When we need to change our state according to the surrounding conditions in the project, we can use the state machine to achieve. Below is the state machine example program I searched on WIKI.
The first is the state machine state and management scripts.
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
//here is the toggle state variable
public enum Transition
{
NullTransition = 0, // Use this transition to represent a non-existing transition in your system
SawPlayer,
LostPlayer
}
//This is the ID of each state
public enum StateID
{
NullStateID = 0, // Use this ID to represent a non-existing State in your system
ChasingPlayer,
FollowingPath
}
public abstract class FSMState
{
protected Dictionary<Transition, StateID> map = new Dictionary<Transition, StateID>();
protected StateID stateID;
public StateID ID { get { return stateID; } }
public void AddTransition(Transition trans, StateID id)
{
// Check if anyone of the args is invalid
if (trans == Transition.NullTransition)
{
Debug.LogError("FSMState ERROR: NullTransition is not allowed for a real transition");
return;
}
if (id == StateID.NullStateID)
{
Debug.LogError("FSMState ERROR: NullStateID is not allowed for a real ID");
return;
}
// Since this is a Deterministic FSM,
// check if the current transition was already inside the map
if (map.ContainsKey(trans))
{
Debug.LogError("FSMState ERROR: State " + stateID.ToString() + " already has transition " + trans.ToString() +
"Impossible to assign to another state");
return;
}
map.Add(trans, id);
}
public void DeleteTransition(Transition trans)
{
// Check for NullTransition
if (trans == Transition.NullTransition)
{
Debug.LogError("FSMState ERROR: NullTransition is not allowed");
return;
}
// Check if the pair is inside the map before deleting
if (map.ContainsKey(trans))
{
map.Remove(trans);
return;
}
Debug.LogError("FSMState ERROR: Transition " + trans.ToString() + " passed to " + stateID.ToString() +
" was not on the state's transition list");
}
public StateID GetOutputState(Transition trans)
{
// Check if the map has this transition
if (map.ContainsKey(trans))
{
return map[trans];
}
return StateID.NullStateID;
}
/// <summary>
/// This method is used to set up the State condition before entering it.
/// It is called automatically by the FSMSystem class before assigning it
/// to the current state.
/// </summary>
public virtual void DoBeforeEntering() { }
/// <summary>
/// This method is used to make anything necessary, as reseting variables
/// before the FSMSystem changes to another one. It is called automatically
/// by the FSMSystem before changing to a new state.
/// </summary>
public virtual void DoBeforeLeaving() { }
/// <summary>
/// This method decides if the state should transition to another on its list
/// NPC is a reference to the object that is controlled by this class
/// </summary>
public abstract void Reason(GameObject player, GameObject npc);//It is generally used to detect whether the state needs to be changed. Details of the NPC code below
/// <summary>
/// This method controls the behavior of the NPC in the game World.
/// Every action, movement or communication the NPC does should be placed here
/// NPC is a reference to the object that is controlled by this class
/// </summary>
public abstract void Act(GameObject player, GameObject npc);//What to do when executing this state
} // class FSMState
/// <summary>
/// FSMSystem class represents the Finite State Machine class.
/// It has a List with the States the NPC has and methods to add,
/// delete a state, and to change the current state the Machine is on.
/// </summary>
public class FSMSystem
{
private List<FSMState> states;
// The only way one can change the state of the FSM is by performing a transition
// Don't change the CurrentState directly
private StateID currentStateID;
public StateID CurrentStateID { get { return currentStateID; } }
private FSMState currentState;
public FSMState CurrentState { get { return currentState; } }
public FSMSystem()
{
states = new List<FSMState>();
}
/// <summary>
/// This method places new states inside the FSM,
/// or prints an ERROR message if the state was already inside the List.
/// First state added is also the initial state.
/// </summary>
public void AddState(FSMState s)
{
// Check for Null reference before deleting
if (s == null)
{
Debug.LogError("FSM ERROR: Null reference is not allowed");
}
// First State inserted is also the Initial state,
// the state the machine is in when the simulation begins
if (states.Count == 0)
{
states.Add(s);
currentState = s;
currentStateID = s.ID;
return;
}
// Add the state to the List if it's not inside it
foreach (FSMState state in states)
{
if (state.ID == s.ID)
{
Debug.LogError("FSM ERROR: Impossible to add state " + s.ID.ToString() +
" because state has already been added");
return;
}
}
states.Add(s);
}
/// <summary>
/// This method delete a state from the FSM List if it exists,
/// or prints an ERROR message if the state was not on the List.
/// </summary>
public void DeleteState(StateID id)
{
// Check for NullState before deleting
if (id == StateID.NullStateID)
{
Debug.LogError("FSM ERROR: NullStateID is not allowed for a real state");
return;
}
// Search the List and delete the state if it's inside it
foreach (FSMState state in states)
{
if (state.ID == id)
{
states.Remove(state);
return;
}
}
Debug.LogError("FSM ERROR: Impossible to delete state " + id.ToString() +
". It was not on the list of states");
}
/// <summary>
/// This method tries to change the state the FSM is in based on
/// the current state and the transition passed. If current state
/// doesn't have a target state for the transition passed,
/// an ERROR message is printed.
/// </summary>
public void PerformTransition(Transition trans)
{
// Check for NullTransition before changing the current state
if (trans == Transition.NullTransition)
{
Debug.LogError("FSM ERROR: NullTransition is not allowed for a real transition");
return;
}
// Check if the currentState has the transition passed as argument
StateID id = currentState.GetOutputState(trans);
if (id == StateID.NullStateID)
{
Debug.LogError("FSM ERROR: State " + currentStateID.ToString() + " does not have a target state " +
" for transition " + trans.ToString());
return;
}
// Update the currentStateID and currentState
currentStateID = id;
foreach (FSMState state in states)
{
if (state.ID == currentStateID)
{
// Do the post processing of the state before setting the new one
currentState.DoBeforeLeaving();
currentState = state;
// Reset the state to its desired condition before it can reason or act
currentState.DoBeforeEntering();
break;
}
}
}
}
Then create an NPC code implementation class to implement our NPC control.
using System;
using System.Collections.Generic;
using System.Text;
using UnityEngine;
[RequireComponent(typeof(Rigidbody))]
public class NPCControl : MonoBehaviour
{
public GameObject player;
public Transform[] path;
private FSMSystem fsm;
public void SetTransition(Transition t) { fsm.PerformTransition(t); }
public void Start()
{
MakeFSM ();
}
public void FixedUpdate()
{
fsm.CurrentState.Reason(player, gameObject);
fsm.CurrentState.Act(player, gameObject);
}
// The NPC has two states: FollowPath and ChasePlayer
// If it's on the first state and SawPlayer transition is fired, it changes to ChasePlayer
// If it's on ChasePlayerState and LostPlayer transition is fired, it returns to FollowPath
private void MakeFSM()//Create a state machine and then add the state to the state machine for management
{
FollowPathState follow = new FollowPathState(path);
follow.AddTransition(Transition.SawPlayer, StateID.ChasingPlayer);
ChasePlayerState chase = new ChasePlayerState();
chase.AddTransition(Transition.LostPlayer, StateID.FollowingPath);
fsm = new FSMSystem();
fsm.AddState(follow); //The first added state is the default state by default. We can also change the default state
fsm.AddState(chase);
}
}
public class FollowPathState : FSMState
{
private int currentWayPoint;
private Transform[] waypoints;
public FollowPathState(Transform[] wp)
{
waypoints = wp;
currentWayPoint = 0;
stateID = StateID.FollowingPath;
}
public override void Reason(GameObject player, GameObject npc)
{
// If the Player passes less than 15 meters away in front of the NPC
RaycastHit hit;
if (Physics.Raycast(npc.transform.position, npc.transform.forward, out hit, 15F))
{
if (hit.transform.gameObject.tag == "Player")
npc.GetComponent<NPCControl>().SetTransition(Transition.SawPlayer);
}
}
public override void Act(GameObject player, GameObject npc)
{
// Follow the path of waypoints
// Find the direction of the current way point
Vector3 vel = npc.GetComponent<Rigidbody>().velocity;
Vector3 moveDir = waypoints[currentWayPoint].position - npc.transform.position;
if (moveDir.magnitude < 1)
{
currentWayPoint++;
if (currentWayPoint >= waypoints.Length)
{
currentWayPoint = 0;
}
}
else
{
vel = moveDir.normalized * 10;
// Rotate towards the waypoint
npc.transform.rotation = Quaternion.Slerp(npc.transform.rotation,
Quaternion.LookRotation(moveDir),
5 * Time.deltaTime);
npc.transform.eulerAngles = new Vector3(0, npc.transform.eulerAngles.y, 0);
}
// Apply the Velocity
npc.GetComponent<Rigidbody>().velocity = vel;
}
} // FollowPathState
public class ChasePlayerState : FSMState
{
public ChasePlayerState()
{
stateID = StateID.ChasingPlayer;
}
public override void Reason(GameObject player, GameObject npc)
{
// If the player has gone 30 meters away from the NPC, fire LostPlayer transition
if (Vector3.Distance(npc.transform.position, player.transform.position) >= 30)
npc.GetComponent<NPCControl>().SetTransition(Transition.LostPlayer);
}
//Go to the chase state npc to start chasing the Player
public override void Act(GameObject player, GameObject npc)
{
// Follow the path of waypoints
// Find the direction of the player
Vector3 vel = npc.GetComponent<Rigidbody>().velocity;
Vector3 moveDir = player.transform.position - npc.transform.position;
// Rotate towards the waypoint
npc.transform.rotation = Quaternion.Slerp(npc.transform.rotation,
Quaternion.LookRotation(moveDir),
5 * Time.deltaTime);
npc.transform.eulerAngles = new Vector3(0, npc.transform.eulerAngles.y, 0);
vel = moveDir.normalized * 10;
// Apply the new Velocity
npc.GetComponent<Rigidbody>().velocity = vel;
}
}