【Unity】Object starts to chase the player approaching

Table of Contents

Overview

There is a sample the Cube Object starts to chase the player who goes in a certain area around it.

Environment

Unity 2020 1.1f1
Windows10

Picture of implementation

Step1 : Set the player

Ethan from the Standard Assets can be used as a human object. Flowwing article explains how to set Ethan and move him.

【Unity】Standard Assetsでサクッと人間をキー操作する

After place Ethan on Terrian, set the Tag in inspector “Player”.

Adding rigidbody and capusule collider is needed.

Step:2 Cube Object chasing player

Next, Set 3D Object Cube.

GameObject > 3D Object Cube

Adding Character Controller and Sphere Collider to the Cube Object.

Character Controller is useful to moving Cube. The parameters as Default is OK.

Shpere Collider can be used to detect Player is in certain area. Is Trigger should be checked.

Step : 3 Script

Following script can realize Cube to chase player when he goes into cube area. Please attach this script.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Approach : MonoBehaviour
{

    CharacterController Controller;
    Transform Target;
    GameObject Player;

    [SerializeField]
    float MoveSpeed = 2.0f;
    int DetecDist = 8;
    bool InArea = false;


    // Use this for initialization
    void Start()
    {

        // Get GameObject of Player by Tag
        Player = GameObject.FindWithTag("Player");
        Target = Player.transform;

        Controller = GetComponent<CharacterController>();

    }

    // Update is called once per frame
    void Update()
    {

        if (InArea)
        {
            // Look at Player
            this.transform.LookAt(Target.transform);

            // Getting direction from Cube object to Player
            Vector3 direction = Target.position - this.transform.position;
            direction = direction.normalized;

            // Velocity toward Player
            Vector3 velocity = direction * MoveSpeed;
            
            // Making y velocity 0 to avoid cube from floating toward y axis
            velocity.y = 0.0f;

            // Move cube
            Controller.Move(velocity * Time.deltaTime);
        }

        //Calculation of distance between the target object and this object
        Vector3 Apos = this.transform.position;
        Vector3 Bpos = Target.transform.position;
        float distance = Vector3.Distance(Apos, Bpos);

        // when distance between cube and player, cube stops tracing.
        if (distance > DetecDist)
        {
            InArea = false;
        }
    }

    // Player gets inside area of cube.
    private void OnTriggerEnter(Collider other)
    {
        InArea = true;
    }

}

Step : 4 Test

Please start game and check of them. You may see the pictures like gif animation at top of this page.