Problems creating a custom blank page with my custom module

Question

I'm trying to upgrade old Drupal 7 modules to 8 and I am struggling to figure out how to create a blank page (by this I mean, a page with zero HTML from enabled themes) for my module. I added routing to my custom controller, my controller method takes care of all the logic and returns the following array:

[
        'showVideo' => [
            '#theme' => 'videoPage',
            '#content' => $content
        ]
]

I already defined "videoPage" in mymodule.module using hook_theme:

Function mymodule_theme($existing, $type, $theme, $path){
  return array(
    'videoPage' => array(
      'variables' => array('content' => NULL),
      'file' => 'mymodule.html.twig'
    )
  );
}

"mymodule.html.twig" is a full stand-alone HTML file from the opening HTML tag to the closing tag. I don't want any other content to show up there but instead I'm getting the content in that Twig file, then followed by the HTML for the currently selected Drupal theme. Also, my {{ content.value }} calls in Twig seem to be getting ignored. And by this I mean, I can literally see {{ content.xyz }} in the markup being printed. The $content being returned by the controller is an array and I'm sure all the values are set. It almost feels like the Twig file is being called while the Controller's logic is being ignored. (this last bit has been solved by Clive's response)

Any help? Am I totally off in this approach?

Answer 1

You can output the html of one twig only in a symfony response:

use Symfony\Component\HttpFoundation\Response;

public function my_page_controller() {

  $build = array(
    'page' => array(
      '#theme' => 'videoPage',
      '#content' => $content,
    ),
  );
  $html = \Drupal::service('renderer')->renderRoot($build);
  $response = new Response();
  $response->setContent($html);

  return $response;
}

Answer 2

The file parameter is:

The file the implementation resides in.

That should be used if you're creating a theme function, rather than template, and it will contain the path to the file that function is in.

What you're looking for is the template parameter:

If specified, the theme implementation is a template file, and this is the template name. Do not add 'html.twig' on the end of the template name. The extension will be added automatically by the default rendering engine (which is Twig.)

(emphasis mine)

So your implementation might look something like this:

function mymodule_theme($existing, $type, $theme, $path){
  return array(
    'videoPage' => array(
      'variables' => array('content' => NULL),
      'template' => 'mymodule'
    )
  );
}

Assuming "mymodule.html.twig" is in the root of your module's folder.

In case you're interested in why your current implementation is doing what it's doing: as you've provided a file, Drupal performs an include on it, and anything not within <?php tags gets written straight out to the buffer.

Source