How to put an external php function in VB's "scope"?
 

What I'm trying to do is this:

Call an external .php module with a click on a button, and somehow have access to variables declared in a plug-in (inside vB's scope).

In other words, a plug-in loads a template and fills it with some buttons, and assigns url links to the buttons. The buttons call a completely separate external php module like:

<a href="http://mydomain.com/forum/external_module.php?dothis=4>

So when the user clicks on a button, a php function in another file is called.

However, I can't seem to figure out how to have access to variables used in the scope of vB when I'm inside my external php code. Maybe this isn't possible...

Is there some specific include file I would need to include to make my external file "a part of" VB's world?

Yes, global.php

Thanks, I have experimented with that and it does seem to work (at least in some preliminary testing). But looking inside global.php, it seems there is a whole bunch of initialization etc. going on. Is this any kind of a serious performance hit to include in an eternal file?

No. All vBulletin front-end pages include it.