Example DB walk tree

This is a simple example program that shows how to walk a geometry database while performing some operation on geometry as it is encountered. In this particular example, we iterate just over regions and simply count them:

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

int incr_region(
    struct db_tree_state *tsp,
    struct db_full_path *pathp,
    const struct rt_comb_internal *combp,
    void *data)
  int *counter = (int*)data;
  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");

  dbip = db_open(argv[1], "r");
  if (dbip == NULL) {
    bu_exit(1, "Unable to open %s\n", argv[1]);

  if (db_dirbuild(dbip) < 0) {
    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));

  if (db_lookup(dbip, argv[2], 1) == NULL) {
    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 );

  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;

If we compile this program and run it on a sample geometry database, we get the following:

# you may need to replace /usr/brlcad with the path to where BRL-CAD is installed on your system
$ gcc -o db_walk_tree_example -I/usr/brlcad/include -I/usr/brlcad/include/brlcad db_walk_tree_example.c -L/usr/brlcad/lib -lrt -lbu

$ ./db_walk_tree_example db/ktank.g tank
Database title is:
Keith's Tank

<... trimmed output ...>
counter is 83