The following method is part of class Animatable:

virtual FPInterface* Animatable::GetInterface(Interface_ID id);

Any future object-based interfaces should be allocated unique Interface_IDs (you can use Gencid.exe for this) and made available through this call.

The default implementation of Animatable::GetInterface() looks up a standalone interface of the given ID on the object's ClassDesc. This gives access to standalone FnPub interfaces via any of a plug-in's objects, without having to dig around for the ClassDesc, so you should fall back to calling the default implementation if you don't recognize an ID in your implementation of Animatable::GetInterface().