Code (Javascript)

MindFusion.Diagramming.ScrollBar.prototype.getThumbRect = function (node, rect)
{
    if (!rect)
        rect = this.getRect();

    if (node.rows.length > 0)
    {
        var allRowsHeight = 0, posHeight = 0;
        for (var i = 0; i < node.rows.length; i++)
        {
            if (i == node.currentScrollRow)
                posHeight = allRowsHeight;
            var rowHeight = node.rows[i] !== undefined ? node.rows[i].height : node.rows[0].height;
            allRowsHeight += rowHeight;
        }

        if (allRowsHeight > rect.height)
        {
            var mm = MindFusion.Drawing.GraphicsUnit.getMillimeter(node.parent.measureUnit);
            var ah = 4 * mm;

            var range = rect.height - 2 * ah;
            var thumbHeight = Math.max(4 * mm, range * rect.height / allRowsHeight);
            range -= thumbHeight;
            var pos = range * posHeight / allRowsHeight;

            var thumbRect = rect.clone();
            thumbRect.height = thumbHeight;
            thumbRect.y += ah + pos;
            return thumbRect;
        }
    }
    return null;
};

MindFusion.Diagramming.ScrollBar.prototype.calcScrollPos = function (mousePosition)
{
    var node = this.node;

    if (node.rows.length > 0)
    {
        var allRowsHeight = 0;
        for (var i = 0; i < node.rows.length; i++)
        {
            var rowHeight = node.rows[i] !== undefined ? node.rows[i].height : node.rows[0].height;
            allRowsHeight += rowHeight;
        }

        var rect = this.getRect();

        if (allRowsHeight > rect.height)
        {
            var mm = MindFusion.Drawing.GraphicsUnit.getMillimeter(node.parent.measureUnit);
            var ah = 4 * mm;

            var range = rect.height - 2 * ah;
            var rellativeY = mousePosition.y - rect.y - ah;
            var relativeScroll = rellativeY / range;
            var totalHeight = 0, scrollPos = node.currentScrollRow;
            for (var i = 0; i < node.rows.length; i++)
            {
                var rowHeight = node.rows[i] !== undefined ? node.rows[i].height : node.rows[0].height;
                var rowLow = totalHeight / allRowsHeight;
                totalHeight += rowHeight;
                var rowHigh = totalHeight / allRowsHeight;
                if (relativeScroll >= rowLow && relativeScroll <= rowHigh)
                {
                    scrollPos = i;
                    break;
                }
            }
            scrollPos = Math.max(0, scrollPos);
            scrollPos = Math.min(scrollPos, node.rows.length - 1);
            return scrollPos;
        }
    }
    return 0;
}