Searching for paths

Contents

• Searching for paths using a Seeker
• Other types of paths
• Calling AstarPath directly

This page is relevant if you want to write your own movement script or you have some other reason to calculate paths. If you use one of the built-in movement scripts (e.g AIPath) then you will most likely not have to do any of this. Instead you might be looking for the destination property.

Searching for paths using a Seeker

You can search for paths in a number of ways. The easiest method is to have Seeker component attached to the GameObject you want to request paths from and then call Seeker.StartPath(). The Seeker will also automatically handle modifiers.

Note

A Seeker will only take one pathfinding call at a time, if you request a new path before the previous one has been completed, the previous path request will be canceled.

using Pathfinding;

public void Start () {
    // Get the seeker component attached to this GameObject
    var seeker = GetComponent<Seeker>();

    // Start a new path request from the current position to a position 10 units forward.
    // When the path has been calculated, it will be returned to the function OnPathComplete unless it was canceled by another path request
    seeker.StartPath (transform.position, transform.position+transform.forward*10, OnPathComplete);

    // Note that the path is NOT calculated at this stage
    // It has just been queued for calculation
}

public void OnPathComplete (Path p) {
    // We got our path back
    if (p.error) {
        // Nooo, a valid path couldn't be found
    } else {
        // Yay, now we can get a Vector3 representation of the path
        // from p.vectorPath
    }
}

A common mistake is to assume that the path is already calculated right after the StartPath call. This is however incorrect. The StartPath call will only put the path in a queue. This is done because when many units are calculating their paths at the same time, it is desriable to spread out the path calculations over several frames to avoid FPS drops. We can also calculate the paths in other threads if multithreading has been enabled. There are of course cases where you need to calculate the path immediately. Then you can use the Pathfinding.Path.BlockUntilCalculated method.

Path p = seeker.StartPath (transform.position, transform.position + Vector3.forward * 10);
p.BlockUntilCalculated();
// The path is calculated now

You can also wait for the path to be calculated in a coroutine using Pathfinding.Path.WaitForPath.

IEnumerator Start () {
    var path = seeker.StartPath (transform.position, transform.position+transform.forward*10, OnPathComplete);
    // Wait... (may take some time depending on how complex the path is)
    // The rest of the game will continue to run while waiting
    yield return StartCoroutine (path.WaitForPath());
    // The path is calculated now
}

You can also create your own path objects instead of using the Seeker's methods. This will enable you to change settings on the path object before calculating it.

// Create a new path object, the last parameter is a callback function
// but it will be used internally by the seeker, so we will set it to null here
// Paths are created using the static Construct call because then it can use
// pooled paths instead of creating a new path object all the time
// which is a nice way to avoid frequent GC spikes.
var p = ABPath.Construct (transform.position, transform.position+transform.forward*10, null);

// By default, a search for the closest walkable nodes to the start and end nodes will be carried out
// but for example in a turn based game, you might not want it to search for the closest walkable node, but return an error if the target point
// was at an unwalkable node. Setting the NNConstraint to None will disable the nearest walkable node search
p.nnConstraint = NNConstraint.None;

// Start the path by sending it to the Seeker
seeker.StartPath (p, OnPathComplete);

It might seem tedious to specify the callback function every time, well, you don't have to. There is a field on the Seeker which can be set to a function which will be called every time a path is returned. For those of you interested in performance, this is also a bit more memory efficient since it does not allocate a new delegate on the heap every time.

// Set the path callback, this should be done once
seeker.pathCallback += OnPathComplete;

// Now we can skip the callback function parameter
seeker.StartPath (transform.position, transform.position+transform.forward*10);

Warning

This callback is permanent, while the component you are calling from might not be, so it's good practise to un-register from the callback when the component is destroyed

public void OnDisable () {
    seeker.pathCallback -= OnPathComplete;
}

A nice thing is that the callback is not limited to one function, you can have several scripts which all get a callback, or just callbacks to more than one function in the script (if you for some reason need that). That's why we have been using + and - when registering and un-registering the callback.

The Seeker component is intended to handle pathfinding requests for a single character in the game. For this reason it will only process a single path request at a time, if you call StartPath when another path was already being calculated it will log a warning saying that the previous path calculation was aborted. If you specifically wanted to cancel the previous path request you can do this without logging a warning by calling Seeker.CancelCurrentPathRequest().

If you want to calculate multiple path simultaneously you can skip the Seeker. Take a look at the Calling AstarPath directly section.

Other types of paths

There are other types of paths than the standard one, for example the MultiTargetPath (Pro feature). These can be started easily as well, especially the MultiTargetPath since the Seeker has a special function for it

// Start a multi target path, where endPoints is a Vector3[] array.
// The last parameter specifies if a path to all end points should be searched for
// or only to the closest one
seeker.StartMultiTargetPath (transform.position, endPoints, true);

The path will be returned as a Path instance, but it can be casted to for example MultiTargetPath to get all the data. A complete example of MultiTargetPath usage can be found here: Multi Target Paths .

Note

The MultiTargetPath is an A* Pathfinding Project Pro Feature, so you will get an error if you try the above code using the Free version of the project.

The generic way to start a type of path is simply

Path p = MyPathType.Construct (...);    // Where MyPathType is for example MultiTargetPath
seeker.StartPath (p, OnPathComplete);

The Construct method is used instead of a consructor so that path pooling can be done more easily.

See also

Path Types

Calling AstarPath directly

There are of course cases where you want even more control of each path. Then you can call the AstarPath component directly. The main function you then use is AstarPath.StartPath. This is useful if you want to calculate a lot of paths at the same time. The Seeker is for agents that only have one active path at a time and if you try to request multiple paths at the same time it will only calculate the last one and cancel the rest.

Note

The paths calculated using AstarPath.StartPath will not be post-processed. However you can call Seeker.PostProcess after a path has been calculated to post process it using the modifiers attached to a particular Seeker.

// There must be an AstarPath instance in the scene
if (AstarPath.active == null) return;

// We can calculate multiple paths asynchronously
for (int i = 0; i < 10; i++) {
    // As there is not Seeker to keep track of the callbacks, we now need to specify the callback every time again
    var p = ABPath.Construct(transform.position, transform.position+transform.forward*i*10, OnPathComplete);

    // Start the path by calling the AstarPath component directly
    // AstarPath.active is the active AstarPath instance in the scene
    AstarPath.StartPath (p);
}