Chapter 4: Simple 3D Coin Collction Game

4.1 Introduction

This chapter teaches you how to build a very basic 3D game where a player moves around and collects coins. It introduces the most important Unity concepts in a hands-on way. By the end, you will understand:

• Unity interface basics
• GameObjects and components
• Materials and visual design
• Prefabs and procedural spawning
• Player movement with physics
• Camera control
• Collision detection and scoring

4.2 Creating New Project

This step sets in Unity Hub up your workspace where your game will be created.

• Select New Project to begin creating a project.
• Choose 3D (Core) template, which is optimized for developing 3D games.
• Name your project (for example, CoinCollector)
• Disable Version Control (optional).
• Click Create to generate the project.

4.3 Creating the Game Environment

4.3.1 Ground Object

• Right-click in Hierarchy → 3D Object → Cube
• Rename to Ground
• Set Transform:
  • Position: (0, 0, 0)
  • Scale: (20, 1, 20)

    4.3.2 Player Object

• Right-click → 3D Object → Cube
• Rename to Player
• Set Position:
  • (0, 1, 0) (on top of ground)

4.4 Adding Materils

4.4.1 Create Materials Folder

Keeps your project organized

• Right-click at Project Create → Folder and name it Materials

  4.4.2 Create and Apply Materials

  We will create three materils by Right-click Create → Material

• Ground → Green (grass-like)
• Player → Red :
• Coin → Yellow/Gold (high smoothness)
• Drag material onto objects in Scene

  4.5 Creating the Coin System

  4.5.1 Create Coin Object

• Create Cube → rename Coin
• Scale to (0.5, 0.5, 0.5)
• Assign coin material

  4.5.2 Convert to Prefab

  Prefac is a gameobject with present value

• Create folder → Prefabs
• Drag Coin into Prefabs folder
• Delete coin from scene through Right-click in Hierachy

  4.6 Coin Spawner Script

• Create empty GameObject:
• Name: CoinSpawner

  4.6.1 Script: CoinSpawner.cs

  This script automatically creates many coins randomly and place them randomly on the ground.

using UnityEngine;

public class CoinSpawner : MonoBehaviour
{
    [SerializeField] private GameObject coinPrefab;
    [SerializeField] private BoxCollider groundCollider;
    [SerializeField] private int coinAmount = 10;

    void Start()
    {
        for (int i = 0; i < coinAmount; i++)
        {
            Vector3 startPos = GetRandomPoint();
            Instantiate(coinPrefab, startPos, Quaternion.identity);
        }
    }

    Vector3 GetRandomPoint()
    {
        Bounds bounds = groundCollider.bounds;

        float x = Random.Range(bounds.min.x, bounds.max.x);
        float z = Random.Range(bounds.min.z, bounds.max.z);

        return new Vector3(x, 1f, z);
    }
}

4.6.2 Setup in Inspector

• Assign Coin Spawner Script:
  • Coin Prefab: Drag and drop the coin from Prefab into Coin Prefab of `Coin Spawner (Script).
  • Ground Collider: drag the ground box and drop into Ground Collider
  • Set Coin Amount to 20.

    4.7 Player Movement

4.7.1 Add Rigidbody

Adds physics so the player can move naturally

• Select Player → Add Component → Rigidbody

  4.7.2 Script: PlayerHandler.cs

  Click Add component in the Player and add new scropt PlayerHandler Allows movement using keyboard keys.

using UnityEngine;

public class PlayerHandler : MonoBehaviour
{
    private Rigidbody rb;
    [SerializeField] private float speed = 10f;
    private int points = 0;

    void Awake()
    {
        rb = GetComponent<Rigidbody>();
    }

    void FixedUpdate()
    {
        float h = Input.GetAxis("Horizontal");
        float v = Input.GetAxis("Vertical");

        Vector3 movement = new Vector3(h, 0, v);

        rb.MovePosition(rb.position + movement * speed * Time.fixedDeltaTime);
    }

    public void IncreasePoints()
    {
        points++;
        Debug.Log("Points: " + points);
    }
}

4.8 Camera Follow System

Click Add Component and add camera and call it FollowPlayer Makes the camera follow the player smoothly.

• Script: FollowPlayer.cs

using UnityEngine;

public class FollowPlayer : MonoBehaviour
{
    [SerializeField] private Transform target;
    [SerializeField] private Vector3 offset;
    [SerializeField] private float smoothTime = 0.25f;

    private Vector3 velocity;

    void FixedUpdate()
    {
        Vector3 targetPosition = target.position + offset;

        transform.position = Vector3.SmoothDamp(
            transform.position,
            targetPosition,
            ref velocity,
            
            smoothTime
        );

        transform.LookAt(target);
    }
    public void IncreasePoints()
    {
        points++;
    }
}

Setup:

• Camera Target → Player
• Offset → (0, 10, -10)

  4.9 Coin Collection Logic

  4.9.1 Enable Trigger

  Allows player to pass through coins and detect overlap.

• Open Coin Prefab
• Check “Is Trigger” in BoxCollider

  4.9.2 Script: Coin.cs

  Detects when player touches coin and remove and updates score.

using UnityEngine;

public class Coin : MonoBehaviour
{
    private void OnTriggerEnter(Collider other)
    {
        PlayerHandler player = other.GetComponent<PlayerHandler>();

        if (player != null)
        {
            player.IncreasePoints();
            Destroy(gameObject);
        }
    }
}

4.10 Testing the Game

Run your game and check if everything works.

• Press ▶ Play:
  • Move using WASD or Arrow Keys
  • Collect coins
  • Watch coins disappear and score increase

4.11 Debugging Tip

To view private variables such as hidden values like score:

• Click three dots in Inspector
• Select Debug Mode