ボールのイージング3D

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

// forked from _wonder's 複数のボール跳ね返り3D
// forked from _wonder's 跳ね返り3D
// forked from _wonder's ボールを動かす3D
// forked from _wonder's 遠ざかるボール
// forked from _wonder's base
package {
    import flash.display.Sprite;
    import flash.events.Event;
    
    public class Easing3D extends Sprite {
        private var ball:Ball3D;
        private var tx:Number;
        private var ty:Number;
        private var tz:Number;
        private var easing:Number = 0.1;
        private var fl:Number = 250;
        private var vpX:Number = stage.stageWidth / 2;
        private var vpY:Number = stage.stageHeight / 2;
        
        public function Easing3D() {
            init();
        }
        
        private function init():void {
            ball = new Ball3D();
            addChild( ball );
            
            tx = Math.random() * 500 - 250;
            ty = Math.random() * 500 - 250;
            tz = Math.random() * 500;
            
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        
        private function onEnterFrame(e:Event):void {
            var dx:Number = tx - ball.xpos;
            var dy:Number = ty - ball.ypos;
            var dz:Number = tz - ball.zpos;
            ball.xpos += dx * easing;
            ball.ypos += dy * easing;
            ball.zpos += dz * easing;
            
            var dist:Number = Math.sqrt( dx*dx + dy*dy + dz*dz );
            
            if( dist < 1 ){
                tx = Math.random() * 500 - 250;
                ty = Math.random() * 500 - 250;
                tz = Math.random() * 500;
            }
            if( ball.zpos > -fl ){
                var scale:Number = fl / ( fl + ball.zpos );
                ball.scaleX = ball.scaleY = scale;
                ball.x = vpX + ball.xpos * scale;
                ball.y = vpY + ball.ypos * scale;
                ball.visible = true;
            } else {
                ball.visible = false;
            }

        }
    }
}

import flash.display.Sprite;

class Ball3D extends Sprite {
    public var radius:Number;
    public var color:uint;
    public var xpos:Number = 0;
    public var ypos:Number = 0;
    public var zpos:Number = 0;
    public var vx:Number = 0;
    public var vy:Number = 0;
    public var vz:Number = 0;
    public var mass:Number = 1;
    
    public function Ball3D(radius:Number=40, color:uint=0Xff0000){
        this.radius = radius;
        this.color = color;
        init();
    }
    
    public function init():void {
        graphics.lineStyle( 0 );
        graphics.beginFill(color);
        graphics.drawCircle(0, 0, radius);
        graphics.endFill();
    }
}