Chapter 3 4 Programming Assignment Detailed Instructions

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Programming Assignment 4
Detailed Instructions
Overview
In this programming assignment (the final increment of our Asteroids game development), you're
making bullets split larger asteroids into smaller asteroids, making bullets destroy asteroids that
are small enough, adding a timer to the game, and adding sound effects to the game.

Step 1: Make it so bullets split asteroids into smaller asteroids
For this step, you're making it so a collision with a bullet splits an asteroid into two smaller
asteroids instead of destroying the asteroid. This is how the original Asteroids game actually
worked.
1. Open the Asteroid script in your IDE.
2. In the OnCollisionEnter2D method, delete the code that destroys the asteroid.
3. Add code that cuts the scale of the asteroid in half in both x and y. Remember, you'll have
to copy the localScale into a Vector3 variable, make the changes, then copy your
variable back into localScale to do this.
4. We also actually need to scale the collider to make sure screen wrapping works for
smaller asteroids. Cut the radius of the Circle Collider 2D attached to the asteroid in half.
5. At this point, shooting asteroids should make them shrink. That's nice, but we actually
want them to split into two asteroids with different velocities. Instantiate the gameObject
twice, then destroy the gameObject. When you remove the original asteroid from the
scene by destroying it, you'll be left with the two new (smaller) asteroids.
6. Unfortunately, the two new (smaller) asteroids aren't actually moving! That's because we
get asteroids moving by calling the Initialize method. Unfortunately, we can't use that
method because we're only allowed to provide a Direction value as the first argument
when we call that method, and we want our new asteroids to move in a random direction
rather than just left, right, up, and down.
7. Pull the block of code that applies the impulse force to the asteroid out of the
Initialize method into a new public StartMoving method. The new method should
have a single float argument for the angle at which to move the asteroid. Call the new
method from the Initialize method to get the initial asteroids moving.
8. Now add code after you instantiate each of the smaller asteroids to call the StartMoving
method with a random angle between 0 and 2 * Mathf.PI. At this point, shooting an
asteroid should yield two smaller asteroids moving in random directions.
9. At this point, it might look strange that the smaller asteroids can be a different color from
the larger asteroid they're splitting from, but I like it that way, so I left that behavior in the
game!
When you run your game, asteroids should split into two smaller asteroids with random
velocities. Of course, they just keep getting smaller and smaller forever.

By the way, testing this was where I got really tired of my bullets going so slowly! I changed the
force to get the bullets moving to 10 and reduced their life to 1 second to make it more fun for
me. Feel free to do the same if you'd like.

Step 2: Make it so bullets destroy asteroids that are smaller than half the
original size
For this step, you're making it so a collision with a bullet actually does destroy an asteroid if the
asteroid is smaller than half the original size. Because we divide the scale of the asteroid in half
for each collision, that means each full-size asteroid can only be split twice before it's destroyed
by a bullet.
1. Open the Asteroid script in your IDE.
2. In the OnCollisionEnter2D method, add an if statement after you destroy the bullet. The
if clause for your new if statement should destroy the asteroid if the x component of its
localScale is less than 0.5; otherwise, you should split the asteroid into two smaller
asteroids as you did in the previous step.
When you run your game, you should be able to still split larger asteroids but destroy asteroids
that have been split to 1/4 their original size.

Step 3: Add game timer
For this step, you're adding a timer that shows how long the player has been playing.
1. Add a Canvas to the Hierarchy window and rename the canvas HUD.
2. Change the UI Scale Mode in the Canvas Scaler component of the canvas to Scale With
Screen Size using a 1280 by 720 Reference Resolution.
3. Add a Text component to the canvas and rename it ScoreText.
4. Change the characteristics of the Text component so that it's reasonably large, white text
centered horizontally near the top of the screen.
5. Create a new HUD script and attach it to the HUD canvas.
6. Open the HUD script in your IDE.
7. Add a documentation comment at the top of the script.
8. Declare a field to hold the Text component, marking it with [SerializeField] so you
can populate it in the Inspector. Remember, the Text class is in the UnityEngine.UI
namespace. Go populate the field in the Inspector.
9. In the Start method, set the text property of your Text field to "0". When you run the
game, 0 should be displayed near the top center of the screen. Of course, that doesn't
change at this point!
10. Although you might think we should add a Timer component to the HUD, that doesn't
work very well for a couple of reasons. First, our current Timer component counts down,
not up. That's of course fixable, but we also need to know the current value of the game
timer to display it in the game. We could also change our Timer script to provide that
information, but it will actually be easier for us to handle the simple game timer ourselves
in the HUD.

11. Declare a float field to store elapsed seconds, initializing the field to 0.
12. In the Update method, add Time.deltaTime to your elapsed seconds field. Set the text
property of your Text field to the value of your elapsed seconds field, cast to an integer
and converted to a string using the ToString method.
When you run the game, the timer should move up by 1 approximately every second.

Step 4: Stop game timer when ship is destroyed
Our game timer should really stop when the ship is destroyed since at that point the player is no
longer playing the game. That's what you're adding in this step.
1. Open the HUD script in your IDE.
2. Add a boolean field to tell whether or not the game timer is running and initialize the
field to true.
3. Change the code in the Update method to only update the timer and the timer text if the
game timer is running.
4. Create a new public method named StopGameTimer. In the method body, change the
field that tells whether or not the game timer is running to false.
5. In the Ship class, declare a field to hold the GameObject for the HUD, marking it with
[SerializeField] so you can populate it in the Inspector. Go populate the field in the
Inspector. It's actually pretty ugly having our ship know about the HUD. Don't worry,
though, you'll learn a much better way to do this in the next course in the specialization!
6. In the Ship OnCollisionEnter2D method, add code that retrieves the HUD component
attached to your HUD field and call its StopGameTimer method before destroying the
ship.
When you run the game, the timer should stop when the ship is destroyed.

Step 5: Add sound effects
For this step, you're adding sound effects to the game. You'll be adding sound effects for
shooting bullets, for when a bullet collides with an asteroid, and for when the ship is destroyed.
It's actually amazing how quickly sound effects get complicated. For example, we want to play a
sound effect when a bullet hits an asteroid. Unfortunately, both of those objects are immediately
destroyed, so even if we tell one of them to play the sound effect we won't hear it in the game.
I've solved this problem by providing you with an AudioManager class you can use to play the
sound effects in the game.
1. Copy the AudioClipName.cs, AudioManager.cs, and GameAudioSource.cs files from the
zip file into the scripts folder for your project.
2. Add a new Resources folder to the Project window. This name has to be exactly that,
starting with a capital R, or the code I provided to you won't work.
3. Copy 3 audio files for the given sound effects into that folder. Those files have to be
named shoot, hit, and die or the code I provided to you won't work.

4. Next, you'll add the AudioSource that actually plays all the sound effects in the game.
Right click in the Hierarchy window and select Create Empty. Change the name of the
new game object to GameAudioSource. In the Inspector, click the Add Component
button and select Audio > Audio Source. There's no need to assign a clip to the Audio
Source because our audio manager will select the appropriate clips to play as the game
runs. Finally, add the GameAudioSource script to the GameAudioSource game object.
5. Add code to the Ship Update method to call the AudioManager Play method when you
shoot a bullet. You'll need to use the AudioClipName enumeration I provided to you for
the argument in the method call.
6. Add code to the Asteroid OnCollisionEnter2D method at the beginning of the if body
(where you know the asteroid collided with a bullet) to call the AudioManager Play
method with the appropriate AudioClipName. You should now hear that sound effect
when you hit the asteroids with a bullet.
7. Add code to the Ship OnCollisionEnter2D method to call the AudioManager Play
method just before you destroy the ship.
When you run your game, you should have full gameplay, with all three sound effects.
Congratulations, you're done with this assignment and the game!
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