载入外部图片作为背景平铺，MC剧中的步骤

import flash.display.StageAlign;
import flash.display.StageScaleMode;
import flash.events.Event;
import flash.display.Loader;
import flash.net.URLRequest;
import flash.display.Sprite;
import flash.display.BitmapData;
import flash.display.Bitmap;



stage.align = StageAlign.TOP_LEFT;
stage.scaleMode = StageScaleMode.NO_SCALE;
stage.addEventListener(Event.RESIZE, resizeHandler);

stage.dispatchEvent(new Event(Event.RESIZE));
var _rootBackGround:Sprite;
var backImage:MovieClip = new MovieClip();
this.addChild(backImage);

var loader:Loader = new Loader();
loader.load(new URLRequest("bg.jpg"));
loader.contentLoaderInfo.addEventListener(Event.COMPLETE,showLoadResult);

function resizeHandler(e:Event):void
{
	banner.y = stage.stageHeight / 2 - banner.height / 2;
	banner.x = stage.stageWidth / 2 - banner.width / 2;
	trace(banner.x + banner.y);
}

function showLoadResult(event:Event):void
{
	var _bitmap:Bitmap = Bitmap(loader.content);
	var matrix:Matrix = new Matrix(1,0,0,1,this.stage.stageWidth / 2,this.stage.stageHeight / 2);
	var sampleSprite:Sprite = new Sprite();
	sampleSprite.graphics.beginBitmapFill(_bitmap.bitmapData, matrix , true , true);
	sampleSprite.graphics.drawRect(0, 0, 20000, 20000);
	sampleSprite.graphics.endFill();
	backImage.addChild(sampleSprite);
	setChildIndex(backImage,0);

}