Code Example: Walking Geometry

BRL-CAD's models are hierarchical. Primitive shapes are combined with boolean operations into more complex shapes, which are in turn built into even more complex shapes with additional operations. Navigating these hierarchies via tree walking is a standard operation in BRL-CAD.

#include "common.h"
#include "raytrace.h"

/* basically this callback function counts how many CSG nodes are underneath
 * a given combination tree hierarchy.
 */
int
incr_region(struct db_tree_state *tsp, struct db_full_path *pathp, const struct rt_comb_internal *combp, genptr_t data)
{
  int *counter = (int*)data;
  bu_log("...incrementing...\n");
  (*counter)++;
  return 0;
}

int
main(int argc, char *argv[])
{
  struct db_i *dbip;
  int counter = 0;
  struct db_tree_state state = rt_initial_tree_state;

  if (argc < 2) {
    bu_exit(0, "need more, db.g obj\n");
  }

  /* open a .g file for reading */
  dbip = db_open(argv[1], "r");
  if (dbip == NULL) {
    bu_exit(1, "Unable to open %s\n", argv[1]);
  }

  /* build a directory of objects */
  if (db_dirbuild(dbip) < 0) {
    db_close(dbip);
    bu_exit(1, "Unable to load %s\n", argv[1]);
  }

  bu_log("Database title is:\n%s\n", dbip->dbi_title);
  bu_log("Units: %s\n", bu_units_string(dbip->dbi_local2base));

  /* load a particular combination object */
  if (db_lookup(dbip, argv[2], 1) == NULL) {
    db_close(dbip);
    bu_exit(1, "Unable to find %s\n", argv[2]);
  }

  state.ts_dbip = dbip;
  state.ts_resp = &rt_uniresource;
  rt_init_resource( &rt_uniresource, 0, NULL );

  /* walk that combination object's hierarchy,
   * calling our incr_region() callback function.
   * we pass a pointer to our counter variable.
   */
  db_walk_tree(dbip, 1, (const char **)argv+2, 1, &state, incr_region, NULL, NULL, &counter);

  bu_log("counter is %d\n", counter);

  return 0;
}