For example, it's very straightforward to have an index.php controller be a procedural script like so:

<?php

//include classes and functions

//get some data from the database
//and/or process a form submission

//render HTML using your template system

?>

Then I can just navigate to http://mysite.com/index.php and the above procedural script is essentially acting as a simple controller. Here the controller mechanism is a basic procedural script.

How then do you make controllers classes instead of procedural scripts? Must the controller class always be tied to the routing mechanism?