Enemy patrol and chase patterns in Unity - Step-by-Step Execution

Concept Flow - Enemy patrol and chase patterns

Start

↓

Patrol between points

↓

Detect player nearby?

No→Continue patrol

Yes↓

Chase player

↓

Player lost?

No→Continue chase

Yes↓

Return to patrol

↩Back to Patrol between points

The enemy moves between patrol points until it detects the player nearby, then chases the player until lost, then returns to patrol.

Execution Sample

Unity

void Update() {
  Patrol();
  if (PlayerInRange()) {
    ChasePlayer();
  }
}

Enemy patrols points and switches to chasing player when detected.

Execution Table

Step	Enemy Position	Player Position	Player Detected?	Action	Output
1	(0,0)	(5,5)	No	Patrol to next point (1,0)	Enemy moves to (1,0)
2	(1,0)	(4,4)	No	Patrol to next point (2,0)	Enemy moves to (2,0)
3	(2,0)	(3,3)	Yes	Start chasing player	Enemy starts chase
4	(2,0)	(3,3)	Yes	Move towards player (2.7,0.7)	Enemy moves closer to player
5	(2.7,0.7)	(3,3)	Yes	Move towards player (3.3,1.4)	Enemy moves closer to player
6	(3.3,1.4)	(6,6)	No	Player lost, return to patrol	Enemy returns to patrol point (3,0)
7	(3,0)	(6,6)	No	Patrol to next point (4,0)	Enemy moves to (4,0)
Exit	(4,0)	(6,6)	No	Patrol continues	Enemy continues patrol

💡 Player is out of detection range, enemy resumes patrol.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	Final
Enemy Position	(0,0)	(1,0)	(2,0)	(2,0)	(2.7,0.7)	(3.3,1.4)	(3,0)	(4,0)	(4,0)
Player Position	(5,5)	(4,4)	(3,3)	(3,3)	(3,3)	(6,6)	(6,6)	(6,6)	(6,6)
Player Detected	No	No	Yes	Yes	Yes	No	No	No	No
Current Action	Patrol	Patrol	Chase	Chase	Chase	Return to Patrol	Patrol	Patrol	Patrol

Key Moments - 3 Insights

Why does the enemy switch from patrolling to chasing at step 3?

At step 3, the player position is close enough to the enemy, so 'Player Detected?' becomes Yes, triggering the chase action as shown in the execution_table.

Why does the enemy stop chasing and return to patrol at step 6?

At step 6, the player moves out of detection range, so 'Player Detected?' is No, causing the enemy to stop chasing and return to patrol, as seen in the execution_table.

Does the enemy immediately chase the player if detected during patrol?

Yes, as soon as 'Player Detected?' is Yes during patrol (step 3), the enemy switches to chase mode, shown by the change in 'Current Action' in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the enemy's position?

A (2,0)

B (3,3)

C (2.7,0.7)

D (1,0)

💡 Hint

Check the 'Enemy Position' column at step 4 in the execution_table.

At which step does the enemy lose sight of the player and return to patrol?

A Step 5

B Step 3

C Step 6

D Step 7

💡 Hint

Look for when 'Player Detected?' changes to No and 'Current Action' changes to 'Return to Patrol' in the execution_table.

If the player stayed within detection range at step 6, what would happen next?

A Enemy stops moving

B Enemy continues chasing the player

C Enemy returns to patrol

D Enemy moves randomly

💡 Hint

Refer to the 'Current Action' and 'Player Detected?' columns in the execution_table for steps 4 and 5.

Concept Snapshot

Enemy patrols between points.
If player detected nearby, enemy chases player.
If player lost, enemy returns to patrol.
Use distance checks to switch states.
Update enemy position each frame accordingly.

Full Transcript

This visual trace shows how an enemy in a game patrols between points and switches to chasing the player when detected nearby. The enemy moves step-by-step between patrol points until the player comes close enough. At that moment, the enemy starts chasing the player by moving towards the player's position. If the player moves out of detection range, the enemy stops chasing and returns to its patrol route. Variables like enemy position, player position, detection status, and current action are tracked at each step to understand the flow. This helps beginners see how patrol and chase patterns work in game programming.

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