What is this project?

This is a very basic state machine for use inside Unity. It uses ScriptableObjects to help make this extremely modular and non-programmer friendly. I primarily made this because I use State Machines in a lot of projects, and don't want to keep rewriting them over and over again.

How do I use it?

Because this state machine is built off of Actions and Decisions, you do not have to make custom state scripts for each state your object will go through. Instead, you create an action, which can be reused by multiple states. An example action that just applys gravity to a CharacterController would look like this:

using UnityEngine;

[CreateAssetMenu(menuName = "Game/Actions/Gravity Action")]
public class GravityAction : Action
{
    private float m_YVelocity;
    private CharacterController m_Controller;
    
    [SerializeField] private float m_TerminalVelocity;
    [SerializeField] private float m_GravityScale;
    
    public override void OnAdded(StateMachine stateMachine, State state)
    {
        m_Controller = stateMachine.GetComponent<CharacterController>();
        m_YVelocity = m_Controller.velocity.y;
    }
    
    public override void OnUpdate()
    {
        if (m_Controller.isGrounded)
            m_YVelocity = 0.0f;
    
        m_YVelocity += Physics.gravity.y * Time.deltaTime * m_GravityScale;
        m_YVelocity = Mathf.Clamp(m_YVelocity, -m_TerminalVelocity, m_TerminalVelocity);
        
        m_Controller.Move(Vector3.up * m_YVelocity * Time.deltaTime);
    }
    
    public override void OnRemoved()
    {
    
    }
}

Then, in the editor, you can go to the Create menu, and go to "Game > Actions > Gravity Action" and add it to a State (which is created by going to "Game > State Machine > State").

To create a decision, it's largely similar, but there is one thing that is different. Here's an example decision that checks to see if the CharacterController is grounded.

using UnityEngine;

[CreateAssetMenu(menuName = "Game/Decisions/Character Controller Grounded Decision")]
public class CharacterControllerGroundedDecision : Decision
{
    private CharacterController m_Controller;
    
    public override void OnAdded(StateMachine stateMachine, State state)
    {
        m_Controller = stateMachine.GetComponent<CharacterController>();
    }
    
    public override bool Decide()
    {
        return m_Controller.isGrounded;
    }
    
    public override void OnRemoved()
    {
    
    }
}

As you can see, the OnUpdate function from the Action class was replaced with a Decide function. OnUpdate doesn't need to be overridden in a class that extends Action, but Decide must be overridden in every class that extends Decision.

An example Action and Decision are provided in the LogAction and DelayDecision classes, which can be used in your game.

To change states to one outside of the current network of states, just call ChangeState on the StateMachine and choose your new state. If you change to a null state, the current state will be cleared.

Changelog

• Version 1.1
  • Added DelayDecision
  • Added LogAction
  • Modified State and StateDecisionTree to allow for multiple decisions that must all be met in order to change state.
• Version 1.0
  • Added Action
  • Added Decision
  • Added State
  • Added StateDecisionTree
  • Added StateMachine