Enemy patrol and chase patterns in Unity - Mini Project: Build & Apply

Enemy patrol and chase patterns

📖 Scenario: You are creating a simple enemy character in a game. The enemy should patrol between two points and chase the player when the player is close enough.

🎯 Goal: Build an enemy script that makes the enemy move back and forth between two patrol points and chase the player when the player enters a certain distance.

📋 What You'll Learn

Create two patrol points as Vector3 variables

Create a chase distance threshold variable

Write code to move the enemy between patrol points

Write code to chase the player when within chase distance

💡 Why This Matters

🌍 Real World

Enemy patrol and chase patterns are common in many games to create engaging and dynamic AI behavior.

💼 Career

Understanding how to implement basic AI movement patterns is important for game developers and interactive experience creators.

1

Set up patrol points

Create two Vector3 variables called pointA and pointB with values new Vector3(0, 0, 0) and new Vector3(5, 0, 0) respectively.

Unity

# Your code here

Hint

Use Vector3 pointA = new Vector3(0, 0, 0); and similarly for pointB.

2

Add chase distance variable

Add a public float variable called chaseDistance and set it to 3.0f.

Unity

using UnityEngine;

public class EnemyPatrol : MonoBehaviour
{
    private Vector3 pointA = new Vector3(0, 0, 0);
    private Vector3 pointB = new Vector3(5, 0, 0);
    // Your code here
}

Hint

Declare public float chaseDistance = 3.0f; inside the class.

3

Implement patrol movement

Add a private Vector3 variable targetPoint initialized to pointB. In Update(), move the enemy towards targetPoint using Vector3.MoveTowards with speed 2f. When the enemy reaches targetPoint, switch targetPoint between pointA and pointB.

Unity

using UnityEngine;

public class EnemyPatrol : MonoBehaviour
{
    private Vector3 pointA = new Vector3(0, 0, 0);
    private Vector3 pointB = new Vector3(5, 0, 0);
    public float chaseDistance = 3.0f;

    // Your code here
}

Hint

Use Vector3.MoveTowards inside Update() and switch targetPoint when close.

4

Add player chase behavior

Add a public Transform variable called player. In Update(), check if the distance between the enemy and player.position is less than chaseDistance. If yes, move the enemy towards player.position with speed 3f. Otherwise, continue patrolling.

Unity

using UnityEngine;

public class EnemyPatrol : MonoBehaviour
{
    private Vector3 pointA = new Vector3(0, 0, 0);
    private Vector3 pointB = new Vector3(5, 0, 0);
    public float chaseDistance = 3.0f;
    // Your code here

    private Vector3 targetPoint;

    private void Start()
    {
        targetPoint = pointB;
    }

    private void Update()
    {
        // Your code here
    }
}

Hint

Use an if statement to check distance to player.position and move accordingly.

Practice

1. What is the main purpose of an enemy patrol pattern in Unity game development?

easy

A. To make the enemy jump randomly

B. To move the enemy between set points repeatedly

C. To make the enemy disappear and reappear

D. To make the enemy shoot projectiles continuously

Solution

1. Step 1: Understand enemy patrol behavior

   Enemy patrol means moving the enemy between fixed points in a loop to simulate guarding or searching.

2. Step 2: Identify correct behavior from options

   Only moving between set points repeatedly matches patrol behavior.

3. Final Answer:

   To move the enemy between set points repeatedly -> Option B

4. Quick Check:

   Enemy patrol = moving between points [OK]

Hint: Patrol means looping between points, not random actions [OK]

Common Mistakes:

• Confusing patrol with attack or random movement
• Thinking patrol involves shooting or disappearing

2. Which of the following is the correct way to check the distance between the enemy and player in Unity C#?

easy

A. float dist = enemy.position.Distance(player.position);

B. float dist = enemy.position - player.position;

C. float dist = Vector3.Distance(enemy, player);

D. float dist = Vector3.Distance(enemy.position, player.position);

Solution

1. Step 1: Recall Vector3.Distance syntax

   The correct method to get distance between two Vector3 points is Vector3.Distance(point1, point2).

2. Step 2: Check each option

   float dist = Vector3.Distance(enemy.position, player.position); uses Vector3.Distance with positions, which is correct. Others have syntax errors or wrong usage.

3. Final Answer:

   float dist = Vector3.Distance(enemy.position, player.position); -> Option D

4. Quick Check:

   Use Vector3.Distance(point1, point2) for distance [OK]

Hint: Use Vector3.Distance with positions, not subtract vectors directly [OK]

Common Mistakes:

• Subtracting vectors without calling Distance method
• Calling Distance on a Vector3 instance incorrectly
• Passing transforms instead of positions

3. Given this code snippet for enemy chase, what will be the output if the player is 3 units away and chaseDistance is 5?

if (Vector3.Distance(transform.position, player.position) < chaseDistance) {
    Debug.Log("Chasing player");
} else {
    Debug.Log("Patrolling");
}

medium

A. No output

B. Patrolling

C. Chasing player

D. Error at runtime

Solution

1. Step 1: Calculate distance and compare

   Distance is 3, chaseDistance is 5, so 3 < 5 is true.

2. Step 2: Determine which branch runs

   Since condition is true, "Chasing player" is printed.

3. Final Answer:

   Chasing player -> Option C

4. Quick Check:

   Distance 3 < 5 triggers chase [OK]

Hint: Compare distance to chaseDistance to decide behavior [OK]

Common Mistakes:

• Confusing less than with greater than
• Assuming no output if condition true
• Thinking code causes error

4. Identify the error in this patrol code snippet:

void Patrol() {
    int currentPoint = 0;
    transform.position = Vector3.MoveTowards(transform.position, patrolPoints[currentPoint].position, speed * Time.deltaTime);
    if (transform.position == patrolPoints[currentPoint].position) {
        currentPoint++;
        if (currentPoint >= patrolPoints.Length) {
            currentPoint = 0;
        }
    }
}

medium

A. currentPoint should be declared outside the method to keep its value

B. Vector3.MoveTowards is used incorrectly

C. Time.deltaTime should not be multiplied by speed

D. The if condition should use < instead of >

Solution

1. Step 1: Check variable scope for currentPoint

   currentPoint is reset to 0 every time Patrol() runs, so it never increments properly.

2. Step 2: Understand how to fix the scope issue

   Declaring currentPoint outside the method (as a class variable) preserves its value between calls.

3. Final Answer:

   currentPoint should be declared outside the method to keep its value -> Option A

4. Quick Check:

   Keep patrol index outside method to track progress [OK]

Hint: Keep patrol index as a class variable, not local [OK]

Common Mistakes:

• Thinking MoveTowards usage is wrong
• Confusing comparison operators in if
• Misunderstanding Time.deltaTime usage

5. How can you combine patrol and chase behaviors so the enemy patrols until the player is within 4 units, then chases the player, and returns to patrol if the player moves away?

hard

A. Use a state variable to switch between patrol and chase based on distance checks

B. Call Patrol() and Chase() methods simultaneously every frame

C. Only use Chase() method and ignore patrol points

D. Use a timer to switch behaviors every 5 seconds regardless of player position

Solution

1. Step 1: Understand behavior switching logic

   The enemy needs to switch between patrol and chase based on player distance dynamically.

2. Step 2: Use a state variable to track current behavior

   A state variable (like enum or bool) can control which method runs each frame depending on distance.

3. Step 3: Implement distance check to update state

   If player is closer than 4 units, set state to chase; else set to patrol.

4. Final Answer:

   Use a state variable to switch between patrol and chase based on distance checks -> Option A

5. Quick Check:

   State variable + distance check = behavior switch [OK]

Hint: Switch states based on distance, don't run both behaviors together [OK]

Common Mistakes:

• Running patrol and chase at the same time causing conflicts
• Ignoring player distance for switching
• Using timers instead of distance checks