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;
  
          public class @ax-animation-ch15-Velocity3D extends Sprite
          {
                  private var ball:animation_ch15_Ball;
                  private var xpos:Number = 0;
                  private var ypos:Number = 0;
                  private var zpos:Number = 0;
                  private var vx:Number = 0;
                  private var vy:Number = 0;
                  private var vz:Number = 0;
                  private var friction:Number = .98;
                  private var fl:Number = 250;
                  private var vpX:Number = stage.stageWidth / 2;
                  private var vpY:Number = stage.stageHeight / 2;
                  
                  public function @ax-animation-ch15-Velocity3D()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          stage.align = StageAlign.TOP_LEFT;
                          stage.scaleMode = StageScaleMode.NO_SCALE;
                          
                          ball = new animation_ch15_Ball();
                          addChild(ball);
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                          stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
                  }
                  
                  private function onEnterFrame(event:Event):void
                  {
                          xpos += vx;
                          ypos += vy;
                          zpos += vz;
                          
                          vx *= friction;
                          vy *= friction;
                          vz *= friction;
                          
                          if(zpos > -fl)
                          {
                                  var scale:Number = fl / (fl + zpos);
                                  ball.scaleX = ball.scaleY = scale;
                                  ball.x = vpX + xpos * scale;
                                  ball.y = vpY + ypos * scale;
                                  ball.visible = true;
                          }
                          else
                          {
                                  ball.visible = false;
                          }
                  }
                  
                  private function onKeyDown(event:KeyboardEvent):void
                  {
                          switch(event.keyCode)
                          {
                                  case Keyboard.UP :
                                  vy -= 1;
                                  break;
                                  
                                  case Keyboard.DOWN :
                                  vy += 1;
                                  break;
                                  
                                  case Keyboard.LEFT :
                                  vx -= 1;
                                  break;
                                  
                                  case Keyboard.RIGHT :
                                  vx += 1;
                                  break;
                                  
                                  case Keyboard.SHIFT :
                                  vz += 1;
                                  break;
                                  
                                  case Keyboard.CONTROL :
                                  vz -= 1;
                                  break;
                                  
                                  default :
                                  break;
                          }
                  }
          }
  }