2D Shooting

Contents

• 2D Shooting

  • Make a sprites in Aseprite

  • Detect mouse down events

  • Create a bullet

  • Create targets

  • Add a bullet script to destroy

  • Calculate angles

There are three main ways to shoot things in Unity.

• For laser-types of things where you insta-hit, you can use ray-casting.

• You can move sprites and check by distance.

• You can move sprites, and use colliders. This is how we are going to demo things here.

Make a sprites in Aseprite

We need a target and a projectile.

• Make a bullet, laser, heart, whatever projectile you want to shoot.

• Make a target to hit.

• Export, and import into Unity changing the normal three things. (pixels per unit, compression, filter)

Detect mouse down events

Now, we will use the mouse button to shoot. First, we need to detect mouse-down events.

In our Update method on cour controller (not FixedUpdate, doesn’t seem to work well), we can detect a mouse-down event with Input.GetMouseButtonDown(0). The 0 is for our left mouse button. An implementation might look like:

// Has the mouse been pressed?
if (Input.GetMouseButtonDown(0))
{
    Debug.Log("Mouse down");
}

Code and confirm it works.

Create a bullet

Now we need something to shoot.

• Create a bullet prefab.

• Add a box collider so we can detect collisions. Set the collider to be a trigger, as we don’t want it bumping into things.

• Add a rigidbody so we can move it via physics.

Go to your character controller cand add a public variable for the prefab. Code would look like:

public GameObject bulletPrefab;

Then drag the prefab into the new blank spot in your character.

Update code to fire the bullet:

// Mouse pressed?
if (Input.GetMouseButtonDown(0))
{
    // Make a bullet
    var bullet = Instantiate(bulletPrefab, body.position, Quaternion.identity);
    // Get the body of the bullet
    var bulletbody = bullet.GetComponent<Rigidbody2D>();
    // Move the bullet to the right
    bulletbody.velocity = new Vector2(4, 0);
}

It would be better code if you make the speed a public variable rather than hard-code it. And we’ll get to aiming in a bit.

Create targets

Now we need something to shoot. Create targets. Add a collider. Add a tag for “Destroyable”.

Add a bullet script to destroy

This bullet script will destroy itself after moving 8 units, or it will destroy an object tagged ‘destroyable’.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class BulletScript : MonoBehaviour
{
    Vector3 _origin;
    public float maxDistance = 8.0f;

    // Start is called before the first frame update
    void Start()
    {
        // Get position we started at, so we can see how far the bullet traveled.
        _origin = transform.position;
    }


    public void OnTriggerEnter2D(Collider2D collision)
    {
        Debug.Log("Trigger");
        if (collision.tag == "Destroyable")
        {

            Debug.Log("Destroyable");
            // Destroy item we hit
            Destroy(collision.gameObject);
            // Cause bullet to destroy itself
            // Put this outside the if to get deleted when hitting non-destroyable objects
            Destroy(gameObject);
        }
    }

    // Update is called once per frame
    void Update()
    {
        // How far has the bullet gone?
        float distance = Vector2.Distance(_origin, transform.position);
        // If too far, then remove ourselves from the game.
        if (distance > maxDistance)
        {
            // Cause bullet to destroy itself
            Destroy(gameObject);
        }
    }
}

Calculate angles

Next, if we want to fire in a particular direction, we need to do some math. Here’s the code with comments.

// Get the angle of a vector
public float GetYRotFromVec(Vector2 v1)
{
    float _r = Mathf.Atan2(v1.y, v1.x);
    float _d = (_r / Mathf.PI) * 180;

    return _d;
}

void Update()
{
    // Get our axis values
    horizontal = Input.GetAxisRaw("Horizontal");
    vertical = Input.GetAxisRaw("Vertical");

    // Has the mouse been pressed?
    if (Input.GetMouseButtonDown(0))
    {
        // -- Fire a bullet

        // Create the bullet
        var bullet = Instantiate(bulletPrefab, body.position, Quaternion.identity);
        // Get a reference to the bullet's rigid body
        var bulletbody = bullet.GetComponent<Rigidbody2D>();
        // Where is the mouse on the screen?
        var mousePosition = Input.mousePosition;
        // Where is the mouse in the world?
        Vector3 target3 = Camera.main.ScreenToWorldPoint(mousePosition);
        // Set the z value of this vector 3
        target3.z = 0;
        // What is the normalized vector from the player to the mouse?
        Vector2 direction = (target3 - transform.position).normalized;
        // What is the angle in degrees?
        float angle = GetYRotFromVec(direction);
        // Rotate the bullet
        bulletbody.rotation = angle;
        // Give the bullet speed
        bulletbody.velocity = direction * bulletSpeed;
    }
}