wonderfl本のクルクル回るやつ

/**
 * Copyright plus-tic ( http://wonderfl.net/user/plus-tic )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/xhOi
 */

//wonderfl本を参考に練習中...
package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class BallFollowingMouse extends Sprite {
        private var ballCount:uint = 50;
        private var speed:Number = 0.2;
        public function BallFollowingMouse() {
            for(var i:uint = 0; i<ballCount; i++){
                addChild(new Ball(this, 200));
            }
            addEventListener(Event.ENTER_FRAME, followMouse);
        }
        private function followMouse(eventObject:Event):void{
            dispatchEvent(new BallEvent(BallEvent.FOLLOW, mouseX, mouseY, speed));
        }

    }
}

import flash.display.Sprite;
import flash.display.Graphics;
import flash.events.Event;
class Ball extends Sprite{
    private const deceleration:Number = 0.2;
    private var angle:Number;
    private var radius:Number;
    private var sizeRate:Number = -0.1;
    public function Ball(timeline:Sprite, maxRadius:Number){
        var randomRate:Number = Math.random();
        angle = 2 * Math.PI * Math.random();
        radius = maxRadius * randomRate;
        createBall(randomRate);
        timeline.addEventListener(BallEvent.FOLLOW,follow);
    }
    private function createBall(randomRate:Number):void{
        var myGraphics:Graphics = graphics;
        myGraphics.beginFill(Math.floor(0xFFFFFFFFFFF * randomRate) + 1);
        myGraphics.drawCircle(0,0,radius * sizeRate);
        alpha = 1 - randomRate;
    }
    private function follow(eventObject:BallEvent):void{
        var randomRate:Number = Math.random();
        angle += eventObject.speed;
        angle %= Math.PI * 2;
        var nX:Number = eventObject.targetX + radius * Math.cos(angle);
        var nY:Number = eventObject.targetY + radius * Math.sin(angle);
        x += (nX -x) * deceleration * randomRate;
        y += (nY -y) * deceleration * randomRate;
    }
}

class BallEvent extends Event{
    public static const FOLLOW:String = "follow";
    public var _targetX:Number;
    public var _targetY:Number;
    public var _speed:Number;
    public function get targetX():Number{
        return _targetX;
    }
    public function get targetY():Number{
        return _targetY;
    }
    public function get speed():Number{
        return _speed;
    }
    public function BallEvent(event_str:String, myTargetX:Number, myTargetY:Number, mySpeed:Number) {
        super(event_str);
        _targetX = myTargetX;
        _targetY = myTargetY;
        _speed = mySpeed;
    }
    public override function clone():Event {
        return new BallEvent(type, targetX, targetY, speed);
    }
    public override function toString():String {
        return formatToString("BallEvent", "type", "bubbles", "cancelable", "eventPhase", "targetX", "targetY", "speed");
    }
}