AS3 位图切割

package  {
	import flash.display.Bitmap;
	import flash.display.BitmapData;
	import flash.display.Loader;
	import flash.display.LoaderInfo;
	import flash.display.MovieClip;
	import flash.events.Event;
	import flash.events.TimerEvent;
	import flash.geom.Point;
	import flash.geom.Rectangle;
	import flash.net.URLRequest;
	import flash.utils.Timer;
	
	public class Main extends MovieClip {
		var bm:Bitmap;
		var playerDataArr:Array;
		var arrIndex = -1;
		public function Main() {
			// constructor code
			var urlRequest:URLRequest = new URLRequest("player.png");
			var loader:Loader = new Loader();
			loader.contentLoaderInfo.addEventListener(Event.COMPLETE,onComplete);
			loader.load(urlRequest);
			
			
		}
		
		private function onComplete(e:Event):void{
			var l:LoaderInfo = e.target as LoaderInfo;
			this.bm = l.content as Bitmap;
			playerDataArr = bitmapDataSlice(bm.bitmapData,4,4);
			bm.bitmapData = null;
			this.addChild(bm);
			var timer:Timer = new Timer(200,0);
			timer.addEventListener(TimerEvent.TIMER,onWalk);
			timer.start();
		}
		
		private function onWalk(e:TimerEvent):void{
			this.arrIndex++;
			if (arrIndex>3) this.arrIndex = 0;
			this.bm.bitmapData = playerDataArr[0][arrIndex];
			
		}
		//位图切割函数
		private function bitmapDataSlice(sourceBitmapData:BitmapData,rows:uint,column:uint):Array{
			var imgWidth:int = sourceBitmapData.width/column;
			var imgHeight:int = sourceBitmapData.height/rows;
			var bufferArr:Array = new Array();
			
			for(var i=0;i