Introduction

In this workshop you will create your first space shooter in C#. You will use an engine that looks like Unity.

Installation

First and foremost, you have to clone this repository :

git clone git@github.com:ArthurVasseur/CSharpIndroductionForUnity.git

Dotnet

Dotnet-core is a free and open-source framework for Linux, Windows and MacOS.

Ubuntu

https://docs.microsoft.com/fr-fr/dotnet/core/install/linux-ubuntu

Fedora

https://docs.microsoft.com/fr-fr/dotnet/core/install/linux-fedora

SFML

Ubuntu

sudo apt install libsfml-dev

Fedora

sudo dnf install SFML

Nuget Package

cd CSharpEngine/CSharpEngine && dotnet add package SFML.Net --version 2.5.0

Understaining OOP

In Oriented Object Programming (OOP) you will create classes to represent an object. Each object contains data and methods to manipulate and access that data.

For example in C you will create a struct for representing data.

struct Vector2D
{
    int x;
    int y;
}

You can access this data by calling :

Vector2D vec = {10, 25};
int x = vec.x;

And to modify this data :

Vector2D vec = {10, 25};
vec.x = 12;

If you want to manipulate this data you will create a function :

Vector2D add(const Vector2D *a, const Vector2D *b)
{
    Vector2D sum;
    sum.x = a->x + b->x;
    sum.y = a->y + b->y;
    return sum;
}

In C# you can simply create a Class :

public class Vector2D
{
    private float _x;
    private float _y;

    public Vector2D(float x, float y)
    {
        _x = x;
        _y = y;
    }

    public int GetX()
    {
        return _x;
    }

    public int GetY()
    {
        return _x;
    }

    public void Add(Vector2D b)
    {
        _x += b.GetX();
        _y += b.GetY());
    }
}

public static void Main(string[] args)
{
    Vector2D position = new Vector2D(10, 15);
    Vector2D otherPosition = new Vector2D(24, 6);
    position.Add(otherPosition);

    Console.WriteLine("X : " + position.GetX() + "Y : " + position.GetY());
}

private is an access modifier meaning that you can only access this data/function inside a class.

public Vector2D(float x, float y) is a constructor, it's a special function that is automaticlly called when a object is created.

new is a keyword for create a class instance (memory allocation), and call the constructor.

Of course the written code can be greatly impoved by using Properties, Auto-Implemented Properties, Operator overloading.

Step 1 - Display your first sprite

The first step of this workshop is simple, you need to create a scene. For this you need to create a class and inherits from Scene class , then in the constructor you can create a gameObject and add it a Transform and Sprite component.

To instantiate gameobject in the scene you have to create a gameobject, then add it to the scene :

Scene scene = new Scene();
GameObject background = new GameObject();
background.AddComponent(new Transform(new Vector2D(0,0),0, new Vector2D(1,1)));
background.AddComponent(new Sprite("../../../Assets/background.png"));
scene.AddGameObject(background);

Or if you are inside a custom class that inherits from Component class you can call Instantiate function.

You can destroy gameObject by calling Destroy function.

Take a look at the GameObject class.

Don't forget to instantiate your class with new keyword, for example : new Sprite("texture path")

Step 2 moving a gameobject with your keyboard

The behavior of GameObjects is controlled by the Components that are attached to them. You can create your own components by inherits from Component class.
Component class implements two functions OnConstruct() and Update(float deltaTime).

OnConstruct() is called when a object is created in a scene.
Update(float deltaTime) is called every frame, the deltatime is the time ealapsed between the last and the curent frame.

Moving a gameObject

This script move an object every frame to the right:

public class Move : Component
{
    public override void OnConstruct()
    {

    }

    public override void Update(float deltaTime)
    {
        Transform.Position.X += deltaTime; // move the gameObject to the right
    }
}

The Transform variable references the Transform component of the current gameObject.

Interacting with keyboard

This script print in the console "Left action pressed" when "Q" is pressed

public class Move : Component
{
    public override void OnConstruct()
    {
        Input.RegisterAction("Left", KeyCode.Q);
        Input.RegisterAction("Right", KeyCode.D);
        Input.RegisterAction("Up", KeyCode.Z);
        Input.RegisterAction("Down", KeyCode.S);
        Input.RegisterAction("Fire", KeyCode.Space);
    }

    public override void Update(float deltaTime)
    {
        if(Input.GetKeyDown("Left"))
            Console.WriteLine("Left action pressed");
    }
}

Step 3 Detecting collisions

When a GameObject collides with another GameObject, Unity calls OnTriggerEnter. You can initialize it like that :

{
    GameObject gameObject = new GameObject();
    gameObject.AddComponent(new Transform(new Vector2D(100, 300), 0, new Vector2D(1, 1));
    gameObject.AddComponent(new Sprite("./index.png"));
    gameObject.AddComponent(new Collider(new Vector2D(10, 10)));
    gameObject.Tag = "objectA";
    scene.AddGameObject(gameObject);
}
{
    GameObject gameObject = new GameObject();
    gameObject.AddComponent(new Transform(new Vector2D(100, 300), 0, new Vector2D(1, 1));
    gameObject.AddComponent(new Sprite("./index.png"));
    gameObject.AddComponent(new Collider(new Vector2D(10, 10)));
    gameObject.Tag = "objectB";
    scene.AddGameObject(gameObject);
}

Now you can create a new script named CollisionDetector and overrides OnCollisionEnter function. Add it to one of the two gameObject :

public override void OnCollisionEnter(GameObject go)
{
    Console.WriteLine("Gameobject : " + GameObject.Tag + " collides with Gameobject " + go.Tag);
}

Now when your are executing your game, you should saw in the console Gameobject : X collides with Gameobject Y

By default the trigger of the collider is disable, enables it by setting IsTrigger to true

Step 4 Creating a space shooter

For this last exercise we will condense all the skills seen in this workshop for create a space shooter, you have no constraints. You can implements theses features :

Enemy
Player shoot
Enemy shoot
Enemy move pattern
Create a UI with the Text and Sprite components

You can download free assets on Itch.io