Unity NavMesh Pathfinding

Overview

NavMesh provides AI pathfinding in Unity. This skill covers safe usage patterns to prevent the 30K+ pathfinding errors seen in production.

When to Use

• AI movement and navigation
• Enemy patrolling and chasing
• NPC pathfinding
• Dynamic obstacle avoidance
• Multi-agent navigation

Critical Safety Patterns

Graph Validation Before Query

using Pathfinding;

public class SafePathfinder
{
    private readonly Seeker _seeker;
    
    public bool TryCalculatePath(Vector3 start, Vector3 end, out Path path)
    {
        path = null;
        
        // CRITICAL: Check graph exists
        if (AstarPath.active == null)
        {
            Debug.LogError("No AstarPath instance active");
            return false;
        }
        
        if (AstarPath.active.graphs == null || AstarPath.active.graphs.Length == 0)
        {
            Debug.LogError("No graphs available");
            return false;
        }
        
        // Check if position is on navmesh
        var startNode = AstarPath.active.GetNearest(start).node;
        var endNode = AstarPath.active.GetNearest(end).node;
        
        if (startNode == null || !startNode.Walkable)
        {
            Debug.LogWarning($"Start position {start} not on walkable navmesh");
            return false;
        }
        
        if (endNode == null || !endNode.Walkable)
        {
            Debug.LogWarning($"End position {end} not on walkable navmesh");
            return false;
        }
        
        // Safe to calculate path
        _seeker.StartPath(start, end, OnPathComplete);
        return true;
    }
    
    private void OnPathComplete(Path p)
    {
        if (p.error)
        {
            Debug.LogWarning($"Path failed: {p.errorLog}");
            return;
        }
        
        // Use path
    }
}

Null Graph Guard (Critical Fix for 30K errors)

public class PathfindingGuard
{
    public static bool IsPathfindingReady()
    {
        // Check 1: AstarPath singleton exists
        if (AstarPath.active == null)
            return false;
        
        // Check 2: Data is loaded
        if (AstarPath.active.data == null)
            return false;
        
        // Check 3: Graphs exist
        if (AstarPath.active.data.graphs == null)
            return false;
        
        // Check 4: At least one graph is scanned
        foreach (var graph in AstarPath.active.data.graphs)
        {
            if (graph != null && graph.CountNodes() > 0)
                return true;
        }
        
        return false;
    }
}

// Usage in AI
public class EnemyAI : MonoBehaviour
{
    private void RequestPath()
    {
        if (!PathfindingGuard.IsPathfindingReady())
        {
            // Defer pathfinding or use fallback behavior
            StartCoroutine(WaitForPathfinding());
            return;
        }
        
        _seeker.StartPath(transform.position, _target.position);
    }
    
    private IEnumerator WaitForPathfinding()
    {
        while (!PathfindingGuard.IsPathfindingReady())
        {
            yield return new WaitForSeconds(0.5f);
        }
        
        RequestPath();
    }
}

NavMeshAgent Wrapper

public class SafeNavMeshAgent : MonoBehaviour
{
    private NavMeshAgent _agent;
    private bool _isNavigating;
    
    private void Awake()
    {
        _agent = GetComponent<NavMeshAgent>();
    }
    
    public bool TrySetDestination(Vector3 destination)
    {
        if (_agent == null || !_agent.isOnNavMesh)
        {
            Debug.LogWarning($"{name} not on NavMesh");
            return false;
        }
        
        // Check if destination is reachable
        NavMeshPath path = new NavMeshPath();
        if (!_agent.CalculatePath(destination, path))
        {
            Debug.LogWarning($"Cannot calculate path to {destination}");
            return false;
        }
        
        if (path.status != NavMeshPathStatus.PathComplete)
        {
            Debug.LogWarning($"Path incomplete: {path.status}");
            return false;
        }
        
        _agent.SetPath(path);
        _isNavigating = true;
        return true;
    }
    
    public void Stop()
    {
        if (_agent != null && _agent.isOnNavMesh)
        {
            _agent.isStopped = true;
            _agent.ResetPath();
        }
        _isNavigating = false;
    }
    
    private void OnDisable()
    {
        Stop();
    }
}

A* Pathfinding Project Patterns

Seeker Configuration

public class AIPathfinder : MonoBehaviour
{
    private Seeker _seeker;
    private AIPath _aiPath;
    
    private void Awake()
    {
        _seeker = GetComponent<Seeker>();
        _aiPath = GetComponent<AIPath>();
        
        // Configure seeker
        _seeker.pathCallback += OnPathComplete;
        
        // Set traversable tags
        _seeker.traversableTags = ~0; // All tags
    }
    
    private void OnDestroy()
    {
        if (_seeker != null)
        {
            _seeker.pathCallback -= OnPathComplete;
            _seeker.CancelCurrentPathRequest();
        }
    }
    
    public void MoveTo(Vector3 destination)
    {
        if (!PathfindingGuard.IsPathfindingReady())
        {
            Debug.LogWarning("Pathfinding not ready");
            return;
        }
        
        _aiPath.destination = destination;
        _aiPath.SearchPath();
    }
    
    private void OnPathComplete(Path p)
    {
        if (p.error)
        {
            HandlePathError(p);
            return;
        }
        
        // Path ready
    }
    
    private void HandlePathError(Path p)
    {
        Debug.LogWarning($"Path error: {p.errorLog}");
        
        // Fallback behavior - move directly or stay
    }
}

Path Caching

public class PathCache
{
    private readonly Dictionary<(Vector3Int, Vector3Int), Path> _cache = new();
    private readonly float _cacheValidTime = 5f;
    private readonly Dictionary<(Vector3Int, Vector3Int), float> _cacheTimestamps = new();
    
    private const float GridSize = 1f;
    
    public bool TryGetCachedPath(Vector3 start, Vector3 end, out Path path)
    {
        var key = (ToGridPos(start), ToGridPos(end));
        
        if (_cache.TryGetValue(key, out path))
        {
            if (_cacheTimestamps.TryGetValue(key, out var timestamp))
            {
                if (Time.time - timestamp < _cacheValidTime)
                {
                    return true;
                }
            }
            
            // Cache expired
            _cache.Remove(key);
            _cacheTimestamps.Remove(key);
        }
        
        path = null;
        return false;
    }
    
    public void CachePath(Vector3 start, Vector3 end, Path path)
    {
        var key = (ToGridPos(start), ToGridPos(end));
        _cache[key] = path;
        _cacheTimestamps[key] = Time.time;
    }
    
    private Vector3Int ToGridPos(Vector3 pos)
    {
        return new Vector3Int(
            Mathf.RoundToInt(pos.x / GridSize),
            Mathf.RoundToInt(pos.y / GridSize),
            Mathf.RoundToInt(pos.z / GridSize)
        );
    }
}

Performance Optimization

Batch Path Requests

public class PathBatcher
{
    private readonly Queue<PathRequest> _pendingRequests = new();
    private readonly int _maxRequestsPerFrame = 3;
    private bool _isProcessing;
    
    public void RequestPath(Vector3 start, Vector3 end, Action<Path> callback)
    {
        _pendingRequests.Enqueue(new PathRequest(start, end, callback));
        
        if (!_isProcessing)
        {
            ProcessBatch().Forget();
        }
    }
    
    private async UniTaskVoid ProcessBatch()
    {
        _isProcessing = true;
        
        while (_pendingRequests.Count > 0)
        {
            var processedThisFrame = 0;
            
            while (_pendingRequests.Count > 0 && processedThisFrame < _maxRequestsPerFrame)
            {
                var request = _pendingRequests.Dequeue();
                var path = await CalculatePathAsync(request.Start, request.End);
                request.Callback?.Invoke(path);
                processedThisFrame++;
            }
            
            await UniTask.Yield();
        }
        
        _isProcessing = false;
    }
    
    private async UniTask<Path> CalculatePathAsync(Vector3 start, Vector3 end)
    {
        var tcs = new UniTaskCompletionSource<Path>();
        
        var seeker = AstarPath.active.GetComponent<Seeker>();
        seeker.StartPath(start, end, p => tcs.TrySetResult(p));
        
        return await tcs.Task;
    }
    
    private readonly struct PathRequest
    {
        public readonly Vector3 Start;
        public readonly Vector3 End;
        public readonly Action<Path> Callback;
        
        public PathRequest(Vector3 start, Vector3 end, Action<Path> callback)
        {
            Start = start;
            End = end;
            Callback = callback;
        }
    }
}

LOD-Based Pathfinding

public class LODPathfinder
{
    private readonly float _preciseRadius = 20f;
    private readonly float _mediumRadius = 50f;
    
    public void RequestPath(Vector3 agent, Vector3 target)
    {
        var distance = Vector3.Distance(agent, target);
        
        if (distance <= _preciseRadius)
        {
            // Use full detail graph
            RequestPrecisePath(agent, target);
        }
        else if (distance <= _mediumRadius)
        {
            // Use simplified graph
            RequestMediumPath(agent, target);
        }
        else
        {
            // Use waypoint system
            RequestWaypointPath(agent, target);
        }
    }
}

Dynamic Obstacles

NavMesh Obstacle Handling

public class DynamicObstacle : MonoBehaviour
{
    private NavMeshObstacle _obstacle;
    private Coroutine _carveDelayCoroutine;
    
    private void Awake()
    {
        _obstacle = GetComponent<NavMeshObstacle>();
        _obstacle.carving = true;
        _obstacle.carveOnlyStationary = true;
    }
    
    public void EnableCarving()
    {
        if (_carveDelayCoroutine != null)
        {
            StopCoroutine(_carveDelayCoroutine);
        }
        
        // Delay carving to prevent rapid updates
        _carveDelayCoroutine = StartCoroutine(DelayedCarveEnable());
    }
    
    private IEnumerator DelayedCarveEnable()
    {
        yield return new WaitForSeconds(0.5f);
        _obstacle.carving = true;
    }
    
    public void DisableCarving()
    {
        if (_carveDelayCoroutine != null)
        {
            StopCoroutine(_carveDelayCoroutine);
        }
        _obstacle.carving = false;
    }
}

Graph Updates

public class NavMeshUpdater
{
    public void UpdateArea(Bounds bounds)
    {
        if (AstarPath.active == null) return;
        
        var graphUpdateObject = new GraphUpdateObject(bounds)
        {
            updatePhysics = true,
            modifyWalkability = true
        };
        
        AstarPath.active.UpdateGraphs(graphUpdateObject);
    }
    
    public void UpdateAreaAsync(Bounds bounds, Action onComplete)
    {
        if (AstarPath.active == null)
        {
            onComplete?.Invoke();
            return;
        }
        
        var graphUpdateObject = new GraphUpdateObject(bounds)
        {
            updatePhysics = true
        };
        
        AstarPath.active.UpdateGraphs(graphUpdateObject, onComplete);
    }
}

Error Recovery

Stuck Detection

public class StuckDetector : MonoBehaviour
{
    private Vector3 _lastPosition;
    private float _stuckTime;
    private const float StuckThreshold = 0.1f;
    private const float StuckTimeout = 3f;
    
    public event Action OnStuck;
    
    private void Update()
    {
        var moved = Vector3.Distance(transform.position, _lastPosition);
        
        if (moved < StuckThreshold)
        {
            _stuckTime += Time.deltaTime;
            
            if (_stuckTime >= StuckTimeout)
            {
                OnStuck?.Invoke();
                _stuckTime = 0f;
            }
        }
        else
        {
            _stuckTime = 0f;
        }
        
        _lastPosition = transform.position;
    }
}

Position Recovery

public class NavMeshRecovery
{
    public bool TryRecoverPosition(Transform agent, float searchRadius = 10f)
    {
        // Sample nearest valid position
        if (NavMesh.SamplePosition(agent.position, out var hit, searchRadius, NavMesh.AllAreas))
        {
            agent.position = hit.position;
            return true;
        }
        
        // Try expanding search
        for (float radius = searchRadius; radius <= 50f; radius += 10f)
        {
            if (NavMesh.SamplePosition(agent.position, out hit, radius, NavMesh.AllAreas))
            {
                agent.position = hit.position;
                return true;
            }
        }
        
        return false;
    }
}

Best Practices

1. Always check graph validity before pathfinding
2. Use path callbacks - Don't block on path calculation
3. Batch path requests - Limit per-frame calculations
4. Cache paths for repeated queries
5. Handle path failures gracefully
6. Use NavMesh.SamplePosition for validation
7. Update graphs async for dynamic obstacles
8. Implement stuck detection with recovery
9. Cancel paths on disable/destroy
10. Profile pathfinding cost on target devices

Troubleshooting

Issue	Solution
NullReferenceException in pathfinding	Add graph null checks
Agent not moving	Check isOnNavMesh
Path incomplete	Verify destination reachable
Slow pathfinding	Batch requests, cache paths
Agent stuck	Implement stuck detection + recovery
Dynamic obstacles ignored	Enable carving, update graphs