Tower

At this point, you have a game scene in which enemies travel along a path and when it reaches the end simply stops. For a player, this is not very exciting and they have little (or no) incentive to try to stop the enemies. In this section, you will add a Tower to your scene that you player will defend from enemies. If enough enemies reach the Tower, the tower will be destroyed.

Challenge: Create a Tower Prefab

Create a new Prefab object and name it Tower
Within the Prefab add a child component called model
Add one or more 3D models to create the visual representation of your Tower

When you have finished you should have a Prefab that looks similar to the image below:

Tower Test Scene

Just as you did before with the Projectile Test and the TurretAttack Test, it is easier to test your new Tower component in isolation to know that it works the way you would like before adding it to your main level.

In this scene you will create a Tower that can withstand 5 points of damage. You will add two enemies to the scene. One enemy will deal 2 damage. The other will deal 3. After both enemies have damaged the tower, it will be destroyed.

Setup Scene

Create a new Scene in your Test Scenes folder called "Tower Test Scene"
Delete the default Main Camera from the Scene
Add a GameCamera Prefab to the Scene
Add your Tower Prefab to the Scene
Add a Waypoint centered on your Tower (Tower Waypoint)
Add a second Waypoint that is a short distance from your tower (Second Waypoint)
Set the second Waypoint to go toward the Tower Waypoint
Add an Enemy and set its starting Waypoint to Second Waypoint (First Enemy)
Add a third Waypoint that is a further distance from your tower (Third Waypoint)
Set the third Waypoint to go toward the Tower Waypoint
Add an Enemy and set its starting Waypoint to Third Waypoint (Second Enemy)

If all went well, you should have a scene that looks and acts similar to the one in the video below:

Challenge: EnemyAttack MonoBehaviour

Before you can damage the tower, your Enemy will need to know how much damage it deals.

Create a new MonoBehaviour called EnemyAttack
Add a int Damage property
Add the EnemyAttack component to your Enemy prefab
In the Inspector set First Enemy's Damage property to 2
In the Inspector set Second Enemy's Damage property to 3

When you have finished, your Hierarchy and Inspector should look similar to the video below:

Practice: Add a Collider to your Tower prefab

To be able to detect when an Enemy has collided with your Tower, you will need to add a Collider. I recommend using a Capsule Collider but, depending on the shape of your Tower, you may choose to use a different Collider.

Add a child component to your Tower prefab (Tower Collider)
Add a Collider to the new child component
Adjust the size of the collider to fit your model
Set the Collider to be a trigger

When you have finished, your Tower Prefab should look similar to the one in the video below:

Challenge: TowerCollisionEvents MonoBehaviour

Recall how you implemented the AreaOfEngagement MonoBehaviour to detect when an enemy moves in range of your turret in 10 - Rotating Turret.

Review 10 - Rotating Turret > Add a Rigidbody to Area of Effect
Review 10 - Rotating Turret > AreaOfEngagement MonoBehaviour
Review 10 - Rotating Turret > OnTriggerEnter(Collider)
Create a new MonoBehaviour called TowerCollisionEvents
Add a property UnityEvent<EnemyAttack> OnEnemyHit
Add a void OnTriggerEnter(Collider other)
In OnTriggerEnter, useother.GetComponentInParent<EnemyAttack>() to get the EnemyAttack component.
If the component is null, do nothing (return)
Otherwise, use OnEnemyHit.Invoke to notify listeners of the collision
Additionally, add Debug.Log(other) to your method so you can verify it works

When you have finished, your prefab and test scene should look and act similar to the video below.

Challenge: TowerController MonoBehaviour

Create a TowerController MonoBehaviour
Add a float BaseHealth property (set the default value to 5)
Add a float Damage property (set the default value to 0)
Add an ApplyHit(EnemyAttack attack) method:
Increase Damage by attack.Damage
Destroy attack.gameObject
If the tower has taken sufficient damage destroy this.gameObject
Add a TowerController component to your Tower Prefab
Register TowerController.ApplyHit as a listener on your TowerCollisionEvents.OnHit event
Enter Play Mode to test your component

If all went well, your Prefab and your Test Scene should look and act similar to the video below:

Challenge: Show Game Over

Update your TowerController MonoBehaviour
Add a UnityEvent<TowerController> OnDestroyed property
In TowerController.ApplyHit
If the tower has taken sufficient damage to be destroyed, use OnDestroyed.Invoke(this) to notify any listeners that the tower was destroyed
Add a Label to your Test Scene
Update the Label to say Game Over
Position your Label in the center of the screen
Disable the Label so it is not enabled when the scene starts
Register your Label's GameObject.SetActive method on your TowerController.OnDestroyed event to enable the Label
Enter Play Mode to test your event

If all went well, your Hierarchy and Test Scene should look and act similar to the video below:

Challenge: Add a Tower to Your Level

Add your Tower Prefab to your main level
Add a Game Over label
Test your level

When you've finished, your level should look and act similar to the video below:

What's Next?

At this point, you have a very simple but playable level that is ready for some polish! In the next lesson, you will add a Level Select screen that will allow your player to select new levels to play.