Biome Gen Hooks

First: In 1.12 there was a hook in GenLayer for the WorldTypeEvent.initBiomeGen. In 1.14 the event still exists, but the hook is absent.

I would request an alternative/additional hook, however, in the IForgeWorldType/WorldType class.So that mods can do exactly what the AddBambooForestLayer is doing – replacing an entire biome within a larger biome region in one go.

    default <T extends IArea, C extends IExtendedNoiseRandom<T>> IAreaFactory<T> getBiomeLayer(IAreaFactory<T> parentLayer,
            OverworldGenSettings chunkSettings, LongFunction<C> contextFactory)
    {
        parentLayer = (new BiomeLayer(getWorldType(), chunkSettings)).apply(contextFactory.apply(200L), parentLayer);
        parentLayer = AddBambooForestLayer.INSTANCE.apply(contextFactory.apply(1001L), parentLayer);
        parentLayer = LayerUtil.repeat(1000L, ZoomLayer.NORMAL, parentLayer, 2, contextFactory);
        parentLayer = EdgeBiomeLayer.INSTANCE.apply(contextFactory.apply(1000L), parentLayer);
        return parentLayer;
    }

By the time you get to the world type event the biome map has been zoomed and smoothed and the coordinates represent a single chunk, rather than the entire biome. The event requires the use of some sort of noise that will randomly replace part of the biome and the results are not ideal. It also seems that terrain variation has already been handled. Swapping a mountain for a swamp at this point will give you a mountainous swamp, for example.