ent_checkpoint *cp = mdl_arritm( &world->ent_checkpoint, next );
ent_gate *gate = mdl_arritm( &world->ent_gate, cp->gate_index );
ent_checkpoint *cp = mdl_arritm( &world->ent_checkpoint, next );
ent_gate *gate = mdl_arritm( &world->ent_gate, cp->gate_index );