int scn_add_object(struct scene *scn, struct object *obj);
int scn_rm_object(struct scene *scn, int idx);
int scn_num_objects(const struct scene *scn);
int scn_add_object(struct scene *scn, struct object *obj);
int scn_rm_object(struct scene *scn, int idx);
int scn_num_objects(const struct scene *scn);