How will this variable be changed? Will it be changed programmatically or just something you want to be able to change like you would any other configurable variable?
You could define it in a constant, then in Volt:
{{ constant('IMGIXIMAGESPATH') }}image-name.png
Or you could add it to your app's config ( https://docs.phalcon.io/3.4/en/config ), then add that config to your DI, which will make it natively accessible in your view:
{{ config.imgix_images_path }}image-name.png
Or, you could simply add it to your View in your bootstrap code when it's defined:
$DI->set('view',function() use($Config,$DI){
$DI = \Phalcon\DI::getDefault();
$View = new \Phalcon\Mvc\View();
$View->setViewsDir($Config->dirs->views);
$View->registerEngines(['.phtml'=>$DI->get('volt',[$View,$DI])]);
$View->imgix_images_path = $Config->imgix_images_path;
return $View;
});
{{ img_images_path }}image-name.png
Personally I'd put it in the app's config and reference it that way.