flash怎么制作粒子慢慢增多并组合成文字的动画

var maxNum:int=3;
var mcAry:Array=new Array();
var timer:Timer=new Timer(20);
timer.addEventListener(TimerEvent.TIMER,UpdateView);
stage.addEventListener(MouseEvent.MOUSE_MOVE,MouseMoveEvent);
timer.start();
mc.alpha=0;
function MouseMoveEvent(e:MouseEvent):void
{
for(var i=0;i<maxNum;i++)
{
var color:uint=Math.random()0xffffff;
mcAry.push(new MovieClip());
mcAry[mcAry.length-1].graphics.beginFill(color,1);
mcAry[mcAry.length-1].graphics.drawCircle(0,0,0.5+Math.random()2);
mcAry[mcAry.length-1].graphics.endFill();
mcAry[mcAry.length-1].spd=1+Math.random()2;
addChild(mcAry[mcAry.length-1]);
mcAry[mcAry.length-1].x=this.mouseX;
mcAry[mcAry.length-1].y=this.mouseY;
}
}
function UpdateView(e:TimerEvent):void
{
for(var i:int=0;i<mcAry.length;i++)
{
if(mcAry[i].y<stage.stageHeight+mcAry[i].height)
{
mcAry[i].y+=mcAry[i].spd;
var temp:int=int(Math.random()10000)%3;
if(mc.hitTestPoint(mcAry[i].x,mcAry[i].y,true)==true&&temp==0)
{
mcAry[i].spd=0;
}
}
}
}