// Preload images: provide as a list of names and filenames
function preload_images() {
	if (document.images) {
		var argv = preload_images.arguments;
		var argc = argv.length;
		if (argc>0 && (argc%2)==0) {
			if (!document.preloadedImages)
				document.preloadedImages = new Array();
			for (var i=0; i<argc; i=i+2) {
				document.preloadedImages[argv[i]] = new Image();
				document.preloadedImages[argv[i]].src = argv[i+1];
			}
		}
	}
}

// Swap an image (with one already preloaded)
function swap_image(imgName, newImgFile) {
	if (document.images && document.preloadedImages)
		document.images[imgName].src = document.preloadedImages[newImgFile].src;
}