How does one inject variables into page templates from a custom Drupal module?

Question

We've created a custom module for organizing and publishing our newsletter content.

The issue I'm running into now -- and I'm new to theming and Drupal module development, so it could just be a knowledge issue as opposed to a Drupal issue -- is how to get each newsletter themed.

At this point the URL structure of our newsletter will be:

/newsletters/{newsletter-name}/{edition-name}/{issue-date} which means that we can create template files in our theme using filenames like page-newsletters-{newsletter-name}-{edition-name}.tpl.php, which is great. The one issue I'm running into is that all of the content comes through in the $content variable of the theme. I'd like to have it come through as different variables (so that I can, inside the theme, place certain content in certain areas.)

Is there a proper way for doing this?

Edit: To answer some questions: The issue is a node (there are issue, edition and newsletter nodes) and the path is being set using hook_menu with wildcards and a router.

Answer 1

If there were better documentation for template preprocess functions, Drupal would be a lot more accessible - as it is, you need to piece together the information from a lot of different explanations. One place to start is here:

http://drupal.org/node/223430

but if you take the time to work through the tutorial below, you'll find you can do most things:

http://11heavens.com/theming-the-contact-form-in-Drupal-6

Answer 2

The best answer I could find was to add a check inside of phptemplate_preprocess_page to send the vars back to the module and have them be updated.

Like so:

function phptemplate_preprocess_page(&$vars) {
    if (module_exists('test_module')) {
        _test_module_injector($vars);
    }
}

then in my test_module.module file I created this function:

function _test_module_injector(&$vars) {
    $vars[] = call_to_other_functions_to_load_vars();
}

It seemed to work. I wish there was a way to do this without having to touch the theme's template.php file, but otherwise this works well.