Sky Island Feature Configuration

Define a floating island overlay — shape, altitude band, biomes, structures, and static object spawns.

A sky island feature defines one kind of floating landmass: its altitude band, shape algorithm, which biomes cover it, and what structures/static objects can spawn on it. Features are referenced by name from a World Builder Configuration preset’s sky-island-features list — either as the sole terrain of a SkyIsland dimension, or as a floating-island overlay on top of a Default dimension’s normal terrain.

File Location

Unlike other catalog files, sky island features are not referenced from your mod’s manifest — every YAML file in a fixed folder is scanned and loaded automatically:

mods/<YourMod>/sky-island-features/<name>.yaml

Each file is a single feature (no wrapping list).

Minimal Example

name: my_islands
min-altitude: 80
max-altitude: 160
shape-generator:
  type: cellular_automata

This registers a feature spanning world-Y 80–160, using a cellular-automata island shape with all its own defaults, no biomes (islands will appear solid but biome-less unless you add at least one), and no structures or static objects.

Full Field Reference

name: my_islands                # Required
min-altitude: 80                  # Required. Must be <= max-altitude
max-altitude: 160                  # Required
biomes:                              # Optional. Registered biome names covering this island type
  - YourMod:my_island_biome
shape-generator:                      # Required. See Shape Generator below
  type: cellular_automata
  noise-scale: 0.015
  smooth-steps: 4
  final-polish: true
  min-region-size: 80
structures:                            # Optional. Names from structure-config.yaml
  - YourMod:my_island_structure
static-object-spawns:                    # Optional. Names of registered trees/interactables
  - YourMod:my_tree

Field	Required	Default	Description
`name`	Yes	—	Feature identifier. Registered as `ModName:name`.
`min-altitude` / `max-altitude`	Yes	—	World-Y range this feature’s islands occupy. `min-altitude` must be less than or equal to `max-altitude`, or the whole feature fails to load.
`biomes`	No	(none)	Registered biome names used across this island type’s surface. A name that doesn’t resolve at biome-load time is skipped with a warning. If empty, islands generate solid but with no biome assigned.
`shape-generator`	Yes	—	The algorithm used to decide which positions are solid island vs. void. See Shape Generator. Missing or invalid fails the whole feature.
`structures`	No	(none)	Structure names (from Structure Configuration, using one of the `island_surface`/`island_underside`/`island_interior` spawn types) that can spawn on this island type.
`static-object-spawns`	No	(none)	Names of registered trees/interactables that can spawn on this island type’s surface.

A biomes/structures/static-object-spawns name without a colon is namespaced to your own mod automatically.

Shape Generator

shape-generator.type selects one of two shape algorithms:

`cellular_automata`

Produces organic, irregular island blobs — the same cellular-automata technique used for cave carving, but inverted (solid instead of open).

shape-generator:
  type: cellular_automata
  noise-scale: 0.015
  smooth-steps: 4
  final-polish: true
  min-region-size: 80

Field	Default	Description
`noise-scale`	`0.05`	Noise frequency — lower values produce fewer, larger islands; higher values produce more, smaller islands. `0.015` (the shipped example) gives sparse ~65-block islands; `0.05` gives dense ~20-block islands.
`smooth-steps`	`3`	Number of cellular-automata smoothing iterations.
`final-polish`	`false`	Whether to apply one extra smoothing pass at the end.
`min-region-size`	`30`	Solid blobs smaller than this (in blocks) are pruned entirely, leaving void.

`simplex_blob`

A faster, more uniform alternative — solid where a single Simplex noise sample exceeds a threshold.

shape-generator:
  type: simplex_blob
  noise-scale: 0.04
  noise-threshold: 0.5
  height-squish: 0.4

Field	Default	Description
`noise-scale`	`0.04`	Noise frequency.
`noise-threshold`	`0.5`	Noise cutoff above which a position is solid. Same name/meaning as a world-builder pool’s and underground feature’s `noise-threshold`.
`height-squish`	`0.4`	Compresses the shape vertically, flattening islands relative to their horizontal extent.

Registering Structures for Sky Islands

Structures placed via a feature’s structures list must also be registered in Structure Configuration with one of the three island-specific spawn types:

- name: my_island_structure
  spawn-type: island_surface   # or island_underside / island_interior
  spacing:
    x: 10
    y: 10
  spawn-chance: 0.5
  max-size:
    width: 5
    height: 5

Complete Example

Based on the real shipped meadow_islands feature:

name: meadow_islands
min-altitude: 80
max-altitude: 160
biomes:
  - meadow_island
shape-generator:
  type: cellular_automata
  noise-scale: 0.015
  smooth-steps: 4
  final-polish: true
  min-region-size: 80
structures:
  - island_base
  - island_underside
  - island_interior
static-object-spawns:
  - cherry_tree