animateBackground-plugin

        (function ($) {
            if (!document.defaultView || !document.defaultView.getComputedStyle) {
                var oldCurCSS = jQuery.curCSS;
                jQuery.curCSS = function (elem, name, force) {
                    if (name === 'background-position') {
                        name = 'backgroundPosition';
                    }
                    if (name !== 'backgroundPosition' || !elem.currentStyle || elem.currentStyle[name]) {
                        return oldCurCSS.apply(this, arguments);
                    }
                    var style = elem.style;
                    if (!force && style && style[name]) {
                        return style[name];
                    }
                    return oldCurCSS(elem, 'backgroundPositionX', force) + ' ' + oldCurCSS(elem, 'backgroundPositionY', force);
                };
            }

            var oldAnim = $.fn.animate;
            $.fn.animate = function (prop) {
                if ('background-position' in prop) {
                    prop.backgroundPosition = prop['background-position'];
                    delete prop['background-position'];
                }
                if ('backgroundPosition' in prop) {
                    prop.backgroundPosition = '(' + prop.backgroundPosition + ')';
                }
                return oldAnim.apply(this, arguments);
            };

            function toArray(strg) {
                strg = strg.replace(/left|top/g, '0px');
                strg = strg.replace(/right|bottom/g, '100%');
                strg = strg.replace(/([0-9\.]+)(\s|\)|$)/g, "$1px$2");
                var res = strg.match(/(-?[0-9\.]+)(px|\%|em|pt)\s(-?[0-9\.]+)(px|\%|em|pt)/);
                return [parseFloat(res[1], 10), res[2], parseFloat(res[3], 10), res[4]];
            }

            $.fx.step.backgroundPosition = function (fx) {
                if (!fx.bgPosReady) {
                    var start = $.curCSS(fx.elem, 'backgroundPosition');

                    if (!start) {//FF2 no inline-style fallback
                        start = '0px 0px';
                    }

                    start = toArray(start);

                    fx.start = [start[0], start[2]];

                    var end = toArray(fx.end);
                    fx.end = [end[0], end[2]];

                    fx.unit = [end[1], end[3]];
                    fx.bgPosReady = true;
                }

                var nowPosX = [];
                nowPosX[0] = ((fx.end[0] - fx.start[0]) * fx.pos) + fx.start[0] + fx.unit[0];
                nowPosX[1] = ((fx.end[1] - fx.start[1]) * fx.pos) + fx.start[1] + fx.unit[1];
                fx.elem.style.backgroundPosition = nowPosX[0] + ' ' + nowPosX[1];
            };
        })(jQuery);

// 
$("#viewBody").animate({ backgroundPosition: '(520px 0)' });