06 - Adding an Enemy

In this section, you will create a simple enemy that can move around the map.

Import Assets

Kenney provides hundreds of free assets to the public domain that can be used to help in your prototypes (and even commercial projects). In this section, you will use the Graveyard Kit to create an enemy using one of the 5 provided models and animations.

Before starting, you should import the FBX Models from this asset pack: Graveyard Kit ยท Kenney

If you need help importing the models, you can refer to the Importing Asset section of 02 - Creating a Tile Grid > Importing Assets

Here is a quick check list to help you:

  • Download the Asset Pack
  • Extract the ZIP archive
  • Find the FBX Model folder
  • Import the FBX Models into your Assets
  • Rename the folder (I recommend Kenny Graveyard Kit)

Creating an Enemy Prefab

Start by creating an Empty Game Object in your Hierarchy that will act as the base for your Enemy.

  • Right click in the Hierarchy
  • Select Create Empty
  • Rename the Game Object. (I recommend calling it Enemy)

create-empty.png

Note: Double check that the new Game Object is not a child of any other object.

ensure-top-level-enemy.png

In the Kenney Graveyard Kit you will find 5 character models that can be used as a model for your Enemy:

  • character-digger
  • character-ghost
  • character-skeleton
  • character-vampire
  • character-zombie

In the Project tab, if you search for character-, you should see the 5 models:

You can search your assets for a specific file by using the search bar at the top of the Project explorer tab.

kenney-character-models.png

  • Drag one of the character models onto your Enemy game object to make it a child object.
    • Note: For this part of the project, I will be using the character-zombie model. However, feel free to use any of the models.

add-model-to-enemy.webp

Practice: Unpack Model Prefab

Can you remember how to unpack a prefab? Notice, the character-xyz model you have selected is a Prefab in the Hierarchy. Can you unpack it?

  • Unpack the enemy-ufo- model in your Hierarchy
  • Rename the game object to be model

When you have finished, your Hierarchy should look similar to the image below:

practice-renaming-unpacking.png

Practice: Create the Enemy Prefab

Now that you have an Enemy game object, turn it into a Prefab. At this point, you now have multiple types of Prefabs (tiles and enemies). Create a folder for each within your Prefabs folder to help organize them.

  • Create a folder for your Enemy prefabs
  • Create a folder for your Tile prefabs
  • Move all of your prefabs to the appropriate folder

When you have finished, your Prefabs folder should look similar to the folders below:

create-prefabs-folders.webp

Creating an EnemyMovement MonoBehaviour

To make your Enemy move, you will need to create a MonoBehaviour. A MonoBehaviour is a scripted component that provides methods for managing the behaviour of your Game Objects while the game is running.

Create a MonoBehaviour script for your enemies movement called EnemyMovement

  • In the Project tab, create a Folder called Scripts

create-scripts-folder.webp

  • Right click inside the Scripts folder
  • Select Create > Scripting > MonoBehaviour Script

create-mono-behaviour-script.png

  • Name the script EnemyMovement
    • Note: You should not use spaces and you should use CameCasing when naming Scripts
  • Double click to open the EnemyMovement script

After the script loads, verify that the class name is EnemyMovement. If you did not rename the script immediately upon creation in Unity, the template will set the name to be NewMonoBehaviourScript. It is important to rename this when you open the file for the first time.

common-mistake.png

When named correctly, it should match the name of the file. For example, in VS Code:

verify-name.png

Attaching a MonoBehaviour to a GameObject

Now that you have a EnemyMovement script, you can attach it to your Enemy Game Object

  • Select your Enemy from the Hierarchy
  • In the Inspector select Add Component
  • Search for EnemyMovement and Select it

If all went well, you should now see an Enemy Movement component in the Inspector

add-enemy-movement.webp

You may have noticed that the Enemy Movement component in your inspector has a small green plus icon next to it. This means that the component you added only exists on this instance of your Enemy and not your Enemy Prefab.

enemy-movement-prefab-overrid.png

Practice

Can you remember how to apply Overrides to your Prefab?

  • Apply the override to your Enemy Prefab to make the Enemy Movement script part of the Prefab

When you are done, the green plus icon should no longer be visible on the Enemy Movement component in the inspector.

enemy-movement-override-applied.png

Moving with the Update Method

One of the most useful methods that are provided by a MonoBehaviour is the Update method. This method is called by the Unity Engine each frame your game is running. This can be used to update the Transform Position of a GameObject each frame to make it move in the game world.

Change your EnemyMovement script's Update method to increase the enemy's transform.position on the X axis each frame.

increment-transform-enemy-movement.png

Be sure to save your work. Then, return to the Unity Editor and enter Play Mode. If all went well, you should see your Enemy moving along the x-axis of your game world. You can verify this in the Inspector.

  • Enter Play Mode
  • Verify your Enemy Movement script is updating the Transform's Position in the Inspector

playmode-move-enemy.webp

Delta Time

You may have noticed the Enemy is not moving at a consistent rate. This is because, the Enemy Movement scripts Update method is being called each frame. This makes the movement of the Enemy dependent on the Frame Rate of the game.

To help with this, you can scale the movement using the amount of time that has passed between frames. In Unity, this value can be accessed using the Time.deltaTime property.

  • Update your movement to be scaled with Time.deltaTime

scale-movement-with-delta-time.png
Once again, enter Play Mode and verify your Enemy's Transform Position is updating. You will notice your Enemy moves much slower than it did before. This is because it is now moving at 0.1 units per second. You can think of the expression * Time.deltaTime as "per second". For example, if you want an object to move 5 units per second, you would use 5 * Time.deltaTime.

playmode-move-enemy-deltaTime.webp

Creating a Speed Property

Different Enemies will move at different speeds. To help accommodate this, add a Speed property to your EnemyMovement script.

  • Add a float Speed property to your EnemyMovement class
    • Following "good" programming practices, create a public getter and a private setter
  • Set the default value of Speed to 1f

add-speed-to-enemy-movement.png

  • In your Update method, use the Speed property rather than the float literal 0.1.

update-method-with-speed-property.png
Once again, enter Play Mode and verify that your Enemy moves at 1 unity per second.

playmode-move-at-1unit-per-second.webp

Serializing Properties in the Inspector

It is useful to be able to modify a property from the Unity Inspector. To do this, you must Serialize your property by adding the [field: SerializeField] attribute to the property that you would like to see in the inspector.

  • Add the [field: SerializeField] to your Speed property

serialize-speed-property.png

Now, when you select your Enemy, you will see the Speed property in the Enemy Movement component in the Inspector. You can adjust this value directly in the Inspector to change the speed of your Enemy. You can even do this while in Play Mode! However, be aware that when you exit Play Mode any changes you made will be reset to their original values.

  • Modify the Enemy's Speed directly in the inspector setting it to 2
  • Enter Play Mode
  • While in Play Mode, adjust the Speed
  • Exit Play Mode
  • Notice, that the Speed resets to the original value: 2

adjusting-speed-in-inspector.webp

Challenge: EnemyRotation Script

Using what you've learned in this lesson, create a new MonoBehaviour Script called "EnemyRotation" that allows you to specify how quickly an Enemy rotates on the Y axis.

  • Read the Friendly Manul: Unity - Scripting API: Transform.Rotate
    • This method allows you to rotate a Game Object
  • Create a EnemyRotation script
  • In Update, rotate the enemy on the Y-axis
  • Add a RotationSpeed property to the script
    • Initialize the default value to 90f (e.g. 90 degrees per second)
  • The script should serialize a RotationSpeed property so the value can be modified in the Inspector
    • Follow good programming practices an use a private setter
  • Be sure to scale the rotation speed using Time.deltaTime

When you have successfully implemented the EnemyRotation script, it should work similar to the image below:

rotation-challenge-complete.webp

What's Next

In the next section you will create a Waypoint component that you can use to specify the path your enemies will take.

07 - Waypoints

Table Of Contents
06 - Adding an Enemy
Import Assets
Creating an Enemy Prefab
Practice: Unpack Model Prefab
Practice: Create the Enemy Prefab
Creating an EnemyMovement MonoBehaviour
Attaching a MonoBehaviour to a GameObject
Practice
Moving with the Update Method
Delta Time
Creating a Speed Property
Serializing Properties in the Inspector
Challenge: EnemyRotation Script
What's Next