var BackgroundTimer;

function ShowModalBackground() {
	$('modal_background').style.display = '';
	$('modal_table').style.display = '';
	$('modal_background').style.opacity = 0;
	BackgroundTimer = window.setInterval("IncreaseOpacity()", 50);
}

function HideModalBackground() {
	if (BackgroundTimer != null) {
		window.clearInterval(BackgroundTimer);
		BackgroundTimer = null;
	}
	BackgroundTimer = window.setInterval("DecreaseOpacity()", 50);
}

function IncreaseOpacity() {
	var opacity = Element.getOpacity($('modal_background'));
	opacity = opacity + 0.05;
	if (opacity > 0.7) {
		opacity = 0.7;
		window.clearInterval(BackgroundTimer);
	}
	Element.setOpacity($('modal_background'), opacity);
}

function DecreaseOpacity() {
	var opacity = Element.getOpacity($('modal_background'));
	opacity = opacity - 0.1;
	if (opacity < 0) {
		opacity = 0;
		$('modal_background').style.display = 'none';
		$('modal_table').style.display = 'none';
		window.clearInterval(BackgroundTimer);
		BackgroundTimer = null;
	}
	Element.setOpacity($('modal_background'), opacity);
}