var debug = 1;

function replace_image(imageId, src)
{
	if(!document.getElementById(imageId))
	{
		if(debug)
			alert('replace_image(): no image with id "'+imageId+'" found.')
	}
	
	try{
		document.getElementById(imageId).src = src;
	}
	catch(e){
		if(debug)
			alert('replace_image(): could not replace image with id "'+imageId+'"\nerror: ' + e);
	}
}

var preloaded_images = new Array();
function preload_images(images)
{
	for(var i=0; i<images.length; i++)
	{
		var tmp = new Image();
		tmp.src=images[i];
		preloaded_images.push(tmp);
	}
}