var prev_href, next_href;
var is_ie = (navigator.appName == "Microsoft Internet Explorer");
var is_ns = (navigator.appName == "Netscape");
var browserversion = parseFloat (navigator.appVersion);
var is_old = browserversion < 4;
var test_document = document ? true : false;
var supported = test_document && !is_old;

// Hide thumbnail display on paintings page and display one painting enlargement.
function fill_canvas (ahref) {
	if (!ahref || !supported) return true;
	for (prev_href = ahref.previousSibling; prev_href && prev_href.tagName != "AREA"; prev_href = prev_href.previousSibling);
	for (next_href = ahref.nextSibling; next_href && next_href.tagName != "AREA"; next_href = next_href.nextSibling);
	var painting_title = document.getElementById ("painting_title");
	var painting = document.getElementById ("painting");
	var thumbs = document.getElementById("thumbs");
	var canvas = document.getElementById("canvas");
//	painting_title.innerText = ahref.title;
	painting_title.firstChild.nodeValue = ahref.title;
	if (painting.style.display != 'inline') {
		last_scroll = document.body.scrollTop;
		painting.style.display = 'inline';
		thumbs.style.display = 'none';
	}
	canvas.src = 'images/loading.gif';
	canvas.src = ahref.href;
	return false;
}

// Restore paintings page to thumbnail display.
function clear_canvas() {
	if (!supported) return true;
	var painting_title = document.getElementById("painting_title");
	var painting = document.getElementById("painting");
	var thumbs = document.getElementById("thumbs");
	var canvas = document.getElementById("canvas");
	thumbs.style.display = 'inline';
	painting.style.display = 'none';
	document.body.scrollTop = last_scroll;
	painting_title.innerText = 'Painting Enlargement';
	canvas.src = 'images/loading.gif';
	return false;
}

// Display the previous painting enlargement in the list.
function prev_canvas() {
	if (!supported) return true;
	if (prev_href) 
		return fill_canvas (prev_href);
	else 
		return clear_canvas();
}

// Display the next painting enlargement in the list.
function next_canvas() {
	if (!supported) return true;
	if (next_href) 
		return fill_canvas (next_href);
	else 
		return clear_canvas();
}

// Use to generate navigation HTML for dynamic display.
function write_canvas_navigation() {
if (supported) with (document) {
		writeln('<div name="painting" id="painting" style="display:none;">');
		writeln('<h1 name="painting_title" id="painting_title">Painting Enlargement</h1>');
		write('<p>');
		write ('<a href="' + document.location + '" onclick="return prev_canvas()">Previous</a>');
		writeln(' | ');
		write ('<a href="' + document.location + '" onclick="return clear_canvas()">Index</a>');
		writeln(' | ');
		write ('<a href="' + document.location + '" onclick="return next_canvas()">Next</a>');
		writeln ('<p>');
		writeln('<img name="canvas" id="canvas" src="images/loading.gif" lowsrc="images/loading.gif" border="" alt="Enlargement" style="filter:progid:DXImageTransform.Microsoft.DropShadow(color=#B9BBC0,offX=8,offY=8)" />');
		writeln('</div>');
	}
}