# 07 - Pregeneration

Pregeneration walks a rectangular (by default square) block radius around a center and forces chunk generation so players do not trigger generation on first visit. Bukkit command `/iris pregen` (alias `pregenerate`) drives a single active `PregeneratorJob` backed by `IrisPregenerator` and a `PregeneratorMethod`. Settings under `settings.json` → `pregen` and `world.globalPregenCache` control timeouts, mantle residency, scheduler mode, and optional durable skip-cache.

See also: `03 - Configuration.md`, `04 - Commands & Permissions.md`, `02 - Getting Started.md`, `06 - Worlds & Lifecycle.md`, `29 - Client HUD & Protocol.md`, `33 - Performance Tuning.md`.

## Commands

| Command | Behavior |
|---------|----------|
| `/iris pregen start <radius> [world=<world>] [center=0,0] [gui=true] [serial=false]` | Start job |
| `/iris pregen stop` / `x` | Request stop; finishes in-flight work then cancels |
| `/iris pregen pause` / `resume` | Toggle pause on the active job |
| `/iris pregen status` | Print progress snapshot (chunks, %, speed, ETA, method, failed) |

Only one pregen job instance is active. Starting a new job closes the previous instance.

### `start` parameters

| Param | Default | Notes |
|-------|---------|-------|
| `radius` | required | Blocks from center on X and Z (`radiusX` = `radiusZ`). Must be `> 0`. Reported span is `(radius * 2)` by `(radius * 2)` blocks |
| `world` | contextual | Target world (Iris preferred; non-Iris uses hybrid method without engine cache wrapper when no access) |
| `center` | `0,0` | Block X/Z center; `me` uses player location when supported by director parsing |
| `gui` | `true` | Open desktop pregen GUI when host supports it; headless servers log and continue |
| `serial` | `false` | One chunk at a time via strict serial hybrid method; **requires Paper** (`supportsStrictSerialPregeneration`) |

If the sender is a player without engine access, Iris warns that the world may not be fully loaded.

## Area model

`PregenTask` builds saturating block bounds `center ± radius`, converts to chunk and region ranges, and iterates regions in spiral order with per-region chunk order pulled toward the center.

| Limit | Value |
|-------|-------|
| Max region span per axis | `117189` regions (~±30M blocks Minecraft world limit) |
| Oversized request | `IllegalArgumentException` at construction (does not hang) |

## Generation methods

| Path | Method |
|------|--------|
| Iris world, parallel | `HybridPregenMethod(world, threadCount)` with concurrency from settings parallelism |
| Iris world, `serial=true` | `HybridPregenMethod.strictSerial(world)` |
| Non-Iris world | Hybrid without engine |
| Cached wrapper | `CachedPregenMethod` around method when caching enabled and runtime scheduler mode is **not** Folia |

Other method classes (`AsyncPregenMethod`, `MedievalPregenMethod`, `AsyncOrMedievalPregenMethod`) exist for specialized/API paths; the command path uses hybrid.

## Cache

| Setting | Location | Behavior |
|---------|----------|----------|
| Per-job skip cache | World `iris/pregen/` via `GlobalCacheSVC.createDefault` | Records generated chunks/regions so restarts can skip work when wrapper is active |
| `world.globalPregenCache` | `settings.json` | When true, maintains global per-world caches on world init/chunk load; when false, service stays idle after enable |
| Folia | Runtime scheduler resolved as Folia | Cached wrapper **disabled** for pregen |

Cache write happens on world unload and service disable. Empty cache is used when the service is disabled.

## Mantle and heap caps

Pregen applies mantle backpressure and heap high-water checks so tectonic plates do not exhaust memory.

| Control | Default / rule |
|---------|----------------|
| `pregen.maxResidentTectonicPlates` | Default `96`, minimum effective floor `16` |
| Effective plate cap | `min(baseCap, heightScaledCap, heapBudgetCap)` using world height vs 384 and ~60% of process heap / estimated plate size |
| Backpressure wait | `mantleBackpressureWaitMs` default `25` (clamped 5–1000) |
| Backpressure timeout | `mantleBackpressureTimeoutMs` default `60000` (clamped 5s–600s) |
| Hard cap trigger | Loaded plates `> effectiveCap * 2` forces wait/evict |
| Heap high water | Pause generation while heap used ≥ **92%**; release at **82%** |
| Heap panic | ≥ **96%** requests panic reclaim / GC (throttled) |
| Save interval | `saveIntervalMs` default `30000` (clamped 5s–900s) during pregen loop |

Raising `maxResidentTectonicPlates` increases memory headroom for speed; lowering reduces peak RAM. See `33 - Performance Tuning.md`.

## Other `pregen` settings

| Key | Default | Role |
|-----|---------|------|
| `runtimeSchedulerMode` | `AUTO` | Influences Folia vs paper-like scheduling for pregen cache and related paths |
| `paperLikeBackendMode` | `AUTO` | Paper-like lifecycle backend selection |
| `chunkLoadTimeoutSeconds` | `15` (5–120) | Chunk load timeout during pregen |
| `timeoutWarnIntervalMs` | `500` (≥250) | Warning interval for stalled loads |
| `moddedPregenInFlight` | `0` → auto `max(16, min(48, cpu*2))` | In-flight cap for modded pregen adapters |

## Pause / stop / status

| Action | Behavior |
|--------|----------|
| Pause | `PregeneratorJob.pauseResume()` flips pause; generator loop spins while paused or heap high-water |
| Stop | `shutdownInstance()` closes pregenerator and interrupts worker asynchronously |
| Status | `progressSnapshot()`: percent, generated, total, chunks/s, ETA, elapsed, method name, paused flag, failed count, world name |

Failed chunks are counted separately and shown in status when non-zero.

## HUD / GUI / protocol

| Surface | Behavior |
|---------|----------|
| Desktop GUI | `PregenRenderer` when `gui=true` and GUI host available; colors mark existing, generating, network, generated, cleaned, mantle states |
| Boss bar / loader HUD | Create and some pregen attach paths use HUD slot claims for progress (creation pregen and studio progress reporters) |
| Client protocol | `IrisProtocolServer.broadcastPregenProgress` sends progress to connected Iris client sessions |

Client HUD details: `29 - Client HUD & Protocol.md`. GUI toggles: `settings.gui.useServerLaunchedGuis`, `maximumPregenGuiFPS`.

## Performance profile

Starting pregen applies `PregenPerformanceProfile` to the engine (or global) before the job runs. Studio `profile` command can also apply the pregen performance profile while measuring pack cost.

## Operator notes

- Radius is in **blocks**, not chunks or regions.
- Re-running pregen over the same area is faster when the chunk cache wrapper is active and cache files under `iris/pregen` remain.
- Unload/remove of a world with active pregen should stop the job for that world identity when lifecycle hooks call shutdown-for-world.
- Serial mode is for diagnosis/stability on Paper, not peak throughput.