MiniGame2: Pizza Carnage

This game consists of eliminating waves of aliens by throwing pieces of pizza at them.

You will learn to:

Create a spawner

Use randomness

Create and use Prefabs

Detect collisions

Model a pizza and an alien with their colliders

Scene Layout

Open the Assets folder named MiniGames

Inside this folder, create a new Scene named: Pizza Carnage

Create a ground of 10mx10m, apply a green color

Create a capsule to represent the player

Create 3 objects to represent the aliens

Player control

Create a controller script for the player:

Player can move left and right using the arrow keys

Add a test to prevent the player from going off the ground

Pizza

Without a doubt, the most interesting part of this project is coming up: modeling a slice of pizza in 3D

Add a script to make the pizza move at a speed of 10m/s in the direction of the aliens

Prefab

The player will throw pizza slices to the aliens, so we need to reuse the same slice of pizza multiple times. For this, we transform our 3D pizza slice into a prefab.

Drag an drop your pizza slice into the MiniGames folder

Delete the pizza from the scene

Enter Play mode

Drag and drop the pizza slice into the hierarchy window, this will instantiate the pizza prefab in real time

Exit Play mode

Firing pizza

Go back in the player controller script

Add a new variable: public GameObject pizzaSlice

Link this variable to your prefab
In the update() function, detect when the spacebar is pressed
if ( Input.GetKeyDown(KeyCode.Space) )
If we look at the documentation:

We notice a version that is interesting:

First parameter: the prefab we want to instantiate

Its position

Its rotation

Instantiate a prefab when spacebar is pressed

At the player position

Using the rotation transform of the prefab

Self-destruction

In order to improve game performance, we need to destroy projectiles when they go out of bounds.

When a pizza slice if far away (> 10m)
Destroy the current object using:
Destroy(gameObject);

Alien Spawner

Transform you three aliens into prefab

Delete aliens from the scene

Our spawn manager script will be associated to a hidden GameObject:

Right click in the Hierarchy windows and select: Create Empty

Rename this object to spawnmanager

Create a script and attach it to the spawn manager
Edit the script and add an array of prefabs as a public member:
public GameObject[] alienPrefabs;
Select the spawnmanager object

In the Inspector window, click on the + sign to set the size of the array to 3

Drag and drop the 3 alien prefabs to fill the array
Create a function Spawn() in the Spawnmanager script
Randomly choose the alien prefabs
int randomValue = Random.Range(0, 3);  // generate a random integer number between 0 and 2
Make the alien appears in front of the player by randomly choosing its location

Call the Spawn() function from the Start() function
Help in case nothing works
void RandomSpawn()
{
        int r = Random.Range(0, 3);

        Vector3 V = alienPrefabs[r].transform.position;
        V.z = Random.Range(-6, 6);
        Instantiate(alienPrefabs[r], V, alienPrefabs[r].transform.rotation);
}
Enter Play mode:
Remove the Spawn() function from the Start() function
We now spawn the aliens on a timer
void Start()
{
        float startDelay = 2;
        float spawnInterval = 3;
        InvokeRepeating("RandomSpawn",  startDelay, spawnInterval);
}

Note

The function InvokeRepeating is a easy-to-use method for repeating actions at fixed intervals. Coroutines are equivalent but they give more flexibility, allowing complex logic and dynamic timing using the keyword yield. Use InvokeRepeating for simplicity, coroutines for control and customization.

Collision

Double click on the pizza prefab

Add a box collider component

Click on the Edit collider icon

Make the collider fit the shape of the pizza

Go back to the scene

Create a new script for aliens and associate this script to each alien prefabs
This script must destroy the alien and also the pizza
Destroy(gameObject);
Destroy(other.gameObject);
Configure the collision system so that the game works properly

Use a collider in trigger mode

Here is the final version of the game:

Alien AI

Our aliens are a bit stupid: they don’t move and they don’t dodge incoming pizza shots. We need to add a simple AI:

First, create white spheres and drag them into the prefab to create the aliens’ eyes
Then, create a script named AlienAI and attach it to the alien prefab

What is the logic?

Create a trigger collider in front of the alien
The collider must be attached to the alien so that it follows its movement
When a pizza enters the trigger, activate the alien’s dodge mode
When entering dodge mode, the alien randomly decides to move 1 meter to the left or to the right
Store this destination in a variable named targetPosition
Use the following function to update the alien’s position at each frame:

transform.position = Vector3.MoveTowards(
    transform.position,
    targetPosition,
    moveSpeed * Time.deltaTime
);

Detect when the destination is reached by computing the distance between the alien’s current position and targetPosition:

Vector3.Distance(PointA, PointB);

When the destination is reached, enter a wait mode.

Objective

Ensure the alien dodges at least one incoming pizza.

For simplicity, we do not handle the case where two aliens may overlap.