Putting random images in the sidebar of a standard Movable Type blog is relatively easy, because Movable Type generates static pages that the web server then dishes out. Tell your web server to run the pages through PHP before sending them out, and include a little bit of code to stick in random image URLs—the PHP will survive intact through Movable Type, and your server will take care of the images before sending the page to the browser.

This is even easier in WordPress, because—by default—pages are dynamically generated (using PHP) when the browser asks for them. Add your image rotation code in, and WordPress will take care of the rest.

The problem occurs when you want to add page caching to WordPress. Generating a page each time a browser asks for it is rather wasteful; I can’t count the number of times that Daring Fireball has crashed a server by linking to a WordPress blog it was hosting. The solution to that is saving those generated pages, and then using that saved copy when some other browser asks for that page.

Which is all well and good, until you realize that the cache has also cached a specific (albeit random!) set of images for your sidebar. Everybody will see the same images when visiting a specific page (say, this front page), and they will continue to see those images until the cache expires and the page is re-cached.

W3 Total Cache, the caching plugin that I’m using, has a workaround: it can cache parts of a page, so long as you use the “Disk (basic)” page cache method. You surround the parts you don’t want to cache with <!--mfunc--> and <!--/mfunc-->, and it’ll cache the rest. Notably, you omit the usual <?php and ?> tags when using this “mfunc” notation. My code looks something like this:

I’ve gotten lazy, and am now using the PHP function glob() to figure out what pictures are available for use—rather than hardcoding the file names into a script. The server I’m on doesn’t support it, but the GLOB_BRACE flag could combine the three calls to glob() into a single one. (I’m also using shuffle() over array_rand(), as the latter apparently isn’t exactly random when it comes to ordering the selected elements.)

…

And that’s pretty much the fruit of half a day’s poking around on my week off. It may be a little bitter for me (really… my week off), but may be useful for someone else.

It took me getting sick on my week off (cry) to sit down and finally do it, but Ye Olde Blogge has been restored to its previous grandeur. (There are some new pictures in the side rotation, too… very exciting.) It turns out that WordPress is pretty OK, until you want to do something that WordPress doesn’t want to do.

My designs butted heads with WordPress in two major areas: combining page caching (to cover the 0.000000001% chance that a major site ever links here) with random side images, and monthly page navigation. Getting things set up just so took something like three full days of hacking (…hacking while sick, mind you); I’ll have to write up something about that for the search engines to find, to hopefully save others some trouble in the future.

Now to see if I actually post anything of value, since I’ve spent so much time getting this place set up again….