Retrogen support

[LemADEC]

Please add support for retrogen to better support existing maps and recovers from non-populated chunks.

Proposed design: add a custom NBT property to the chunk with a signature. If key is missing, no signature or different from the one set in configuration, then chunk needs a repopulation.
You could even propose a default signature that is computed as the checksum of cog configuration data so it's automatically handled (and still live the option to force the signature for fine tuning).

[lawremi]

I am becoming convinced that this is a good idea, as it may also help with the deferred generation issues, which seem to break mods like Galacticraft. I could see having a save-level "version" option (like the key you suggested). If bumped, older chunks get updated. The only issue is that COG populations are not independent. Running COG twice over a chunk is not necessarily the same as running it once. So updates may not be quite the same as a fresh run.

[LemADEC]

At least it gives a more solid approach to world-gen, allowing to recover from crashes, conflict with other mods and such.
Also, we could have a new boolean variable in the script to mark it as 'retrogen' so the script could decide what to do. Maybe even export the old 'key' value so you could 'upgrade' a map.

[LemADEC]

I'm giving another try to Custom oregen for my modpack. Have you been able to fix that issue?

[lawremi]

Not yet. Would you please clarify what exactly you would need for your modpack? Some sort of versioning might work. I think it would have to be associated with individual distributions, so we would know which need to be re-run. Please note that it's challenging to design distributions so that they are commutative, i.e., that they can be run again and achieve the desired effect. Adding a new distribution would be easier to configure and support.

[LemADEC]

My main concern is to recover from crash or non-generated chunks.
My second concern is being able to retrogen:

• I add a new distribution and it needs to be run in all chunks, existing or not
• I modify an existing distribution and it re-runs (it's up to me to clear the previous distribution, when possible)

[lawremi]

I will try to work on this this weekend.