// array of cars to animate
var cars=[];
var cars_div_height=60;
var cars_max_left=900;
var cars_min_speed=3;
var cars_max_speed=6;

function init_animation() {
	var idx=0;
	var elms=document.getElementsByTagName("div");
	var elm;

	for(var item=0;item<elms.length;item++) {
		if(elms[item].getAttribute("name")=="car") {
			elm=document.getElementById(elms[item].getAttribute("id"));
		
			// init information
			cars[idx]={};
			cars[idx]["id"]=elm.id;
			cars[idx]["left"]=-100 + parseInt(Math.random() * cars_max_left);
			cars[idx]["step"]=cars_min_speed + parseInt(Math.random() * cars_max_speed);
			
			// set positions
			elm.style.top=String(-(idx * cars_div_height)) + "px";
			elm.style.left=cars[idx].left + "px";
			//elms[item].style.zIndex=cars[item].step;
			idx++;
		}
	}
}

function animate_car(idx) {
	cars[idx].left+=cars[idx].step;
	if(cars[idx].left>cars_max_left) {
		cars[idx].left=-100;
	}
	document.getElementById(cars[idx].id).style.left=cars[idx].left + "px";
}

function animate() {
	for(var item=0;item<cars.length;item++) {
		animate_car(item);
	}
	window.setTimeout(function() { animate(); },30);
}