var shown_pointer = '';

function hide_current_pointer() {
    if (shown_pointer != '')
    {
        p = document.getElementById(shown_pointer);
        p.style.visibility = "hidden";
    }
}

function show_pointer(pointer) {

    hide_current_pointer();

    p = document.getElementById(pointer);
    p.style.visibility = "visible";

    shown_pointer = pointer;
}