var rot_pc = [] ;
var rot_inc = [] ;

function startRotate(cur_pos_id) {
	switchPos(cur_pos_id) ;
	
	new PeriodicalExecuter(function() {
		switchPos(cur_pos_id) ;
	}, 7) ;
}

function switchPos(cur_pos_id) {
	$A(rot_pc[cur_pos_id]).each(function(cur_pc_id, cur_inc) {
		$("position_"+cur_pos_id+"_"+cur_inc).hide() ;
	}) ;
				
	var cur_id = "position_"+cur_pos_id+"_"+rot_inc[cur_pos_id] ;
	$(cur_id).show() ;

	rot_inc[cur_pos_id] += 1 ;
	
	if (!$("position_"+cur_pos_id+"_"+rot_inc[cur_pos_id])) {
		rot_inc[cur_pos_id] = 0 ;
	}
}