Required inputs

Practically since the first day I started using Filter Forge I've been wondering why certain components require a "real" map source (and thereby prevent control connection).

All components in the Adjustment category seem to require a map source and several other components in other categories too.

I can understand most of the cases for the non adjustment components, but why the heck is a mapped source required for e.g. Invert? There is no processing going on here that takes neighboring samples into account... Many other "required input" components confuse me too..

Is there something special going on under the hood that requires this?



Here is a list of these seemingly unfair "I'm special" components/properties:

Category: Adjustments
- All of the components in this category seem unfair in requirements, except Tone Curve: the Curve property makes sense to require, but why require Source?

Category: Gradients

Elevation Gradient: This one is very similar to the Tone Curve, it makes sense to require the Gradient, but why require the elevation?


The rest of the required input components make sense to me.