Intermediate Unity Sushi

Creating Obstacles

You’ll write a few scripts for your asteroids, so it’s a good idea to make a special folder for them to keep everything organized.

  • Create a folder called Asteroids inside the Scripts folder. Now, you will need two new C# scripts: CreateAsteroids and DestroyAsteroid, so go ahead and create those as well.

  • Attach the CreateAsteroids script to the Asteroids object

  • Then add this code in the CreateAsteroids file:

public GameObject asteroid;

void Update()
{
  Vector3 createPosition = Vector3.zero;
  GameObject asteroidClone = Instantiate(asteroid, createPosition, asteroid.transform.rotation);
}

What does the code do?

To understand what’s happening here, you need to know what ‘instantiate’ means.

Instantiating something is like building something from plans or instructions. If you’re baking a cake, the cake is the instance and the recipe is the Instantiate() function. In the game world, what’s being instantiated with this code is not a cake but instead a GameObject called asteroidClone, using the asteroid ‘recipe’.

  • Drag the Asteroid prefab from the Prefabs folder and, in the Inspector for your Asteroids object, drop it into the asteroid box for your CreateAsteroids script.

The asteroid prefab in the script

  • Save everything (File > Save Scenes) and try running your game.

WOAH! That was a lot of asteroid clones!

Lots of asteroid clone game objects

The Update() function runs really fast, so it makes asteroids really quickly. You can control how fast the asteroids are created with the InvokeRepeating() function.

  • Add this to your existing code:
public float creationTime = 1f;

// Use this for initialization
void Start()
{
  // 0f is when to start invoking repeat
  InvokeRepeating("createAsteroid", 0f, creationTime);
}

  • Now change Update() to createAsteroid() and put the Asteroid prefab into the the script’s asteroid box in the Asteroids object Inspector.

  • Save the script, and try running the game again. It should create asteroids much more slowly now.

Cleaning up asteroids

If you create too many objects, your computer wont be able to keep track of them all. So when you create an asteroid, you need to make sure it is destroyed at some point. Let’s use the Destroy() function in the DestroyAsteroid script:

  • Attach the DestroyAsteroid script to the Asteroids object in the Hierarchy.

  • Add Destroy(gameObject, 10f); to the Start() function of the script.

What does the code do?

Your Start() function should look like this:

void Start () {
  Destroy(gameObject, 10f);
}

  • gameObject is the object the script is attached to (i.e. the asteroid clone)

  • 10f means the asteroid will get destroyed after ten seconds

Make your asteroids move!

  • Go back to the CreateAsteroids script and add this above Start():
public float asteroidSpeed;
  • Change the createAsteroid() function so that it looks like this:
void createAsteroid () {
  Vector3 createPosition = Vector3.zero;
  GameObject asteroidClone = Instantiate(asteroid, createPosition, asteroid.transform.rotation);

  // make the asteroid move
  Rigidbody asteroidCloneRB = asteroidClone.GetComponent<Rigidbody>();
  asteroidCloneRB.velocity = -(transform.up * asteroidSpeed);
}

What does the code do?

To make an asteroid move, you need to give it a velocity (a speed), and to do that, you need to get the asteroid’s Rigidbody.

The line:

Rigidbody asteroidCloneRB = asteroidClone.GetComponent<Rigidbody>();

looks at the asteroid clone you just created and gets its Rigidbody.

With the last line, you’re changing the Rigidbody’s velocity property. -(transform.up) is the direction to move.

  • Back in Unity, click on the Asteroid object in the Hierarchy and set asteroidSpeed to 2 in the script section of the Inspector.

Randomise where the asteroids appear

Lets make it more fun by creating asteroids in different places. To do this, you can write a function that returns a random position!

  • Add this function to the CreateAsteroids script:
Vector3 getRandomPosition()
{
    float xPos = Random.Range(.05f, .95f);
    Vector3 randomPosition = Camera.main.ViewportToWorldPoint(new Vector3(xPos, 1.1f, 15f));
    return randomPosition;
}

What does the code do?

Putting Vector3 instead of void in front of a function declaration means that the function will return a Vector3 object.

Random.Range(.05f, .95f) returns a random number between the two numbers given in the parameters (a parameter is anything within the parentheses following a function). In this case, that will be a random number in between 0.05 and 0.95.

The camera’s viewpoint dimensions are 1 × 1 (the bottom left being (0,0) and the top right being (1,1)). So the random number xPos you’ll be using as the X coordinate will always be within the dimensions of the viewpoint.

You then create a Vector3 object called randomPosition and set it to:
x — your randomly generated x position
y — a y position that will lead to asteroid clones being created ‘above’ the screen
z — the z position that is level with your Player object

You then return randomPosition.

  • Finally, change Vector3 createPosition = Vector3.zero; to Vector3 createPosition = getRandomPosition();.

  • Try the game out!

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