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;}}}}