https://eurogen-ern.eu/wp-content/themes/dante/js/lib/jquery.parallax.min.js

1(function( $ ){
2	var $window = $(window);
3	var windowHeight = $window.height();
4
5	$window.resize(function () {
6		windowHeight = $window.height();
7	});
8
9	$.fn.parallax = function(xpos, speedFactor, outerHeight) {
10		var $this = $(this);
11		var getHeight;
12		var firstTop;
13		var paddingTop = 0;
14		
15		//get the starting position of each element to have parallax applied to it		
16		$this.each(function(){
17		    firstTop = $this.offset().top;
18		});
19
20		if (outerHeight) {
21			getHeight = function(jqo) {
22				return jqo.outerHeight(true);
23			};
24		} else {
25			getHeight = function(jqo) {
26				return jqo.height();
27			};
28		}
29			
30		// setup defaults if arguments aren't specified
31		if (arguments.length < 1 || xpos === null) xpos = "50%";
32		if (arguments.length < 2 || speedFactor === null) speedFactor = 0.1;
33		if (arguments.length < 3 || outerHeight === null) outerHeight = true;
34		
35		// function to be called whenever the window is scrolled or resized
36		function update(){
37			var pos = $window.scrollTop();				
38
39			$this.each(function(){
40				var $element = $(this);
41				var top = $element.offset().top;
42				var height = getHeight($element);
43
44				// Check if totally above or totally below viewport
45				if (top + height < pos || top > pos + windowHeight) {
46					return;
47				}
48
49				$this.css('backgroundPosition', xpos + " " + Math.round((firstTop - pos) * speedFactor) + "px");
50			});
51		}		
52
53		$window.bind('scroll', update).resize(update);
54		update();
55	};
56})(jQuery);