unity-performance

What this skill does

# Unity Performance Optimization

## Overview

Systematic approach to profiling and optimizing Unity games. Covers profiling tools, CPU/GPU optimization, memory management, rendering optimization, and platform-specific considerations.

## Profiling Tools

| Tool | What It Shows | When to Use |
|------|--------------|-------------|
| **Unity Profiler** | CPU, GPU, memory, audio, physics per frame | First stop for any perf issue |
| **Frame Debugger** | Draw call breakdown, shader/material state | Rendering bottlenecks |
| **Memory Profiler** | Heap snapshots, texture/mesh memory | Memory leaks, bloat |
| **Profile Analyzer** | Compare captures, statistical analysis | Before/after optimization |
| **Physics Debugger** | Collider visualization, contact points | Physics performance |

### Profiler Workflow

1. Build with Development Build + Autoconnect Profiler enabled
2. Profile on target device (not in Editor -- Editor overhead distorts results)
3. Identify the bottleneck category: CPU-bound, GPU-bound, or memory pressure
4. Drill into the specific system causing the issue
5. Optimize, re-profile, and compare

### Reading the Profiler

```text
If frame time > 16.6ms (60 FPS target):
  CPU timeline > GPU timeline -> CPU-bound
  GPU timeline > CPU timeline -> GPU-bound
  GC.Alloc column shows per-frame allocations -> GC pressure
```

Look for spikes (single bad frames) vs. sustained high times (baseline too heavy).

## CPU Optimization

### Reduce Per-Frame Allocations (GC)

| Anti-Pattern | Fix |
|-------------|-----|
| `string + string` in Update | Use `StringBuilder` or cache |
| `new List<T>()` every frame | Allocate once, `Clear()` and reuse |
| LINQ in hot paths | Replace with manual loops |
| `GetComponent<T>()` per frame | Cache in Awake/Start |
| `GameObject.Find()` per frame | Cache reference or use events |
| `foreach` on non-generic collections | Use `for` loop or generic collections |
| `SendMessage()` / `BroadcastMessage()` | Use direct calls, events, or interfaces |
| Boxing value types | Use generic collections, avoid `object` casts |

### Object Pooling

```csharp
public class ObjectPool<T> where T : Component
{
    readonly Queue<T> _pool = new();
    readonly T _prefab;
    readonly Transform _parent;

    public ObjectPool(T prefab, int preWarm, Transform parent = null)
    {
        _prefab = prefab;
        _parent = parent;
        for (int i = 0; i < preWarm; i++)
            _pool.Enqueue(CreateInstance());
    }

    public T Get(Vector3 position, Quaternion rotation)
    {
        var obj = _pool.Count > 0 ? _pool.Dequeue() : CreateInstance();
        obj.transform.SetPositionAndRotation(position, rotation);
        obj.gameObject.SetActive(true);
        return obj;
    }

    public void Return(T obj)
    {
        obj.gameObject.SetActive(false);
        _pool.Enqueue(obj);
    }

    T CreateInstance()
    {
        var obj = Object.Instantiate(_prefab, _parent);
        obj.gameObject.SetActive(false);
        return obj;
    }
}
```

Pool bullets, particles, enemies, UI elements -- anything instantiated/destroyed frequently. Unity 2021+ also has `UnityEngine.Pool.ObjectPool<T>` built-in.

### Update Optimization

| Technique | Description |
|-----------|-------------|
| Stagger updates | Don't update all AI every frame; use tick groups |
| Distance-based LOD | Reduce update frequency for distant objects |
| Event-driven | Replace polling with events where possible |
| Disable unused scripts | `enabled = false` on off-screen components |
| Use `InvokeRepeating` | For periodic checks (cheaper than coroutine yielding) |

## GPU / Rendering Optimization

### Draw Call Reduction

| Technique | How | Savings |
|-----------|-----|---------|
| **Static Batching** | Mark non-moving objects as Static | Combines meshes at build time |
| **Dynamic Batching** | Automatic for small meshes (<300 verts) | URP/Built-in only |
| **GPU Instancing** | Enable on materials for repeated objects | Trees, grass, rocks |
| **SRP Batcher** | Enabled by default in URP/HDRP | Reduces SetPass calls |
| **Texture Atlasing** | Combine textures into atlas | Fewer material switches |
| **Mesh Combining** | `CombineMeshes()` at runtime | Custom batching |

### LOD (Level of Detail)

```text
LOD Group Setup:
  LOD 0 (0-30%):  Full-detail mesh (5000 tris)
  LOD 1 (30-60%): Medium mesh (2000 tris)
  LOD 2 (60-90%): Low mesh (500 tris)
  Culled (90%+):  Not rendered
```

Use LOD for meshes, but also reduce script complexity, particle counts, and physics at distance.

### Occlusion Culling

Bake occlusion data for indoor/complex scenes. Mark large static occluders (walls, floors). Configure cell size based on scene scale. Use the Occlusion Culling window to visualize and test.

### Shader Optimization

| Issue | Solution |
|-------|----------|
| Complex fragment shaders | Reduce texture samples, simplify math |
| Overdraw | Minimize transparent objects, use opaque when possible |
| Too many variants | Strip unused shader variants in build settings |
| Expensive post-processing | Disable effects on mobile, use cheaper alternatives |

## Memory Management

### Common Memory Issues

| Issue | Symptom | Fix |
|-------|---------|-----|
| Texture bloat | High memory, long loads | Compress textures, reduce max size per platform |
| Unloaded scenes holding refs | Memory climbs over time | Use `Resources.UnloadUnusedAssets()` after scene transitions |
| Addressables not released | Bundles stay in memory | Call `Addressables.Release(handle)` |
| Audio clips uncompressed | Huge memory footprint | Use compressed in memory for music, decompress on load for SFX |
| Mesh read/write enabled | Double memory per mesh | Disable Read/Write if not needed at runtime |

### Texture Compression Per Platform

| Platform | Format | Notes |
|----------|--------|-------|
| PC/Console | BC7 (DXT) | Best quality/size ratio |
| Android | ASTC 6x6 | Universal, scalable quality |
| iOS | ASTC 6x6 | Same as Android |
| WebGL | ETC2 / DXT | Depends on target GPU |

Use "Override for [Platform]" in texture import settings. Set max texture size to the minimum needed (512 for UI icons, 1024 for props, 2048 for hero assets).

## Platform-Specific Considerations

| Platform | Key Constraints |
|----------|----------------|
| **Mobile** | Thermal throttling, limited memory, battery drain, fill-rate limited |
| **WebGL** | No threads (pre-Unity 6), large download size, no compute shaders |
| **Console** | Certification requirements, fixed hardware, memory budgets |
| **VR/XR** | 72-90 FPS minimum, stereo rendering cost, motion sickness from drops |

## Addressables and Asset Loading

Use Addressables for async asset loading to avoid load-time hitches:

```csharp
// Preload during loading screen
var handle = Addressables.LoadAssetAsync<GameObject>("enemy_boss");
await handle;

// Release when done
Addressables.Release(handle);
```

Use Addressable groups to control bundle granularity. Mark infrequently used assets as remote/on-demand. Profile bundle memory with the Addressables Event Viewer.

## Quick Optimization Checklist

- [ ] Profile on target device, not in Editor
- [ ] Zero per-frame GC allocations in gameplay code
- [ ] Object pooling for all frequently spawned objects
- [ ] Static batching enabled for non-moving objects
- [ ] LOD groups on all 3D models visible at varying distances
- [ ] Textures compressed per platform with appropriate max sizes
- [ ] Disable Read/Write on meshes and textures not modified at runtime
- [ ] Audio clips use appropriate compression settings
- [ ] Occlusion culling baked for indoor/complex scenes
- [ ] Shader variants stripped in build settings

## Additional Resources

### Reference Files
- **`references/profiling-deep-dive.md`** -- Advanced Profiler usage, memory profiler snapshots, frame-by-frame analysis, custom profiler markers, automated performance testing, build size analysis, ECS/DOTS performance patterns