package
{
	import flash.display.Sprite;
	import flash.display.StageAlign;
	import flash.display.StageScaleMode;
	import flash.events.Event;
	
	public class 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 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;
		}
	}
}