เปลี่ยนฟังก์ชัน scrollTo เพื่อให้รูปภาพถัดไป/ก่อนหน้ามาอยู่ตรงกลางแทนที่จะเป็นด้านซ้าย

ตรวจสอบความคิดเห็น // CHANGED ของฉันใน JSFiddle

$(document).ready(function() {
    // cache here reusable elements
    var container = $("#sg-scroll"),
        child = $(".sg-pic_wrap"),
        current;

    // CURRENT ELEMENT CHECK
    function currentElem() {
        // .each() instead of for(i = 0; i < var;i++)
        child.each(function() {

            // these variables must  be updated each time
            // we launch the function, so we cache them inside
            var x = $(this).offset().left,
                w = $(this).width(),
                cW = $('#sg-container').width() / 2; // CHANGED

            if (x < cW && x + w > cW) { // CHANGED
                current = $(this);
            }



        })
    }

    // MOVE TO ELEM
    function scrollTo(elem, width) {
        elem = elem + (width/2) - ($('#sg-container').width()/2); // CHANGED
        container.scrollLeft(elem);
    }


    // CLICK
    container.on("click", function(e) {
        var _w = $(window).width();
        if ((e.pageX) <= (_w / 2)) { // LEFT
            // we only need to check the current element each time we click, not on scroll
            // doing this will result in faster js
            currentElem();
            if (current.prev().length > 0) { // otherwise we get undefined error
                //scrollTo( parseInt((container.scrollLeft()) + (current.prev().offset().left) + 5) );
                scrollTo(container.scrollLeft() + current.prev().position().left, current.prev().width()); // CHANGED
            }
        } else { // RIGHT
            currentElem();
            //scrollTo( parseInt((container.scrollLeft()) + (current.next().offset().left) + 5 ) );
            scrollTo(container.scrollLeft() + current.next().position().left, current.next().width()); // CHANGED
        }
    });


    // CURSOR ...
    container.on("mousemove", function(e) {
        var _w = $(window).width();
        if ((e.pageX) <= (_w / 2)) { // LEFT
            //change cursor here
        } else { // RIGHT
            // or here
        }
    });



}); //document.ready