サイン波を利用した上下運動

[swf]/blog/wp-content/uploads/2008/10/Bobbing.swf, 550, 400[/swf]

package 
{
    import flash.display.Sprite;
    import flash.events.Event;

    public class Bobbing extends Sprite{
        private var _ball:Ball;
        private var _angle:Number = 0;
        private var _rangeY:Number = 70;
        private var _speedX:Number = 5;
        private var _speedY:Number = 0.2;
        
        public function Bobbing() {
            init();
        }
        
        private function init():void {
            _ball = new Ball();
            addChild(_ball);
            _ball.x = stage.stageWidth / 2;
            addEventListener(Event.ENTER_FRAME, onEnterFrame, false, 0, true);
        }
        
        private function onEnterFrame(e:Event):void {
            _ball.y = stage.stageHeight / 2 + Math.sin(_angle) * _rangeY;
            _angle += _speedY;
            //ステージの隅まで到達したら跳ね返る
            if (_ball.x > stage.stageWidth - _ball.width/2 || _ball.x < _ball.width/2) {
                _speedX = -_speedX;
            }
            _ball.x += _speedX;
        }
    }
}