Game development with Unity and C#

Why Unity?

Unity is used for a large share of mobile games, many PC and console games, and AR/VR apps, and also outside games: architecture walkthroughs, training simulators and car configurators. Indian studios and outsourcing companies hire Unity developers, and the C# you have learned carries straight over. Install it through Unity Hub from unity.com; the personal licence is free within Unity's revenue limits (check the current terms).

How Unity differs from the .NET you know

• There is no Main method or Program.cs. The Unity engine owns the game loop and calls your methods at the right times.
• Unity runs C# on its own scripting runtime, not the latest .NET, so not every new C# feature or .NET API is available. Check the Unity manual for the C# version your Unity version supports.
• You attach scripts to objects in the Unity Editor, and public or [SerializeField] fields appear in the Inspector window so designers can tweak values without code.

GameObjects and components

Everything in a scene is a GameObject: the player, an enemy, a coin, the camera, a light. On its own a GameObject does nothing. Components give it abilities: Transform (position, rotation, scale; every object has one), a Renderer (to be seen), a Collider (a shape for collisions), a Rigidbody (to be moved by physics) and your scripts (behaviour). This is composition, not deep inheritance, which you met in module 5.

Your first script

using UnityEngine;

public class PlayerMove : MonoBehaviour
{
    [SerializeField] private float speed = 5f;   // editable in the Inspector

    void Start()
    {
        Debug.Log("Player ready");                // prints to Unity's Console window
    }

    void Update()
    {
        float x = Input.GetAxis("Horizontal");    // -1 to 1 from arrow keys / A and D
        float z = Input.GetAxis("Vertical");
        Vector3 move = new Vector3(x, 0f, z) * speed * Time.deltaTime;
        transform.Translate(move);
    }
}

Time.deltaTime: speed that does not depend on the device

Update runs once per frame. A fast PC might draw 144 frames a second; an old phone might draw 30. If you move 0.1 units per frame, the object moves almost five times faster on the PC. Time.deltaTime is the time in seconds since the last frame, so speed * Time.deltaTime means "speed units per second" on every device.

The main lifecycle methods

Physics and collisions

using UnityEngine;

public class Ball : MonoBehaviour
{
    [SerializeField] private float jumpForce = 6f;
    private Rigidbody rb;
    private bool jumpRequested;
    private int coins;

    void Awake() => rb = GetComponent<Rigidbody>();          // cache once, not every frame

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space)) jumpRequested = true;   // read input every frame
    }

    void FixedUpdate()
    {
        if (jumpRequested)
        {
            rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);  // physics in FixedUpdate
            jumpRequested = false;
        }
    }

    void OnTriggerEnter(Collider other)
    {
        if (other.CompareTag("Coin"))
        {
            coins++;
            Destroy(other.gameObject);
            Debug.Log($"Coins: {coins}");
        }
    }
}

Prefabs and spawning

A prefab is a saved GameObject template (for example an enemy with all its components). Instantiate(prefab, position, Quaternion.identity) creates a copy in the scene at run time, and Destroy(obj) removes it. You never create MonoBehaviour scripts with new; Unity creates them when they are attached, or you call AddComponent<T>().

Common mistakes and fixes

• Movement without Time.deltaTime: speed changes with frame rate. Multiply by Time.deltaTime.
• Calling GetComponent or GameObject.Find every frame: slow. Cache references in Awake or Start.
• Applying forces in Update: physics becomes jittery. Read input in Update, apply forces in FixedUpdate.
• Script name and class name differ: Unity cannot attach the script. Keep them identical.
• Writing new PlayerMove(): not allowed for MonoBehaviour. Attach it in the Editor or use AddComponent<PlayerMove>().