package
  {
          import flash.display.Sprite;
          import flash.display.StageAlign;
          import flash.display.StageScaleMode;
          import flash.events.Event;
          
          public class @ax-animation-ch06-Friction1 extends Sprite
          {
                  private var ball:animation_ch06_Ball;
                  private var vx:Number = 0;
                  private var vy:Number = 0;
                  private var friction:Number = 0.1;
                  
                  public function @ax-animation-ch06-Friction1()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          stage.scaleMode = StageScaleMode.NO_SCALE;
                          stage.align=StageAlign.TOP_LEFT;
  
                          ball = new animation_ch06_Ball();
                          ball.x = stage.stageWidth / 2;
                          ball.y = stage.stageHeight / 2;
                          vx = Math.random() * 10 - 5;
                          vy = Math.random() * 10 - 5;
                          addChild(ball);
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                  }
                  
                  private function onEnterFrame(event:Event):void
                  {
                    var speed:Number = Math.sqrt(vx * vx + vy * vy);
                    var angle:Number = Math.atan2(vy, vx);
                    if (speed > friction)
                    {
                                  speed -= friction;
                    }
                    else
                    {
                                  speed = 0;
                    }
                    vx = Math.cos(angle) * speed;
                    vy = Math.sin(angle) * speed;
                    ball.x += vx;
                    ball.y += vy;
                  }
          }
  }