---
id: wiki-2026-0508-skybound-enemy-orientation-fix
title: Skybound Enemy Orientation Fix
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Enemy Facing Bug, Sprite Flip Fix, Orientation Update Loop]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [skybound, combat-ai, sprite, orientation, bugfix]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: typescript
  framework: skybound-engine
---

# Skybound Enemy Orientation Fix

## 매 한 줄
> **"매 enemy facing 의 source-of-truth 는 velocity, not last-input"**. Skybound 의 enemy 가 stationary 시 wrong direction face 하던 bug — orientation 을 velocity-derived 로 unify 하고, idle fallback 으로 player-facing 적용. 매 2D action game 의 standard fix.

## 매 핵심

### 매 문제
- Enemy 가 path target 에 도달 후 멈추면 last-known facing 유지.
- Player 가 옆에 다가가도 그대로 → unrealistic + hitbox mismatch.
- Sprite flip 이 movement input 에만 react.

### 매 fix axes
- **Velocity-driven facing**: |vx| > epsilon 시 sign(vx) 로 flip.
- **Idle fallback to player**: |v| < eps 일 때 face nearest threat.
- **Hysteresis**: rapid flip 방지 (oscillation guard).
- **Animation sync**: orientation change 시 anim state machine 의 transition.

### 매 응용
1. Skybound enemy AI.
2. 2D platformer enemy facing.
3. Top-down shooter NPC orientation.

## 💻 패턴

### Velocity-driven facing
```typescript
const FACING_EPS = 0.05;
function updateFacing(enemy: Enemy, dt: number): void {
  if (Math.abs(enemy.velocity.x) > FACING_EPS) {
    enemy.facing = enemy.velocity.x > 0 ? "right" : "left";
    enemy.idleTime = 0;
    return;
  }
  enemy.idleTime += dt;
  if (enemy.idleTime > 0.2) {
    const player = enemy.world.player;
    enemy.facing = player.position.x >= enemy.position.x ? "right" : "left";
  }
}
```

### Hysteresis guard (anti-flip)
```typescript
const FLIP_HYSTERESIS_MS = 120;
function setFacing(enemy: Enemy, target: Facing, now: number): void {
  if (enemy.facing === target) return;
  if (now - enemy.lastFlipMs < FLIP_HYSTERESIS_MS) return;
  enemy.facing = target;
  enemy.lastFlipMs = now;
  enemy.sprite.flipX = target === "left";
}
```

### Animation state sync
```typescript
function syncAnimToFacing(enemy: Enemy): void {
  const dir = enemy.facing;
  const stateName = `${enemy.animState}_${dir}`;
  if (enemy.sprite.currentAnim !== stateName) {
    enemy.sprite.play(stateName, { preserveFrame: true });
  }
}
```

### 8-direction variant
```typescript
type Dir8 = "N" | "NE" | "E" | "SE" | "S" | "SW" | "W" | "NW";
function vecToDir8(v: Vec2): Dir8 {
  const angle = Math.atan2(v.y, v.x); // -π..π
  const idx = Math.round(((angle + Math.PI) / (Math.PI / 4))) % 8;
  return (["W", "SW", "S", "SE", "E", "NE", "N", "NW"] as Dir8[])[idx];
}
```

### Hitbox mirror with facing
```typescript
function getHitboxWorld(enemy: Enemy): Rect {
  const local = enemy.attackHitbox;
  const x = enemy.facing === "right"
    ? enemy.position.x + local.x
    : enemy.position.x - local.x - local.w;
  return { x, y: enemy.position.y + local.y, w: local.w, h: local.h };
}
```

### Test: facing follows velocity
```typescript
test("facing follows velocity sign", () => {
  const e = makeEnemy({ position: { x: 0, y: 0 } });
  e.velocity = { x: 2, y: 0 };
  updateFacing(e, 0.016);
  expect(e.facing).toBe("right");
  e.velocity = { x: -2, y: 0 };
  updateFacing(e, 0.016);
  expect(e.facing).toBe("left");
});
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Pure 2D side-scroller | velocity sign(vx) 만 사용 |
| Top-down 4/8-dir | vecToDir8 with hysteresis |
| Stationary turret | always face nearest threat |
| Flying enemy | facing = velocity dir, decoupled from gravity |

**기본값**: velocity-driven + idle fallback + hysteresis + anim sync.

## 🔗 Graph
- 부모: [[Combat AI]] · [[Sprite Animation]]
- 변형: [[NPC Pathfinding Facing]] · [[Player Facing]]
- 응용: [[Skybound Knowledge Hub]] · [[Boss Orientation]]
- Adjacent: [[Hitbox System]] · [[Animation State Machine]]

## 🤖 LLM 활용
**언제**: 2D action game enemy facing bug, hitbox mirror, anim sync.
**언제 X**: 3D character (use root motion + IK), turn-based grid.

## ❌ 안티패턴
- **Last-input facing**: stationary 시 stale.
- **No hysteresis**: zigzag motion 에서 sprite flicker.
- **Hitbox not mirroring**: visual ↔ collision mismatch.
- **Anim transition snap**: facing change 시 frame reset → ugly.

## 🧪 검증 / 중복
- Verified (Skybound bugfix 2026-04 + 2D game dev standard practice).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — FULL spec rewrite with orientation patterns |
