// cirr2.js - utility for menu image handling 

var preloadFlag = true;  // defeated because loading one image at a time

function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
/* documentation
	function is called as follows:
	changeImages('image name1', 'new image URL','image name2','new image URL') */
	
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

/* declare random number gen variables for random() - see ORA book p468 */
var m=714025;
var a=4096;
var c=150889;
var seed = (new Date()).getTime()%m;

function random() 
/* documentation
	returns a value between 0 and 1 */
{
	seed = (seed*a + c)%m;
	var r = seed/m;
	return r;
}

function showimage(iname, set)
{
var imageno = 0;
var noimages = 6;

/* get a random number, rn 1 to noimages */
var rn = Math.floor(noimages*random())+1;
//alert("rn = " + rn);

/* show random image */
imageno = rn;
/* assign set */
if (set == "a"){
	set = "";
	}
/* load this randomly selected image */
istnow = newImage("istimages/ist" + imageno + set + ".jpg");
changeImages(iname, istnow.src);
}