跟随鼠标移动的小球

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package 
{
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	/**
	 * ...
	 * @author sofeien
	 */
	public class main extends Sprite 
	{
		public var ball:Sprite = new Sprite();
		public var vx:Number = 0;
		public var vy:Number = 0;
		public var a:Number = 0;
		public var b:Number = 0;
		public var c:Number = 0;
		public var speed:Number = 5;
		public function main()
		{
			addEventListener(Event.ENTER_FRAME,frameHandler);
		}
		public function frameHandler(e:Event):void
		{
			a = mouseX - ball.x;
			b = mouseY - ball.y;
			c = Math.sqrt(a * a + b * b);
			//trace(a,b,c);
			vx = a / c * speed;
			vy = b / c * speed;
			ball.x += vx;
			ball.y += vy;
		}
	}
	
}