Using a graphics library, be GD, ImageMagick or anything else, is convenient, but carries a price to pay: unlike most Drupal parts, which are generally database-bound, image generation is typically CPU-bound: generating many images on the fly can significantly increase the CPU load on a system, while Drupal setups are typically not optimized for this, and could result in problems if you are using Drupal on a shared hosting account. So what ?

In the previous post, we saw how to create a XHTML progress bar widget for Forms API, using theme_progress_bar. The next logical step is now to create a graphical equivalent to that progress bar, as an example for far more advanced fully graphical widgets made possible using a similar mechanism.

As a Drupal user, you certainly noticed that update.php displays a nice progress bar to make you wait during its batch operations. And maybe you also noticed theme_progress_bar in the API reference.

The question

Wouldn't it be nice to have that progress bar available as an extended version of markup that would graphically display a value in your forms without stuffing it in a markup element ?

For some reason or another, I've noticed several new Drupal developers these last few days sweating on Forms API, and thought it would be nice to have a smallish example to complement the unavoidable FAPI reference and Guick start guide, for a typical non-basic form: one including set of checkboxes in a table, with a customized display, like the core user, content or modules administration forms. So follow me while we build this example.