// ie5.5+ png alpha fix v2.0 alpha: background tiling support
// (c) 2008-2009 angus turnbull http://www.twinhelix.com

// this is licensed under the gnu lgpl, version 2.1 or later.
// for details, see: http://creativecommons.org/licenses/lgpl/2.1/

var iepngfix = window.iepngfix || {};

iepngfix.tilebg = function(elm, pngsrc, ready) {
	// params: a reference to a dom element, the png src file pathname, and a
	// hidden "ready-to-run" passed when called back after image preloading.

	var data = this.data[elm.uniqueid],
		elmw = math.max(elm.clientwidth, elm.scrollwidth),
		elmh = math.max(elm.clientheight, elm.scrollheight),
		bgx = elm.currentstyle.backgroundpositionx,
		bgy = elm.currentstyle.backgroundpositiony,
		bgr = elm.currentstyle.backgroundrepeat;

	// cache of divs created per element, and image preloader/data.
	if (!data.tiles) {
		data.tiles = {
			elm: elm,
			src: '',
			cache: [],
			img: new image(),
			old: {}
		};
	}
	var tiles = data.tiles,
		pngw = tiles.img.width,
		pngh = tiles.img.height;

	if (pngsrc) {
		if (!ready && pngsrc != tiles.src) {
			// new image? preload it with a callback to detect dimensions.
			tiles.img.onload = function() {
				this.onload = null;
				iepngfix.tilebg(elm, pngsrc, 1);
			};
			return tiles.img.src = pngsrc;
		}
	} else {
		// no image?
		if (tiles.src) ready = 1;
		pngw = pngh = 0;
	}
	tiles.src = pngsrc;

	if (!ready && elmw == tiles.old.w && elmh == tiles.old.h &&
		bgx == tiles.old.x && bgy == tiles.old.y && bgr == tiles.old.r) {
		return;
	}

	// convert english and percentage positions to pixels.
	var pos = {
			top: '0%',
			left: '0%',
			center: '50%',
			bottom: '100%',
			right: '100%'
		},
		x,
		y,
		pc;
	x = pos[bgx] || bgx;
	y = pos[bgy] || bgy;
	if (pc = x.match(/(\d+)%/)) {
		x = math.round((elmw - pngw) * (parseint(pc[1]) / 100));
	}
	if (pc = y.match(/(\d+)%/)) {
		y = math.round((elmh - pngh) * (parseint(pc[1]) / 100));
	}
	x = parseint(x);
	y = parseint(y);

	// handle backgroundrepeat.
	var repeatx = { 'repeat': 1, 'repeat-x': 1 }[bgr],
		repeaty = { 'repeat': 1, 'repeat-y': 1 }[bgr];
	if (repeatx) {
		x %= pngw;
		if (x > 0) x -= pngw;
	}
	if (repeaty) {
		y %= pngh;
		if (y > 0) y -= pngh;
	}

	// go!
	this.hook.enabled = 0;
	if (!({ relative: 1, absolute: 1 }[elm.currentstyle.position])) {
		elm.style.position = 'relative';
	}
	var count = 0,
		xpos,
		maxx = repeatx ? elmw : x + 0.1,
		ypos,
		maxy = repeaty ? elmh : y + 0.1,
		d,
		s,
		isnew;
	if (pngw && pngh) {
		for (xpos = x; xpos < maxx; xpos += pngw) {
			for (ypos = y; ypos < maxy; ypos += pngh) {
				isnew = 0;
				if (!tiles.cache[count]) {
					tiles.cache[count] = document.createelement('div');
					isnew = 1;
				}
				var clipr = math.max(0, xpos + pngw > elmw ? elmw - xpos : pngw),
					clipb = math.max(0, ypos + pngh > elmh ? elmh - ypos : pngh);
				d = tiles.cache[count];
				s = d.style;
				s.behavior = 'none';
				s.left = (xpos - parseint(elm.currentstyle.paddingleft)) + 'px';
				s.top = ypos + 'px';
				s.width = clipr + 'px';
				s.height = clipb + 'px';
				s.clip = 'rect(' +
					(ypos < 0 ? 0 - ypos : 0) + 'px,' +
					clipr + 'px,' +
					clipb + 'px,' +
					(xpos < 0 ? 0 - xpos : 0) + 'px)';
				s.display = 'block';
				if (isnew) {
					s.position = 'absolute';
					s.zindex = -999;
					if (elm.firstchild) {
						elm.insertbefore(d, elm.firstchild);
					} else {
						elm.appendchild(d);
					}
				}
				this.fix(d, pngsrc, 0);
				count++;
			}
		}
	}
	while (count < tiles.cache.length) {
		this.fix(tiles.cache[count], '', 0);
		tiles.cache[count++].style.display = 'none';
	}

	this.hook.enabled = 1;

	// cache so updates are infrequent.
	tiles.old = {
		w: elmw,
		h: elmh,
		x: bgx,
		y: bgy,
		r: bgr
	};
};


iepngfix.update = function() {
	// update all png backgrounds.
	for (var i in iepngfix.data) {
		var t = iepngfix.data[i].tiles;
		if (t && t.elm && t.src) {
			iepngfix.tilebg(t.elm, t.src);
		}
	}
};
iepngfix.update.timer = 0;

if (window.attachevent && !window.opera) {
	window.attachevent('onresize', function() {
		cleartimeout(iepngfix.update.timer);
		iepngfix.update.timer = settimeout(iepngfix.update, 100);
	});
}