二维小球跟随鼠标移动

import flash.display.Sprite;
import flash.events.Event;

//var ball:Ball;
var spring:Number = 0.1;
var gravity:Number = 0.9;
var friction:Number = 0.9;
var vx:Number = 0;
var vy:Number = 0;

//ball=new Ball();
//addChild(ball);
ball.y = stage.stageHeight / 2;
addEventListener(Event.ENTER_FRAME,onEnterFrame);

function onEnterFrame(e:Event):void
{
 var dx:Number = mouseX - ball.x;
 var dy:Number = mouseY - ball.y;
 var ax:Number = dx * spring;
 var ay:Number = dy * spring;
 vx +=  ax;
 vy +=  ay;
 vy +=  gravity;
 vx *=  friction;
 vy *=  friction;
 ball.x +=  vx;
 ball.y +=  vy;
 graphics.clear();
 graphics.lineStyle(1);
 graphics.moveTo(ball.x,ball.y);
 graphics.lineTo(mouseX,mouseY);
}