window.onresize = function(){
	fixBackground();
}
function fixBackground() {
	if(0 == img_width || 0 == img_height) {
		return;	
	}
	var window_width = getClientWidth();
	var window_height = getClientHeight();
	var new_width = img_width*window_height/img_height;
	var new_height = img_height*window_width/img_width;
	if(new_width > window_width) {
		document.getElementById('background_img').style.width=new_width+"px";
		document.getElementById('background_img').style.height=window_height+"px";
		document.getElementById('background_img').style.left=(0-(new_width-window_width)/2)+"px";
		document.getElementById('background_img').style.top=0+"px";
	}
	else {
		document.getElementById('background_img').style.width=window_width+"px";
		document.getElementById('background_img').style.height=new_height+"px";
		document.getElementById('background_img').style.left=0+"px";
		document.getElementById('background_img').style.top=(0-(new_height-window_height)/2)+"px";
	}
	document.getElementById('background_img').style.display='block';
};

function getClientWidth()
{
  var x = window.innerWidth ||
          document.documentElement.clientWidth ||
          document.body.clientWidth;

  return x ? x : 0;
};

function getClientHeight()
{
  var x = window.innerHeight ||
          document.documentElement.clientHeight ||
          document.body.clientHeight;


  return x ? x : 0;
};