Hi Peer,

re:
> I think what I'm asking about is something like defining the fillet width as the distance between the
> theoretical sharp corner and the tangent edge of the fillet:

Unfortunately I don't know of any CAD programs or libraries that define it in such a way.

The most standard definition in CAD is that the fillet size is controlled by a radius value, and the radius value is expressed as an offset distance of each surface, then the offset surfaces are extended and intersected to form the fillet centerline rail.

That gives the so-called "rolling ball" type fillet shape.

It's not really feasible to experiment with replacing just one aspect of filleting with a different definition because it's an overall complex mechanism with interconnected dependencies on handling corner juncture pieces.

The closest thing that could be experimented with is if your alternate width definition could be expressed in terms of surface offsets at any given point and then that might be formulated as a variable radius fillet.

- Michael