trimesh.h

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/*                      T R I M E S H . H
 * BRL-CAD
 *
 * Copyright (c) 2004-2026 United States Government as represented by
 * the U.S. Army Research Laboratory.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * version 2.1 as published by the Free Software Foundation.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this file; see the file named COPYING for more
 * information.
 */
 
/*----------------------------------------------------------------------*/
/* @file trimesh.h */
/** @addtogroup bg_trimesh */
/** @{ */
 
/**
 * @brief
 * Algorithms related to 3D meshes built from triangles.
 */
 
#ifndef BG_TRIMESH_H
#define BG_TRIMESH_H
 
#include "common.h"
#include "vmath.h"
#include "bg/defines.h"
#include "bu/vls.h"
 
__BEGIN_DECLS
 
struct bg_trimesh_halfedge {
    int va, vb;
    int flipped;
};
 
/* every pair of contiguous elements is the start and end vertex index of an edge */
struct bg_trimesh_edges {
    int count;
    int *edges;
};
 
struct bg_trimesh_faces {
    int count;
    int *faces;
};
 
struct bg_trimesh_solid_errors {
    struct bg_trimesh_faces degenerate;
    struct bg_trimesh_edges unmatched;
    struct bg_trimesh_edges excess;
    struct bg_trimesh_edges misoriented;
};
 
#define BG_TRIMESH_EDGES_INIT_NULL {0, NULL}
#define BG_TRIMESH_FACES_INIT_NULL {0, NULL}
#define BG_TRIMESH_SOLID_ERRORS_INIT_NULL {BG_TRIMESH_FACES_INIT_NULL, BG_TRIMESH_EDGES_INIT_NULL, BG_TRIMESH_EDGES_INIT_NULL, BG_TRIMESH_EDGES_INIT_NULL}
 
BG_EXPORT extern void bg_free_trimesh_edges(struct bg_trimesh_edges *edges);
BG_EXPORT extern void bg_free_trimesh_faces(struct bg_trimesh_faces *faces);
BG_EXPORT extern void bg_free_trimesh_solid_errors(struct bg_trimesh_solid_errors *errors);
 
/**
 * Check if a mesh is topologically closed and manifold. True if for
 * every edge, there is exactly one other edge with the same two end
 * vertices.
 */
BG_EXPORT extern int bg_trimesh_manifold_closed(int vcnt, int fcnt, fastf_t *v, int *f);
 
/**
 * Check if a mesh is consistently oriented. True if for every edge
 * that has exactly one matching edge, the two edges have opposite
 * orientations. Note that an open mesh can be oriented, but a
 * non-manifold mesh cannot.
 */
BG_EXPORT extern int bg_trimesh_oriented(int vcnt, int fcnt, fastf_t *v, int *f);
 
/**
 * Check if a mesh is topologically solid. Returns 1 if the mesh is NOT SOLID
 * and 0 if the mesh is SOLID. A SOLID (0) outcome indicates the mesh satisfies
 * all three criteria:  Closed, Manifold, Oriented
 */
BG_EXPORT extern int bg_trimesh_solid(int vcnt, int fcnt, fastf_t *v, int *f, int **bedges);
 
/* The below functions are for use as arguments to error tests. Given
 * a face/edge, they return true if the caller should continue
 * iterating through faces/edges, and false otherwise.
 *
 * The *_exit and *_continue functions just return false and true
 * respectively. The *_gather functions expect the data argument to
 * be a struct bg_trimesh_faces or struct bg_trimesh_edges with
 * pre-allocated members of the correct size and count members set to
 * 0, that they will populate.
 */
typedef int (*bg_face_error_func_t)(int face_idx, void *data);
typedef int (*bg_edge_error_funct_t)(struct bg_trimesh_halfedge *edge, void *data);
 
BG_EXPORT extern int bg_trimesh_face_exit(int face_idx, void *data);
BG_EXPORT extern int bg_trimesh_face_continue(int face_idx, void *data);
BG_EXPORT extern int bg_trimesh_face_gather(int face_idx, void *data);
BG_EXPORT extern int bg_trimesh_edge_exit(struct bg_trimesh_halfedge *edge, void *data);
BG_EXPORT extern int bg_trimesh_edge_continue(struct bg_trimesh_halfedge *edge, void *data);
BG_EXPORT extern int bg_trimesh_edge_gather(struct bg_trimesh_halfedge *edge, void *data);
 
/* These functions return 0 if no instances of the error are found.
 * Otherwise, they return the number of instances of the error found
 * before the error function argument returned false (at least 1).
 */
BG_EXPORT extern int bg_trimesh_degenerate_faces(int num_faces, int *fpoints, bg_face_error_func_t degenerate_func, void *data);
BG_EXPORT extern int bg_trimesh_unmatched_edges(int num_edges, struct bg_trimesh_halfedge *edge_list, bg_edge_error_funct_t error_edge_func, void *data);
BG_EXPORT extern int bg_trimesh_misoriented_edges(int num_edges, struct bg_trimesh_halfedge *edge_list, bg_edge_error_funct_t error_edge_func, void *data);
BG_EXPORT extern int bg_trimesh_excess_edges(int num_edges, struct bg_trimesh_halfedge *edge_list, bg_edge_error_funct_t error_edge_func, void *data);
BG_EXPORT extern int bg_trimesh_solid2(int vcnt, int fcnt, fastf_t *v, int *f, struct bg_trimesh_solid_errors *errors);
BG_EXPORT extern int bg_trimesh_hanging_nodes(int num_vertices, int num_faces, fastf_t *vertices, int *faces, struct bg_trimesh_solid_errors *errors);
 
BG_EXPORT extern struct bg_trimesh_halfedge * bg_trimesh_generate_edge_list(int fcnt, int *f);
 
/**
 * @brief
 * Calculate an axis aligned bounding box (RPP) for a triangle mesh.
 *
 * NOTE:  This routine bounds only those points that are active in the triangle
 * mesh, not all points present in the supplied points array.
 *
 * @param[out] min XYZ coordinate defining the minimum bbox point
 * @param[out] max XYZ coordinate defining the maximum bbox point
 * @param[in] faces array of trimesh faces
 * @param[in] num_faces size of faces array
 * @param[in] p array that holds the points defining the trimesh
 * @param[in] num_pnts size of pnts array
 */
BG_EXPORT extern int
bg_trimesh_aabb(point_t *min, point_t *max, const int *faces, size_t num_faces, const point_t *p, size_t num_pnts);
 
/**
 * @brief
 * Calculate the surface area of a triangle mesh.
 *
 * @param[in] faces array of trimesh faces
 * @param[in] num_faces size of faces array
 * @param[in] p array that holds the points defining the trimesh
 * @param[in] num_pnts size of pnts array
 *
 * @return -1 if error, else area of mesh in millimeters
 */
BG_EXPORT extern fastf_t
bg_trimesh_area(const int *faces, size_t num_faces, const point_t *p, size_t num_pnts);
 
 
/**
 * Calculate the volume enclosed by a closed, consistently-oriented triangle
 * mesh using the divergence theorem (signed-tetrahedra method).
 *
 * The mesh must be closed and consistently oriented (all face normals pointing
 * outward or all inward).  Consistent orientation is guaranteed for meshes
 * that pass bg_trimesh_solid2() with zero unmatched edges.  The function
 * returns the absolute value of the signed result, so it works correctly
 * regardless of whether normals point inward or outward.
 *
 * @param[in] faces  flat array of triangle indices (3 ints per face)
 * @param[in] num_faces  number of triangles
 * @param[in] p  array of vertex positions
 * @param[in] num_pnts  number of vertices
 *
 * @return -1 if inputs are invalid, else volume in cubic millimeters
 */
BG_EXPORT extern fastf_t
bg_trimesh_volume(const int *faces, size_t num_faces, const point_t *p, size_t num_pnts);
 
 
/* Structure holding user-adjustable decimation settings */
struct bg_trimesh_decimation_settings {
    int method;            // Select decimation method to use
    fastf_t feature_size;  // Smallest feature size (mm) to leave undecimated
    fastf_t max_runtime;   // If the decimation takes more than max_runtime seconds, abort
    size_t max_threads;    // Don't use more than max_threads when processing.
    struct bu_vls msgs;    // Messages reported during decimation
};
#define BG_TRIMESH_DECIMATION_METHOD_DEFAULT 0
#define BG_TRIMESH_DECIMATION_SETTINGS_INIT {BG_TRIMESH_DECIMATION_METHOD_DEFAULT, 0.0, 0.0, 0, BU_VLS_INIT_ZERO}
 
/**
 * @brief
 * Decimate a mesh and return the decimated faces.
 *
 * @param[out] ofaces faces array for the new output mesh
 * @param[out] n_ofaces length of ofaces array
 * @param[in] ifaces array of input trimesh
 * @param[in] n_ifaces size of input faces array
 * @param[in] p array that holds the points defining the trimesh
 * @param[in] n_p size of points array
 * @param[in] s decimation settings
 *
 * NOTE: This routine will not produce a points array that includes only the
 * points used in the decimated mesh - to generate that output, use the
 * bg_trimesh_3d_gc routine with the ofaces set produced by this function.
 *
 * @return -1 if error, 0 if successful */
BG_EXPORT extern int bg_trimesh_decimate(int **ofaces, int *n_ofaces,
    int *ifaces, int n_ifaces, point_t *p, int n_p, struct bg_trimesh_decimation_settings *s);
 
 
/* Make an attempt at a trimesh intersection calculator that returns the sets
 * of faces intersecting and inside the other for each mesh. Doesn't attempt
 * a boolean evaluation, just characterizes faces */
BG_EXPORT extern int
bg_trimesh_isect(
    int **faces_inside_1, int *num_faces_inside_1, int **faces_inside_2, int *num_faces_inside_2,
    int **faces_isect_1, int *num_faces_isect_1, int **faces_isect_2, int *num_faces_isect_2,
    int *faces_1, int num_faces_1, point_t *vertices_1, int num_vertices_1,
    int *faces_2, int num_faces_2, point_t *vertices_2, int num_vertices_2);
 
/**
 * @brief
 * Compute vertex normals for a mesh based on the connected faces.
 *
 * @param[out] onorms array of normals - will have the same length as the input points array
 * @param[in] ifaces array of input trimesh
 * @param[in] n_ifaces size of input faces array
 * @param[in] p array that holds the points defining the trimesh
 * @param[in] n_p size of points array
 *
 * NOTE: Any vertex point not used by the triangles in the trimesh will have a
 * zero normal in the onorms array.  This routine does not repack the data to
 * eliminate unused vertices - for that use bg_trimesh_optimize
 *
 * @return -1 if error, 0 if successful */
BG_EXPORT extern int bg_trimesh_normals(vect_t **onorms, int *ifaces, int n_ifaces, point_t *p, int n_p);
 
 
/* Various additional mesh optimization steps that can be enabled
 * NOTE:  If we want to look at exposing the capabilities of something like
 * https://github.com/zeux/meshoptimizer this would be the place to start... */
struct bg_trimesh_optimization_settings {
    int collapse_degenerate;  // Remove degenerate faces
    fastf_t degenerate_edge_length;  // If near zero and collapse_degenerate is set, only collapse triangles with two or more uses of the exact same vertex
    fastf_t max_runtime;   // If the optimization takes more than max_runtime seconds, abort
    size_t max_threads;    // Don't use more than max_threads when processing.
};
 
#define BG_TRIMESH_OPTIMIZATION_SETTINGS_INIT {0, 0.0, 0.0, 0}
 
/**
 * @brief
 * Return trimesh information for a 3D mesh that contains just the date needed
 * to represent in the mesh.  Used to finalize intermediate processing meshes
 * to generate a compact mesh for export or storage.
 *
 * @param[out] ofaces faces array for the new output mesh with new indices based on opnts array.
 * @param[out] n_ofaces length of ofaces array
 * @param[out] opnts compact points array for the new output mesh.
 * @param[out] onorms (optional) compact normals array for the output mesh's points.
 * @param[out] n_opnts length of opnts array.
 * @param[in] ifaces array of input trimesh
 * @param[in] n_ifaces size of input faces array
 * @param[in] ipnts array that holds the points defining the original trimesh
 * @param[in] inorms (optional) array that holds the normals for the mesh vertices
 * @param[in] s (optional) settings to enable various additional processing steps
 *
 * @return -1 if error, number of faces in new trimesh if successful
 */
BG_EXPORT extern int bg_trimesh_optimize(
        int **ofaces, int *n_ofaces,
        point_t **opnts, vect_t **onorms, int *n_opnts,
        const int *ifaces, int n_ifaces,
        const point_t *ipnts, const vect_t *inorms,
        struct bg_trimesh_optimization_settings *s);
 
 
/**
 * @brief
 * Return trimesh information for a planar (2D) mesh that contains just the set
 * of points active in the mesh.
 *
 * @param[out] ofaces faces array for the new output mesh
 * @param[out] n_ofaces length of ofaces array
 * @param[out] opnts points array for the new output mesh
 * @param[out] n_opnts length of opnts array
 * @param[in] ifaces array of input trimesh
 * @param[in] n_ifaces size of input faces array
 * @param[in] ipnts array that holds the points defining the original trimesh
 *
 * @return -1 if error, number of faces in new trimesh if successful (should
 * match the original face count)
 */
BG_EXPORT extern int bg_trimesh_2d_gc(int **ofaces, int *n_ofaces, point2d_t **opnts, int *n_opnts,
        const int *ifaces, int n_ifaces, const point2d_t *ipnts);
 
/**
 * @brief
 * Return trimesh information for a 3D mesh that contains just the set
 * of points active in the mesh.
 *
 * @param[out] ofaces   faces array for the new output mesh.
 * @param[out] opnts    points array for the new output mesh.
 * @param[out] n_opnts  length of opnts array.
 * @param[in] faces     array of input trimesh
 * @param[in] num_faces size of input faces array
 * @param[in] in_pts    holds the points defining the original trimesh
 *
 * @return -1 if error, number of faces in new trimesh if successful (should
 * match the original face count)
 */
BG_EXPORT extern int bg_trimesh_3d_gc(int **ofaces, point_t **opnts, int *n_opnts,
        const int *faces, int num_faces, const point_t *in_pts);
 
/**
 * @brief
 * Return a face set where all topologically connected faces are oriented
 * consistently relative to their neighbors.
 *
 * @param[out] of   faces array for the new output mesh (of==f is valid).
 * @param[in]  f    input set of faces.
 * @param[in]  fcnt input face count
 *
 * @return -1 if error, otherwise return the number of times a face flipping
 * operation was performed
 */
BG_EXPORT extern int
bg_trimesh_sync(int *of, int *f, int fcnt);
 
/**
 * @brief
 * Return a set of face sets where all topologically connected faces are
 * grouped into common sets.
 *
 * @param[out] ofs  array of faces arrays containing the new output face sets.
 * @param[out] ofc  array of face counts for the new output face sets.
 * @param[in]  f    input set of faces.
 * @param[in]  fcnt input face count
 *
 * @return -1 if error, otherwise return the number of face sets created
 */
BG_EXPORT extern int
bg_trimesh_split(int ***ofs, int **ofc, int *f, int fcnt);
 
/**
 * @brief
 * Return a set of face sets where all topologically connected faces are
 * grouped into common sets.
 *
 * @param[in]  fname     plot file name
 * @param[in]  faces     face index array
 * @param[in]  num_faces number of faces
 * @param[in]  pnts      points array
 * @param[in]  num_pnts  number of points
 *
 * @return BRLCAD_ERROR if error, otherwise return BRLCAD_OK
 */
BG_EXPORT extern int
bg_trimesh_2d_plot3(const char *fname, const int *faces, size_t num_faces, const point2d_t *pnts, size_t num_pnts);
 
/**
 * @brief
 * Compare two trimeshes to determine if they (within tolerance) define the
 * same mesh.
 *
 * This is a fairly focused function whose purpose is to spot meshes that have
 * potentially gone through numerical or topological reordering but still
 * define the same volume (for example, meshes that have been rotated or
 * translated and then returned to an origin with PCA.)  By design it does not
 * analyze the differences to report on why two meshes differ - it simply
 * returns a yes/no decision.  Different vertex or face counts are grounds
 * for immediate declaration the meshes differ - no effort is made to look for
 * duplicate vertices or degenerate faces.  Any such clean-ups must be performed
 * before calling this function.
 *
 * The specification of a distance tolerance is used for vertex comparisons.
 * Below the specified threshold, vertices that would otherwise be considered
 * rejection criteria for being different will be considered the same.
 * HOWEVER, that tolerance does NOT merge vertices - rather, when vertices are
 * organized and sorted for comparison the candidate pairing vertices in the
 * arrays are compared using the tolerance.
 *
 * Both vertex positions and face topology must be compatible - faces may use a
 * different starting vertex (i.e. 0->1->2 and 1->2->0 are considered to be the
 * same) but the ordering must be consistent (i.e. 0->2->1 would not be
 * considered the same.)
 *
 * @param[in]  f1       face index array referencing points in p1
 * @param[in]  num_f1   number of faces in f1
 * @param[in]  p1       first points array
 * @param[in]  num_p1   number of points in p1
 * @param[in]  f2       face index array referencing points in p2
 * @param[in]  num_f2   number of faces in f2
 * @param[in]  p2       second points array
 * @param[in]  num_p2   number of points in p2
 * @param[in]  dist_tol distance in mm below which points are considered the same
 *
 * @return 0 if same, otherwise return 1.
 */
BG_EXPORT extern int
bg_trimesh_diff(
        const int *f1, size_t num_f1, const point_t *p1, size_t num_p1,
        const int *f2, size_t num_f2, const point_t *p2, size_t num_p2,
        fastf_t dist_tol
        );
 
/**
 * @brief
 * Generate a hash from the mesh data, using the tolerance parameter to
 * clamp the numerical values.  Both vertex positions and face topology
 * are considered, in a style similar to bg_trimesh_diff.
 *
 * The clamping needed to generate a hash value will increase the chances of
 * two similar meshes having the same hash, but the nature of numerical
 * clamping results in some very close but not exact values clamping in
 * opposite directions.  Without global awareness of all vertex points at play
 * in a database it is not possible to establish a binning that will work for
 * all meshes in the same way (and there are no guarantees it is possible even
 * with that knowledge, strictly speaking.)  For a proper distance-based
 * comparison of two meshes, bg_trimesh_diff should be used rather than
 * comparing hash values.  However, if mesh hash values DO match then the
 * associated meshes should be quite close to being the same geometry per the
 * specified tolerance - and in practice there are situations where we can get
 * enough matching hashes to be useful - trial runs of PCA oriented BoT object
 * grouping on a large database were able to identify matching hashes for
 * about 80% of the cases were bg_trimesh_diff was able to geometrically
 * identify fuzzy matches.
 *
 * Applications for this hash include looking up data associated with meshes
 * via hash keys - if a large majority of duplicate meshes can be spotted in a
 * .g database and indexed this way, it makes it possible to reduce the amount
 * of duplicate data being stored.  It is also possible to associated meshes
 * with their hashes and then use a bg_trimesh_diff result to further map those
 * hashes to unique data copies.
 *
 * TODO - look into whether some form of similarity hash might do better for
 * our purposes here:
 * https://github.com/seomoz/simhash-cpp
 * https://github.com/FALCONN-LIB/FALCONN
 * https://github.com/trendmicro/tlsh
 *
 * @param[in]  f        face index array referencing points in p
 * @param[in]  num_f    number of faces in f
 * @param[in]  p        points array
 * @param[in]  num_p    number of points in p
 * @param[in]  dist_tol tolerance used when clamping points
 *
 * @return the bu_data_hash value of the mesh.
 */
BG_EXPORT extern unsigned long long
bg_trimesh_hash(
        const int *f, size_t num_f, const point_t *p, size_t num_p,
        fastf_t dist_tol
        );
 
 
 
 
/**
 * Options governing triangle mesh repair operations.
 *
 * Repair attempts to produce a closed, consistently-oriented, manifold
 * mesh from a defective input by colocating near-duplicate vertices,
 * removing degenerate / duplicate faces, and filling boundary holes up
 * to the caller-specified size limit.
 */
struct bg_trimesh_repair_opts {
    fastf_t max_hole_area;          /**< Largest hole area (mm^2) eligible for filling; 0 = use percentage */
    fastf_t max_hole_area_percent;  /**< Largest hole area as percentage of total mesh area; ignored when max_hole_area > 0 */
};
 
/** Default repair options: fill holes up to 5% of the total mesh area. */
#define BG_TRIMESH_REPAIR_OPTS_DEFAULT {0.0, 5.0}
 
/**
 * @brief
 * Attempt to repair a non-manifold triangle mesh so that it becomes a
 * closed, consistently-oriented solid.
 *
 * The function:
 *  1. Colocates near-duplicate vertices (epsilon derived from bounding-box
 *     diagonal), removes degenerate and duplicate faces.
 *  2. Removes small disconnected components (< 3% of total surface area).
 *  3. Fills boundary holes whose area is at most the limit set in @p opts.
 *
 * @param[out] ofaces   output face index array (caller must bu_free)
 * @param[out] n_ofaces number of faces in @p ofaces
 * @param[out] opnts    output point array (caller must bu_free)
 * @param[out] n_opnts  number of points in @p opnts
 * @param[in]  ifaces   input face index array (3 ints per face)
 * @param[in]  n_ifaces number of faces in @p ifaces
 * @param[in]  ipnts    input point array
 * @param[in]  n_ipnts  number of points in @p ipnts
 * @param[in]  opts     repair options; NULL uses @c BG_TRIMESH_REPAIR_OPTS_DEFAULT
 *
 * @return  1  input mesh was already solid – @p ofaces / @p opnts are not set
 * @return  0  repair succeeded – caller owns @p ofaces / @p opnts
 * @return -1  error or repair failed to produce a valid result
 */
BG_EXPORT extern int
bg_trimesh_repair(
        int **ofaces, int *n_ofaces,
        point_t **opnts, int *n_opnts,
        const int *ifaces, int n_ifaces,
        const point_t *ipnts, int n_ipnts,
        struct bg_trimesh_repair_opts *opts);
 
 
/**
 * Options governing triangle mesh remeshing operations.
 *
 * Remeshing regenerates the connectivity of a mesh so that its triangles
 * are more uniform in size and shape while preserving the overall surface.
 * The Geogram CVT (Centroidal Voronoi Tessellation) algorithm is used
 * internally.
 */
struct bg_trimesh_remesh_opts {
    int target_count;           /**< Desired vertex count in output; 0 = use count_multiplier */
    fastf_t count_multiplier;   /**< Multiply input vertex count by this to obtain target (default 10.0) */
    fastf_t anisotropy;         /**< Anisotropy weight for surface-normal direction; 0.0 = isotropic remesh (default 0.04) */
    int lloyd_iters;            /**< Number of Lloyd relaxation iterations (default 5) */
    int newton_iters;           /**< Number of Newton iterations for CVT optimization (default 30) */
};
 
/** Default remesh options: 10× input vertex density, moderate anisotropy. */
#define BG_TRIMESH_REMESH_OPTS_DEFAULT {0, 10.0, 0.04, 5, 30}
 
/**
 * @brief
 * Remesh a triangle mesh to improve element quality and/or change density.
 *
 * A Geogram-based pre-repair pass is run on the input before remeshing so
 * that degenerate or near-duplicate geometry does not confuse the CVT solver.
 * The output mesh is a new triangulation of the same surface.
 *
 * @param[out] ofaces   output face index array (caller must bu_free)
 * @param[out] n_ofaces number of faces in @p ofaces
 * @param[out] opnts    output point array (caller must bu_free)
 * @param[out] n_opnts  number of points in @p opnts
 * @param[in]  ifaces   input face index array (3 ints per face)
 * @param[in]  n_ifaces number of faces in @p ifaces
 * @param[in]  ipnts    input point array
 * @param[in]  n_ipnts  number of points in @p ipnts
 * @param[in]  opts     remesh options; NULL uses @c BG_TRIMESH_REMESH_OPTS_DEFAULT
 *
 * @return  0 on success – caller owns @p ofaces / @p opnts
 * @return -1 on error
 */
BG_EXPORT extern int
bg_trimesh_remesh(
        int **ofaces, int *n_ofaces,
        point_t **opnts, int *n_opnts,
        const int *ifaces, int n_ifaces,
        const point_t *ipnts, int n_ipnts,
        struct bg_trimesh_remesh_opts *opts);
 
 
__END_DECLS
 
#endif  /* BG_TRIMESH_H */
/** @} */
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