function center_dialog(dialog_id) {
	if (dialog_id == undefined) {
		dialog_id = 'dialog';
	}
	if ($(dialog_id)) {
		var wx_center = window.getSize().x / 2;
		var wy_center = window.getSize().y / 2;
		var dx_center = $(dialog_id).getSize().x / 2;
		var dy_center = $(dialog_id).getSize().y / 2;
		var dialog_container = $(dialog_id).getParent();

		dialog_container
			.setStyle('margin', '0')
			.setStyle('width', '100%')
			.setStyle('height', '100%')
			.setStyle('position', 'fixed')
			.setStyle('z-index', '10')
			.setStyle('top', '0')
			.setStyle('left', '0');

		$(dialog_id)
			.setStyle('position', 'fixed')
			.setStyle('z-index', '11')
			.setStyle('top', wy_center - dy_center)
			.setStyle('left', wx_center - dx_center);
	}
}

function close_dialog(dialog_id) {
	if (dialog_id == undefined) {
		dialog_id = 'dialog';
	}
	if ($(dialog_id)) {
		var dialog_container = $(dialog_id).getParent();
		var dialog_tween = new Fx.Tween($(dialog_id).getParent(), {duration: 1000, transition: Fx.Transitions.Circ.easeOut});
		dialog_tween.start('opacity', 1.0, 0.0).chain(
			function() {
				dialog_container.destroy();
			});
	}
}

function hide_dialog(dialog_id) {
	if (dialog_id == undefined) {
		dialog_id = 'dialog';
	}
	if ($(dialog_id)) {
		var dialog_container = $(dialog_id).getParent();
		var dialog_tween = new Fx.Tween($(dialog_id).getParent(), {duration: 1000, transition: Fx.Transitions.Circ.easeOut});
		dialog_tween.start('opacity', 1.0, 0.0);
	}
}