world as source instead of seed

[username-pass]

Is your feature request related to a problem? Please describe.
Currently, seedmapper doesn't work with the new terrain. As I understand it, it is related to the generation tool that you use.

Describe the solution you'd like
The ability to input a singleplayer world, and use that as the "seed" to overlay and do all the features from. Essentially, it overlays the "source" world's blocks, etc. instead of generating the seed. If I understand it correctly, it should just be as simple as inputting a singleplayer world (where the player is in spectator, for simplicity), simultaneously loading both that world and the server/other world you want to have the overlay, then just overlaying any different blocks. As the player moves around in the other world, it could move the player in the "source" world, so as to make it simpler for generation. This wouldn't be useful for locating structures (unless you just run the command from the "source" world) or loot, but it could be useful for overlaying blocks, and finding blocks. I think it could lead to interesting usage, such as custom world-gen, and checking structure integrity, though I don't know exactly how useful it would be in practice, or how easy it would be to implement.

Describe alternatives you've considered
Not having it at all, Different generation tool, maybe the virtual world thing described in the pull request (As I understand it) Though I suppose it could just be an additional feature you add to that PR.

Additional context
I think that's it?

[xpple]

Interesting idea. I would probably adapt the create world GUI to make this entirely configurable. But as I've come to realise in #61, doing stuff like this is not trivial. The reason that PR is not merged yet is because I simply do not find it implemented well enough to be included in the mod.