2nd/10_Wiki/Topics/Backend/Preserving-State-in-Procedural-Worlds.md

---
id: wiki-2026-0508-preserving-state-in-procedural-w
title: Preserving State in Procedural Worlds
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Procedural World Persistence, Seed-Based State]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [procedural-generation, game-dev, state, persistence]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript
  framework: any
---

# Preserving State in Procedural Worlds

## 매 한 줄
> **"매 infinite-world 의 finite-memory tradeoff"**. 매 Minecraft, No Man's Sky, Dwarf Fortress 매 procedural-generated world → 매 player modifications 매 persist 매 only-visited chunks. 매 seed + delta-overlay 의 standard pattern.

## 매 핵심

### 매 problem
- World 매 effectively infinite (2^64 seed space).
- Cannot store every chunk (memory + disk).
- But player modifications must survive.

### 매 standard pattern
1. Deterministic seed-based generator G(seed, x, y, z) → chunk.
2. Delta overlay D(x, y, z) → player edits relative to G.
3. On load: chunk = G(seed, ...) ⊕ D(...).
4. Disk: store only non-empty D entries.

### 매 응용
1. Sandbox games (Minecraft, Terraria).
2. Roguelikes (Dwarf Fortress, Caves of Qud).
3. Open-world MMOs (No Man's Sky regions).

## 💻 패턴

### Seed-based deterministic generator (Perlin/Simplex)
```ts
import { createNoise2D } from 'simplex-noise';

class WorldGen {
  private noise2D: ReturnType<typeof createNoise2D>;
  constructor(seed: number) {
    const rng = mulberry32(seed);
    this.noise2D = createNoise2D(rng);
  }
  height(x: number, z: number): number {
    return Math.floor(64 + 32 * this.noise2D(x * 0.01, z * 0.01));
  }
}
function mulberry32(a: number) { return () => { /* ... */ }; }
```

### Delta-overlay storage (sparse)
```ts
type ChunkKey = `${number},${number}`;            // chunk coord
type BlockKey = `${number},${number},${number}`;  // block coord within chunk

class DeltaStore {
  private deltas = new Map<ChunkKey, Map<BlockKey, BlockId | null>>();

  set(cx: number, cz: number, bx: number, by: number, bz: number, b: BlockId | null) {
    const key: ChunkKey = `${cx},${cz}`;
    let chunk = this.deltas.get(key);
    if (!chunk) this.deltas.set(key, (chunk = new Map()));
    chunk.set(`${bx},${by},${bz}`, b);
  }

  applyTo(cx: number, cz: number, generated: Block[][][]): Block[][][] {
    const chunk = this.deltas.get(`${cx},${cz}`);
    if (!chunk) return generated;
    for (const [bk, b] of chunk) {
      const [bx, by, bz] = bk.split(',').map(Number);
      generated[bx][by][bz] = b ?? AIR;
    }
    return generated;
  }
}
```

### Chunk persistence (NBT-style binary)
```ts
import { writeFile } from 'fs/promises';
import { gzipSync } from 'zlib';

async function saveChunk(cx: number, cz: number, store: DeltaStore) {
  const data = store.deltas.get(`${cx},${cz}`);
  if (!data || data.size === 0) return;
  const buf = encodeNBT([...data.entries()]);
  await writeFile(`world/c.${cx}.${cz}.dat`, gzipSync(buf));
}
```

### LRU chunk cache (memory bound)
```ts
import LRU from 'lru-cache';
const cache = new LRU<ChunkKey, Chunk>({ max: 256, dispose: (chunk, k) => persist(k, chunk) });

function getChunk(cx: number, cz: number): Chunk {
  const key: ChunkKey = `${cx},${cz}`;
  let c = cache.get(key);
  if (!c) {
    c = applyDeltas(generate(cx, cz), key);
    cache.set(key, c);
  }
  return c;
}
```

### Player-modification log (event-sourced variant)
```ts
type Edit = { t: number; x: number; y: number; z: number; before: BlockId; after: BlockId };
const log: Edit[] = [];
function setBlock(x: number, y: number, z: number, after: BlockId) {
  const before = world.get(x, y, z);
  log.push({ t: Date.now(), x, y, z, before, after });
  world.set(x, y, z, after);
}
// rebuild deltas by replaying log (audit + rollback)
```

## 매 결정 기준
| 상황 | Pattern |
|---|---|
| Few edits, infinite world | Seed + sparse delta |
| Heavy editing, finite world | Full chunk storage |
| Audit / rollback needed | Event-sourced log |
| Multi-player concurrent | Authoritative server + delta sync |

**기본값**: Seed + delta-overlay + LRU cache + on-demand disk persistence.

## 🔗 Graph
- 부모: [[Procedural-Generation]]
- 변형: [[Event Sourcing]]
- Adjacent: [[Perlin Noise]]

## 🤖 LLM 활용
**언제**: voxel/sandbox game architecture, infinite-world design, save-system design.
**언제 X**: linear-level games (use whole-state save).

## ❌ 안티패턴
- **Storing every chunk**: 매 disk explosion.
- **Non-deterministic generator**: 매 seed-replay 매 broken.
- **No LRU bound**: 매 OOM on long sessions.

## 🧪 검증 / 중복
- Verified (Minecraft Anvil format docs, Perlin noise paper, "Dwarf Fortress" GDC talks).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — Procedural state preservation FULL with seed+delta pattern |