package
  {
          import flash.display.Sprite;
          import flash.events.Event;
          import flash.events.KeyboardEvent;
          import flash.ui.Keyboard;
          import flash.display.StageAlign;
          import flash.display.StageScaleMode;
          
          public class @ax-animation-ch06-ShipSimFriction extends Sprite
          {
                  private var ship:animation_ch06_Ship;
                  private var vr:Number = 0;
                  private var thrust:Number = 0;
                  private var vx:Number = 0;
                  private var vy:Number = 0;
                  private var friction:Number = 0.97;
                  
                  public function @ax-animation-ch06-ShipSimFriction()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          stage.scaleMode = StageScaleMode.NO_SCALE;
                          stage.align=StageAlign.TOP_LEFT;
                          ship = new animation_ch06_Ship();
                          addChild(ship);
                          ship.x = stage.stageWidth / 2;
                          ship.y = stage.stageHeight / 2;
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                          stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
                          stage.addEventListener(KeyboardEvent.KEY_UP, onKeyUp);
                  }
                  
                  private function onKeyDown(event:KeyboardEvent):void
                  {
                          switch(event.keyCode)
                          {
                                  case Keyboard.LEFT :
                                  vr = -5;
                                  break;
                                  
                                  case Keyboard.RIGHT :
                                  vr = 5;
                                  break;
                                  
                                  case Keyboard.UP :
                                  thrust = 0.2;
                                  ship.draw(true);
                                  break;
                                  
                                  default :
                                  break;
                          }
                  }
                  
                  private function onKeyUp(event:KeyboardEvent):void
                  {
                          vr = 0;
                          thrust = 0;
                          ship.draw(false);
                  }
                  
                  private function onEnterFrame(event:Event):void
                  {
                          ship.rotation += vr;
                          var angle:Number = ship.rotation * Math.PI / 180;
                          var ax:Number = Math.cos(angle) * thrust;
                          var ay:Number = Math.sin(angle) * thrust;
                          vx += ax;
                          vy += ay;
                          vx *= friction;
                          vy *= friction;
                          ship.x += vx;
                          ship.y += vy;
                          var left:Number = 0;
                          var right:Number = stage.stageWidth;
                          var top:Number = 0;
                          var bottom:Number = stage.stageHeight;
                          if (ship.x - ship.width / 2 > right)
                          {
                                  ship.x = left - ship.width / 2;
                          }
                          else if (ship.x + ship.width / 2 < left)
                          {
                                  ship.x = right + ship.width / 2;
                          }
                          if (ship.y - ship.height / 2 > bottom)
                          {
                                  ship.y = top - ship.height / 2;
                          }
                          else if (ship.y < top - ship.height / 2)
                          {
                                  ship.y = bottom + ship.height / 2;
                          }
                  }
          }
  }