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====== Adding World Presets [1.19.2 AND BELOW] ====== 
A ''WorldPreset'' is a wrapper class around a ''ChunkGenerator'' that allows you to create a world with a preconfigured chunk generator. The preset is shown on the "More World Options" screen, on the "World Type" button. The vanilla world presets are Default, Large Biomes, AMPLIFIED, Single Biome, Superflat, and Debug Mode.

In this tutorial, we will add a simple world preset which generates nothing in a world.

===== Creating a World Preset =====

A world preset requires a ''ChunkGenerator''. You can [[tutorial:chunkgenerator|create your own]]((99% of the time, this is not necessary-- see the chunk generator page for more details)), but here, we will modify the ''FlatChunkGenerator'' to create a void world.

In order to implement a preset, we first need access to the ''WorldPresets$Registrar'' inner class. For that, we can use a simple [[tutorial:accesswidening|access widener]]. This could be done without an access widener, but it is much simpler to use one in this case. Your access widener should look like this:

<code>
accessWidener   v1      named
accessible      class   net/minecraft/world/gen/WorldPresets$Registrar
</code>

Don't forget to add the neccessary entries to your fabric.mod.json and build.gradle files!

Once we have access to the ''Registrar'' class, the preset can be implemented in one mixin:

<code java>
// if you can't mixin here, make sure your access widener is set up correctly!
@Mixin(WorldPresets.Registrar.class)
public abstract class WorldPresetMixin {
    // defining our registry key. this key provides an Identifier for our preset, that we can use for our lang files and data elements.
    private static final RegistryKey<WorldPreset> VOID_WORLD = RegistryKey.of(Registry.WORLD_PRESET_KEY, new Identifier("wiki-example", "void_world"));
    @Shadow protected abstract RegistryEntry<WorldPreset> register(RegistryKey<WorldPreset> key, DimensionOptions dimensionOptions);
    @Shadow protected abstract DimensionOptions createOverworldOptions(ChunkGenerator chunkGenerator);

    @Inject(method = "initAndGetDefault", at = @At("RETURN"))
    private void addPresets(CallbackInfoReturnable<RegistryEntry<WorldPreset>> cir) {
        // the register() method is shadowed from the target class
        this.register(VOID_WORLD, this.createOverworldOptions(
                // a FlatChunkGenerator is the easiest way to get a void world, but you can replace this FlatChunkGenerator constructor with a NoiseChunkGenerator, or your own custom ChunkGenerator.
                new FlatChunkGenerator(
                        // passing null will use the default structure set
                        null,
                        new FlatChunkGeneratorConfig(
                                // we don't need to overwrite the structure set
                                Optional.empty(),
                                BuiltinRegistries.BIOME)
                        )
                )
        );
    }
}
</code>

Don't forget to add the mixin to your ''mixins.json'' file!

Our preset is registered, but if you load up the game, nothing will show up in the menu. This is because the presets that are actually displayed in the More World Options menu are controlled via [[tutorial:tags|tags]].

In order for the preset to show up, we'll need to add it to the ''normal'' WorldPreset tag. Create a new file in your resources directory, at ''src/main/resources/data/minecraft/tags/worldgen/world_preset'' called ''normal.json''. Note that the tag is stored under the ''minecraft'' namespace, not your mod's.

<code>
{
  "replace": false,
  "values": [
    "wiki-example:void_world"
  ] 
}
</code>

And, of course, you'll probably want a translation file. I'm using English, so my lang file will be at ''src/main/resources/assets/wiki-example/lang/en_us.json'':
<code>
{
  "generator.wiki-example.void_world": "Nothing but Void"
}
</code>

And you're done!