void (*expand_bound)( void *user, boxf bound, u32 item_index );
float (*item_centroid)( void *user, u32 item_index, int axis );
void (*item_closest)( void *user, u32 item_index, v3f point, v3f closest );
void (*expand_bound)( void *user, boxf bound, u32 item_index );
float (*item_centroid)( void *user, u32 item_index, int axis );
void (*item_closest)( void *user, u32 item_index, v3f point, v3f closest );