var listenerStageResize:Object = new Object(); listenerStageResize.onResize = function() { if (Stage.width < Stage.height || objectBackground._width <= objectBackground._height) { objectBackground._height = Stage.width / (objectBackground._width / objectBackground._height); objectBackground._width = Stage.width; } else if (Stage.width > Stage.height || objectBackground._width >= objectBackground._height) { objectBackground._width = Stage.height / (objectBackground._height / objectBackground._width); objectBackground._height = Stage.height; } objectBackground._x = (Stage.width / 2) - (objectBackground._width / 2); objectBackground._y = (Stage.height / 2) - (objectBackground._height / 2); }; Stage.addListener(listenerStageResize); // Call the function at the start to ensure the first frame is rendered correctly as well. listenerStageResize.onResize();