https://www.howtopay.com/js/parallaxie.js

1/*! Copyright (c) 2016 THE ULTRASOFT (http://theultrasoft.com)
2 * Licensed under the MIT License (LICENSE.txt).
3 *
4 * Project: Parallaxie
5 * Version: 0.5
6 *
7 * Requires: jQuery 1.9+
8 */
9
10(function( $ ){
11	"use strict";
12    $.fn.parallaxie = function( options ){
13
14        var options = $.extend({
15            speed: 0.2,
16            repeat: 'no-repeat',
17            size: 'cover',
18            pos_x: 'center',
19            offset: 0,
20        }, options );
21
22        this.each(function(){
23
24            var $el = $(this);
25            var local_options = $el.data('parallaxie');
26            if( typeof local_options !== 'object' ) local_options = {};
27            local_options = $.extend( {}, options, local_options );
28
29            var image_url = $el.data('image');
30            if( typeof image_url === 'undefined' ){
31                image_url = $el.css('background-image');
32                if( !image_url ) return;
33
34                // APPLY DEFAULT CSS
35                var pos_y =  local_options.offset + ($el.offset().top - $(window).scrollTop()) * (1 - local_options.speed );
36                $el.css({
37                    'background-image': image_url,
38                    'background-size': local_options.size,
39                    'background-repeat': local_options.repeat,
40                    'background-attachment': 'fixed',
41                    'background-position': local_options.pos_x + ' ' + pos_y + 'px',
42                });
43
44                $(window).scroll( function(){
45                        //var pos_y = - ( $(window).scrollTop() - $el.offset().top ) * ( 1 + local_options.speed ) - ( $el.offset().top * local_options.speed );
46                        var pos_y =  local_options.offset + ($el.offset().top - $(window).scrollTop()) * (1 - local_options.speed );
47                        $el.data( 'pos_y', pos_y );
48                        $el.css( 'background-position', local_options.pos_x + ' ' + pos_y + 'px' );
49                    }
50                );
51            }
52        });
53        return this;
54    };
55}( jQuery ));