Fixes the jsPlumb getOffset function to ignore parent element scroll offsets.

jsPlumb.getOffsetFix.js

// Fixes the jsPlumb getOffset function to ignore parent element scroll offsets.
// Note - This is a hack. It may have unintended side-effects including 
//        breaking your page, your computer, and/or your universe.
jsPlumbInstance.prototype.getOffset = function(el, relativeToRoot) {
    var current_element, container, out, parent_element;

    // Initialization
    current_element = jsPlumb.getDOMElement(el);
    container = this.getContainer();
    out = {
        left: current_element.offsetLeft,
        top: current_element.offsetTop
    };

    // Walk up the tree until exhausing the parent elements for offset calculation
    parent_element = (relativeToRoot || (container != null && current_element.offsetParent != container)) ? current_element.offsetParent : null;
    while (parent_element != null) {
        // Include the parent element offset in the total offset calculations
        out.left += parent_element.offsetLeft;
        out.top += parent_element.offsetTop;

        // Some sort of scroll thing
        if (!relativeToRoot) {
            if (parent_element != null && parent_element.scrollTop > 0 || parent_element.scrollLeft > 0) {
                var p = this.getStyle(current_element, "position");
                if (p !== "fixed") {
                    //out.left -= parent_element.scrollLeft;
                    //out.top -= parent_element.scrollTop;
                }
            }
        }

        // Control how far up the tree to walk
        if (relativeToRoot) {
            // Walk up to root
            parent_element = parent_element.offsetParent;
        } else {
            // Walk up to container
            parent_element =  parent_element.offsetParent == container ? null : parent_element.offsetParent;
        }
    }

    // if container is scrolled and the element (or its offset parent) is not absolute or fixed, adjust accordingly.
    if (container != null && !relativeToRoot && (container.scrollTop > 0 || container.scrollLeft > 0)) {
        var parent_position = current_element.offsetParent != null ? this.getStyle(current_element.offsetParent, "position") : "static",
            current_position = this.getStyle(current_element, "position");
        if (current_position !== "absolute" && current_position !== "fixed" && parent_position !== "absolute" && parent_position != "fixed") {
            out.left -= container.scrollLeft;
            out.top -= container.scrollTop;
        }
    }
    return out;
}