I was looking at the older source at www.tibed.net that I
downloaded yesterday. I cut all the visual stuff out of
voxel.pas, and kept just voxel.pas and voxel_tools.pas.

The tool is looking much much better, btw :)

You are on the right track. Determining the adjacency of
empty outside voxel space and marking this in
TvoxelUnpacked.Flags and then using a lookup for the
normals value is going to be a very good solution.

The difficulty will be dealing with voxels that have
adjaceny on both front and back, or top or bottom, or left
or right etc. Make sure you allow for this!

I can't compile here because I don't have delphi! But I
can write the code, just as soon as I download rar etc..