cnam-geometry-dash/Documentation/unity.md

Unity

Documentation about the basics of Unity (cross-platform game engine) and most useful things to know, to develop a 2D game.

Links

• Unity 6 User Manual
• YouTube (Game Maker's Toolkit) - The Unity Tutorial For Complete Beginners

Unity Interface (4 panels by default)

• Project (bottom): Contains everything that is in our game, like sprites (2D graphical object/image), sound effects, scripts, fonts, etc. Some of them are made in Unity. We can also import files from our computer.
• Hierarchy (left): Contains all the stuff that's in the current scene.
• Scene (middle): A scene is a level in our game. Scene are made up of GameObjects.
• Inspector (right): Shows the properties and components of the selected GameObject.

GameObject

GameObject is an invisible container. Properties:

• Name
• Transform
  • a Position (X, Y, Z)
  • a Rotation (X, Y, Z)
  • a Scale (X, Y, Z)
• Components: to add extra features (e.g: SpriteRenderer to display a sprite, BoxCollider2D to detect collisions, etc).

To create a new GameObject, we can right-click in the Hierarchy panel and select Create Empty.

GameObject can have children GameObjects. Nesting GameObjects is useful to group objects together, and for example, move them all at once, just by moving the parent GameObject.

Components

SpriteRenderer

The SpriteRenderer component renders the Sprite and controls how it visually appears in a Scene. Fields:

• Sprite: to select the sprite to render. We can drag a sprite from the Project panel.

Camera

The Camera component renders the scene from the point of view of the camera. Fields:

• Size: to zoom in and out.
• Background: background color.

Rigidbody2D

The Rigidbody2D component allows a GameObject to react to physics (gravity, mass).

Collider2D

The Collider2D component allows a GameObject to interact with other GameObjects. It allows to detect collisions (control hitboxes).

There are different types of colliders:

• BoxCollider2D: a box-shaped collider.
• CircleCollider2D: a circle-shaped collider.

etc.

Script

Allows to make our own custom component with C# code.

MonoBehaviour is the base class from which script derives. It offers life cycle functions: Start, Update, OnEnable etc.

It has a property called gameObject which is the GameObject to which the script is attached. For example, to change the name of the GameObject to which the script is attached, we can write gameObject.name = "New Name";.

using UnityEngine;

public class BirdScript : MonoBehaviour
{
  // Start is called once before the first execution of Update after the MonoBehaviour is created
  public void Start()
  {

  }

  // Update is called every frame over, over and over again, run as often as it can depending on the frame rate and computer performance
  public void Update()
  {

  }
}

UnityEngine C#

Script communication with other components (for example with Rigidbody2D)

By default, the script is unaware of the other components attached to the GameObject.

To access the Rigidbody2D component from the script, we can create a public field of type Rigidbody2D in the script.

using UnityEngine;

public class BirdScript : MonoBehaviour
{
  public Rigidbody2D myRigidBody;
}

In the Unity Editor, the myRigidBody field will appear in the Inspector panel. We can drag the Rigidbody2D component from the GameObject to the myRigidBody field.

Input

To get input from the player, we can use the Input class.

For example, to detect when the player presses the Space key, we can use the Input.GetKeyDown method.

In the following example, when the player presses the Space key, the bird object will jump.

using UnityEngine;

public class BirdScript : MonoBehaviour
{
  public Rigidbody2D rigidBody;

  public void Update()
  {
    if (Input.GetKeyDown(KeyCode.Space))
    {
      rigidBody.linearVelocity = Vector2.up * 10;
    }
  }
}

Time.deltaTime

Time.deltaTime is the interval in seconds from the last frame to the current one.

It's useful to make the game frame rate independent, as it ensures that the game runs at the same speed on different computers, (code inside Update method).

using UnityEngine;

public class BirdScript : MonoBehaviour
{
  public Rigidbody2D rigidBody;

  public void Update()
  {
    // Move the bird to the right, 5 units per second
    transform.position = transform.position + (5 * Time.deltaTime * Vector3.right);
  }
}

Debug.Log

Debug.Log is a method that prints a message to the console, helpful for debugging.

using UnityEngine;

public class BirdScript : MonoBehaviour
{
  public void Start()
  {
    Debug.Log("Hello World!");
  }
}

Destroy

To destroy a GameObject, we can use the Destroy method. Useful for performance optimization, for example to destroy a pipe that is no longer visible on the screen.

For example, to destroy a pipe when it reaches a certain position on the left side of the screen (deadZone):

using UnityEngine;

public class PipeMoveScript : MonoBehaviour
{
  public float moveSpeed = 5;
  public float deadZone = -45;

  public void Update()
  {
    transform.position = transform.position + (Time.deltaTime * moveSpeed * Vector3.left);

    if (transform.position.x < deadZone)
    {
      Destroy(gameObject);
    }
  }
}

Prefabricated GameObject

GameObject can be prefabricated. Prefabs are reusable GameObjects that can be created and modified in the Project panel (like a blueprint), for example to spawn objects in the scene dynamically at runtime, with Instantiate.

using UnityEngine;

public class PipeSpawnScript : MonoBehaviour
{
  public GameObject pipe;

  public void Start()
  {
    Instantiate(pipe, transform.position, transform.rotation);
  }
}

[ContextMenu]

The [ContextMenu] attribute allows to add a custom function to the context menu of the script in the Unity Editor.

It's useful for debugging, to be able to call a function directly from the Unity Editor.

using UnityEngine;

public class LogicManagerScript : MonoBehaviour
{
  [ContextMenu("AddScore")]
  public void AddScore()
  {
    Debug.Log("Score added!");
  }
}