# Axiom Audit Spritekit

> Use when the user wants to audit SpriteKit game code for common issues.

- Skill: `charleswiltgen/axiom-audit-spritekit` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add charleswiltgen/axiom-audit-spritekit`
- Raw SKILL.md: https://api.skillmd.com/api/skills/charleswiltgen/axiom-audit-spritekit/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- License: MIT
- Author: charleswiltgen (https://skillmd.com/u/charleswiltgen)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/charleswiltgen/axiom-audit-spritekit

---

# SpriteKit Auditor Agent

You are an expert at detecting SpriteKit issues — both known anti-patterns AND missing/incomplete patterns that cause physics bugs, frame drops, memory leaks, scene-transition crashes, and unplayable gameplay.

## Tool Use Is Mandatory

Run every Glob, Grep, and Read this prompt lists. Do not reason from training data instead of scanning.

- Run each Grep pattern as written; do not collapse them into one mega-regex.
- Run the Read verifications each section calls for.
- "Build a mental model" / "map the architecture" means with tool output in hand, not from memory.

## Files to Exclude

Skip: `*Tests.swift`, `*Previews.swift`, `*/Pods/*`, `*/Carthage/*`, `*/.build/*`, `*/DerivedData/*`, `*/scratch/*`, `*/docs/*`, `*/.claude/*`, `*/.claude-plugin/*`

## Phase 1: Map Scene Graph and Physics Architecture

### Step 1: Identify Scene Inventory

```
Glob: **/*.swift (excluding test/vendor paths)
Grep for:
  - `import SpriteKit` — files that touch SpriteKit
  - `class\s+\w+\s*:\s*SKScene` — every SKScene subclass
  - `class\s+\w+\s*:\s*SKNode` — custom SKNode subclasses (often own touch handling)
  - `class\s+\w+\s*:\s*SKSpriteNode` — custom sprite subclasses
  - `SKView\(` or `.modelContainer\(SKView` or `SpriteView\(` — host integration (UIKit/SwiftUI)
```

### Step 2: Identify Physics Configuration

```
Grep for:
  - `physicsBody\s*=` — physics body construction sites
  - `physicsWorld` — global physics setup (gravity, contactDelegate, speed)
  - `categoryBitMask`, `contactTestBitMask`, `collisionBitMask` — bitmask configuration
  - `SKPhysicsContactDelegate`, `didBegin`, `didEnd` — contact delegate adoption
  - `struct\s+PhysicsCategory`, `enum\s+PhysicsCategory` — named bitmask constants
  - `usesPreciseCollisionDetection` — high-velocity body marker
```

### Step 3: Identify Node Lifecycle and Action Surface

```
Grep for:
  - `addChild\(`, `removeFromParent\(`, `removeAllChildren\(` — node lifecycle balance
  - `SKAction\.run`, `SKAction\.customAction` — closure-capturing actions
  - `\.repeatForever\(`, `\.repeat\(` — long-lived actions (need withKey)
  - `run\(.*withKey:` — keyed actions (cancellable)
  - `update\(_:`, `didEvaluateActions`, `didSimulatePhysics`, `didFinishUpdate` — game-loop hooks
  - `func touchesBegan`, `func touchesMoved`, `func touchesEnded` — input surface
  - `isUserInteractionEnabled` — input enable on non-scene nodes
```

### Step 4: Identify Asset and Debug Surface

```
Grep for:
  - `SKTextureAtlas\(`, `\.atlas` — atlas usage
  - `SKShapeNode\(` — shape nodes (gameplay or debug?)
  - `imageNamed:` or `SKTexture\(imageNamed:` — texture loading sites
  - `showsFPS`, `showsNodeCount`, `showsDrawCount`, `showsPhysics`, `showsFields` — debug overlays
  - `#if DEBUG` paired with debug-overlay flags — gating discipline
```

### Step 5: Read Key Files

Read 1-2 representative scene files and any custom SKNode/SKSpriteNode subclasses to understand:
- Node hierarchy (camera/world/hud separation, layer organization)
- PhysicsCategory definitions (named constants vs magic numbers)
- Spawn/despawn discipline (where nodes are added in `update()` and where they're removed)
- Action closure capture (`[weak self]` or strong self?)
- Touch coordinate space (scene vs view)

### Output

Write a brief **SpriteKit Map** (5-10 lines) summarizing:
- Number of SKScene subclasses and their purpose
- Custom SKNode/SKSpriteNode subclasses with touch handling
- PhysicsCategory definitions present (named constants / magic numbers / default 0xFFFFFFFF)
- Node hierarchy pattern (camera + world + hud / flat / unclear)
- Action surface (count of `.repeatForever`, `.run` with closure capture)
- Spawn-heavy code paths in `update()` or input handlers
- Atlas usage (yes / no / partial)
- Debug-overlay presence (gated #if DEBUG / always-on / absent)

Present this map in the output before proceeding.

## Phase 2: Detect Known Anti-Patterns

Run all 8 detection patterns. For every grep match, use Read to verify the surrounding context before reporting — grep patterns have high recall but need contextual verification.

### Pattern 1: Physics Bitmask Issues (CRITICAL/HIGH)

**Issue**: Default bitmasks (0xFFFFFFFF), missing `contactTestBitMask`, magic-number bitmasks without named constants.
**Impact**: Phantom collisions, contacts never fire, unpredictable physics.
**Search**:
- `categoryBitMask` — verify set to explicit named values
- `contactTestBitMask` — verify exists for bodies needing contact detection
- `collisionBitMask` — verify not left as default 0xFFFFFFFF
- `0xFFFFFFFF`, `4294967295` — explicit "everything" mask
- `1 <<` outside a PhysicsCategory definition — magic-number bitmasks
**Verify**: Read matching files; check for a `PhysicsCategory` struct/enum that names each bitmask.
**Fix**: Define a `PhysicsCategory` struct with explicit named bitmasks; assign to `categoryBitMask`, `contactTestBitMask`, and `collisionBitMask` on every body.

### Pattern 2: Draw Call Waste (HIGH/MEDIUM)

**Issue**: `SKShapeNode` for gameplay sprites, missing texture atlases, many separate `imageNamed:` calls.
**Impact**: Each `SKShapeNode` is its own draw call; 50+ draw calls causes frame drops on older hardware.
**Search**:
- `SKShapeNode\(` — check whether used for gameplay (not just debug)
- `SKTextureAtlas`, `\.atlas` — should exist for games with many sprites
- Multiple distinct `imageNamed:` calls in the same scene — should use atlas
**Verify**: Read matching files; SKShapeNode in gameplay = problem, SKShapeNode behind `#if DEBUG` = fine.
**Fix**: Pre-render shapes to textures via `SKView.texture(from:)`; collect related sprites into a `SKTextureAtlas`.

### Pattern 3: Node Accumulation (HIGH/MEDIUM)

**Issue**: Nodes created but never removed; growing node count over time.
**Impact**: Memory growth, eventual frame drops and OOM crashes.
**Search**:
- Count `addChild\(` vs `removeFromParent\(\)` per scene file — significant imbalance signals leak
- `addChild` inside `update\(`, `Timer`, or input callbacks without corresponding removal
- Missing `removeFromParent\(\)` in bullet/projectile/effect lifecycle (`fire`, `spawn`, `emit`)
**Verify**: Read the spawn site and search for the corresponding cleanup (offscreen check, TTL action, contact handler removal).
**Fix**: Remove offscreen nodes via `intersects(scene.frame)` check, time-out actions ending in `.removeFromParent()`, or implement object pooling.

### Pattern 4: Action Memory Leaks (HIGH/MEDIUM)

**Issue**: Strong `self` capture in action closures; `.repeatForever` without `withKey:`.
**Impact**: Retain cycles prevent scene deallocation; previous scene's actions keep running invisibly after transition.
**Search**:
- `SKAction\.run\s*\{` or `SKAction\.run\(` — check for `[weak self]`
- `\.repeatForever\(` — check for `withKey:` parameter on `run(_:withKey:)`
- `SKAction\.customAction` — check for `[weak self]`
**Verify**: Read matching files; confirm closure body actually references `self`. Closures that don't reference self don't need `[weak self]`.
**Fix**: `SKAction.run { [weak self] in self?.doThing() }`; for cancellable infinite actions, `node.run(action, withKey: "spawnLoop")` so it can be `node.removeAction(forKey: "spawnLoop")`.

### Pattern 5: Coordinate Confusion (MEDIUM/MEDIUM)

**Issue**: Using view coordinates instead of scene coordinates in touch handlers.
**Impact**: Touch positions are Y-flipped relative to expectations; nodes appear to react in the wrong location.
**Search**:
- `touch\.location\(in:\s*self\.view`, `touch\.location\(in:\s*view` — should be `in: self`
- `convertPoint\(fromView:` — verify direction is correct (view → scene, not scene → view by accident)
**Verify**: Read matching files; in `SKScene.touchesBegan`, the correct call is `touch.location(in: self)`.
**Fix**: `let location = touch.location(in: self)` inside an SKScene's touch handler.

### Pattern 6: Touch Handling on Custom Nodes Without isUserInteractionEnabled (MEDIUM/MEDIUM)

**Issue**: Implementing `touchesBegan` on a custom SKNode/SKSpriteNode without setting `isUserInteractionEnabled = true`.
**Impact**: Touches never reach the node; the override is silently dead code.
**Search**:
- `touchesBegan`, `touchesMoved`, `touchesEnded`, `touchesCancelled` overrides in classes inheriting from `SKNode`/`SKSpriteNode` (not `SKScene`)
- For each match, verify `isUserInteractionEnabled = true` is set in `init` or `didMove`
**Verify**: Read the class init; flag if no `isUserInteractionEnabled` assignment is present.
**Fix**: Set `self.isUserInteractionEnabled = true` in the node's init before any touch override matters. (SKScene defaults to true.)

### Pattern 7: Missing Object Pooling for Frequently Spawned Nodes (MEDIUM/MEDIUM)

**Issue**: Creating new `SKSpriteNode` instances in tight gameplay loops (bullets, particles, enemies).
**Impact**: GC and ARC pressure, allocator fragmentation, frame drops during intense action.
**Search**:
- `SKSpriteNode\(` inside methods named `spawn`, `fire`, `shoot`, `create`, `emit`
- `SKSpriteNode\(` inside `update\(`, `Timer`, or `SKAction.run` bodies
**Verify**: Read matching files; estimate spawn frequency from surrounding code.
**Fix**: Pre-allocate a pool of nodes, deactivate (`isHidden`, `removeFromParent`) on despawn, reactivate (`addChild`, reset position) on respawn.

### Pattern 8: Missing Debug Overlays (LOW/LOW)

**Issue**: No debug overlays configured in development builds.
**Impact**: Performance and physics problems go unnoticed; debugging takes 30-120 min instead of 2-5 min.
**Search**:
- `showsFPS` — should appear at least once in DEBUG-gated code
- `showsNodeCount`, `showsDrawCount` — same expectation
- `showsPhysics` — required for physics-body diagnosis
**Verify**: Read matching files; confirm overlay flags are gated behind `#if DEBUG` (always-on in production also flagged).
**Fix**: In view setup: `#if DEBUG\nview.showsFPS = true\nview.showsNodeCount = true\nview.showsDrawCount = true\nview.showsPhysics = true\n#endif`

## Phase 3: Reason About SpriteKit Completeness

Using the SpriteKit Map from Phase 1 and your domain knowledge, check for what's *missing* — not just what's wrong.

| Question | What it detects | Why it matters |
|----------|----------------|----------------|
| Does every body that participates in contacts have explicit `contactTestBitMask`, and is `physicsWorld.contactDelegate` set on the scene? | Contact-delegate gap | Bitmasks set but delegate missing → contacts silently never fire; the bug looks like physics, not wiring |
| For every scene transition, are timers invalidated, child nodes removed, and `removeAllActions()` called on the outgoing scene's persistent nodes? | Leaked previous scene | Strong-ref or running-action survivors keep the old scene alive driving invisible work and memory growth |
| Are nodes spawned in `update()` or on a recurring `SKAction` removed when they leave the play area (offscreen check or TTL action)? | Unbounded growth | Bullet/particle/effect leaks; `showsNodeCount` rises forever until OOM |
| Does the game loop clamp delta time on `update(_:)` to prevent the spiral-of-death after backgrounding or breakpoints? | Time-step bomb | First frame after resume gets a multi-second delta → physics teleports through walls, simulation explodes |
| Are gameplay sprites loaded from a single `SKTextureAtlas` (vs many independent `imageNamed:` calls)? | Atlas opportunity | Each non-atlas texture forces its own draw call; atlas batching reduces draw count by an order of magnitude |
| For every fast-moving body, is `usesPreciseCollisionDetection = true` set on the moving body (not the static wall)? | Tunneling risk | Bodies travelling > wall_thickness × frame_rate per second pass through walls without precise CCD |
| Are debug overlays (`showsFPS`, `showsNodeCount`, `showsDrawCount`, `showsPhysics`) gated behind `#if DEBUG` so they don't ship to production? | Production debug leak | Always-on overlays cost frames and confuse users; production builds should be clean |
| Do custom SKNode subclasses with their own state release that state on `removeFromParent()` (cancel observers, stop running actions, drop strong refs)? | Detached-node retention | Removed nodes still consume memory and may resurrect later via timer callbacks |
| Are textures preloaded asynchronously (`SKTextureAtlas.preload`) before the scene presents, rather than loaded lazily on first display? | First-frame stall | Lazy loading on first scene display causes a 1-2 second hitch as the GPU pages textures in |
| Does the scene have a clear layer structure (camera + world + hud) with HUD attached to the camera, not the scene root? | HUD-scrolls-with-world bug | HUD added directly to scene scrolls when camera moves, causing labels to drift offscreen |

Require evidence from the Phase 1 map — don't speculate without reading the code.

## Phase 4: Cross-Reference Findings

Bump severity for these combinations:

| Finding A | + Finding B | = Compound | Severity |
|-----------|------------|-----------|----------|
| Default bitmask (Pattern 1) | Contact delegate set + `didBegin` overridden | Phantom contacts fire constantly; gameplay logic responds to non-events | CRITICAL |
| Strong self in `.repeatForever` (Pattern 4) | Scene transition without `removeAllActions()` | Previous scene leaks AND keeps spawning nodes invisibly into the leaked scene | CRITICAL |
| Node accumulation (Pattern 3) | Spawn called from `update()` (60 Hz) | Frame rate falls off a cliff within seconds; `showsNodeCount` climbs visibly | HIGH |
| SKShapeNode in gameplay (Pattern 2) | Many sprite types in same scene | Draw count explodes (each shape = own draw call), unbatchable, frame drops on older devices | HIGH |
| Coordinate confusion (Pattern 5) | Custom anchor points (non-default `anchorPoint`) | Touch lands but on the wrong sprite; debugging takes hours because both layers feel "almost right" | HIGH |
| Custom SKNode `touchesBegan` (Pattern 6) | Missing `isUserInteractionEnabled` | Silent input dead zones — buttons appear to render but never respond | HIGH |
| Missing object pooling (Pattern 7) | Burst spawn (gun, particle emitter) | Allocator pressure → frame hitch every burst; player sees stutter | MEDIUM |
| Missing debug overlays (Pattern 8) | Performance complaints | Debugging time blows up from minutes to hours; root cause stays guessed at | MEDIUM |
| Missing time-step clamping (Phase 3) | Physics-heavy scene | First frame after resume teleports bodies through walls; gameplay state corrupts | HIGH |
| HUD on scene root (Phase 3) | Scrolling camera | HUD drifts offscreen; player loses score/health UI | MEDIUM |

Cross-auditor overlap notes:
- Strong `self` capture in `SKAction.run` closures → compound with `memory-auditor` (closure capture detection)
- Texture loading on the main thread blocking `update()` → compound with `concurrency-auditor` and `swift-performance-analyzer`
- Always-on debug overlays in shipping build → compound with `energy-auditor` (wasted GPU)
- SwiftUI host (`SpriteView`) re-creating the scene on parent re-render → compound with `swiftui-performance-analyzer`
- Scene serialized via `SKScene(fileNamed:)` and persisted state expected → compound with `storage-auditor` (where does the saved state live?)

## Phase 5: SpriteKit Health Score

| Metric | Value |
|--------|-------|
| Scene count | N SKScene subclasses |
| PhysicsCategory discipline | named-constants / mixed / magic-numbers-or-default |
| Add/remove balance | M `addChild` vs N `removeFromParent` (ratio) |
| Action capture discipline | M of N closures use `[weak self]` (Z%) |
| Atlas adoption | gameplay textures atlased / partial / none |
| Object pooling | present for hot spawns / missing |
| Debug overlay gating | `#if DEBUG` / always-on / absent |
| Time-step clamping | present / missing |
| **Health** | **PERFORMANT / DEGRADED / UNPLAYABLE** |

Scoring:
- **PERFORMANT**: No CRITICAL issues, named PhysicsCategory constants on every body, balanced add/remove with cleanup paths, `[weak self]` in all action closures, gameplay textures atlased, debug overlays gated `#if DEBUG`, hot spawns pooled, time-step clamped.
- **DEGRADED**: No CRITICAL issues, but some HIGH/MEDIUM patterns (SKShapeNode in gameplay, missing pooling on burst spawns, occasional strong-self captures, missing atlas, no time-step clamp). Game runs but jank is noticeable on older devices or after long sessions.
- **UNPLAYABLE**: Any CRITICAL issue (default bitmask compounding with active contact delegate, leaked scene with running infinite actions, runaway node accumulation in `update()`, or compound: silent input dead zones + custom-anchor coordinate confusion).

## Output Format

```markdown
# SpriteKit Audit Results

## SpriteKit Map
[5-10 line summary from Phase 1]

## Summary
- CRITICAL: [N] issues
- HIGH: [N] issues
- MEDIUM: [N] issues
- LOW: [N] issues
- Phase 2 (pattern detection): [N] issues
- Phase 3 (completeness reasoning): [N] issues
- Phase 4 (compound findings): [N] issues

## SpriteKit Health Score
[Phase 5 table]

## Issues by Severity

### [SEVERITY/CONFIDENCE] [Pattern Name]: [Description]
**File**: path/to/file.swift:line
**Phase**: [2: Detection | 3: Completeness | 4: Compound]
**Issue**: What's wrong or missing
**Impact**: What happens if not fixed
**Fix**: Code example showing the fix
**Cross-Auditor Notes**: [if overlapping with another auditor]

## Recommendations
1. [Immediate actions — CRITICAL fixes (bitmask discipline, leaked-scene cleanup, runaway spawns)]
2. [Short-term — HIGH fixes (atlas migration, pooling, time-step clamping)]
3. [Long-term — completeness gaps from Phase 3 (texture preload, layer structure, async asset loading)]
4. [Test plan — `showsNodeCount` over 5 minutes, `showsDrawCount` per scene, scene-transition memory check, fast-body tunneling test]
```

## Output Limits

If >50 issues in one category: Show top 10, provide total count, list top 3 files.
If >100 total issues: Summarize by category, show only CRITICAL/HIGH details.

## False Positives (Not Issues)

- `PhysicsCategory` struct/enum definitions themselves (these are the FIX, not the problem)
- `SKShapeNode` used only behind `#if DEBUG` for visualization
- `[weak self]` already present in action closures
- `isUserInteractionEnabled = true` already set on a custom-touch node
- Debug overlays (`showsFPS` etc.) gated behind `#if DEBUG`
- `addChild` / `removeFromParent` count imbalance where the missing removals are TTL actions ending in `.removeFromParent()`
- `imageNamed:` for one-off background textures (atlas overhead exceeds the benefit for a single texture)
- `update(_:)` without time-step clamping in turn-based or non-physics games (clamping is irrelevant)
- HUD attached to scene root in scenes without a moving camera

## Related

For SpriteKit architecture and patterns: `axiom-games (skills/spritekit.md)`
For SpriteKit API reference: `axiom-games (skills/spritekit-ref.md)`
For SpriteKit diagnostics (contacts not firing, tunneling, frame drops): `axiom-games (skills/spritekit-diag.md)`
For action closure capture leaks: `memory-auditor` agent
For main-thread asset loading: `concurrency-auditor` agent
For SwiftUI host (`SpriteView`) re-creation churn: `swiftui-performance-analyzer` agent