First Script

Script structure

In Unity, a script is used to control the behavior of GameObjects and define game logic. Scripts are written in C# and allow developers to create interactions, manage physics, handle inputs or control animations.

The line: using UnityEngine; imports the internal Unity libraries and their classes.

A script typically extends the MonoBehaviour class through inheritance. Thus we can override built-in Unity methods like:

Start(): Runs once when the object is initialized

Update(): Runs every frame, useful for real-time updates

First Script

Scene setup

Navigate to AssetsScenesIntro

Create a new scene called « FirstScript »

Double click to open it

Create a plane for the ground and apply a green material

Create a cube, apply a blue material and and move it upwards

Create a script

In the Assetsintro folder, right click to open the context menu

Select Create > Scripting > MonoBehaviour Script

Rename it « Bonus »

Avertissement

At this point the script and the cube are not associated

Association

To associate a script with an object, drag and drop the script icon onto:

The object in the Scene view

Or the object in the Hierarchy

Select the cube and check that the script is now part of the gameobject:

Open a script

In the Assets window, double click on the script icon

The script opens in Visual Studio

Copy paste the following code:
using UnityEngine;

public class BonusScript : MonoBehaviour
{
        void Start()      { }

        void Update()
        {
                transform.Rotate(0, 0.1f, 0);
        }
}
The Rotate function makes the object rotate around the vertical axis

Press CTRL-S to save the script

Notice that this triggers the recompilation of the script in the Unity

Run

In the scene view, make sure the cube is properly centered in the view

In the Hierarchy window, right click on the camera

Select Align With View to obtain the same view during Play mode

Press the Play button

The cube rotates automatically

External variables

You can add variables to your script to parameterize its behavior. Moreover, you can « export » these variables into the Inspector to edit them directly without opening the source code.

Rotation speed

Unity uses degrees for rotation, so each time the Update() function is called, the cube rotates by 1 degree. However, we don’t know how many times per second this function is executed. Additionally, the execution rate constantly varies depending on the current cpu load.

To precisely control the rotation speed, we must use physics” law. Here, we recall the formula that gives the rotation angle based on the rotation speed and the time interval:

\[angle = dT \times Rot_{speed}\]

Unity provides the variable Time.deltaTime which corresponds to dT.

In Visual Studio, create a public float variable RotSpeed

In the Update() function, apply the given formula

Select the cube and scale it to obtain a tube shape

In the Inspector, look at the script section

The variable rotSpeed is now present

Set its value to 180 which corresponds to 1/2 turn per second

Enter Play mode

The bar makes one full turn every 2 seconds

Change the rotation speed value to 360

The bar makes one full turn every second
Help in case nothing works
using UnityEngine;

public class BonusScript : MonoBehaviour
{
         public float rotSpeed;

        void Start()      { }

        void Update()
        {
                transform.Rotate(0,rotSpeed * Time.deltaTime, 0);
        }
}
Avertissement

You can interactively modify any values in the Inspector during Play mode. This is very useful for testing and debugging. However, keep in mind that any changes made in Play mode will be lost once you exit. Only values set in Edit mode are permanently retained.

Blinking light

Exit Play mode
Add two external variables: public Material
- In the Assets folder, go to AssetsSolidColorMaterials
- In the Inspector, drag and drop two colors to initialize the two materials
To retrieve the elapsed time since the start of the game, use the Time.time float variable
Every second, change the cube’s material:
- Renderer r = GetComponent<Renderer>();
- r.material = …