A* Pathfinding Project  4.1.16
The A* Pathfinding Project for Unity 3D
AIPath Class Reference

AI for following paths. More...

Detailed Description

AI for following paths.

This AI is the default movement script which comes with the A* Pathfinding Project. It is in no way required by the rest of the system, so feel free to write your own. But I hope this script will make it easier to set up movement for the characters in your game. This script works well for many types of units, but if you need the highest performance (for example if you are moving hundreds of characters) you may want to customize this script or write a custom movement script to be able to optimize it specifically for your game.

This script will try to move to a given destination. At regular intervals, the path to the destination will be recalculated. If you want to make the AI to follow a particular object you can attach the AIDestinationSetter component. Take a look at the Get Started With The A* Pathfinding Project tutorial for more instructions on how to configure this script.

Here is a video of this script being used move an agent around (technically it uses the Pathfinding.Examples.MineBotAI script that inherits from this one but adds a bit of animation support for the example scenes):

Quick overview of the variables

In the inspector in Unity, you will see a bunch of variables. You can view detailed information further down, but here's a quick overview.

The repathRate determines how often it will search for new paths, if you have fast moving targets, you might want to set it to a lower value. The destination field is where the AI will try to move, it can be a point on the ground where the player has clicked in an RTS for example. Or it can be the player object in a zombie game. The maxSpeed is self-explanatory, as is rotationSpeed. however slowdownDistance might require some explanation: It is the approximate distance from the target where the AI will start to slow down. Setting it to a large value will make the AI slow down very gradually. pickNextWaypointDist determines the distance to the point the AI will move to (see image below).

Below is an image illustrating several variables that are exposed by this class (pickNextWaypointDist, steeringTarget, desiredVelocity)

This script has many movement fallbacks. If it finds an RVOController attached to the same GameObject as this component, it will use that. If it finds a character controller it will also use that. If it finds a rigidbody it will use that. Lastly it will fall back to simply modifying Transform.position which is guaranteed to always work and is also the most performant option.

How it works

In this section I'm going to go over how this script is structured and how information flows. This is useful if you want to make changes to this script or if you just want to understand how it works a bit more deeply. However you do not need to read this section if you are just going to use the script as-is.

This script inherits from the AIBase class. The movement happens either in Unity's standard Update or FixedUpdate method. They are both defined in the AIBase class. Which one is actually used depends on if a rigidbody is used for movement or not. Rigidbody movement has to be done inside the FixedUpdate method while otherwise it is better to do it in Update.

From there a call is made to the MovementUpdate method (which in turn calls MovementUpdateInternal). This method contains the main bulk of the code and calculates how the AI *wants* to move. However it doesn't do any movement itself. Instead it returns the position and rotation it wants the AI to move to have at the end of the frame. The Update (or FixedUpdate) method then passes these values to the FinalizeMovement method which is responsible for actually moving the character. That method also handles things like making sure the AI doesn't fall through the ground using raycasting.

The AI recalculates its path regularly. This happens in the Update method which checks shouldRecalculatePath and if that returns true it will call SearchPath. The SearchPath method will prepare a path request and send it to the Seeker component which should be attached to the same GameObject as this script. Since this script will when waking up register to the Seeker.pathCallback delegate this script will be notified every time a new path is calculated by the OnPathComplete method being called. It may take one or sometimes multiple frames for the path to be calculated, but finally the OnPathComplete method will be called and the current path that the AI is following will be replaced.

Public Member Functions

Vector3 CalculateVelocity (Vector3 position)
 Current desired velocity of the agent (excluding physics and local avoidance but it includes gravity). More...
 
virtual void OnTargetReached ()
 The end of the path has been reached. More...
 
override void Teleport (Vector3 newPosition, bool clearPath=true)
 Instantly move the agent to a new position. More...
 
- Public Member Functions inherited from AIBase
virtual void FinalizeMovement (Vector3 nextPosition, Quaternion nextRotation)
 Moves the agent to a position. More...
 
virtual Vector3 GetFeetPosition ()
 Position of the base of the character. More...
 
virtual void Move (Vector3 deltaPosition)
 Move the agent. More...
 
void MovementUpdate (float deltaTime, out Vector3 nextPosition, out Quaternion nextRotation)
 Calculate how the character wants to move during this frame. More...
 
virtual void SearchPath ()
 Recalculate the current path. More...
 
void SetPath (Path path)
 Make the AI follow the specified path. More...
 
Quaternion SimulateRotationTowards (Vector3 direction, float maxDegrees)
 Simulates rotating the agent towards the specified direction and returns the new rotation. More...
 
- Public Member Functions inherited from IAstarAI
void FinalizeMovement (Vector3 nextPosition, Quaternion nextRotation)
 Move the agent. More...
 
void Move (Vector3 deltaPosition)
 Move the agent. More...
 
void MovementUpdate (float deltaTime, out Vector3 nextPosition, out Quaternion nextRotation)
 Calculate how the character wants to move during this frame. More...
 
void SearchPath ()
 Recalculate the current path. More...
 
void SetPath (Path path)
 Make the AI follow the specified path. More...
 

Public Attributes

bool alwaysDrawGizmos
 Draws detailed gizmos constantly in the scene view instead of only when the agent is selected and settings are being modified. More...
 
bool constrainInsideGraph = false
 Ensure that the character is always on the traversable surface of the navmesh. More...
 
float endReachedDistance = 0.2F
 Distance to the end point to consider the end of path to be reached. More...
 
float maxAcceleration = -2.5f
 How quickly the agent accelerates. More...
 
float pickNextWaypointDist = 2
 How far the AI looks ahead along the path to determine the point it moves to. More...
 
float rotationSpeed = 360
 Rotation speed in degrees per second. More...
 
float slowdownDistance = 0.6F
 Distance from the end of the path where the AI will start to slow down. More...
 
bool slowWhenNotFacingTarget = true
 Slow down when not facing the target direction. More...
 
CloseToDestinationMode whenCloseToDestination = CloseToDestinationMode.Stop
 What to do when within endReachedDistance units from the destination. More...
 
- Public Attributes inherited from AIBase
bool canMove = true
 Enables or disables movement completely. More...
 
bool canSearch = true
 Enables or disables recalculating the path at regular intervals. More...
 
float centerOffset = 1
 Offset along the Y coordinate for the ground raycast start position. More...
 
Vector3 gravity = new Vector3(float.NaN, float.NaN, float.NaN)
 Gravity to use. More...
 
LayerMask groundMask = -1
 Layer mask to use for ground placement. More...
 
float maxSpeed = 1
 Max speed in world units per second. More...
 
IMovementPlane movementPlane = GraphTransform.identityTransform
 Plane which this agent is moving in. More...
 
float repathRate = 0.5f
 Determines how often the agent will search for new paths (in seconds). More...
 
bool rotationIn2D = false
 If true, the forward axis of the character will be along the Y axis instead of the Z axis. More...
 
bool updatePosition = true
 Determines if the character's position should be coupled to the Transform's position. More...
 
bool updateRotation = true
 Determines if the character's rotation should be coupled to the Transform's rotation. More...
 

Protected Member Functions

virtual void CalculateNextRotation (float slowdown, out Quaternion nextRotation)
 
override Vector3 ClampToNavmesh (Vector3 position, out bool positionChanged)
 Constrains the character's position to lie on the navmesh. More...
 
override void MovementUpdateInternal (float deltaTime, out Vector3 nextPosition, out Quaternion nextRotation)
 Called during either Update or FixedUpdate depending on if rigidbodies are used for movement or not. More...
 
override void OnDisable ()
 
override void OnPathComplete (Path newPath)
 Called when a requested path has been calculated. More...
 
override int OnUpgradeSerializedData (int version, bool unityThread)
 Handle serialization backwards compatibility. More...
 
- Protected Member Functions inherited from AIBase
 AIBase ()
 
void ApplyGravity (float deltaTime)
 Accelerates the agent downwards. More...
 
Vector2 CalculateDeltaToMoveThisFrame (Vector2 position, float distanceToEndOfPath, float deltaTime)
 Calculates how far to move during a single frame. More...
 
virtual void CalculatePathRequestEndpoints (out Vector3 start, out Vector3 end)
 Outputs the start point and end point of the next automatic path request. More...
 
void CancelCurrentPathRequest ()
 
virtual void FindComponents ()
 
virtual void FixedUpdate ()
 Called every physics update. More...
 
virtual void OnDrawGizmos ()
 
virtual void OnDrawGizmosSelected ()
 
virtual void OnEnable ()
 Called when the component is enabled. More...
 
Vector3 RaycastPosition (Vector3 position, float lastElevation)
 Checks if the character is grounded and prevents ground penetration. More...
 
Quaternion SimulateRotationTowards (Vector2 direction, float maxDegrees)
 Simulates rotating the agent towards the specified direction and returns the new rotation. More...
 
virtual void Start ()
 Starts searching for paths. More...
 
virtual void Update ()
 Called every frame. More...
 
void UpdateVelocity ()
 
- Protected Member Functions inherited from VersionedMonoBehaviour
virtual void Awake ()
 

Protected Attributes

PathInterpolator interpolator = new PathInterpolator()
 Helper which calculates points along the current path. More...
 
Path path
 Current path which is followed. More...
 
- Protected Attributes inherited from AIBase
CharacterController controller
 Cached CharacterController component. More...
 
Vector2 lastDeltaPosition
 Amount which the character wants or tried to move with during the last frame. More...
 
float lastDeltaTime
 Delta time used for movement during the last frame. More...
 
float lastRepath = float.NegativeInfinity
 Time when the last path request was started. More...
 
int prevFrame
 Last frame index when prevPosition1 was updated. More...
 
Vector3 prevPosition1
 Position of the character at the end of the last frame. More...
 
Vector3 prevPosition2
 Position of the character at the end of the frame before the last frame. More...
 
Rigidbody rigid
 Cached Rigidbody component. More...
 
Rigidbody2D rigid2D
 Cached Rigidbody component. More...
 
RVOController rvoController
 Cached RVOController component. More...
 
Seeker seeker
 Cached Seeker component. More...
 
Vector3 simulatedPosition
 Position of the agent. More...
 
Quaternion simulatedRotation
 Rotation of the agent. More...
 
Transform tr
 Cached Transform component. More...
 
Vector2 velocity2D
 Current desired velocity of the agent (does not include local avoidance and physics). More...
 
float verticalVelocity
 Velocity due to gravity. More...
 
bool waitingForPathCalculation = false
 Only when the previous path has been calculated should the script consider searching for a new path. More...
 

Properties

bool IAstarAI. canMove [get, set]
 Enables or disables movement completely. More...
 
bool IAstarAI. canSearch [get, set]
 Enables or disables recalculating the path at regular intervals. More...
 
bool hasPath [get]
 True if this agent currently has a path that it follows. More...
 
float IAstarAI. maxSpeed [get, set]
 Max speed in world units per second. More...
 
bool pathPending [get]
 True if a path is currently being calculated. More...
 
bool reachedEndOfPath [get, protected set]
 True if the agent has reached the end of the current path. More...
 
float remainingDistance [get]
 Remaining distance along the current path to the end of the path. More...
 
float speed [get, set]
 Maximum speed in world units per second. More...
 
Vector3 steeringTarget [get]
 Point on the path which the agent is currently moving towards. More...
 
Vector3 targetDirection [get]
 Direction that the agent wants to move in (excluding physics and local avoidance). More...
 
bool TargetReached [get]
 True if the end of the path has been reached. More...
 
float turningSpeed [get, set]
 Rotation speed. More...
 
- Properties inherited from AIBase
Vector3 desiredVelocity [get]
 Velocity that this agent wants to move with. More...
 
Vector3 destination [get, set]
 Position in the world that this agent should move to. More...
 
bool isStopped [get, set]
 Gets or sets if the agent should stop moving. More...
 
System.Action onSearchPath [get, set]
 Called when the agent recalculates its path. More...
 
Vector3 position [get]
 Position of the agent. More...
 
Quaternion rotation [get]
 Rotation of the agent. More...
 
virtual bool shouldRecalculatePath [get]
 True if the path should be automatically recalculated as soon as possible. More...
 
Transform target [get, set]
 Target to move towards. More...
 
bool usingGravity [get, private set]
 Indicates if gravity is used during this frame. More...
 
Vector3 velocity [get]
 Actual velocity that the agent is moving with. More...
 
- Properties inherited from IAstarAI
bool canMove [get, set]
 Enables or disables movement completely. More...
 
bool canSearch [get, set]
 Enables or disables recalculating the path at regular intervals. More...
 
Vector3 desiredVelocity [get]
 Velocity that this agent wants to move with. More...
 
Vector3 destination [get, set]
 Position in the world that this agent should move to. More...
 
bool hasPath [get]
 True if this agent currently has a path that it follows. More...
 
bool isStopped [get, set]
 Gets or sets if the agent should stop moving. More...
 
float maxSpeed [get, set]
 Max speed in world units per second. More...
 
System.Action onSearchPath [get, set]
 Called when the agent recalculates its path. More...
 
bool pathPending [get]
 True if a path is currently being calculated. More...
 
Vector3 position [get]
 Position of the agent. More...
 
bool reachedEndOfPath [get]
 True if the agent has reached the end of the current path. More...
 
float remainingDistance [get]
 Remaining distance along the current path to the end of the path. More...
 
Quaternion rotation [get]
 Rotation of the agent. More...
 
Vector3 steeringTarget [get]
 Point on the path which the agent is currently moving towards. More...
 
Vector3 velocity [get]
 Actual velocity that the agent is moving with. More...
 

Static Private Attributes

static NNConstraint cachedNNConstraint = NNConstraint.Default
 

Additional Inherited Members

- Static Protected Attributes inherited from AIBase
static readonly Color GizmoColorRaycast = new Color(118.0f/255, 206.0f/255, 112.0f/255)
 

Member Function Documentation

◆ CalculateNextRotation()

virtual void CalculateNextRotation ( float  slowdown,
out Quaternion  nextRotation 
)
protectedvirtual

◆ CalculateVelocity()

Vector3 CalculateVelocity ( Vector3  position)

Current desired velocity of the agent (excluding physics and local avoidance but it includes gravity).

Deprecated:
This method no longer calculates the velocity. Use the desiredVelocity property instead.

◆ ClampToNavmesh()

override Vector3 ClampToNavmesh ( Vector3  position,
out bool  positionChanged 
)
protectedvirtual

Constrains the character's position to lie on the navmesh.

Not all movement scripts have support for this.

Parameters
positionCurrent position of the character.
positionChangedTrue if the character's position was modified by this method.
Returns
New position of the character that has been clamped to the navmesh.

Reimplemented from AIBase.

◆ MovementUpdateInternal()

override void MovementUpdateInternal ( float  deltaTime,
out Vector3  nextPosition,
out Quaternion  nextRotation 
)
protectedvirtual

Called during either Update or FixedUpdate depending on if rigidbodies are used for movement or not.

Implements AIBase.

◆ OnDisable()

override void OnDisable ( )
protectedvirtual

Reimplemented from AIBase.

◆ OnPathComplete()

override void OnPathComplete ( Path  newPath)
protectedvirtual

Called when a requested path has been calculated.

A path is first requested by #UpdatePath, it is then calculated, probably in the same or the next frame. Finally it is returned to the seeker which forwards it to this function.

Implements AIBase.

Reimplemented in LegacyAIPath.

◆ OnTargetReached()

virtual void OnTargetReached ( )
virtual

The end of the path has been reached.

If you want custom logic for when the AI has reached it's destination add it here. You can also create a new script which inherits from this one and override the function in that script.

This method will be called again if a new path is calculated as the destination may have changed. So when the agent is close to the destination this method will typically be called every repathRate seconds.

◆ OnUpgradeSerializedData()

override int OnUpgradeSerializedData ( int  version,
bool  unityThread 
)
protectedvirtual

Handle serialization backwards compatibility.

Reimplemented from AIBase.

◆ Teleport()

override void Teleport ( Vector3  newPosition,
bool  clearPath = true 
)
virtual

Instantly move the agent to a new position.

This will trigger a path recalculation (if clearPath is true, which is the default) so if you want to teleport the agent and change its destination it is recommended that you set the destination before calling this method.

The current path will be cleared by default.

See also
Works similarly to Unity's NavmeshAgent.Warp.
SearchPath

Reimplemented from AIBase.

Member Data Documentation

◆ alwaysDrawGizmos

bool alwaysDrawGizmos

Draws detailed gizmos constantly in the scene view instead of only when the agent is selected and settings are being modified.

◆ cachedNNConstraint

NNConstraint cachedNNConstraint = NNConstraint.Default
staticprivate

◆ constrainInsideGraph

bool constrainInsideGraph = false

Ensure that the character is always on the traversable surface of the navmesh.

When this option is enabled a GetNearest query will be done every frame to find the closest node that the agent can walk on and if the agent is not inside that node, then the agent will be moved to it.

This is especially useful together with local avoidance in order to avoid agents pushing each other into walls.

See also
Local Avoidance for more info about this.

This option also integrates with local avoidance so that if the agent is say forced into a wall by other agents the local avoidance system will be informed about that wall and can take that into account.

Enabling this has some performance impact depending on the graph type (pretty fast for grid graphs, slightly slower for navmesh/recast graphs). If you are using a navmesh/recast graph you may want to switch to the RichAI movement script which is specifically written for navmesh/recast graphs and does this kind of clamping out of the box. In many cases it can also follow the path more smoothly around sharp bends in the path.

It is not recommended that you use this option together with the funnel modifier on grid graphs because the funnel modifier will make the path go very close to the border of the graph and this script has a tendency to try to cut corners a bit. This may cause it to try to go slightly outside the traversable surface near corners and that will look bad if this option is enabled.

Warning
This option makes no sense to use on point graphs because point graphs do not have a surface. Enabling this option when using a point graph will lead to the agent being snapped to the closest node every frame which is likely not what you want.

Below you can see an image where several agents using local avoidance were ordered to go to the same point in a corner. When not constraining the agents to the graph they are easily pushed inside obstacles.

◆ endReachedDistance

float endReachedDistance = 0.2F

Distance to the end point to consider the end of path to be reached.

When the end is within this distance then OnTargetReached will be called and reachedEndOfPath will return true.

◆ interpolator

PathInterpolator interpolator = new PathInterpolator()
protected

Helper which calculates points along the current path.

◆ maxAcceleration

float maxAcceleration = -2.5f

How quickly the agent accelerates.

Positive values represent an acceleration in world units per second squared. Negative values are interpreted as an inverse time of how long it should take for the agent to reach its max speed. For example if it should take roughly 0.4 seconds for the agent to reach its max speed then this field should be set to -1/0.4 = -2.5. For a negative value the final acceleration will be: -acceleration*maxSpeed. This behaviour exists mostly for compatibility reasons.

In the Unity inspector there are two modes: Default and Custom. In the Default mode this field is set to -2.5 which means that it takes about 0.4 seconds for the agent to reach its top speed. In the Custom mode you can set the acceleration to any positive value.

◆ path

Path path
protected

Current path which is followed.

◆ pickNextWaypointDist

float pickNextWaypointDist = 2

How far the AI looks ahead along the path to determine the point it moves to.

In world units. If you enable the alwaysDrawGizmos toggle this value will be visualized in the scene view as a blue circle around the agent.

Here are a few example videos showing some typical outcomes with good values as well as how it looks when this value is too low and too high.

{aipath/picknext/video_02_default.mp4} A too low value and a too low acceleration will result in the agent overshooting a lot and not managing to follow the path well.
{aipath/picknext/video_02_100.mp4} A low value but a high acceleration works decently to make the AI follow the path more closely. Note that the AILerp component is better suited if you want the agent to follow the path without any deviations.
{aipath/picknext/video_07_default.mp4} A reasonable value in this example.
{aipath/picknext/video_10_default.mp4} A reasonable value in this example, but the path is followed slightly more loosely than in the previous video.
{aipath/picknext/video_20_default.mp4} A too high value will make the agent follow the path too loosely and may cause it to try to move through obstacles.

◆ rotationSpeed

float rotationSpeed = 360

Rotation speed in degrees per second.

Rotation is calculated using Quaternion.RotateTowards. This variable represents the rotation speed in degrees per second. The higher it is, the faster the character will be able to rotate.

◆ slowdownDistance

float slowdownDistance = 0.6F

Distance from the end of the path where the AI will start to slow down.

◆ slowWhenNotFacingTarget

bool slowWhenNotFacingTarget = true

Slow down when not facing the target direction.

Incurs at a small performance overhead.

◆ whenCloseToDestination

What to do when within endReachedDistance units from the destination.

The character can either stop immediately when it comes within that distance, which is useful for e.g archers or other ranged units that want to fire on a target. Or the character can continue to try to reach the exact destination point and come to a full stop there. This is useful if you want the character to reach the exact point that you specified.

Note
reachedEndOfPath will become true when the character is within endReachedDistance units from the destination regardless of what this field is set to.

Property Documentation

◆ canMove

bool IAstarAI. canMove
getsetprivate

Enables or disables movement completely.

If you want the agent to stand still, but still react to local avoidance and use gravity: use isStopped instead.

This is also useful if you want to have full control over when the movement calculations run. Take a look at MovementUpdate

See also
canSearch
isStopped

◆ canSearch

bool IAstarAI. canSearch
getsetprivate

Enables or disables recalculating the path at regular intervals.

Setting this to false does not stop any active path requests from being calculated or stop it from continuing to follow the current path.

Note that this only disables automatic path recalculations. If you call the SearchPath() method a path will still be calculated.

See also
canMove
isStopped

◆ hasPath

bool hasPath
get

True if this agent currently has a path that it follows.

◆ maxSpeed

float IAstarAI. maxSpeed
getsetprivate

Max speed in world units per second.

◆ pathPending

bool pathPending
get

True if a path is currently being calculated.

◆ reachedEndOfPath

bool reachedEndOfPath
getprotected set

True if the agent has reached the end of the current path.

This is the approximate distance the AI has to move to reach the end of the path it is currently traversing.

Note that setting the destination does not immediately update the path, nor is there any guarantee that the AI will actually be able to reach the destination that you set. The AI will try to get as close as possible.

It is very hard to provide a method for detecting if the AI has reached the destination that works across all different games because the destination may not even lie on the navmesh and how that is handled differs from game to game (see also the code snippet in the docs for destination).

See also
remainingDistance

◆ remainingDistance

float remainingDistance
get

Remaining distance along the current path to the end of the path.

For the RichAI movement script this may not always be precisely known, especially when far away from the destination. In those cases an approximate distance will be returned.

If the agent does not currently have a path, then positive infinity will be returned.

See also
reachedEndOfPath

◆ speed

float speed
getset

Maximum speed in world units per second.

Deprecated:
Use maxSpeed instead

◆ steeringTarget

Vector3 steeringTarget
get

Point on the path which the agent is currently moving towards.

This is usually a point a small distance ahead of the agent or the end of the path.

If the agent does not have a path at the moment, then the agent's current position will be returned.

◆ targetDirection

Vector3 targetDirection
get

Direction that the agent wants to move in (excluding physics and local avoidance).

Deprecated:
Only exists for compatibility reasons. Use desiredVelocity or steeringTarget instead instead.

◆ TargetReached

bool TargetReached
get

True if the end of the path has been reached.

Deprecated:
When unifying the interfaces for different movement scripts, this property has been renamed to reachedEndOfPath

◆ turningSpeed

float turningSpeed
getset

Rotation speed.

Deprecated:
This field has been renamed to rotationSpeed and is now in degrees per second instead of a damping factor.

The documentation for this class was generated from the following files: