Getting started
Perquisites

• Java 17.
• A pre-generated world to use as a reference (Such as a WorldPainter world).
• A Spigot(of forks) Minecraft Server of version 1.19.4.

Single player or non-Bukkit
Underilla is currently only implemented as a Spigot plugin, so it runs only on Spigot servers. If you have a Vanilla, Forge or non Bukkit-based server; or looking for a singel player experience; you may use a local Spigot server to pre-generate a fully-merged world and then copy the resulting world folder to your actual saves folder.

Instalation

1. Set up your Spigot server.
2. Download Underilla's .jar.
3. Place Underilla's .jar file into the ./plugins directory of your server. Create the folder if it doesn't exist already.
4. Into the ./plugins folder, create a new folder called Underilla and place a config.yml file in it. You may get the file from this repo.
5. Open the bukkit.ymlfile in your server's root and add the following lines on top:worlds:
   world:
   generator: Underilla
   This will tell Spigot to use Underilla's chunk generator.
   
   
6. In your server's root, create a new folder called world_base.
7. From the folder of your reference world, copy the region folder, and paste it into the world_base folder you just created.
8. If existing, delete the world folder fom your server's root.
9. (Optional) Open the server.properties file in your server's root, and tweak the level-seed property. This has a direct impact on the generated underground.
10. Run the server. You'll notice Underilla generating merged chunks during world creation.

Pregenerate
Underilla is significantly slower than the vanilla generator, as it doesn't relly on noise generation but on reading the reference world's region nbt files and analizing it's patterns to 'clone' its surface to a vanilla world. So, if your world is intended for heavy duty in a big server. It's recommended to pre-generate the whole reference world area with a chunk generator plugin, such as Chunky. I'm planning adding a build-in pre-generation system in the future.

Known issues

• Underilla's generation disables Minecraft's chunk blender, which means there will be sharp old-shool chunk borders at the edge of the reference world's chunks. This may be tackled by trimming your custom world chunks arround the edges to generate blended chunks ahead of time.
• Due to Spigot's generation API, outside of the reference world's area, heightmaps are broken, which has an impact on structures. You may work arround this by pre-generating the whole reference world area, and then disabling Underilla.
• NMS is used for biome placing, so this plugin isn't cross-version-compatible. A new release per every Minecraft release, and thus, this plugin won't work for any new prior-1.19.4 version.

WorldPainter considerations
If you're going to plug your custom WorldPainter world into Underilla, consider before exporting:

• Disable caves, caverns, and chasms altogether, allow Underilla to take over that step. This is due to biome placement, every underground non-solid block in the reference_world drags its biome over along with it, this interfiers with propper underground vanilla biomes.
• Always disable the Allow Minecraft to populate the entire terrain option. Rather use the vanilla_population option in Underilla's config.yml file.
• The Populate layer has no effect. Weather all or none of the terrain will be populated based on the above point.
• If you have custom cave/tunnels layers and want to preserve them during the merge, you'd want to use the Relative merge strategy