Roll a Ball (Unity 3D + NavMesh AI)

Intro

A 3D Unity game where the player rolls a ball while AI-controlled enemies navigate using NavMesh

Built With

• Unity 6 (6000.0.65f1 (LTS))
• Csharp
• Rigidbody Physics
• Unity Input System
• NavMesh – AI pathfinding for enemy navigation

Roll a Ball (Unity 3D + NavMesh AI)

A 3D Unity game that implements NavMesh for AI enemy navigation

Built With

• Unity 6 (6000.0.65f1 (LTS))
• C#
• Rigidbody Physics
• Unity Input System
• NavMesh – AI pathfinding for enemy navigation

Unity Learn- Roll-a-Ball

In this learning project, you’ll:

• Use Unity Editor and its built-in capabilities to set up a simple game environment
• Write your own custom scripts to create the game functionality
• Create a basic user interface to improve the game experience
• Build your game, so other people can play it!

Setting up the game

Create Unity Project

Select Project Template

• Open Unity Hub → Select New Project → Select the Universal 3D template (may need to Download template) →

Create Project

• In project settings, enter a project name (e.g. “Roll a ball”) and Location, then click Create Project, and wait for Unity Editor to open

Create new scene

• Use default layout
• Create new scene (ctrl + N) → Basic URP
• Save as “MiniGame” in Scenes folder

Create a primitive plane

• Use the hierarchy menu to add a 3D Objectject → Plane, then name it “Ground”
• Select the Ground GameObject, then select Reset for the Transform component to place the Ground at the origin (0,0,0)
• Press F to frame it within the scene view

Scale the Ground plane

• Use R to scale
• Scale precisely by setting X and Z scale values in the Transform component to 2

Create a Player GameObject

• Create 3D Object Sphere named “Player”, set at origin, and press F
• Change Y position to 0.5 to make it sit up on plane

Adjust the default lighting

• Change tint of directional light from yellow to pure white by expanding the Emission component and editing the RGB values in the Color window to 255, 255, 255.

Add colors with Materials

• Create a folder named “Material”, then right click it → Create Material named “Background”
• Change Base Map color to pale gray (130, 130,130)
• Set metallic map smoothness to 0.25
• Drag the background to the Ground object
• Create Material named “Player” and set its color to blue (0, 220, 255)
  • Give it a shiny finish (Set metallic smoothness to 0.75)
  • Assign it to the sphere
• Rotate the Directional Light to provide better lighting to the Player by setting its Rotation to (50, 50, 0)
  • This will add a more dramatic silhouette

Moving the Player

Add a Rigidbody to the Player

• Allow the Player Object to interact with the Physics system by selecting Add Component → Rigidbody

Add a Player Input component

• select Add Component → Player Input

Create a script

• Create a Scripts folder
• Select Player → Add Component → New Script → name it “Player Controller”
• Move the script asset from the root level into the Scripts folder
• Double-click it to open in a script editor (Visual Studio by default)

using UnityEngine;
 
public class PlayerController : MonoBehaviour
{
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        
    }
 
    // Update is called once per frame
    void Update()
    {
        
    }
}
 

Write the OnMove function declaration

using UnityEngine;
using UnityEngine.InputSystem;
 
public class PlayerController : MonoBehaviour
{
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        
    }
 
    void OnMove(InputValue movementValue)
    {
 
    }
}
 

Apply input data to the Player

using UnityEngine;
using UnityEngine.InputSystem;
 
public class PlayerController : MonoBehaviour
{
    private Rigidbody rb;
    
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        // Get a reference to the Rigidbody component attached to Player object
        rb = GetComponent<Rigidbody>();
    }
 
    void OnMove(InputValue movementValue)
    {
        Vector2 movementVector = movementValue.Get<Vector2>();
    }
 
    void FixedUpdate()
    {
        
    }
}
 

Apply force to the Player

using UnityEngine;
using UnityEngine.InputSystem;
 
public class PlayerController : MonoBehaviour
{
    private Rigidbody rb;
    private float movementX;
    private float movementY;
    
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        // Get a reference to the Rigidbody component attached to Player object
        rb = GetComponent<Rigidbody>();
    }
 
    void OnMove(InputValue movementValue)
    {
        Vector2 movementVector = movementValue.Get<Vector2>();
        movementX = movementVector.x;
        movementY = movementVector.y;
    }
 
    void FixedUpdate()
    {
        Vector3 movement = new Vector3(movementX, 0.0f, movementY);
        rb.AddForce(movement);
    }
}
 

Fix the Player movement speed

• Create a public variable speed so that it can be viewed in the Inspector.

Final script

PlayerController.cs

using UnityEngine;
using UnityEngine.InputSystem;
 
public class PlayerController : MonoBehaviour
{
    private Rigidbody rb;
    private float movementX;
    private float movementY;
    public float speed = 0;
    
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        // Get a reference to the Rigidbody component attached to Player object
        rb = GetComponent<Rigidbody>();
    }
 
    void OnMove(InputValue movementValue)
    {
        Vector2 movementVector = movementValue.Get<Vector2>();
        movementX = movementVector.x;
        movementY = movementVector.y;
    }
 
    void FixedUpdate()
    {
        Vector3 movement = new Vector3(movementX, 0.0f, movementY);
        rb.AddForce(movement * speed);
    }
}

Moving the Camera

• Move the camera to 3rd person view by setting Y position to 10 and X rotation to 45
• Make the camera a child of the Player Object so that the camera moves with the Player
• Test the game and then undo the parent-child relationship

Create CameraController script

• For follower cameras, its best to use LateUpdate() to run after all other updates are done, so that the camera position won’t be set until the player has moved for that frame
• Create a reference to the Player GameObject by dragging it into the Player slot in CameraController in the Inspector window

CameraController.cs

using System;
using System.Collections.Generic;
using UnityEngine;
 
public class CameraController : MonoBehaviour
{
    public GameObject player;
    private Vector3 offset;
 
    void Start()
    {
        offset = transform.position - player.transform.position;
    }
 
    void LateUpdate()
    {
        transform.position = player.transform.position + offset;
    }
}

Set up play area

Create walls

• Create a parent object for wall game objects by creating a new GameObject named “Walls” and reset its transforms, • Create a Cube object named “West Wall”, then reset Transform, and make it a child of Walls • Press F, then turn it into a wall by setting the scale to (0.5, 2, 20.5) and position it by setting x to -10 • Create a material named “Walls” with the following properties and then drag it to West Wall ○ set Base Map’s RBG to (79,79,79) for a darker gray ○ Metallic Map smoothness: 0.25 (matte finish)

Create remaining walls

• Duplicate the West Wall and name it “East Wall” and set Transform position x = 10
• Do the same for North Wall but set position x = 0, z=10 and rotate it 90 degrees around Y axis
• Duplicate North Wall and rename it “South Wall” and set position z=-10
• The Box Collider component allows for wall collisions- make sure Is Trigger is unchecked to make sure its used for collisions and not trigger events via script

Creating Collectibles

• Create a PickUp GameObject
• Create a Rotator.cs script to rotate the PickUp object in Update()
• Create a Prefabs folder and drag PickUp into it to create a PickUp prefab
• Make an empty parent object called “PickUp Parent”

Detecting Collisions with Collectibles

Display score and text

Store value of collected PickUps

Create a UI text element

• Create a Text (TMP) object called “CountText” by right clicking → UI → Text - TextMeshPro → Import TMP Essentials, and set “Count Text” as placeholder
• Select the Canvas object → press F → Select 2D view
• Anchor CountText to upper left corner of Canvas
  • In the Rect Transform component, open Anchors and Presets, hold Alt + Shift → select top left anchor point
  • Note: Unlike other Unity objects, for UI objects, the standard Transform is replaced with the Rect Transform, which takes into account anchoring, positioning, and other features for a UI system

Display count value

• Create SetCountText() to update score UI
• In Player’s Inspector, drag CountText object into the Count Text slot

Create game end message

• Create a TextMeshPro object named “WinText” with text “You Win!”
• In the PlayerController script, create a variable “winTextObject” for displaying the text
• Assign the winTextObject variable to Player

Adding AI Navigation

Create an ememy

• Create an empty GameObject named “Enemy” positioned at the origin
• Right click Enemy, and add a Cube named “EnemyBody” with position (0, 0.5, 0) and scale (0.5, 1, 0.5)
• Create a material named “Enemy” and choose a color and then assign the material to the EnemyBody

Bake a NavMesh

• Add a NavMeshSurface component to the Ground object and select Bake
• To configure what to include, expand the Object Collection module → click Current Object Hierarchy → select Bake

Make the enemy chase the player

• Select Enemy object → add Nav MeshAgent component, then set Speed to 2.5
• Add new script “EnemyMovement”
• In the script, create a NavMeshAgent variable to reference the Enemy and set its destination to Player
• Assign Player object in the EnemyMovement script in the Inspector

using UnityEngine;
using UnityEngine.AI;
 
public class EnemyMovement : MonoBehaviour
{
    public Transform player;
    private NavMeshAgent navMeshAgent;
    
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        navMeshAgent = GetComponent<NavMeshAgent>();
    }
 
    // Update is called once per frame
    void Update()
    {
        // Every frame, check if player exists
        if (player != null)
        {
            navMeshAgent.SetDestination(player.position);
        }
    }
}

• Test the game to make sure that the AI follows the player

Create static obstacles

• Create obstacles by creating Cube objects of various shapes (scale and rotate) including a ramp to test the AI’s slope climbing
• Make the obstacles child game objects of Ground so that the NavMesh includes them when baking
• In Ground’s NavMeshSurface component, regenerate the NavMesh by clicking Bake- the area around the obstacles will be carved out of the NavMesh surface
• Select Agent Type → open agent settings → adjust properties
  • Increase step height to allow agent to hop up onto higher surfaces
  • Increase max slope will allow the agent to climb steeper hills

Create dynamic obstacles

• Create a Cube object named “Dynamic Box”
• Create a new material named “Dynamic Obstacle” with any color and assign it to the Dynamic Box object
• Add a RigidBody component and set the mass value to 0.2 to make it easier to be pushed around
• Add a NavMesh Obstacle component to allow moving obstacles to affect the NavMesh during the game
  • by default, it will make the AI pathfinda round the obstacle
  • enble the Carve option creates a larger hole around the NavMesh to ensure the obstacle doesn’t get too close
• Drag the DynamicBox into the Prefas folder to create a prefab
• Make an empty parent object and duplicate and scatter DynamicBox prefab objects

Set win and lose conidtions

• Select EnemyBody → Tag → Add Tag → create a tag named “Enemy”
• Add an OnCollisionEnter() lose condition that destroys the player and says “You lose!”

private void OnCollisionEnter(Collision collision)
{
    if (collision.gameObject.CompareTag("Enemy"))
    {
        // Destroy current object
        Destroy(gameObject);
        // Update winText to display "You Lose!"
        //winTextObject.gameObject.SetActive(true);
        //winTextObject.GetComponent<TextMeshProUGUI>().text = "You Lose!";
    }
}
 

Final scripts

PlayerController.cs

using UnityEngine;
using UnityEngine.InputSystem;
using TMPro;
 
public class PlayerController : MonoBehaviour
{
    private Rigidbody rb;
    private int count;
    private float movementX;
    private float movementY;
    public float speed = 0;
    // UI text component to dislpay count of "PickUp"
    public TextMeshProUGUI countText;
    // UI object to display winning text
    public GameObject winTextObject;
    private int numPickups = 12;
 
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        // Get a reference to the Rigidbody component attached to Player object
        rb = GetComponent<Rigidbody>();
        count = 0;
        SetCountText();
        winTextObject.SetActive(false);
    }
 
    void OnTrigger()
    {
        count = count + 1;
    }
 
 
    void OnMove(InputValue movementValue)
    {
        Vector2 movementVector = movementValue.Get<Vector2>();
        movementX = movementVector.x;
        movementY = movementVector.y;
    }
 
 
    void FixedUpdate()
    {
        Vector3 movement = new Vector3(movementX, 0.0f, movementY);
        rb.AddForce(movement * speed);
        Debug.Log(movement * speed);
    }
 
    private void OnTriggerEnter(Collider other)
    {
        if (other.gameObject.CompareTag("PickUp"))
        {
            other.gameObject.SetActive(false);
            count = count + 1;
            SetCountText();
        }
 
    }
 
    void SetCountText()
    {
        countText.text = "Count: " + count.ToString();
 
        if (count >= numPickups)
        {
            // Display the win text
            winTextObject.SetActive(true);
            // Destroy the Enemy GameObject
            Destroy(GameObject.FindGameObjectWithTag("Enemy"));
        }
    }
 
    private void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.CompareTag("Enemy"))
        {
            // Destroy current object
            Destroy(gameObject);
            // Update winText to display "You Lose!"
            winTextObject.gameObject.SetActive(true);
            winTextObject.GetComponent<TextMeshProUGUI>().text = "You Lose!";
            Debug.Log("You Lose!");
        }
    }
}
 

EnemyMovement.cs

using UnityEngine;
using UnityEngine.AI;
using TMPro;
public class EnemyMovement : MonoBehaviour
{
    public Transform player;
    private NavMeshAgent navMeshAgent;
    
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {
        navMeshAgent = GetComponent<NavMeshAgent>();
    }
 
    // Update is called once per frame
    void Update()
    {
        // Every frame, check if player exists
        if (player != null)
        {
            navMeshAgent.SetDestination(player.position);
        }
    }
 
}

Building the Game

• Press ctrl + shift + B to open Build Settings
• Select Scene List → Open Scene List → Add Open Scenes to add the game to the build (make sure SampleScene is diabled)