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40c0886 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | # Unity Navigation (NavMesh, Pathfinding, AI)
## Overview
Unity's AI Navigation package (`com.unity.ai.navigation`) bakes a
**NavMesh** -- a simplified walkable surface -- and provides
`NavMeshAgent` to move characters along it. This is the standard solution
for AI NPCs in the generated project.
## Baking a NavMesh
1. Mark static colliders as **Navigation Static** (Window > AI >
Navigation > Object).
2. Bake the NavMesh (Window > AI > Navigation > Bake).
3. At runtime, every `NavMeshAgent` on the scene automatically walks on
the baked NavMesh.
> For a procedurally generated city, baking at design time is impossible.
> Either:
> * Bake at runtime via `NavMeshSurface.BuildNavMesh()` (AI Navigation
> package), or
> * Use the simpler approach in `NPCController.cs`: pick random points via
> `NavMesh.SamplePosition` so the agent always lands on a valid walkable
> spot.
## NavMeshAgent
```csharp
[RequireComponent(typeof(NavMeshAgent))]
public class NPCController : MonoBehaviour
{
private NavMeshAgent _agent;
private void Awake() => _agent = GetComponent<NavMeshAgent>();
private void Start()
{
PickNewDestination();
}
private void PickNewDestination()
{
Vector3 random = transform.position + Random.insideUnitSphere * 20f;
if (NavMesh.SamplePosition(random, out NavMeshHit hit, 20f, NavMesh.AllAreas))
_agent.SetDestination(hit.position);
}
}
```
Key properties:
| Property | Meaning |
|---------------------|------------------------------------------------------------|
| `speed` | Max movement speed (m/s) |
| `angularSpeed` | Max turning speed (deg/s) |
| `acceleration` | How quickly the agent reaches `speed` |
| `stoppingDistance` | Distance at which the agent considers the destination reached |
| `autoBraking` | Whether to slow down near the destination |
| `isStopped` | Pause the agent without clearing the path |
| `remainingDistance` | Distance to the end of the current path |
| `pathPending` | True while a new path is still being computed |
## State machines for AI
A common pattern is a small finite state machine:
```
Idle --(timer)--> Wander --(player in range)--> Chase
^ | |
| (lost sight) +---------------------------------+
+--------------------+
```
The generated `NPCController.cs` implements exactly this pattern with three
states (`Idle`, `Wander`, `Chase`) and switch-based dispatch in `Update()`.
## Pathfinding details
* `NavMeshAgent.SetDestination(target)` is async -- the path may not be
ready on the same frame. Check `!agent.pathPending` before reading
`remainingDistance`.
* `agent.pathStatus` tells you whether a path is `PathComplete`,
`PathPartial` or `PathInvalid`.
* `NavMesh.CalculatePath(source, target, mask, out path)` lets you compute a
path without an agent (useful for "can the NPC reach this point?" checks).
## NavMeshObstacle
For dynamic obstacles (a car parked across a road, a door that closes), add
a `NavMeshObstacle` component. Set `carve = true` to actually cut a hole in
the NavMesh; otherwise the obstacle only pushes agents around.
## Off-mesh links
When the walkable surface is disconnected (e.g. a gap between rooftops),
drop an `OffMeshLink` to let agents jump or teleport across. You can also
use them for ladders, climbing walls, and jumping down from ledges.
## Performance
* Keep the agent count under ~100 simultaneous active agents on desktop.
* For larger crowds use the **ECS/DOTS navigation** solutions or batch
pathfinding across frames.
* Set `agent.autoRepath = false` if you do not need the agent to follow
moving targets, and call `SetDestination` less often (e.g. every 0.5 s).
|