// configuration variables
var timeout = 250; // milliseconds
var fadeSpeed = 1;  // milliseconds
var useFade = true;

// timers array
var timers = new Array();

// state array -- by id, value = active, false = inactive
var state = new Array();

// lastOpacity: used to prevent multiple timers from making the fade flicker
var lastOpacity = new Array();

// MSIE has its own way of setting opacity, so we have to detect it
// all the other major browsers support the standard DOM opacity property
var msie = false;
if (navigator.appName == "Microsoft Internet Explorer") msie = true;

// entry point: set element to visible and clear its timers
function setMenu(id) {
    var e = document.getElementById(id);
    e.style.visibility = "visible";
    state[id] = true;
    setOpacity(id, 1);
    if (timers[id]) {
        clearTimeout(timers[id]);
        timers[id] = undefined;
    }
}

// set element to hidden and reset its opacity
// typically called by a timer
// may be used as an entry point to bypass timers and fades
function hideMenu(id) {
    var e = document.getElementById(id);
    state[id] = false;
    e.style.visibility = "hidden";
    if (useFade) setOpacity(id, 1);
}

// entry point: hide the menu using fade (if enabled)
function clearMenu(id) {
    if (useFade) timers[id] = setTimeout('fadeMenu( "' + id + '" )', timeout);
    else timers[id] = setTimeout('hideMenu( "' + id + '" )', timeout);
}

// set the opacity
// special support for MSIE
function setOpacity(id, value) {
    var e = document.getElementById(id);

    if (state[id]) value = 1;    // menu fade was interrupted
    else if (lastOpacity[id] && (lastOpacity[id] < value)) value = lastOpacity[id];  // prevents flicker if multiple timers set

    if (msie) e.style.filter = 'alpha(opacity=' + value * 100 + ')'; // MS Internet Explorer
    else e.style.opacity = (value);     // Everyone else (standard DOM)

    if (value == 0) hideMenu(id);    // when all faded, reset the menu state
    lastOpacity[id] = value;
}

// fade a menu
// typically called by a timer
function fadeMenu(id) {
    var start = 0;
    var end = 0;
    var s = Math.round(fadeSpeed / 1);   // fade in 1ms increments
    var timer = 0;
    var i;

    state[id] = false;

    for (i = s; i >= 0; i--) {
        setTimeout("setOpacity('" + id + "'," + (i / s) + ")", timer++ * fadeSpeed / s)
    }
}