Unity 3D Enemy AI for 2D Platformer

by NSDG • Jul 23, 2018 • 0 Comments
1333
Creating a Platformer in Unity 3D is relatively easy, but when it comes to enemy AI, the solution may not be as straightforward.

In this post I will be showing how to create a simple AI for a 2D platformer game.

Generally in 2D platformers the player can only walk front/back, jump and in some cases climb up/down the ladder, if the map is multileveled.
Knowing that, we could use a modular approach where the same controller is shared between the player and the AI.

Part 1


Let's begin by creating all the necessary scripts. Check the source code below:

Ladder2D.cs
//Copyright @2018 sharpcoderr.com
//You are free to use this script in free or commercial projects
//Selling the source code of this script is not allowed

using UnityEngine;

public class Ladder2D : MonoBehaviour
{
    Collider2D ladderCollider;
    [HideInInspector]
    public Vector3 boundsCenter;

    void Start()
    {
        //t = transform;
        ladderCollider = GetComponent<Collider2D>();
        if (ladderCollider)
        {
            ladderCollider.isTrigger = true;
            ladderCollider.gameObject.layer = 2; //Set ladder collider layer to IgnoreRaycast
        }
    }

    void OnTriggerEnter2D(Collider2D other)
    {
        if (other.CompareTag("Player"))
        {
            if (ladderCollider)
            {
                boundsCenter = ladderCollider.bounds.center;
            }
            other.SendMessage("AssignLadder", this, SendMessageOptions.DontRequireReceiver);
        }
    }

    void OnTriggerExit2D(Collider2D other)
    {
        if (other.CompareTag("Player"))
        {
            other.SendMessage("RemoveLadder", this, SendMessageOptions.DontRequireReceiver);
        }
    }
}

PlayerController2D.cs
//Copyright @2018 sharpcoderr.com
//You are free to use this script in free or commercial projects
//Selling the source code of this script is not allowed

using System.Collections.Generic;
using UnityEngine;

public class PlayerController2D : MonoBehaviour
{
    //Move player in 2D space
    public float maxSpeed = 2.57f;
    public float jumpHeight = 6.47f;
    public float playerHP = 100;

    [HideInInspector]
    public bool facingRight = true;
    [HideInInspector]
    public float moveDirection = 0;
    [HideInInspector]
    public Rigidbody2D r2d;
    [HideInInspector]
    public Collider2D mainCollider;
    [HideInInspector]
    public Vector2 playerDimensions;
    [HideInInspector]
    public bool isGrounded = false;
    //Check every collider except Player and Ignore Raycast
    LayerMask layerMask = ~(1 << 2 | 1 << 8); //Make sure our player has Layer 8

    [HideInInspector]
    public Ladder2D currentLadder;
    List<Ladder2D> allLadders = new List<Ladder2D>();
    float moveDirectionY = 0;
    float distanceFromLadder;
    [HideInInspector]
    public bool isAttachedToLadder = false;
    bool ladderGoingDown = false;
    //bool isMovingOnLadder = false;
    [HideInInspector]
    public bool canGoDownOnLadder = false;
    [HideInInspector]
    public bool canClimbLadder = false;

    //Bot movement directions
    [HideInInspector]
    public bool isBot = false;
    [HideInInspector]
    public float botMovement = 0;
    [HideInInspector]
    public float botVerticalMovement = 0;
    [HideInInspector]
    public bool botJump = false;
    [HideInInspector]
    public Transform t;
    [HideInInspector]
    public int selectedWeaponTmp = 0;

    float gravityScale;

    // Use this for initialization
    void Start()
    {
        r2d = GetComponent<Rigidbody2D>();
        r2d.freezeRotation = true;
        mainCollider = GetComponent<Collider2D>();
        t = transform;

        gravityScale = r2d.gravityScale;
        selectedWeaponTmp = -100;

        facingRight = t.localScale.x > 0;

        //sr = GetComponent<SpriteRenderer>();
        playerDimensions = BotController2D.ColliderDimensions(GetComponent<Collider2D>());
    }

    void OnDisable()
    {
        r2d.bodyType = RigidbodyType2D.Static;
        r2d.velocity = Vector3.zero;
    }

    // Update is called once per frame
    void Update()
    {
        if (!isBot)
        {
            if ((Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.D)) &&
                (isGrounded || r2d.velocity.x > 0.01f || isAttachedToLadder))
            {
                moveDirection = Input.GetKey(KeyCode.A) ? -1 : 1;
            }
            else
            {
                if (isGrounded || r2d.velocity.magnitude < 0.01f)
                    moveDirection = 0;
            }
        }
        else
        {
            if (botMovement != 0 && (isGrounded || r2d.velocity.x > 0.01f))
            {
                moveDirection = botMovement < 0 ? -1 : 1;
            }
            else
            {
                if (isGrounded || r2d.velocity.magnitude < 0.01f)
                    moveDirection = 0;
            }
        }

        //Change facing position
        if (moveDirection != 0)
        {
            if (moveDirection > 0 && !facingRight)
            {
                facingRight = true;
            }
            if (moveDirection < 0 && facingRight)
            {
                facingRight = false;
            }
        }

        if (facingRight)
        {
            if (t.localScale.x < 0)
            {
                t.localScale = new Vector3(Mathf.Abs(t.localScale.x), t.localScale.y, transform.localScale.z);
            }
        }
        else
        {
            if (t.localScale.x > 0)
            {
                t.localScale = new Vector3(-Mathf.Abs(t.localScale.x), t.localScale.y, t.localScale.z);
            }
        }

        //Vector2 velocityTmp = r2d.velocity;
        bool canGoDownTmp = false;

        // LADDER CONTROL START
        if (currentLadder)
        {
            distanceFromLadder = Mathf.Abs(currentLadder.boundsCenter.x - t.position.x);
            canClimbLadder = distanceFromLadder < 0.34f;
            if (!isAttachedToLadder)
            {
                if (canClimbLadder)
                {
                    if (currentLadder.boundsCenter.y > t.position.y)
                    {
                        if (!isBot)
                        {
                            if (Input.GetKey(KeyCode.W))
                            {
                                isAttachedToLadder = true;
                            }
                        }
                        else
                        {
                            if (botVerticalMovement > 0)
                            {
                                isAttachedToLadder = true;
                            }
                        }
                    }
                    if (currentLadder.boundsCenter.y < t.position.y)
                    {
                        if (!isBot)
                        {
                            if (Input.GetKey(KeyCode.S))
                            {
                                isAttachedToLadder = true;
                            }
                        }
                        else
                        {
                            if (botVerticalMovement < 0)
                            {
                                isAttachedToLadder = true;
                            }
                        }

                        canGoDownTmp = true;
                    }
                }

                if (isAttachedToLadder)
                {
                    r2d.gravityScale = 0;
                    moveDirection = 0;
                    moveDirectionY = 0;
                }
            }
            else
            {
                //Make our collider trigger if we stand on top of the ladder (To prevent collision with the ground while going down)
                mainCollider.isTrigger = currentLadder.boundsCenter.y < t.position.y; 

                //Ladder movement
                if ((!isBot && Input.GetKey(KeyCode.W)) || (isBot && botVerticalMovement > 0))
                {
                    moveDirectionY = 3.97f;
                    ladderGoingDown = false;
                    //For sound controller
                    //isMovingOnLadder = true;
                }
                else if ((!isBot && Input.GetKey(KeyCode.S)) || (isBot && botVerticalMovement < 0))
                {
                    moveDirectionY = -3.97f;
                    ladderGoingDown = true;
                    if (!mainCollider.isTrigger && isGrounded)
                    {
                        //RemoveLadder(currentLadder);
                        isAttachedToLadder = false;
                        mainCollider.isTrigger = false;
                        r2d.gravityScale = gravityScale;
                        moveDirectionY = 0;
                    }
                    //For sound controller
                    //isMovingOnLadder = true;
                }
                else
                {
                    //isMovingOnLadder = false;
                    moveDirectionY = 0;
                }
            }

            if (distanceFromLadder > playerDimensions.x * 2)
            {
                RemoveLadder(currentLadder);
            }
        }
        canGoDownOnLadder = canGoDownTmp;
        // LADDER CONTROL END

        if (!isBot)
        {
            //Jumping
            if (Input.GetKeyDown(KeyCode.W))
            {
                Jump();
            }
        }
        else
        {
            if (botJump)
            {
                botJump = false;
                Jump();
            }
        }

        if (!isBot)
        {
            //Weapon firing
            if (Input.GetKeyDown(KeyCode.LeftControl))
            {
                Attack();
            }
        }
    }

    void FixedUpdate()
    {
        Bounds colliderBounds = mainCollider.bounds;
        Vector3 groundCheckPos = colliderBounds.min + new Vector3(colliderBounds.size.x * 0.5f, 0.1f, 0);
        //Check if player is grounded
        isGrounded = Physics2D.OverlapCircle(groundCheckPos, 0.25f, layerMask);

        Debug.DrawLine(groundCheckPos, groundCheckPos - new Vector3(0, 0.25f, 0), isGrounded ? Color.green : Color.red);

        //Apply player velocity
        r2d.velocity = new Vector2((moveDirection) * maxSpeed, isAttachedToLadder ? moveDirectionY : r2d.velocity.y);
    }

    void AssignLadder(Ladder2D ladderTmp)
    {
        currentLadder = ladderTmp;
        allLadders.Add(ladderTmp);
    }

    void RemoveLadder(Ladder2D ladderTmp)
    {
        //print("On trigger out");
        allLadders.Remove(ladderTmp);
        if (currentLadder == ladderTmp)
        {
            currentLadder = null;

            if (allLadders.Count > 0)
            {
                currentLadder = allLadders[allLadders.Count - 1];
            }
        }

        if (isAttachedToLadder && !currentLadder)
        {
            isAttachedToLadder = false;
            //r2d.bodyType = RigidbodyType2D.Dynamic;
            mainCollider.isTrigger = false;

            r2d.gravityScale = gravityScale;
            r2d.velocity = Vector3.zero;

            if (!ladderGoingDown)
            {
                r2d.velocity = new Vector2(r2d.velocity.x, 1.47f);
            }
            ladderGoingDown = false;
        }
    }

    public void Jump()
    {
        if (isGrounded && !isAttachedToLadder)
        {
            r2d.velocity = new Vector2(r2d.velocity.x, jumpHeight);
            //Tip: Play jump sound here
        }
    }

    public void Attack()
    {
        print(gameObject.name + " is Attacking");

        //Tip: Write your attack function here (ex. Raycast toward the enemy to inflict the damage)
    }
}

CameraFollow2D.cs
//Copyright @2018 sharpcoderr.com
//You are free to use this script in free or commercial projects
//Selling the source code of this script is not allowed

using UnityEngine;

public class CameraFollow2D : MonoBehaviour
{
    public Transform target;
    public Vector3 offset = new Vector3(0, 2.8f, 0);
    public bool smoothFollow = true;

    Vector2 moveToPos;
    bool beginMove = false;
    float distanceTmp = 0f;

    // Update is called once per frame
    void LateUpdate()
    {
        if (!target)
            return;

        if (smoothFollow)
        {
            distanceTmp = ((target.position + offset) - transform.position).sqrMagnitude;
            if (beginMove)
            {
                moveToPos = Vector3.Lerp(moveToPos, target.position + offset, Time.fixedDeltaTime * 7.75f);
                transform.position = new Vector3(moveToPos.x, moveToPos.y, -10);

                if (distanceTmp < 0.05f * 0.05f)
                {
                    beginMove = false;
                }
            }
            else
            {
                if (distanceTmp > 0.5f * 0.5f)
                {
                    beginMove = true;
                }
            }
        }
        else
        {
            transform.position = new Vector3(target.position.x, target.position.y, -10);
        }

    }

    void StopFollowing()
    {
        beginMove = false;
    }
}

BotController2D.cs
//Copyright @2018 sharpcoderr.com
//You are free to use this script in free or commercial projects
//Selling the source code of this script is not allowed

using System.Collections;
using UnityEngine;

public class BotController2D : MonoBehaviour
{
    //This script will handle bot control
    public enum BotType { Enemy, Friendly }
    public BotType botType = BotType.Enemy;
    public enum BotDifficulty { Easy, Medium, Hard }
    public BotDifficulty botDifficulty = BotDifficulty.Medium;
    public enum InitialState { Idle, Explore }
    public InitialState initialState = InitialState.Idle; //Should the Bot stand in place until approached or begin exploring the level right away
    public bool canJump = true; //Can this bot jump?

    public enum CurrentState { Idle, MovingLeft, MovingRight, GoinUPLadder, GoingDownLadder, Attack }
    CurrentState currentState;
    InitialState appliedState;
    PlayerController2D pc2d;
    RaycastHit2D hitLeft;
    RaycastHit2D hitRight;
    RaycastHit2D groundHit;
    Vector3 leftOrigin;
    Vector3 rightOrigin;
    float distanceLeft = -1;
    float distanceRight = -1;

    int encounteredLadders = 0;
    int encounteredLaddersCacche = 0;
    Ladder2D previousLadder;
    Ladder2D lastAttachedLadder;
    bool previousCanGoDownOnLadder = false;
    bool previousCanClimbLadder = false;

    //Everything except "Player" and "IgnoreRaycast" layers
    LayerMask layerMask = ~(1 << 2 | 1 << 8);
    //Only "Player" layer
    LayerMask playerLayerMask = 1 << 8;

    float timeMotionless = 0.0f;
    bool statePause = false;

    float trVelocity;
    Vector3 previousPos;

    Collider2D[] detectedPlayers = new Collider2D[0];
    Collider2D[] previousDetectedPlayers = new Collider2D[0];
    PlayerController2D enemyToFollow;
    int followPriority = 0; //0 = Easy, 1 = Medium (This player inflicted the damage)

    [HideInInspector]
    public Transform t;

    bool checkingTotalEnemies = false;
    bool runAway = false;

    int attackingFromLeft = 0;
    int attackingFromRight = 0;

    //Limit attack rate for easy bots
    float attackTimer = 0;
    float nextAttackTime = 0;

    Camera mainCamera;
    float cameraWidth; //Horizontal size of camera view

    // Use this for initialization
    void Start()
    {
        pc2d = GetComponent<PlayerController2D>();
        pc2d.isBot = true;
        t = transform;
        appliedState = initialState;

        if (Random.Range(-10, 10) > 0)
        {
            StartCoroutine(StatePause(CurrentState.Idle, true));
        }
    }

    // Update is called once per frame
    void FixedUpdate()
    {
        //Draw rays back and forth

        if (!mainCamera)
        {
            mainCamera = Camera.main;
            cameraWidth = mainCamera.aspect * mainCamera.orthographicSize;
        }

        rightOrigin = t.position + t.right * (pc2d.playerDimensions.x / 2f);
        hitRight = Physics2D.Raycast(rightOrigin, t.right, cameraWidth, layerMask);
        if (hitRight)
        {
            Debug.DrawLine(rightOrigin, hitRight.point, Color.red);
            distanceRight = hitRight.distance;
        }
        else
        {
            Debug.DrawLine(rightOrigin, rightOrigin + t.right * cameraWidth, Color.cyan);
            distanceRight = -1;
        }

        leftOrigin = t.position - t.right * (pc2d.playerDimensions.x / 2f);
        hitLeft = Physics2D.Raycast(leftOrigin, -t.right, cameraWidth, layerMask);
        if (hitLeft)
        {
            Debug.DrawLine(leftOrigin, hitLeft.point, Color.red);
            distanceLeft = hitLeft.distance;
        }
        else
        {
            Debug.DrawLine(leftOrigin, leftOrigin - t.right * cameraWidth, Color.cyan);
            distanceLeft = -1;
        }

        if (appliedState == InitialState.Explore)
        {
            if (currentState == CurrentState.Idle)
            {
                if (!statePause)
                {
                    //Decide which direction to move
                    if (distanceRight == -1 && distanceLeft == -1)
                    {
                        //Decide random direaction
                        currentState = Random.Range(-10, 10) > 0 ? CurrentState.MovingRight : CurrentState.MovingLeft;
                    }
                    else if (distanceRight == -1 && distanceLeft >= 0)
                    {
                        currentState = CurrentState.MovingRight;
                    }
                    else if (distanceRight >= 0 && distanceLeft == -1)
                    {
                        currentState = CurrentState.MovingLeft;
                    }
                    else if (distanceRight > distanceLeft)
                    {
                        currentState = CurrentState.MovingRight;
                    }
                    else if (distanceRight < distanceLeft)
                    {
                        currentState = CurrentState.MovingLeft;
                    }
                }
            }
            else if (currentState == CurrentState.MovingLeft)
            {
                if (!statePause && pc2d.isGrounded)
                {
                    pc2d.botMovement = -1;
                    float jumpHeightTmp = pc2d.jumpHeight * 0.25f;

                    if (distanceLeft > 0 && distanceLeft < pc2d.playerDimensions.x)
                    {
                        if (hitLeft && canJump &&
                            !Physics2D.Linecast(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) - t.right * pc2d.playerDimensions.x * 2, layerMask) &&
                            Random.Range(-2, 10) > 0
                        )
                        {
                            StartCoroutine(DoJump());
                        }
                        else
                        {
                            if (!enemyToFollow)
                            {
                                StartCoroutine(StatePause(CurrentState.Idle, true));
                            }
                        }
                    }

                    /*if(!Physics2D.Linecast(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) - t.right * pc2d.playerDimensions.x * 2)){
                        Debug.DrawLine(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) - t.right * pc2d.playerDimensions.x * 2, Color.yellow);
                    }
                    else
                    {
                        Debug.DrawLine(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) - t.right * pc2d.playerDimensions.x * 2, Color.red);
                    }*/

                    //Jump if there is no groun in front
                    groundHit = Physics2D.Raycast(leftOrigin, -t.up, pc2d.playerDimensions.y * 2.1f, layerMask);
                    if (groundHit)
                    {
                        Debug.DrawLine(leftOrigin, groundHit.point, Color.red);
                    }
                    else
                    {
                        Debug.DrawLine(leftOrigin, leftOrigin - t.up * (pc2d.playerDimensions.y * 2.1f), Color.blue);
                        if (canJump)
                        {
                            StartCoroutine(DoJump());
                        }
                        else
                        {
                            //StartCoroutine(StatePause(CurrentState.MovingRight, true));
                            StartCoroutine(CheckEnemiesEnumerator(1, 0, false));
                        }
                    }
                }
            }
            else if (currentState == CurrentState.MovingRight)
            {
                if (!statePause && pc2d.isGrounded)
                {
                    pc2d.botMovement = 1;
                    float jumpHeightTmp = pc2d.jumpHeight * 0.25f;

                    if (distanceRight > 0 && distanceRight < pc2d.playerDimensions.x)
                    {
                        if (hitRight && canJump &&
                            !Physics2D.Linecast(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) + t.right * pc2d.playerDimensions.x * 2, layerMask) &&
                            Random.Range(-2, 10) > 0
                        )
                        {
                            StartCoroutine(DoJump());
                        }
                        else
                        {
                            if (!enemyToFollow)
                            {
                                StartCoroutine(StatePause(CurrentState.Idle, true));
                            }
                        }
                    }

                    /*if (!Physics2D.Linecast(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) + t.right * pc2d.playerDimensions.x * 2))
                    {
                        Debug.DrawLine(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) + t.right * pc2d.playerDimensions.x * 2, Color.yellow);
                    }
                    else
                    {
                        Debug.DrawLine(t.position + t.up * jumpHeightTmp, (t.position + t.up * jumpHeightTmp) + t.right * pc2d.playerDimensions.x * 2, Color.red);
                    }*/

                    //Jump if there is no groun in front
                    groundHit = Physics2D.Raycast(rightOrigin, -t.up, pc2d.playerDimensions.y * 2.1f, layerMask);
                    if (groundHit)
                    {
                        Debug.DrawLine(rightOrigin, groundHit.point, Color.red);
                    }
                    else
                    {
                        Debug.DrawLine(rightOrigin, rightOrigin - t.up * (pc2d.playerDimensions.y * 2.1f), Color.blue);
                        if (canJump)
                        {
                            StartCoroutine(DoJump());
                        }
                        else
                        {
                            //StartCoroutine(StatePause(CurrentState.MovingLeft, true));
                            StartCoroutine(CheckEnemiesEnumerator(0, 1, false));
                        }
                    }
                }
            }
            else if (currentState == CurrentState.GoinUPLadder)
            {
                if (!statePause)
                {
                    pc2d.botVerticalMovement = 1;
                    if (!pc2d.currentLadder)
                    {
                        StartCoroutine(StatePause(CurrentState.Idle, true));
                    }
                }
            }
            else if (currentState == CurrentState.GoingDownLadder)
            {
                if (!statePause)
                {
                    pc2d.botVerticalMovement = -1;
                    if (!pc2d.currentLadder)
                    {
                        StartCoroutine(StatePause(CurrentState.Idle, true));
                    }
                }
            }
            else if (currentState == CurrentState.Attack)
            {
                if (!statePause)
                {
                    if (!enemyToFollow)
                    {
                        StartCoroutine(StatePause(CurrentState.Idle, true));
                    }
                    else
                    {
                        //Firing weapon
                        if (attackTimer >= nextAttackTime)
                        {
                            //Check if player is above us and jump
                            if (enemyToFollow.t.position.y > t.position.y && enemyToFollow.t.position.y - t.position.y > pc2d.playerDimensions.y * 0.95f)
                            {
                                if (Random.Range(-5, 10) > 0)
                                {
                                    StartCoroutine(DoJump());
                                }
                            }
                            //

                            pc2d.Attack();

                            if (botDifficulty == BotDifficulty.Easy)
                            {
                                attackTimer = 0;
                                nextAttackTime = Random.Range(0.25f, 0.95f);
                            }
                            if (botDifficulty == BotDifficulty.Medium)
                            {
                                attackTimer = 0;
                                nextAttackTime = Random.Range(0.01f, 0.37f);
                            }
                            if (botDifficulty == BotDifficulty.Hard)
                            {
                                attackTimer = 0;
                                nextAttackTime = Random.Range(0.01f, 0.24f);
                            }
                        }
                        else
                        {
                            attackTimer += Time.deltaTime;
                        }


                        if (enemyToFollow && !checkingTotalEnemies)
                        {
                            if (enemyToFollow.t.position.x > t.position.x && !pc2d.facingRight)
                            {
                                pc2d.facingRight = true;
                            }
                            if (enemyToFollow.t.position.x < t.position.x && pc2d.facingRight)
                            {
                                pc2d.facingRight = false;
                            }

                            attackingFromLeft = 0;
                            attackingFromRight = 0;

                            //Check if there too many player attacking us and run away
                            for (int i = 0; i < detectedPlayers.Length; i++)
                            {
                                if (detectedPlayers[i])
                                {
                                    BotController2D bcTmp = detectedPlayers[i].GetComponent<BotController2D>();
                                    if (bcTmp && bcTmp.botType != botType && bcTmp.enemyToFollow == pc2d && bcTmp.currentState == CurrentState.Attack)
                                    {
                                        if (bcTmp.t.position.x > t.position.x)
                                        {
                                            attackingFromRight++;
                                        }
                                        else
                                        {
                                            attackingFromLeft++;
                                        }
                                    }
                                }
                            }

                            //If the value playerHP from PlayerController2D get too low, and the bot is being attacked, increase the probability to run away
                            if (attackingFromRight >= 2 || attackingFromLeft >= 2 || (pc2d.playerHP < 70 && botDifficulty == BotDifficulty.Hard && (attackingFromRight > 0 || attackingFromLeft > 0)) || (pc2d.playerHP < 40 && botDifficulty == BotDifficulty.Medium && (attackingFromRight > 0 || attackingFromLeft > 0)))
                            {
                                StartCoroutine(CheckEnemiesEnumerator(attackingFromLeft, attackingFromRight, false));
                            }
                        }
                    }
                }
            }
        }

        if (pc2d.currentLadder && (previousLadder != pc2d.currentLadder || previousCanGoDownOnLadder != pc2d.canGoDownOnLadder || previousCanClimbLadder != pc2d.canClimbLadder))
        {
            previousLadder = pc2d.currentLadder;
            previousCanGoDownOnLadder = pc2d.canGoDownOnLadder;
            previousCanClimbLadder = pc2d.canClimbLadder;

            if (!pc2d.isAttachedToLadder)
            {
                if (pc2d.canClimbLadder)
                {
                    encounteredLadders++;

                    if ((lastAttachedLadder != pc2d.currentLadder || encounteredLadders > 1) && !statePause)
                    {
                        if (Random.Range(-10, 10) > 0)
                        {
                            if (pc2d.canGoDownOnLadder)
                            {
                                StartCoroutine(StatePause(CurrentState.GoingDownLadder, true));
                            }
                            else
                            {
                                StartCoroutine(StatePause(CurrentState.GoinUPLadder, true));
                            }
                        }
                    }
                }
            }
            else
            {
                encounteredLadders = 0;
                lastAttachedLadder = pc2d.currentLadder;
            }
        }

        trVelocity = ((t.position - previousPos).magnitude) / Time.deltaTime;
        previousPos = t.position;

        if (trVelocity < 0.01f && !statePause)
        {
            timeMotionless += Time.deltaTime;

            if (timeMotionless > 0.5f)
            {
                StartCoroutine(StatePause(CurrentState.Idle, true));
            }
        }
        else
        {
            timeMotionless = 0;
        }

        //Detect and attack enemy players
        detectedPlayers = Physics2D.OverlapCircleAll(t.position, cameraWidth, playerLayerMask);

        if (!enemyToFollow)
        {
            if (!runAway)
            {
                if (previousDetectedPlayers.Length != detectedPlayers.Length || previousDetectedPlayers[0] != detectedPlayers[0])
                {
                    previousDetectedPlayers = detectedPlayers;

                    for (int i = 0; i < detectedPlayers.Length; i++)
                    {
                        BotController2D bcTmp = detectedPlayers[i].GetComponent<BotController2D>();
                        PlayerController2D pc2dTmp = null;
                        if (!bcTmp)
                        {
                            pc2dTmp = detectedPlayers[i].GetComponent<PlayerController2D>();
                        }
                        if ((pc2dTmp && botType == BotType.Enemy) || (bcTmp && bcTmp.botType != botType))
                        {
                            Vector3 enemyPos = bcTmp ? bcTmp.t.position : pc2dTmp.t.position;
                            float yDistance = Mathf.Abs(enemyPos.y - t.position.y);
                            if (yDistance < pc2d.playerDimensions.y * 2)
                            {
                                if (!enemyToFollow || Mathf.Abs(enemyPos.x - t.position.x) < Mathf.Abs(enemyToFollow.t.position.x - t.position.x))
                                {
                                    enemyToFollow = bcTmp ? bcTmp.pc2d : pc2dTmp;
                                    appliedState = InitialState.Explore;
                                }
                            }

                        }
                    }
                }
            }
        }
        else
        {
            float yDistance = enemyToFollow.t.position.y - t.position.y;
            float xDistance = enemyToFollow.t.position.x - t.position.x;
            if (Mathf.Abs(yDistance) >= pc2d.playerDimensions.y * 2 || Mathf.Abs(xDistance) > cameraWidth || !enemyToFollow.enabled)
            {
                enemyToFollow = null;
            }
            else
            {
                if (Mathf.Abs(xDistance) > pc2d.playerDimensions.x * 1.45f)
                {
                    if (!statePause && pc2d.botVerticalMovement == 0)
                    {
                        if (xDistance > 0)
                        {
                            if (currentState != CurrentState.MovingRight)
                            {
                                statePauseCoroutine = StartCoroutine(StatePause(CurrentState.MovingRight, false));
                            }
                        }
                        else if (xDistance < 0)
                        {
                            if (currentState != CurrentState.MovingLeft)
                            {
                                statePauseCoroutine = StartCoroutine(StatePause(CurrentState.MovingLeft, false));
                            }
                        }
                    }
                    else
                    {
                        StopPauseCoroutine();
                    }
                }
                else
                {
                    if (pc2d.botVerticalMovement == 0)
                    {
                        if (currentState != CurrentState.Attack)
                        {
                            if (!statePause)
                            {
                                statePauseCoroutine = StartCoroutine(StatePause(CurrentState.Attack, true));
                            }
                        }
                        else
                        {
                            if (Mathf.Abs(xDistance) < pc2d.playerDimensions.x / 3 && !checkingTotalEnemies)
                            {
                                //print("Enemies are too close!!!");
                                StartCoroutine(CheckEnemiesEnumerator(attackingFromLeft, attackingFromRight, true));
                            }
                        }
                    }
                }
            }
        }
    }

    Coroutine statePauseCoroutine = null;

    void StopPauseCoroutine()
    {
        if (statePauseCoroutine != null)
        {
            StopCoroutine(statePauseCoroutine);
            statePauseCoroutine = null;
            statePause = false;
        }
    }

    IEnumerator StatePause(CurrentState newState, bool stopMovement)
    {
        //print("State pause");
        statePause = true;
        if (stopMovement)
        {
            pc2d.botMovement = 0;
            pc2d.botVerticalMovement = 0;
        }
        currentState = newState;

        if (newState == CurrentState.Attack && botDifficulty == BotDifficulty.Hard)
        {
            yield return new WaitForSeconds(Random.Range(0.15f, 0.45f));
        }
        else
        {
            yield return new WaitForSeconds(Random.Range(0.45f, 0.75f));
        }


        statePause = false;
    }

    IEnumerator DoJump()
    {
        //print("Do jump");
        statePause = true;
        pc2d.botJump = true;

        yield return new WaitForSeconds(0.65f);

        statePause = false;
    }

    IEnumerator CheckEnemiesEnumerator(int attackingFromLeft, int attackingFromRight, bool doNotRunAway)
    {
        checkingTotalEnemies = true;

        //print("CHECKING FOR TOTAL ENEMIES");

        yield return new WaitForSeconds(Random.Range(0.27f, 0.75f));

        if (Random.Range(-10, 10) > 0)
        {
            runAway = true;
            enemyToFollow = null;

            if (attackingFromLeft > attackingFromRight)
            {
                currentState = CurrentState.MovingRight;
            }
            else
            {
                currentState = CurrentState.MovingLeft;
            }
        }

        checkingTotalEnemies = false;

        if (runAway)
        {
            if (doNotRunAway)
            {
                //Simply walk away a bit
                yield return new WaitForSeconds(Random.Range(0.37f, 0.75f));
            }
            else
            {
                //Run away
                yield return new WaitForSeconds(Random.Range(1.57f, 2.45f));
            }


            runAway = false;
        }
    }

    public static Vector2 ColliderDimensions(Collider2D sp)
    {
        return new Vector2(sp.bounds.max.x - sp.bounds.min.x, sp.bounds.max.y - sp.bounds.min.y);
    }
}



Part 2


Now it's time setup our player and the enemy AI using the scripts above.

First we setup our player instance:

  • Create a new GameObject and name it "Player"
  • Change the Tag of that object to "Player"
  • Change the object's layer to 8 (If there is no Layer 8 in selection, add one by clicking Add Layer..., name it "Player")
  • Create another GameObject, call it "Body" and add a SpriteRenderer component
  • Assign your player Sprite to a "Body" and move it inside "Player" object
  • Select "Player" object and add CapsuleCollider2D, Rigidbody2D and PlayerController2D components
  • Scale the CapsuleCollider2D until it fits the player Sprite





As you can see PlayerController2D has a couple of variables, most of them are self explanatory, however one of them need a bit of explanation:

PlayerHP - this value does nothing at the moment. However it is used in BotController2D to decide whether the AI should run away when it's HP is too low.
Use this variable when implementing the attack function (Check void Attack() at the end of PlayerController2D.cs).

Now let's setup the player Camera

  • Select the Main Camera and add the CameraFollow2D component
  • Assign the Player into a Target variable
  • Optionally you can tweak the Offset variable (If you don't want the Camera to be centered exactly in the middle)



Setting up a ladder

PlayerController2D also supports climbable Ladders.
Setting up a new ladder is really easy:

  • Create a new GameObject and call it "Ladder"
  • Change it's layer to "IgnoreRaycast"
  • Create another game object with a SpriteRenderer and assign a sprite of your ladder and move it inside the Ladder object
  • Add a BoxCollider2D and Ladder2D components to a "Ladder" object
  • Scale the collider dimensions to match the ladder Sprite and mark it as Trigger





And lastly let's setup the enemy AI

  • First go to the Physics2D panel and disable a collision between the Player layer, so the bots and players are not stuck between each other.




Now to the actual steps:

  • Duplicate the Player instance
  • Add a BotController2D component
  • The bot is now ready

2D Bot AI Properties

Check the gif below to see the enemy AI in action (White instance is our player, Red instances are controlled by the AI):

Enemy AI in action