math-essentials

---
name: "math-essentials"
description: "Use when implementing game math — vectors, transforms, interpolation, curves, random number generation, and common geometric recipes"
license: "MIT"
---

# Game Math in Godot 4.3+

All examples target Godot 4.3+ with no deprecated APIs. GDScript is shown first, then C#.

> **Related skills:** **player-controller** for movement physics, **ai-navigation** for pathfinding math, **camera-system** for camera interpolation, **tween-animation** for easing curves, **physics-system** for collision math.

---

## 1. Vector Operations

### Essential Vector Methods

| Method                  | Returns   | Description                                   |
|-------------------------|-----------|-----------------------------------------------|
| `length()`              | `float`   | Magnitude of the vector                       |
| `length_squared()`      | `float`   | Squared magnitude (faster, skip sqrt)         |
| `normalized()`          | `Vector`  | Unit vector (length 1) in the same direction  |
| `distance_to(b)`        | `float`   | Distance between two points                   |
| `distance_squared_to(b)` | `float` | Squared distance (faster for comparisons)     |
| `direction_to(b)`       | `Vector`  | Normalized direction from this to b           |
| `angle_to(b)`           | `float`   | Angle in radians between two vectors          |
| `angle_to_point(b)`     | `float`   | Angle from this point to b (2D)               |
| `dot(b)`                | `float`   | Dot product                                   |
| `cross(b)`              | `float/Vector3` | Cross product (2D returns float, 3D returns vector) |
| `rotated(angle)`        | `Vector2` | Rotated by radians (2D)                       |
| `move_toward(to, delta)` | `Vector` | Move toward target by at most delta           |
| `clamp(min, max)`       | `Vector`  | Clamp each component                          |
| `snapped(step)`         | `Vector`  | Snap to grid                                  |
| `reflect(normal)`       | `Vector`  | Reflect off a surface                         |
| `bounce(normal)`        | `Vector`  | Bounce off a surface (inverted reflect)       |
| `slide(normal)`         | `Vector`  | Slide along a surface                         |

### Direction and Distance

```gdscript
# Get direction from A to B (normalized)
var dir: Vector2 = global_position.direction_to(target.global_position)

# Get distance
var dist: float = global_position.distance_to(target.global_position)

# Use squared distance for comparisons (faster — avoids sqrt)
if global_position.distance_squared_to(target.global_position) < detection_range * detection_range:
    chase_target()
```

```csharp
Vector2 dir = GlobalPosition.DirectionTo(target.GlobalPosition);
float dist = GlobalPosition.DistanceTo(target.GlobalPosition);

if (GlobalPosition.DistanceSquaredTo(target.GlobalPosition) < detectionRange * detectionRange)
    ChaseTarget();
```

### Dot Product

The dot product tells you how aligned two vectors are.

```gdscript
# Is the target in front of us? (dot > 0 = in front, < 0 = behind)
var forward: Vector2 = Vector2.RIGHT.rotated(rotation)
var to_target: Vector2 = global_position.direction_to(target.global_position)
var dot: float = forward.dot(to_target)

if dot > 0.7:  # roughly within ~45° cone
    print("Target is ahead")
elif dot < -0.7:
    print("Target is behind")
```

```csharp
Vector2 forward = Vector2.Right.Rotated(Rotation);
Vector2 toTarget = GlobalPosition.DirectionTo(target.GlobalPosition);
float dot = forward.Dot(toTarget);

if (dot > 0.7f) GD.Print("Target is ahead");
```

### Cross Product (3D)

The cross product gives a vector perpendicular to two input vectors.

```gdscript
# Get the surface normal from two edge vectors
var edge1: Vector3 = vertex_b - vertex_a
var edge2: Vector3 = vertex_c - vertex_a
var normal: Vector3 = edge1.cross(edge2).normalized()
```

```csharp
Vector3 edge1 = vertexB - vertexA;
Vector3 edge2 = vertexC - vertexA;
Vector3 normal = edge1.Cross(edge2).Normalized();
```

---

## 2. Transforms

### Transform2D

A 2D transform holds position, rotation, and scale.

```gdscript
# Get the global transform
var xform: Transform2D = global_transform

# Convert between local and global space
var local_point: Vector2 = to_local(global_point)
var world_point: Vector2 = to_global(local_point)

# Apply transform to a point
var transformed: Vector2 = xform * Vector2(10, 0)  # point in local space → global

# Inverse transform
var local: Vector2 = xform.affine_inverse() * global_point
```

```csharp
Transform2D xform = GlobalTransform;
Vector2 localPoint = ToLocal(globalPoint);
Vector2 worldPoint = ToGlobal(localPoint);
Vector2 transformed = xform * new Vector2(10, 0);
Vector2 local = xform.AffineInverse() * globalPoint;
```

### Transform3D & Basis

```gdscript
# Basis holds rotation and scale as 3 column vectors
var basis: Basis = global_transform.basis

# Forward direction (looking along -Z in Godot)
var forward: Vector3 = -basis.z
var right: Vector3 = basis.x
var up: Vector3 = basis.y

# Look at a target
look_at(target.global_position, Vector3.UP)

# Rotate around an axis
rotate_y(deg_to_rad(90.0))
rotate_object_local(Vector3.UP, deg_to_rad(45.0))

# Interpolate between two transforms (smooth transition)
var a: Transform3D = $Start.global_transform
var b: Transform3D = $End.global_transform
global_transform = a.interpolate_with(b, 0.5)  # halfway
```

```csharp
Basis basis = GlobalTransform.Basis;
Vector3 forward = -basis.Z;
Vector3 right = basis.X;
Vector3 up = basis.Y;

LookAt(target.GlobalPosition, Vector3.Up);
RotateY(Mathf.DegToRad(90.0f));

Transform3D a = GetNode<Node3D>("Start").GlobalTransform;
Transform3D b = GetNode<Node3D>("End").GlobalTransform;
GlobalTransform = a.InterpolateWith(b, 0.5f);
```

### is_orthonormal() (Godot 4.7+)

`Basis.is_orthonormal()` (const) returns `true` if the basis is *orthogonal* (axes perpendicular to each other) **and** *normalized* (every axis has length `1.0`) — especially useful during physics calculations. It complements `orthonormalized()`: check first, and only re-orthonormalize when accumulated floating-point drift has denormalized the basis.

```gdscript
if not global_transform.basis.is_orthonormal():
    global_transform.basis = global_transform.basis.orthonormalized()
```

```csharp
if (!GlobalTransform.Basis.IsOrthonormal())
{
    GlobalTransform = new Transform3D(
        GlobalTransform.Basis.Orthonormalized(), GlobalPosition);
}
```

---

## 3. Interpolation

### lerp — Linear Interpolation

```gdscript
# Interpolate between two values (t = 0.0 to 1.0)
var mid: float = lerp(0.0, 100.0, 0.5)   # 50.0
var pos: Vector2 = lerp(start_pos, end_pos, 0.75)  # 75% of the way

# Smooth following — lerp with delta for frame-rate independence
func _process(delta: float) -> void:
    position = position.lerp(target_position, 5.0 * delta)
```

```csharp
float mid = Mathf.Lerp(0.0f, 100.0f, 0.5f);
Vector2 pos = startPos.Lerp(endPos, 0.75f);

public override void _Process(double delta)
{
    Position = Position.Lerp(targetPosition, 5.0f * (float)delta);
}
```

> **Warning:** `lerp(a, b, speed * delta)` is frame-rate dependent and never fully reaches the target. For precise movement, use `move_toward()` instead.

### move_toward — Fixed-Speed Approach

```gdscript
# Move exactly `speed * delta` units toward target each frame
position.x = move_toward(position.x, target_x, speed * delta)

# Vector version
position = position.move_toward(target_position, speed * delta)
```

```csharp
float newX = Mathf.MoveToward(Position.X, targetX, speed * (float)delta);
Position = Position.MoveToward(targetPosition, speed * (float)delta);
```

### slerp — Spherical Interpolation

For smooth rotation interpolation (preserves arc, not straight line).

```gdscript
# Quaternion slerp for smooth 3D rotation
var current_quat: Quaternion = global_transform.basis.get_rotation_quaternion()
var target_quat: Quaternion = target_transform.basis.get_rotation_quaternion()
var result: Quaternion = current_quat.slerp(target_quat, 5.0 * delta)
global_transform.basis = Basis(result)
```

```csharp
Quaternion currentQuat = GlobalTransform.Basis.GetRotationQuaternion();
Quaternion targetQuat = targetTransform.Basis.GetRotationQuaternion();
Quaternion result = currentQuat.Slerp(targetQuat, 5.0f * (float)delta);
GlobalTransform = new Transform3D(new Basis(result), GlobalPosition);
```

### smoothstep — S-Curve Easing

```gdscript
# Returns 0.0 when x <= from, 1.0 when x >= to, smooth curve between
var t: float = smoothstep(0.0, 10.0, distance)  # 0→1 as distance goes 0→10

# Useful for soft thresholds (fog density, volume falloff)
var fog_intensity: float = smoothstep(50.0, 100.0, camera_distance)
```

### cubic_interpolate — Smooth Path Following

```gdscript
# Smooth interpolation using 4 control points (catmull-rom style)
var point: Vector2 = p1.cubic_interpolate(p2, p0, p3, t)
# p0 = before start, p1 = start, p2 = end, p3 = after end
```

### Interpolation Comparison

| Function           | Speed          | Reaches Target | Smooth | Use For                    |
|--------------------|----------------|----------------|--------|----------------------------|
| `lerp(a, b, t)`   | Variable       | Only at t=1    | Yes    | UI transitions, blending   |
| `move_toward()`    | Constant       | Yes            | No     | Movement, timers           |
| `slerp()`          | Variable       | Only at t=1    | Yes    | Rotation blending          |
| `smoothstep()`     | S-curve        | Soft threshold | Yes    | Fog, volume, thresholds    |
| `cubic_interpolate()` | Variable    | Only at t=1    | Very   | Paths, camera rails        |

---

## 4. Curves and Paths

`Curve` resource for value-over-time (e.g., damage falloff curves). `Path2D` / `Path3D` for spatial paths sampled by `PathFollow2D` / `PathFollow3D` — use for moving platforms, missile guidance, camera rails.

> See [references/curves-and-paths.md](references/curves-and-paths.md) for `Curve` setup, Path nodes, PathFollow properties.

---

## 5. Random Number Generation

Global functions (`randf()`, `randi() % N`, `randf_range(a, b)`) for one-shot randomness. `RandomNumberGenerator` for seeded, reproducible randomness (procgen, replay, save-state). Weighted selection via cumulative-sum or alias method.

> See [references/random-numbers.md](references/random-numbers.md) for full GDScript on each pattern, plus `FastNoiseLite` for procedural generation noise.

---

## 6. Common Game Math Recipes

Five recipes: **look at target** (2D `Vector2.angle_to_point`), **orbit around a point** (polar coordinates), **sine-wave bob** (floating UI elements, treasure), **angle wrapping** (-PI..PI canonicalization), **clamped approach with deadzone** (analog input + small-input ignore).

> See [references/game-math-recipes.md](references/game-math-recipes.md) for ready-to-use code on each recipe.

---

## 7. Common Pitfalls

| Symptom                              | Cause                                       | Fix                                                              |
|--------------------------------------|----------------------------------------------|------------------------------------------------------------------|
| `lerp` never reaches target          | Using `lerp(a, b, speed * delta)` each frame | Use `move_toward()` for exact arrival                            |
| Rotation jumps at 180°               | Using `lerp` instead of `lerp_angle`         | Always use `lerp_angle()` for angle interpolation                |
| Object faces wrong direction (3D)    | Forgot Godot uses -Z as forward              | Forward direction is `-global_transform.basis.z`                 |
| Distance check too slow              | Calling `distance_to` on many objects        | Use `distance_squared_to` and compare against `range * range`    |
| Normalized zero vector crashes       | Calling `normalized()` on `Vector2.ZERO`     | Check `length() > 0` first, or use `direction_to()`             |
| Transform interpolation looks wrong  | Lerping euler angles instead of quaternions  | Use `Quaternion.slerp()` or `Transform3D.interpolate_with()`    |
| Random results repeat after restart  | Using `RandomNumberGenerator` with fixed seed | Godot 4.x auto-seeds global RNG; for `RandomNumberGenerator` use `randomize()` or set `seed` |
| Noise values are all ~0              | `frequency` too low                          | Increase `FastNoiseLite.frequency` (try 0.01–0.1)               |

---

## 8. Implementation Checklist

- [ ] Distance comparisons use `distance_squared_to()` for performance
- [ ] Angle interpolation uses `lerp_angle()`, not `lerp()`
- [ ] 3D forward direction is `-transform.basis.z`, not `+z`
- [ ] `move_toward()` is used when exact arrival at target is needed
- [ ] `lerp(a, b, speed * delta)` is understood as frame-rate dependent smooth following, not exact movement
- [ ] `RandomNumberGenerator` is used for deterministic/seeded randomness (procedural generation, replays)
- [ ] Noise-based generation uses `FastNoiseLite` with appropriate frequency and seed
- [ ] Weighted random selection is used for loot tables and probability-based systems
- [ ] Path following uses `PathFollow2D/3D` with `progress` or `progress_ratio`
- [ ] Quaternion slerp is used for 3D rotation interpolation instead of euler angles