2012.FFWD; high performance Twenty Twelve child theme

Twenty Twelve is beautiful but slow, so I created 2012.FFWD. This Twenty Twelve child theme looks pretty much the same as the original, but comes with the following performance-boosting changes under the hood:

  • no webfont downloaded: loading fonts slow sites down, always. Fallback-fonts as defined in Twenty Twelve (Arial, Helvetica, Sans-Serif) are used instead.
  • minimized style.css: the amount of CSS is staggering, even minimized we’re still at 28KB!
  • minimized and inlined navigation.js: the overhead for doing a separate request for small javascript-files is bigger then the increase in filesize when inlining.

And these small changes indeed seem to have a pretty good impact on performance when comparing my previous test with Twenty Twelve with a new one for 2012.FFWD;

  • from 9 to 3 requests
  • from 142KB to 15KB downloaded size
  • loadtime from 2.457s to 0.937s

You can download the child theme here for now, but I might upload it to wordpress.org’s theme repository later.
Before applying 2012.FFWD on my own blog, I had to do some emergency bugfixing in Autoptimize. Autoptimize is the plugin I use to aggregate and minify JS and CSS (including data-uri magic on background images), but it is currently unmaintained. It messed Twenty Twelve (and hence 2012.FFWD) up severely when viewed in IE7 and IE8, aggregating html5.js into a javascript-file loaded at the bottom of the HTML and loading the IE-specific CSS before the aggregated generic CSS. If anyone is interested in my bugfixed version of Autoptimize (there’s some other fixes in there as well), drop me a line.

Dipping below the magical 1 second page load time

A couple of weeks ago I started looking into data-uri’s as a way to further optimize the performance of this personal playground of mine. Testing was easy enough; Autoptimize, the javascript/ css/ html opitimizing plugin I now use in conjunction with WP Super Cache, comes with support for data-uri’s in CSS and switching that option on indeed immediately resulted in less requests being made.
While testing I did find a small bug in Autoptimize (in /wp-content/autoptimize/classes/autoptimizeStyles.php) which caused jpeg images not to be taken into account. The regular expression in the code was ‘jpe?j’, while just below in a switch/case block ‘jpej’ and ‘jpg’ were referenced, resulting in neither ‘.jpg’ nor .’jpeg’ files ever being turned into data-uri’s. While reading the code I also noticed that the upper filesize limit for images to be turned into data-uri’s was set at 5120 bytes, but as base64-encoding does come with overhead, I decided to lower that limit to 2560 bytes.
So I made some minor changes in autoptimizeStyles.php on lines 207 and following:

if($path != false && preg_match('#\.(jpe?g|png|gif|bmp)$#',$path) && file_exists($path) && is_readable($path) && filesize($path) <= 2560) {
   switch(end(explode('.',$path))) {
      case 'jpeg':
         $dataurihead = 'data:image/jpeg;base64,';
      case 'jpg':
         $dataurihead = 'data:image/jpeg;base64,';
      case 'gif':

I also  switched my “subscribe” widget from a paragraph- to a bulleted list-approach with the rss- and mail-icons as background images and defined the adfreeblog and creative commons badges as background-images as well. And then I was ready to test the real impact of using data-uri’s on webpagetest.org. Behold the results for my current blog homepage (i.e. the one just before this post got published) with and without the use of data-uri’s (but excluding those dog-slow calls to stats.wordpress.com):

 No data-uri’sWith data-uri’s
webpagetest results URLhttp://www.webpagetest.org/result/121106_12_6FZ/http://www.webpagetest.org/result/121106_4H_71R/
#requests (full page)2619
Bytes in (full page)116KB114KB
Start render (median)0.615s0.634s
Doc Complete time (median)0.969s0.870s
Full page load time (median)1.932s1.332s

Let it be clear that the use of data-uri’s for background-images is not a silver bullet, but if you have images that are on every page of your site and they’re small in file-size, migrating those into your CSS as background-images with data-uri’s can result in an important performance improvement for your site.