as3.0 判断圆圈正转还是倒转

import flash.events.MouseEvent;
import flash.display.MovieClip;

var arr:Array=[]

mc.addEventListener(MouseEvent.MOUSE_DOWN,onDown)
function onDown(e:MouseEvent){
    stage.addEventListener(MouseEvent.MOUSE_UP,onUp)
    stage.addEventListener(MouseEvent.MOUSE_MOVE,onMove)
}
function onMove(e:MouseEvent){
    mc.rotation=180/Math.PI*Math.atan2(mouseY-mc.y,mouseX-mc.x)+90
    arr.push(mc.rotation)
    var num:Number=arr[arr.length-1]-arr[arr.length-2]
    if(num>0){
        trace("正转")
    }else{
        trace("倒转")
    }
    if(arr.length>3){
        arr.shift()
    }
}
function onUp(e:MouseEvent){
    stage.removeEventListener(MouseEvent.MOUSE_MOVE,onMove)
    stage.removeEventListener(MouseEvent.MOUSE_UP,onUp)
}