function ImageRotation() {
    // options
    var scrollType = 'vertical'; // 'horizontal', 'vertical', 'none';

    // private
    var currentNumber = 0;
    var objWrap = null;
    var objContentBox = null;
    var objWrapLIs = null;
    var cellWidth = 0;
    var cellHeight = 0;
    this.GoodsSetTime = null;

    // scroll animation variables.
    var scroll = { time: 1, start: 0, change: 0, duration: 25, timer: null };
    var originaltime = scroll.time;

    this.setScrollType = function(type) {
        switch (type) {
            case 'vertical':
            case 'horizontal':
            case 'none':
                scrollType = type;
                break;
            default:
                alert('!');
                break;
        }
    }
    // constructor
    this.initialize = function() {
        objWrap = document.getElementById(this.wrapId);
        objContentBox = document.getElementById(this.listId);
        objWrapLIs = objWrap.getElementsByTagName('li');
        cellWidth = objWrapLIs[0].offsetWidth;
        cellHeight = objWrapLIs[0].offsetHeight;

        objWrap.style.overflow = 'hidden'; //

        switch (scrollType) {
            case 'vertical':
                this.objWrapSize = cellHeight * this.listNum;
                this.objSize = objWrapLIs.length * cellHeight;
                break;
            case 'none':
                this.objWrapSize = cellWidth * this.listNum;
                this.objSize = objWrapLIs.length * cellWidth;
                break;
            default:
                this.objWrapSize = cellWidth * this.listNum;
                this.objSize = objWrapLIs.length * cellWidth;
                break;
        }

        if (this.objWrapSize < this.objSize) {

            if (objWrapLIs.length > 0) {
                switch (scrollType) {
                    case 'vertical':
                        objContentBox.style.height = objWrapLIs.length * cellHeight + 'px';
                        //objWrap.style.height = this.listNum * cellHeight + 'px';
                        break;
                    case 'none':
                        objContentBox.style.width = objWrapLIs.length * cellWidth + 'px';
                        objWrap.style.width = this.listNum * cellWidth + 'px';
                        break;
                    default:
                        objContentBox.style.width = objWrapLIs.length * cellWidth + 'px';
                        objWrap.style.width = this.listNum * cellWidth + 'px';
                        break;
                }
            }
            
            if (this.btnPrev)
                document.getElementById(this.btnPrev).href = "javascript:" + this.objName + ".prev();";
            if (this.btnNext)
                document.getElementById(this.btnNext).href = "javascript:" + this.objName + ".next();";

            if (this.autoScroll == 'none') {
            } else {
                if (this.scrollDirection == 'direction') {
                    this.GoodsSetTime = setInterval(this.objName + ".next()", this.scrollGap);
                } else {
                    this.GoodsSetTime = setInterval(this.objName + ".prev()", this.scrollGap);
                }
            }
        }
    }

    this.next = function() {

        if (currentNumber == objWrapLIs.length - 1) {
            var objLastNode = objContentBox.removeChild(objContentBox.getElementsByTagName('li').item(0));
            objContentBox.appendChild(objLastNode);
            switch (scrollType) {
                case 'vertical':
                    objWrap.scrollTop -= cellHeight;
                    break;
                case 'none':
                    objWrap.scrollLeft -= cellWidth;
                    break;
                default:
                    objWrap.scrollLeft -= cellWidth;
                    break;
            }
            currentNumber--;

        }

        //objWrap.scrollLeft += cellWidth;
        var position = getActionPoint('direct');
        startScroll(position.start, position.end);

        currentNumber = currentNumber + 1;

        if (currentNumber < objWrapLIs.length - 1)
            currentNumber = objWrapLIs.length - 1;

        if (this.autoScroll == 'none') {
            // do nothing.
        } else {
            this.scrollDirection = 'indirection';
            clearInterval(this.GoodsSetTime);
            this.GoodsSetTime = setInterval(this.objName + ".next()", this.scrollGap);
        }
    }

    this.prev = function() {
        if (currentNumber == 0) {
            var objLastNode = objContentBox.removeChild(objContentBox.getElementsByTagName('li').item(objWrapLIs.length - 1));
            objContentBox.insertBefore(objLastNode, objContentBox.getElementsByTagName('li').item(0));
            switch (scrollType) {
                case 'vertical':
                    objWrap.scrollTop += cellHeight;
                    break;
                case 'none':
                    objWrap.scrollLeft += cellWidth;
                    break;
                default:
                    objWrap.scrollLeft += cellWidth;
                    break;
            }
            currentNumber++;

        }

        //objWrap.scrollLeft -= cellWidth;
        var position = getActionPoint('indirect');
        startScroll(position.start, position.end);

        currentNumber = currentNumber - 1;

        if (currentNumber > 0)
            currentNumber = 0;
        if (this.autoScroll == 'none') {
            // do nothing.
        } else {
            this.scrollDirection = 'direction';
            clearInterval(this.GoodsSetTime);
            this.GoodsSetTime = setInterval(this.objName + ".prev()", this.scrollGap);
        }
    }

    var startScroll = function(start, end) {
        if (scroll.timer != null) {
            clearInterval(scroll.timer);
            scroll.timer = null;
        }

        scroll.start = start;
        scroll.change = end - start;

        switch (scrollType) {
            case 'vertical':
                scroll.timer = setInterval(scrollVertical, 15);
                break;
            case 'none':
                objWrap.scrollLeft = end;
                break;
            default:
                scroll.timer = setInterval(scrollHorizontal, 15);
                break;
        }
    }

    var scrollVertical = function() {
        if (scroll.time > scroll.duration) {
            clearInterval(scroll.timer);
            scroll.time = originaltime;
            scroll.timer = null;
        } else {
            objWrap.scrollTop = sineInOut(scroll.time, scroll.start, scroll.change, scroll.duration);
            scroll.time++;
        }
    }

    var scrollHorizontal = function() {
        if (scroll.time > scroll.duration) {
            clearInterval(scroll.timer);
            scroll.time = originaltime;
            scroll.timer = null;
        } else {
            objWrap.scrollLeft = sineInOut(scroll.time, scroll.start, scroll.change, scroll.duration);
            scroll.time++;
        }
    }

    var getActionPoint = function(dir) {
        if (dir == 'direct') {
            var position = findElementPos(objWrap.getElementsByTagName('li').item(currentNumber + 1)); // target image.
            var offsetPos = findElementPos(objWrap.getElementsByTagName('li').item(currentNumber)); // first image.
        } else {
            var position = findElementPos(objWrap.getElementsByTagName('li').item(currentNumber - 1)); // target image.
            var offsetPos = findElementPos(objWrap.getElementsByTagName('li').item(currentNumber)); // first image.
        }

        switch (scrollType) {
            case 'vertical':
                var start = objWrap.scrollTop;
                var end = position[1] - offsetPos[1];
                break;
            case 'none':
                // do nothing.
                break;
            default:
                var start = objWrap.scrollLeft;
                var end = position[0] - offsetPos[0];
                break;
        }

        var position = { start: 0, end: 0 };
        position.start = start;
        position.end = end;

        return position;
    }

    var sineInOut = function(t, b, c, d) {
        return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
    }

    var findElementPos = function(elemFind) {
        var elemX = 0;
        var elemY = 0;
        do {
            elemX += elemFind.offsetLeft;
            elemY += elemFind.offsetTop;
        } while (elemFind = elemFind.offsetParent)

        return Array(elemX, elemY);
    }

}