# Appendix C: Unity to Unreal Conversion Notes

[← Appendix B: Troubleshooting](appendix-b-troubleshooting.md) | [Back to Index](README.md)

---

## Scale Conversion

| Unity            | Unreal                | Notes                        |
| ---------------- | --------------------- | ---------------------------- |
| 1 unit = 1 meter | 1 unit = 1 centimeter | Multiply Unity values by 100 |

**Example:**

- Unity speed: `7.5` → Unreal speed: `750`
- Unity position: `(5, 10, 0)` → Unreal position: `(500, 1000, 0)`

---

## Coordinate System

| Axis    | Unity | Unreal |
| ------- | ----- | ------ |
| Up      | Y     | Z      |
| Forward | Z     | X      |
| Right   | X     | Y      |

**For 2D top-down games:**

- Both use X for horizontal
- Y/Z swap for vertical

---

## Common Operations Comparison

### Input

**Unity:**

```csharp
float h = Input.GetAxisRaw("Horizontal");
float v = Input.GetAxisRaw("Vertical");
```

**Unreal (Enhanced Input):**

1. Create Input Action (IA_Move) with Axis2D type
2. Create Input Mapping Context with key bindings
3. Add Mapping Context in BeginPlay
4. Use "Get Action Value" node to read input

---

### Instantiate / Spawn

**Unity:**

```csharp
Instantiate(prefab, position, rotation);
```

**Unreal:**

```
Spawn Actor from Class
├── Class: YourBlueprintClass
├── Spawn Transform Location: position
└── Spawn Transform Rotation: rotation
```

---

### Destroy

**Unity:**

```csharp
Destroy(gameObject);
```

**Unreal:**

```
Destroy Actor
└── Target: Self (or reference)
```

---

### Delta Time

**Unity:**

```csharp
Time.deltaTime
```

**Unreal:**

```
Get World Delta Seconds
```

---

### Find Objects

**Unity:**

```csharp
FindObjectOfType<PlayerController>();
FindObjectsOfType<Enemy>();
```

**Unreal:**

```
Get All Actors of Class
├── Actor Class: BP_Player
└── Out Actors: (array)

Then: Get (a ref) → index 0
```

---

### Singleton Pattern

**Unity:**

```csharp
public static GameManager Instance { get; private set; }

void Awake() {
    Instance = this;
}
```

**Unreal Options:**

1. **Game Instance** - Persists across levels
2. **Subsystem** - Engine-managed singleton
3. **Get All Actors of Class** - Find at runtime

---

### Coroutines vs Timers

**Unity:**

```csharp
StartCoroutine(DelayedAction());

IEnumerator DelayedAction() {
    yield return new WaitForSeconds(2.0f);
    DoSomething();
}
```

**Unreal:**

```
Set Timer by Function Name
├── Function Name: "DelayedAction"
├── Time: 2.0
└── Looping: false
```

Or use **Delay** node in blueprints.

---

### Physics Layers vs Collision Channels

**Unity:**

- Layer-based collision matrix
- `Physics.IgnoreLayerCollision()`

**Unreal:**

- Collision Channels (Object Types)
- Collision Presets
- Per-component collision settings

---

### Tags

**Unity:**

```csharp
if (other.CompareTag("Enemy")) { }
```

**Unreal:**

```
Actor Has Tag
├── Target: Other Actor
└── Tag: "Enemy"
```

Or use **Cast To** for type checking (preferred).

---

### Vector Math

| Operation     | Unity                 | Unreal               |
| ------------- | --------------------- | -------------------- |
| Normalize     | `vector.normalized`   | `Normalize` node     |
| Magnitude     | `vector.magnitude`    | `Vector Length` node |
| Dot Product   | `Vector3.Dot(a, b)`   | `Dot Product` node   |
| Cross Product | `Vector3.Cross(a, b)` | `Cross Product` node |

---

### Random

**Unity:**

```csharp
Random.Range(0f, 1f);
Random.Range(0, 10); // int, exclusive max
```

**Unreal:**

```
Random Float in Range
├── Min: 0.0
└── Max: 1.0

Random Integer in Range
├── Min: 0
└── Max: 9  // inclusive!
```

> ⚠️ **Note:** Unreal's integer range is INCLUSIVE on both ends!

---

### Debug

**Unity:**

```csharp
Debug.Log("Message");
Debug.DrawLine(start, end, Color.red);
```

**Unreal:**

```
Print String
└── In String: "Message"

Draw Debug Line
├── Line Start: start
├── Line End: end
└── Line Color: Red
```

---

## Quick Reference Table

| Concept   | Unity            | Unreal                |
| --------- | ---------------- | --------------------- |
| Script    | C# MonoBehaviour | Blueprint / C++ Actor |
| Prefab    | .prefab asset    | Blueprint Class       |
| Scene     | .unity scene     | Level (.umap)         |
| Inspector | Inspector window | Details panel         |
| Hierarchy | Hierarchy window | Outliner              |
| Project   | Project window   | Content Browser       |
| Console   | Console window   | Output Log            |
| Play      | Play button      | Play (Alt+P)          |

---

[← Appendix B: Troubleshooting](appendix-b-troubleshooting.md) | [Back to Index](README.md)