弹性多个物体

1.构建小球精灵

package 
{
    import flash.display.Sprite;

    public class Ball extends Sprite
    {
        public var radius:Number;
        public var color:uint;
        public var vx:Number=0;
        public var vy:Number=0;

        public function Ball (radius:Number,color:uint)
        {
            this.radius=radius;
            this.color=color;
            Init ();
        }
        public function Init ():void
        {
            graphics.beginFill (color);
            graphics.drawCircle (0,0,radius);
            graphics.endFill ();
        }
    }
}

2.构建两个精灵的弹性动画

package
{
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    
    public class DoubleSpring extends Sprite
    {
        private var ball0:Ball;
        private var ball1:Ball;
        private var ball0Dragging:Boolean=false;
        private var ball1Dragging:Boolean=false;
        private var spring:Number=0.1;
        private var friction:Number=0.8;
        private var springLength:Number=150;
        
        public function DoubleSpring()
        {
            Init();
        }
        private function Init():void
        {
            ball0=new Ball(20,0xFF0000);
            ball0.x=Math.random()*stage.stageWidth;
            ball0.y=Math.random()*stage.stageHeight;
            ball0.addEventListener(MouseEvent.MOUSE_DOWN,MouseDown);
            addChild(ball0);
            
            ball1=new Ball(20,0xFF0000);
            ball1.x=Math.random()*stage.stageWidth;
            ball1.y=Math.random()*stage.stageHeight;
            ball1.addEventListener(MouseEvent.MOUSE_DOWN,MouseDown);
            addChild(ball1);
            
            addEventListener(Event.ENTER_FRAME,EnterFrame);
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUp);
        }
        private function EnterFrame(e:Event):void
        {
            if(!ball0Dragging)
            {
                SpringTo(ball0,ball1);
            }
            if(!ball1Dragging)
            {
                SpringTo(ball1,ball0);
            }
            
            graphics.clear();
            graphics.lineStyle(1);
            graphics.moveTo(ball0.x,ball0.y);
            graphics.lineTo(ball1.x,ball1.y);
        }
        private function SpringTo(ballA:Ball,ballB:Ball):void
        {
            var dx:Number=ballB.x-ballA.x;
            var dy:Number=ballB.y-ballB.y;
            var angle:Number=Math.atan2(dy,dx);
            var targetX:Number=ballB.x-Math.cos(angle)*springLength;
            var targetY:Number=ballB.y-Math.sin(angle)*springLength;
            ballA.vx+=(targetX-ballA.x)*spring;
            ballA.vy+=(targetY-ballA.y)*spring;
            ballA.vx*=friction;
            ballA.vy*=friction;
            ballA.x+=ballA.vx;
            ballA.y+=ballA.vy;    
        }
        private function MouseDown(e:MouseEvent):void
        {
            e.target.startDrag();
            if(e.target==ball0)
            {
                ball0Dragging=true;
            }
            if(e.target==ball1)
            {
                ball1Dragging=true;
            }
        }
        private function MouseUp(e:MouseEvent):void
        {
            ball0.stopDrag();
            ball1.stopDrag();
            ball0Dragging=false;
            ball1Dragging=false;
        }
    }
}