Bevy procedural generation

When to use

Load this when a level, loot table, or map should be reproducible from a seed, and you need the ECS shape. Spawning the finished layout uses Commands on Startup or a later schedule you already use. Saving the seed belongs on bevy-save-load.

ECS shape

• Components: cell, room, or prop facts you define. The ECS page shows plain Component structs and commands.spawn.
• Resources: one seed and a generator state you own as a Resource (see bevy-data-resources). Do not invent a Bevy RNG type.
• Systems: fill the resource on Startup, then spawn entities from that data. Use .chain() so spawn sees the finished grid.
• Schedule: Startup for a one-shot map. A streaming map is a later system on Update. Check the docs for a background-thread API before leaving the main schedules.

Coming from Godot

Godot idea	Bevy idiom
Seeded run	A Resource holding a seed you define
Chunk or dungeon grid	Your components, spawned with Commands
Noise, BSP, walk, collapse	Algorithm names from the Godot skill are ideas only. Check the docs.rs crate index before treating them as Bevy functions.
Tile write	No tile API here. Wait for a later tile skill
Nav bake after generation	Nav bake after generation belongs on bevy-navigation.

Scope

• Check docs.rs bevy latest for a noise, RNG, or constraint-solver module before writing one.
• Check the docs for worker threads and off-main-thread spawn before writing a pool type.
• The assets catalog was not used to pick a generation plugin.
• Large-grid batching and navigation rebake are unverified.

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A Godot node script
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official docs first	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No Godot noise, tile, or thread-pool types. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented noise, wave-function, or chunk APIs. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No named third-party generation crate as the chosen tool. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

docs.rs links use the unversioned latest permalink. The library pin on bevy-master stays 0.20.0.

Official Documentation

• Migration guides - Unversioned hop index.
• bevy crate - Unversioned API index. No procedural module was opened.
• Assets - Official asset catalog. No generation plugin was selected.
• Examples - Example tree on the latest branch.
• ECS - Component, Commands, Startup, and .chain().
• Resources - App-wide seed state. API limits are on bevy-data-resources.

Related Skills

Prerequisites

• bevy-master - ECS ownership.
• bevy-data-resources - Resource versus Component.
• bevy-ecs-composition - Spawn tuples and .chain().

Complements

• bevy-asset-scenes - Spawn a scene asset. Not a generator.
• bevy-save-load - Seed persistence.
• bevy-navigation - No bake after a generated map.
• godot-procedural-generation - Equivalent Godot skill.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.