LDADD = libctlgeom.la
 geomtst_CPPFLAGS = -I$(top_srcdir)/src
 
-check_PROGRAMS = test-prism
+check_PROGRAMS = test-prism test-mesh
 
 test_prism_SOURCES = test-prism.c
 test_prism_LDADD   = libctlgeom.la
 test_prism_CPPFLAGS = -I$(top_srcdir)/src
 
-TESTS = test-prism
+test_mesh_SOURCES = test-mesh.c
+test_mesh_LDADD   = libctlgeom.la
+test_mesh_CPPFLAGS = -I$(top_srcdir)/src
+
+TESTS = test-prism test-mesh
 
 dist_man_MANS = gen-ctl-io.1
 

utils/ctlgeom.h

@@ -173,6 +173,15 @@ GEOMETRIC_OBJECT make_slanted_prism_with_center(MATERIAL_TYPE material, vector3
                                         const vector3 *vertices, int num_vertices, double height,
                                         vector3 axis, double sidewall_angle);
 
+// mesh with center computed as centroid of vertices
+GEOMETRIC_OBJECT make_mesh(MATERIAL_TYPE material, const vector3 *vertices, int num_vertices,
+                           const int *triangles, int num_triangles);
+
+// mesh with explicit center (vertices shifted so centroid = center)
+GEOMETRIC_OBJECT make_mesh_with_center(MATERIAL_TYPE material, vector3 center,
+                                       const vector3 *vertices, int num_vertices,
+                                       const int *triangles, int num_triangles);
+
 int vector3_nearly_equal(vector3 v1, vector3 v2, double tolerance);
 
 /**************************************************************************/