Hi Steven,
Now that I read some more details of your project I'm not sure if Thermite3D is what you are looking for. Thermite3D is based on the concept of voxels, but if you are making an editor for an existing game engine then probably that engine is not based on voxels.
The technology you are after is probably what is known as 'Constructive Solid Geometry'. If you didn't know that term then just sticking it in to google will find you some useful information. It's basically the process of taking two or more meshes and adding or subtracting them from eachother:
http://en.wikipedia.org/wiki/Constructi ... d_geometryIn particular, this approach is used by UnrealEd (the Unreal level editor). It can also be performed in realtime (though I have never tried this).
Have a look at this video to see if it is similar to what you are trying to do:
http://video.google.com/videoplay?docid ... 981648678#If you like it, a series of articles about the technoloigy start here:
http://sandervanrossen.blogspot.com/200 ... art-1.htmlBe warned though - it's complex stuff!