Create custom conditions

Conditions can be thought of as the gate keeper for branches. A condition must be passed before the rest of the sibling nodes can be executed. Conditions are usually game specific, and I have yet to encounter a generic one. This demo project will have two conditions.

Like the other node types, you will need to create a Condition class to inherit from. Create a new abstract class in /WUG/Scripts/Behaviors called Condition, which will inherit from Node. Add the following code:

    public abstract class Condition : Node
    {

        public Condition(string name)
        {
            Name = name;
        }

    }

There is nothing inherently special about this base class but having it will allow the Behavior Tree Visualizer to stylize all conditions a specific way. It also sets each condition up to easily have custom name set, as you will see shortly.

IsNavigationActivityTypeOf

The IsNavigationActivityTypeOf condition is quite simple - it will look at the NavigationActivity property on the NPC class and confirm that it is the desired value. If it is, it will return NodeStatus.Success and if not, it returns NodeStatus.Failure. It will take one property, which is the NavigationActivity to look for.

1. Add a new Conditions folder in /WUG/Scripts/Behaviors/.
2. Create a new class in the Conditions folder called IsNavigationActivityTypeOf, which will inherit from Condition.
3. Add the following global variable and code for the constructor:

public class IsNavigationActivityTypeOf : Condition
{
    private NavigationActivity m_ActivityToCheckFor;

    public IsNavigationActivityTypeOf(NavigationActivity activity) : base($"Is Navigation Activity {activity}?")
    {
        m_ActivityToCheckFor = activity;
    }
}

The constructor will set the global variable m_ActivityToCheckFor to the desired value to search for and pass a predefined Name to the base class. The name will be displayed on the node when using Behavior Tree Visualizer.

Add the following methods for OnReset() and OnRun():

protected override void OnReset() { }

protected override NodeStatus OnRun()
{
    if (GameManager.Instance == null || GameManager.Instance.NPC == null)
    {
        StatusReason = "GameManager and/or NPC is null";
        return NodeStatus.Failure;
    }

    StatusReason = $"NPC Activity is {m_ActivityToCheckFor}";

    return GameManager.Instance.NPC.MyActivity == m_ActivityToCheckFor ? NodeStatus.Success : NodeStatus.Failure; 
}

OnRun() will first check for references to the necessary scripts and if those pass it’ll do a check against NPC.MyActivity for the value needed.

AreItemsNearBy

The AreItemsNearBy condition will check to see if an item is a specific distance from the player. It will take one property, which is the maxDistance to search. Create a new class in the Conditions folder called AreItemsNearBy, which will inherit from Condition. Add the following global variable and code for the constructor:

public class AreItemsNearBy : Condition
{
    private float m_DistanceToCheck;

    public AreItemsNearBy(float maxDistance) : base($"Are Items within {maxDistance}f?") 
    { 
        m_DistanceToCheck = maxDistance; 
    }
}

Add the following methods for OnReset() and OnRun():

protected override void OnReset() { }

protected override NodeStatus OnRun()
{
    //Check for references
    if (GameManager.Instance == null || GameManager.Instance.NPC == null)
    {
        StatusReason = "GameManager and/or NPC is null";
        return NodeStatus.Failure;
    }

    //Get the closest item
    GameObject item = GameManager.Instance.GetClosestItem();

    //Check to see if something is close by
    if (item == null)
    {
        StatusReason = "No items near by";
        return NodeStatus.Failure;

    }
    else if (Vector3.Distance(item.transform.position, GameManager.Instance.NPC.transform.position) > m_DistanceToCheck)
    {
        StatusReason = $"No items within range of {m_DistanceToCheck} meters";
        return NodeStatus.Failure;
    }

    return NodeStatus.Success;
}

OnRun() will do the same instance check and if it passes, will call GameManager.GetClosestItem for the next item. If that item is null or not within the range of m_DistanceToCheck then the condition will return NodeStatus.Failure. Otherwise, it will return NodeStatus.Success.