Implementing behavior trees

Behavior trees can be seen as a synthesis of a number of other artificial intelligence techniques, such as finite-state machines, planning, and decision trees. In fact, they share some resemblance to FSMs, but instead of states, we think in terms of actions spanned across a tree structure.

Getting ready

This recipe requires us to understand Coroutines.

How to do it...

Just like decisions trees, we will create three pseudo-abstract classes for handling the process:

1. Create the base class, Task:

   using UnityEngine;
   using System.Collections;
   using System.Collections.Generic;
   
   public class Task : MonoBehaviour
   {
       public List<Task> children;
       protected bool result = false;
       protected bool isFinished = false;
   }

2. Implement the finalization function:

   public virtual void SetResult(bool r)
   {
       result = r;
       isFinished = true;
   }

3. Implement the function for creating behaviors:

   public virtual IEnumerator Run()
   {
       SetResult(true);
       yield break;
   }

4. Implement the general...