var overlay_visible = 0;
function toggle_overlay(textObjId,backgroundImage){
	var style = '';
	if (overlay_visible == 0){
		document.getElementById('overlay').style.backgroundImage = backgroundImage;		
		style = 'visible';		
		overlay_visible = 1;
	} else {
		style = 'hidden';
		overlay_visible = 0;
	}
	document.getElementById('overlay').style.visibility = style;	
	if (document.getElementById(textObjId) != null){
		document.getElementById(textObjId).style.visibility = style;		
	}
}