$(document).ready(function() {
 
	if(Modernizr.csstransforms3d)
	{
		transformMode = 0;
	}
	else if(Modernizr.csstransforms)
	{
		transformMode = 1;
	}
	else
	{
		transformMode = 2;
	}
	
	bg1 = document.getElementById("bg1");
	window.onscroll = onScroll;//$.proxy(onScroll, this);
});

function onScroll()
{
	var docHeight = $(document).height();
	var ratio = (window.pageYOffset) / (docHeight);
	
	var pos = window.pageYOffset + (ratio * -700);
	setElementPosition(bg1, window.innerHeight + pos - 200)
	
}

setElementPosition = function(element, value)
{
	
	switch(transformMode)
	{
		case 0:
			element.style["-webkit-transform"] = element.style["-moz-transform"] = "translate3d( 0px,"+value+"px, 0.1px)";
			break;
		case 1:
			element.style["-webkit-transform"] = element.style["-moz-transform"] = "translate( 0px,"+value+"px)";
		case 2:
			element.style.top = value+"px";
	}
}