package {
          import flash.display.Sprite;
          import flash.display.StageAlign;
          import flash.display.StageScaleMode;
          import flash.events.Event;
          import flash.events.KeyboardEvent;
          import flash.ui.Keyboard;
          import flash.events.MouseEvent;
  
          public class @ax-animation-ch15-Spring3D extends Sprite
          {
                  private var ball:animation_ch15_Ball3D;
                  private var tx:Number;
                  private var ty:Number;
                  private var tz:Number;
                  private var spring:Number = .1;
                  private var friction:Number = .94;
                  private var fl:Number = 250;
                  private var vpX:Number = stage.stageWidth / 2;
                  private var vpY:Number = stage.stageHeight / 2;
                  
                  public function @ax-animation-ch15-Spring3D()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          stage.align = StageAlign.TOP_LEFT;
                          stage.scaleMode = StageScaleMode.NO_SCALE;
                          
                          ball = new animation_ch15_Ball3D();
                          addChild(ball);
                          
                          tx = Math.random() * 500 - 250;
                          ty = Math.random() * 500 - 250;
                          tz = Math.random() * 500
  
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                          stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);
                  }
                  
                  private function onEnterFrame(event:Event):void
                  {
                          var dx:Number = tx - ball.xpos;
                          var dy:Number = ty - ball.ypos;
                          var dz:Number = tz - ball.zpos;
                          ball.vx += dx * spring;
                          ball.vy += dy * spring;
                          ball.vz += dz * spring;
                          ball.xpos += ball.vx;
                          ball.ypos += ball.vy;
                          ball.zpos += ball.vz;
                          ball.vx *= friction;
                          ball.vy *= friction;
                          ball.vz *= friction;
                          
                          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;
                          }
                  }
                  
                  private function onMouseDown(event:MouseEvent):void
                  {
                          tx = Math.random() * 500 - 250;
                          ty = Math.random() * 500 - 250;
                          tz = Math.random() * 500
                  }
          }
  }