Modular Finite State Machine Unity (C#)

A finite-state machine is a model used to represent and control execution flow. It is perfect for implementing AI in games and producing great results without a complex code. In this FSM modularity and Pluggablity managed with Scriptable Object. Open-closed and Single responsibility is in high periority.

Use Cases

• None-Player Character (NPC) AI behaviours, Animations
• Dynamic (Self-adjusting)) game difficulity
• Gameplay objects in specific states (Pause, Continue, Game over, Restart, etc)

Simplicity

Blank State as a code sluts No need to Develope every state from scratch. just focuse on your custom actions and conditions that make an State to be switched with another State. Reusable and Pluggable Code Wrap all your codes in ScriptableObject , and let even non-coders build their own custom AI with Drag&Drop

Usage

Action

Action is a script that execute within main body of States, Inheritate from IAction

public abstract class IAction : ScriptableObject
{
	public abstract void Entry(StateController fsm);
	public abstract void Execute(StateController fsm);
	public abstract void Exit(StateController fsm);
}

Sample of a custom action Character wandering around the scene randomly between a list of path points

	[CreateAssetmenu]
    public class PatrolAction : IAction
	{
	    public override void Entry(StateController fsm)
	    {
	        fsm.AIActivator(true);
	    }

	    public override void Execute(StateController fsm)
	    {
            if (fsm.wayPoints.Count < 1 || !fsm.agent) return;
            if (fsm.agent.destination == null || fsm.agent.remainingDistance <= 1.0f)
	        {
	            fsm.agent.destination = fsm.GetRandomWayPoint().position;
	        }
	    }

	    public override void Exit(StateController fsm)
	    {
	        fsm.AIActivator(false);
	    }
}

Decision

Decision return a Boolean value in a certain condition, according to True/False result a transition occurs from one state to another.

public abstract class IDecision : ScriptableObject
{
    public abstract bool Check(StateController fsm);
}

Sample of a custom decision Check if current Health Point Value is less than specified threshold

[CreateAssetMenu]
public class HPThresholdDecision : IDecision
{
	    public int threshold;
	    public override bool Check(StateController fsm)
	    {
	        return fsm.HP.GetHP() <= Mathf.Abs(threshold);
	    }
}

Setup