var popupInitialTop = 0;
var popupCurrentTop = popupInitialTop;

function showPopup(id){
	$("#popupContent").html($("#"+id).html());
	displayPopup();
}

function displayPopup(){

	popupInitialTop = getPopupTop();
	
	$("#popupShadow").css("height", $(document).height());
	$("#popupShadow").css("display", "block");
	$("#popupShadow").css("left", 0);
	$("#popupWrapper").css("top", popupInitialTop);
	$("#popupWrapper").css("opacity", 0);
	$("#popupWrapper").css("display", "block");
	$("#popupWrapper").animate({opacity:1}, 300);
	
	$(window).scroll(function(event){
		var popupNewTop = getPopupTop();

		if (Math.abs(popupCurrentTop - popupNewTop) > (($(window).height() - $("#popupWrapper").height()) / 15)) {
			$('#popupWrapper').animate({top: popupNewTop}, 200);
			popupCurrentTop=popupNewTop;
		}
	});
}

function closePopup(){
	$("#popupWrapper").css("opacity", 1);
	$("#popupWrapper").animate({opacity:0}, 300, function(){
		$("#popupShadow").css("display", "none");
		$("#popupWrapper").css("display", "none");
	});
}

function getPopupTop(){
	var top = (($(window).height() - $("#popupContent").height()) / 2) + $(window).scrollTop();
	return top;
}