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+---
+id: wiki-2026-0508-tetris-project-retrospective
+title: Tetris Project Retrospective
+category: 10_Wiki/Topics
+status: verified
+canonical_id: self
+aliases: [Tetris Retro, Tetris Postmortem]
+duplicate_of: none
+source_trust_level: B
+confidence_score: 0.85
+verification_status: applied
+tags: [retrospective, project, tetris, game-development, lessons-learned]
+raw_sources: []
+last_reinforced: 2026-05-10
+github_commit: pending
+tech_stack:
+  language: TypeScript
+  framework: Canvas/React
+---
+
+# Tetris Project Retrospective
+
+## 매 한 줄
+> **"매 small game project = 매 architecture concept 의 condensed lab"**. Tetris 의 well-defined rule + finite scope 가 SRP, state machine, game loop, testability 의 매 trade-off 를 명확히 노출. 매 retrospective 는 매 lesson 의 codification.
+
+## 매 핵심
+
+### 매 lesson layers
+- **Architecture**: pure game logic vs render separation.
+- **State**: deterministic state machine — 매 replay 가능.
+- **Testing**: pure logic 의 100% coverage, render 의 visual test.
+- **Performance**: 60fps 의 frame budget 16.67ms.
+
+### 매 핵심 결정
+- **Immutable state**: 매 board 의 매 frame 의 new copy — 매 undo/replay free.
+- **Tick-based loop**: 매 wall-clock 분리 — deterministic test.
+- **Wallkick algorithm**: SRS (Super Rotation System) — 매 official Tetris guideline.
+
+### 매 응용
+1. 매 게임 logic 의 pure function 추출 — UI swap (Canvas/SVG/Terminal) 자유.
+2. 매 deterministic seed RNG — 매 bug reproduction.
+3. 매 retrospective template 의 reuse for 다른 small project.
+
+## 💻 패턴
+
+### Pure game state
+```typescript
+type Cell = 0 | 'I' | 'O' | 'T' | 'S' | 'Z' | 'J' | 'L';
+type Board = ReadonlyArray<ReadonlyArray<Cell>>;
+
+interface GameState {
+  readonly board: Board;            // 20 x 10
+  readonly active: Piece;
+  readonly next: Piece[];
+  readonly hold: Piece | null;
+  readonly score: number;
+  readonly level: number;
+  readonly linesCleared: number;
+  readonly tick: number;
+  readonly status: 'playing' | 'paused' | 'gameover';
+}
+```
+
+### Reducer-style transitions
+```typescript
+type Action =
+  | { type: 'MOVE'; dir: -1 | 1 }
+  | { type: 'ROTATE'; cw: boolean }
+  | { type: 'SOFT_DROP' }
+  | { type: 'HARD_DROP' }
+  | { type: 'HOLD' }
+  | { type: 'TICK' };
+
+export function reduce(state: GameState, action: Action): GameState {
+  switch (action.type) {
+    case 'MOVE': {
+      const moved = movePiece(state.active, action.dir, 0);
+      if (collides(state.board, moved)) return state;
+      return { ...state, active: moved };
+    }
+    case 'ROTATE':
+      return tryRotate(state, action.cw);
+    case 'HARD_DROP':
+      return lockAndSpawn(dropToBottom(state));
+    case 'TICK':
+      return tickGravity(state);
+    // ...
+  }
+}
+```
+
+### SRS wallkick
+```typescript
+// JLSTZ piece kick offsets (rotation 0 → R)
+const KICKS_JLSTZ_0_R: Array<[number, number]> = [
+  [0, 0], [-1, 0], [-1, 1], [0, -2], [-1, -2],
+];
+
+function tryRotate(state: GameState, cw: boolean): GameState {
+  const rotated = rotatePiece(state.active, cw);
+  const kicks = lookupKicks(state.active.kind, state.active.rot, cw);
+  for (const [dx, dy] of kicks) {
+    const candidate = { ...rotated, x: rotated.x + dx, y: rotated.y + dy };
+    if (!collides(state.board, candidate)) {
+      return { ...state, active: candidate };
+    }
+  }
+  return state;  // rotation rejected
+}
+```
+
+### Deterministic 7-bag RNG
+```typescript
+function* sevenBag(seed: number): Generator<PieceKind> {
+  const rng = mulberry32(seed);
+  const kinds: PieceKind[] = ['I', 'O', 'T', 'S', 'Z', 'J', 'L'];
+  while (true) {
+    const bag = [...kinds];
+    for (let i = bag.length - 1; i > 0; i--) {
+      const j = Math.floor(rng() * (i + 1));
+      [bag[i], bag[j]] = [bag[j], bag[i]];
+    }
+    yield* bag;
+  }
+}
+```
+
+### Game loop with fixed timestep
+```typescript
+const TICK_MS = 16.67;
+let acc = 0;
+let last = performance.now();
+
+function frame(now: number) {
+  const dt = now - last;
+  last = now;
+  acc += dt;
+  while (acc >= TICK_MS) {
+    state = reduce(state, { type: 'TICK' });
+    acc -= TICK_MS;
+  }
+  render(state);
+  if (state.status === 'playing') requestAnimationFrame(frame);
+}
+requestAnimationFrame(frame);
+```
+
+### Pure logic test
+```typescript
+it('clears completed line', () => {
+  const board = makeBoard([
+    /* ... 19 empty rows ... */
+    ['I','I','I','I','I','I','I','I','I','I'],  // bottom full
+  ]);
+  const state = { ...emptyState, board, active: makePiece('O', 0, 0) };
+  const result = lockPiece(state);
+  expect(result.linesCleared).toBe(1);
+  expect(result.score).toBe(100);  // 1 line × level 1
+});
+```
+
+## 매 결정 기준 (lessons)
+| 결정 | 결과 | 재사용? |
+|---|---|---|
+| Immutable state | 매 replay/undo trivial | ✓ |
+| SRS wallkick | 매 standard 준수 — player familiarity | ✓ |
+| Canvas render | 매 60fps 안정 | ✓ |
+| React render (실험) | 매 30fps drop 발생 | ✗ |
+| Pure reducer | 매 unit test 의 ease | ✓ |
+| Web Workers (실험) | 매 overhead > benefit (small state) | ✗ |
+
+**기본값**: 매 small game = pure reducer + Canvas + fixed-timestep loop.
+
+## 🔗 Graph
+- 변형: [[State Machine]]
+- 응용: [[Game Loop]]
+- Adjacent: [[Testability_Architecture]] · [[Technical-Architecture]] · [[Test-Driven_Development]]
+
+## 🤖 LLM 활용
+**언제**: small game architecture 설계 reference, retrospective template, SRS wallkick 구현 question.
+**언제 X**: 매 specific Tetris ranking algorithm (TGM, etc.) 의 deep detail — 매 specialized guide 필요.
+
+## ❌ 안티패턴 (실수 회고)
+- **Mutable board**: 매 undo/replay 가 fragile — debug 의 nightmare.
+- **Render in reducer**: 매 testability 의 손실 — separate concerns.
+- **Wall-clock dependency**: 매 nondeterministic test — fixed-timestep 가 essential.
+- **Ad-hoc rotation**: SRS 미준수 — 매 player 의 muscle memory 와 conflict.
+
+## 🧪 검증 / 중복
+- Verified (Tetris Guideline 2009; SRS spec; project commit history).
+- 신뢰도 B (project-specific retrospective, generalizable patterns).
+
+## 🕓 Changelog
+| 날짜 | 변경 |
+|---|---|
+| 2026-05-08 | Phase 1 |
+| 2026-05-10 | Manual cleanup — full retro with SRS + reducer + lessons table |