holder/holder.js

/*

Holder - 1.2 - client side image placeholders
(c) 2012 Ivan Malopinsky / http://imsky.co

Provided under the Apache 2.0 License: http://www.apache.org/licenses/LICENSE-2.0
Commercial use requires attribution.

*/

var Holder = Holder || {};
(function (app, win) {

//http://javascript.nwbox.com/ContentLoaded by Diego Perini with modifications
function contentLoaded(n,t){var l="complete",s="readystatechange",u=!1,h=u,c=!0,i=n.document,a=i.documentElement,e=i.addEventListener?"addEventListener":"attachEvent",v=i.addEventListener?"removeEventListener":"detachEvent",f=i.addEventListener?"":"on",r=function(e){(e.type!=s||i.readyState==l)&&((e.type=="load"?n:i)[v](f+e.type,r,u),!h&&(h=!0)&&t.call(n,null))},o=function(){try{a.doScroll("left")}catch(n){setTimeout(o,50);return}r("poll")};if(i.readyState==l)t.call(n,"lazy");else{if(i.createEventObject&&a.doScroll){try{c=!n.frameElement}catch(y){}c&&o()}i[e](f+"DOMContentLoaded",r,u),i[e](f+s,r,u),n[e](f+"load",r,u)}};

//https://gist.github.com/991057 by Jed Schmidt with modifications
function selector(a){
	a=a.match(/^(\W)?(.*)/);var b=document["getElement"+(a[1]?a[1]=="#"?"ById":"sByClassName":"sByTagName")](a[2]);
	var ret=[];	b!=null&&(b.length?ret=b:b.length==0?ret=b:ret=[b]);	return ret;
}

//shallow object property extend
function extend(a,b){var c={};for(var d in a)c[d]=a[d];for(var e in b)c[e]=b[e];return c}

function draw(ctx, dimensions, template) {
	var dimension_arr = [dimensions.height, dimensions.width].sort();
	var maxFactor = Math.round(dimension_arr[1] / 16),
		minFactor = Math.round(dimension_arr[0] / 16);
	var text_height = Math.max(template.size, maxFactor);
	canvas.setAttribute("width", dimensions.width);
	canvas.setAttribute("height", dimensions.height);
	ctx.textAlign = "center";
	ctx.textBaseline = "middle";
	ctx.fillStyle = template.background;
	ctx.fillRect(0, 0, dimensions.width, dimensions.height);
	ctx.fillStyle = template.foreground;
	ctx.font = "bold " + text_height + "px sans-serif";
	var text = template.text ? template.text : (dimensions.width + "x" + dimensions.height);
	if (Math.round(ctx.measureText(text).width) / dimensions.width > 1) {
		text_height = Math.max(minFactor, template.size);
	}
	ctx.font = "bold " + text_height + "px sans-serif";
	ctx.fillText(text, (dimensions.width / 2), (dimensions.height / 2), dimensions.width);
	return canvas.toDataURL("image/png");
}
var dimensions_regex = /([0-9]+)x([0-9]+)/;
var hex_regex = /#([0-9a-f]{3,})\:#([0-9a-f]{3,})/i;
var text_regex = /text\:(.*)/;
var preempted = false,
	fallback = false;
var canvas = document.createElement('canvas');
if (!canvas.getContext) {
	fallback = true;
} else {
	if (canvas.toDataURL("image/png").indexOf("data:image/png") < 0) {
		//Android doesn't support data URI
		fallback = true;
	} else {
		var ctx = canvas.getContext("2d");
	}
}

var settings = {
	domain: "holder.js",
	images: "img",
	themes: {
		"gray": {
			background: "#eee",
			foreground: "#aaa",
			size: 12
		},
		"social": {
			background: "#3a5a97",
			foreground: "#fff",
			size: 12
		},
		"industrial": {
			background: "#434A52",
			foreground: "#C2F200",
			size: 12
		}
	}
};

app.add_theme = function (name, theme) {
	name != null && theme != null && (settings.themes[name] = theme);
	return app;
};

app.add_image = function (src, el) {
	var node = selector(el);
	if (node.length) {
		for (var i = 0, l = node.length; i < l; i++) {
			var img = document.createElement("img")
			img.setAttribute("data-src", src);
			node[i].appendChild(img);
		}
	}
	return app;
};

app.run = function (o) {
	var options = extend(settings, o),
		images = selector(options.images),
		preempted = true;
	for (var l = images.length, i = 0; i < l; i++) {
		var dimensions, theme = settings.themes.gray;
		var src = images[i].getAttribute("data-src") || images[i].getAttribute("src");
		if ( !! ~src.indexOf(options.domain)) {
			var render = false;
			for (var flags = src.substr(src.indexOf(options.domain) + options.domain.length + 1).split("/"), sl = flags.length, j = 0; j < sl; j++) {
				var exec;
				if (flags[j].match(dimensions_regex)) {
					exec = dimensions_regex.exec(flags[j]);
					dimensions = {
						width: +exec[1],
						height: +exec[2]
					};
					render = true;
				} else if (flags[j].match(hex_regex)) {
					exec = hex_regex.exec(flags[j]);
					theme = {
						size: settings.themes.gray.size,
						foreground: "#" + exec[2],
						background: "#" + exec[1]
					};
				}
				else if (options.themes[flags[j]]) {
					theme = options.themes[flags[j]];
				}
				else if(flags[j].match(text_regex)){
						exec = text_regex.exec(flags[j]);
						theme.text = exec[1];
				}
			}
			if (render) {
				images[i].setAttribute("data-src", src);
				var dimensions_caption = dimensions.width+"x"+dimensions.height;
				images[i].setAttribute("alt", theme.text ? theme.text + " ["+dimensions_caption+"]" : dimensions_caption);
				
				//Fallback
				images[i].style.width = dimensions.width + "px";
				images[i].style.height = dimensions.height + "px";
				images[i].style.backgroundColor = theme.background;
				
				if(!fallback){
				images[i].setAttribute("src", draw(ctx, dimensions, theme));
				}
			}
		}
	}
	return app;
};
contentLoaded(win, function () {
	preempted || app.run()
})

})(Holder, window);