window.onload = roll_imgs

function roll_imgs() {
	var grp, imgs, i
	if(grp = document.getElementById('main_nav')) {
		if(imgs = grp.getElementsByTagName('img')) {
			for(i=0; i<imgs.length; i++) {
				roll_img(imgs[i])
			}
		}
	}
}

function roll_img(img) {
	if(roll_img_selected(img)) {
		img.src = img.src.replace(/[.](gif|jpe?g)$/, '_sel.$1')
	} else {
		img.onmouseover = o_m_over
		img.onmouseout  = o_m_out
		var preload = new Image()
		preload.src = img.src.replace(/[.](gif|jpe?g)$/, '_omo.$1')
	}
}

//is the html name of the image in the image's url between a "/" and a "."
function roll_img_selected(img) {
	return (document.location.href.indexOf('/'+img.name+'.') != -1)
}

//replace .gif or .jpg w/ _omo.gif or _omo.jpg
function o_m_over() {
	this.src = this.src.replace(/[.](gif|jpe?g)$/, '_omo.$1')
}

//replace _omo.gif w/ .gif
function o_m_out() {
	this.src = this.src.replace(/_omo[.](gif|jpe?g)$/, '.$1')
}