function calcParallax(tileheight, speedratio, scrollposition) {
	//    by Brett Taylor http://inner.geek.nz/
	//    originally published at http://inner.geek.nz/javascript/parallax/
	//    usable under terms of CC-BY 3.0 licence
	//    http://creativecommons.org/licenses/by/3.0/
	return (tileheight - (Math.floor(scrollposition / speedratio) % (tileheight+1)));
}
window.onload = function() {
	window.onscroll = function() {
		var posY = (document.documentElement.scrollTop) ? document.documentElement.scrollTop : window.pageYOffset;
		var ground = document.getElementById('ground');
		var groundparallax = calcParallax(200, 20, posY);
		ground.style.backgroundPosition = "0 " + groundparallax + "px"; 
		
		var clouds = document.getElementById('clouds');
		var cloudsparallax = calcParallax(300, 13, posY);
		clouds.style.backgroundPosition = "0 " + cloudsparallax + "px";
		
	}
	
	document.getElementById('javascriptcode').onscroll = function() {
		var posX = (this.scrollLeft) ? this.scrollLeft : this.pageXOffset;
		var j = calcParallax(53, 16, posX);
		console.log('scroll js: '+ j);
		document.getElementById('javascriptcode').style.backgroundPosition = j + "px 0";
	}
}