Closed Planar Volume offset valence n

Hi,

I would like to ask if there is a method / paper describing how to offset n valence planar solids?

I used approach described below, but this only works if a vertex shares 3 edges.

With 4 you can see that this does not produce good result.

I simply intersecting offset neighbour planes.

I could offset meshes using vertex normals but this method not necessary result in planar polylines.