var direction = 'G2C';
var imgs = [
	'images/bgleft_cad.jpg',
	'images/bgleft_cad_25.jpg',
	'images/bgleft_cad_50.jpg',
	'images/bgleft_cad_75.jpg',
	'images/bgleft_cad_100.jpg',
	'images/bgleft_cad_125.jpg',
	'images/bgleft_cad_150.jpg',
	'images/bgleft_cad_175.jpg',
	'images/bgleft_cad_200.jpg',
	'images/bgleft_cad_225.jpg',
	'images/bgleft_gis.jpg',
	'images/bgleft_gis_25.jpg',
	'images/bgleft_gis_50.jpg',
	'images/bgleft_gis_75.jpg',
	'images/bgleft_gis_100.jpg',
	'images/bgleft_gis_125.jpg',
	'images/bgleft_gis_150.jpg',
	'images/bgleft_gis_175.jpg',
	'images/bgleft_gis_200.jpg',
	'images/bgleft_gis_225.jpg'
	];
var imgsLen = imgs.length;
var cache = [];

//cache the images
for(var i=0; i<imgsLen; i++)
{
	cache[i] = new Image;
	cache[i].src = imgs[i];
}

setInterval('changeBackgroundImage()',1000);

function changeBackgroundImage(){
	var image = document.body.style.backgroundImage;
	var urlprefix = "";
	if (image.indexOf("http://") > -1) {
		// this is for Google Chrome
		urlprefix = image.substring(image.indexOf("http://"),image.indexOf("images"));
	}
	if (image == "url("+urlprefix+"images/bgleft_gis.jpg)") {
		document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_gis_25.jpg)";
		direction = "G2C";
	} else if (image.indexOf("images/bgleft_gis_") > -1 && direction == "G2C") {
		var step = parseInt(image.substring(image.indexOf("images/bgleft_gis_") + "images/bgleft_gis_".length, image.indexOf(".jpg")))
		if (step == 225) {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_cad_225.jpg)";
		} else {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_gis_"+(step + 25)+".jpg)";
		}
	} else if (image.indexOf("images/bgleft_gis_") > -1 && direction == "C2G") {
		var step = parseInt(image.substring(image.indexOf("images/bgleft_gis_") + "images/bgleft_gis_".length, image.indexOf(".jpg")))
		if (step == 25) {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_gis.jpg)";
		} else {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_gis_"+(step - 25)+".jpg)";
		}
	} else if (image.indexOf("images/bgleft_cad_") > -1 && direction == "G2C") {
		var step = parseInt(image.substring(image.indexOf("images/bgleft_cad_") + "images/bgleft_cad_".length, image.indexOf(".jpg")))
		if (step == 25) {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_cad.jpg)";
		} else {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_cad_"+(step - 25)+".jpg)";
		}
	} else if (image.indexOf("images/bgleft_cad_") > -1 && direction == "C2G") {
		var step = parseInt(image.substring(image.indexOf("images/bgleft_cad_") + "images/bgleft_cad_".length, image.indexOf(".jpg")))
		if (step == 225) {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_gis_225.jpg)";
		} else {
			document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_cad_"+(step + 25)+".jpg)";
		}
	} else if (image == "url("+urlprefix+"images/bgleft_cad.jpg)") {
		document.body.style.backgroundImage = "url("+urlprefix+"images/bgleft_cad_25.jpg)";
		direction = "C2G";
	}
}

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