package {
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.ui.Mouse;
    import flash.ui.MouseCursor;
     
    public class Easing1 extends Sprite {
        private var ball:Ball;
        private var easing:Number=0.15;
        private var targetX:Number=stage.stageWidth/2;
        private var targetY:Number=stage.stageHeight/2;
         
        public function Easing1() {
            trace(targetX,targetY);
            init();
        }
         
        private function init():void {
            ball=new Ball(10)  ;
            ball.x = Math.random() * stage.stageWidth;
            ball.y = Math.random() * stage.stageHeight;
            addChild(ball);
            addEventListener(Event.ENTER_FRAME,EnterFrameHandler);      
             
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDownHandler);      
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
            ball.addEventListener(MouseEvent.MOUSE_OVER,function(){ Mouse.cursor = MouseCursor.HAND;});
             
            //在中心画个十字架
            graphics.lineStyle(1);
            graphics.moveTo(targetX-15,targetY);
            graphics.lineTo(targetX+15,targetY);
            graphics.moveTo(targetX,targetY -15);
            graphics.lineTo(targetX,targetY +15);
             
        }
         
         
        private function EnterFrameHandler(e:Event):void {
            var vx:Number = (targetX - ball.x) * easing; //x轴速度与距离成正比缩小
            var vy:Number = (targetY - ball.y) * easing; //y轴速度与距离成正比缩小     
            ball.x += vx;
            ball.y += vy;
             
            var dx = ball.x - targetX;
            var dy = ball.y - targetY;
            var dist = Math.sqrt(dx*dx + dy*dy);
            //当物体达到目标点时，停止处理，以节省CPU资源           
            if (dist<=1){
                removeEventListener(Event.ENTER_FRAME,EnterFrameHandler);
            }
             
        }
         
        //开始拖动
        private function MouseDownHandler(e:MouseEvent):void{           
            ball.startDrag();
            removeEventListener(Event.ENTER_FRAME,EnterFrameHandler);
             
        }
         
        //停止拖动
        private function MouseUpHandler(e:MouseEvent):void{
            ball.stopDrag();
            addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
            Mouse.cursor = MouseCursor.AUTO;
        }
    }
}