Unity Beginner to Hero Part 10: Damaging Enemies

Lesson 10. A milestone. Gone are the days when words like Vector3 or World-Space were confusing and meaningless to you. You have passed beyond your neophyte days. Greatness is within grasp.

Alright this is wordpress not FictionPress. On with the tutorial. This time around, we’re going to create a new script that will allow objects to be damaged and destroyed by the rockets we created in the previous lessons. Let’s begin by creating a new script, calling it “EnemyHealth.” Since I think we’re getting quite advanced over here, I’m not going to paste the script piecemeal—I don’t think we need to go over public fields for the third (fourth?) time.

using UnityEngine;
using System.Collections;

public class EnemyHealth : MonoBehaviour {

    public float initialHealth = 10.0f;

    private float currentHealth;

    void Start () {
        currentHealth = initialHealth;
    }

    public void TakeDamage(float damage)
    {
        currentHealth -= damage;

        if (currentHealth < 0)
        {
            Destroy(gameObject);
        }
    }
}

We have the usual crop of fields, which we initialize in the Start method, another of the special methods that are part of all Unity components. Start is called once and only once for each component, when it is enabled. If the script is never enabled, Start is never called.

We’ve added a new method named TakeDamage, this time with the public access modifier in front of it. Despite never having stated it explicitly, all of our previous methods have been private—fields and methods are private by default in C#.

TakeDamage is fairly simple in concept and execution. A single float variable is passed into the method that decrements the current amount of health the enemy has. Once it is below zero, the enemy is destroyed.

This script is finished, but we’re not quite—we need to make it so that the rockets call TakeDamage on enemies they collide with. Back in the Rocket script, add a new public float field named damageDealt. In the OnTriggerEnter method, add the following lines at the top.

EnemyHealth health = col.gameObject.GetComponent<EnemyHealth>();

if (health != null)
{
	health.TakeDamage(damageDealt);
}

We’re using GetComponent again, but this time it’s to grab one of the components we built ourselves! We store the component in the health variable, and then check to see if it’s null or not—GetComponent returns null if there is no such component attached to the object, since not all objects the rocket will collide with (walls, ground, ceiling) are enemies and can be damaged. Last but not least, we call the TakeDamage method and pass in damageDealt as an argument. We are able to call this method on health as we gave the method the public access modifier.

Back in the editor, add the EnemyHealth script to a few of the boxes we dropped into the level. You should be able to play the game now and destroy them with a few rockets!

I added particle effects for some personality. Definitely a topic that would be fun to cover in a future lesson!

Before concluding the first set of these tutorials, let’s add one more thing. By now you’ve probably noticed that it can be somewhat annoying to play a shooter game with the mouse wandering all over the screen. In most shooters, and many other kinds of games, the mouse is hidden from view and locked to the center of the screen. Let’s do this now. Create a new script and name it “MouseLock.” Add the following lines in the Update method.

if (Input.GetButtonDown("Fire1"))
{
	Cursor.lockState = CursorLockMode.Locked;
	Cursor.visible = false;
}

if (Input.GetKeyDown(KeyCode.Escape))
{
	Cursor.lockState = CursorLockMode.None;
	Cursor.visible = true;
}

This allows us to lock the hide the cursor and lock it’s movement when the mouse button is pushed. As well, we add in some code to handle unlocking (and unhiding) when the Escape key is pressed.

Now add this script to an object in the scene—it doesn’t necessarily have to be added to your player object, since it doesn’t reference any scripts on variables on it. On starting the game now the mouse will be hidden and locked to the center of the screen.

Lesson 10 Complete Project

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Thanks for reading! If you have any problems with the above tutorial, general comments or suggestions, please post below. It’s always appreciated!

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