Question Quaternion not working and having weird effects.

Sorry if this is a stupid question (and spaghetti code) but I'm 14 and new to programming. My problem is that I can never get math inside quaternion to work.

Here's an example:
bullet rotation is the rotation in which I want the bullet to come out of the gun.
it works normally until I try to do math in it.
*this is not the full script. I removed parts that don't have to do with the problem

Code (CSharp):

1.  
2.  
3. public GameObject player;
4.  
5.     // shooting
6.     private float TimeTillNextShot;
7.  
8.     // AssaultRifle
9.     public GameObject AssaultRifle;
10.     public GameObject AssaultRifleProjectile;
11.     public float AssaultRifleProjectileSpeed;
12.     public float AssaultRifleShootDelay;
13.     public float AssaultRifleSpread;
14.     public float AssaultRifleDamage;
15.  
16. private void Update()
17.     {
18.  
19.         if (TimeTillNextShot > 0)
20.         {
21.             TimeTillNextShot -= Time.deltaTime;
22.         }
23.  
24.         if (TimeTillNextShot < 0)
25.         {
26.             TimeTillNextShot = 0;
27.         }
28.  
29.         // shooting
30.         if (Input.GetMouseButton(0) && weaponEquiped == 2 && TimeTillNextShot == 0)
31.         {
32.             AssaultRifleShoot();
33.         }
34.  
35. void AssaultRifleShoot()
36.     {
37.         var nextShotSpread = Random.Range(-AssaultRifleSpread, AssaultRifleSpread);
38.         var bulletRotation = new Quaternion(player.transform.rotation.x, player.transform.rotation.y, player.transform.rotation.z, player.transform.rotation.w);
39.  
40.         Instantiate(AssaultRifleProjectile, transform.position, bulletRotation);
41.  
42.         TimeTillNextShot = AssaultRifleShootDelay;
43.     }
44.     }

here's it with spread added

Code (CSharp):

1. var bulletRotation = new Quaternion(player.transform.rotation.x, player.transform.rotation.y + nextShotSpread, player.transform.rotation.z, player.transform.rotation.w);

*note the + nextShotSpread

As you can see the player always shoots downwards

I also tried it with

Code (CSharp):

1. Instantiate(AssaultRifleProjectile, transform.position, Quaternion.Euler(player.transform.rotation.x, player.transform.rotation.y + nextShotSpread, player.transform.rotation.z));

but I does the same thing but always shoots upwards.

 

Your problem is that you don't understand Quaternions. That's ok. Most people don't. the x/y/z/w components of a quaternion are not angles and cannot be simply treated and manipulated as such. It's better to forget about individual components of Quaternions and use the Quaternion API to do what you need. First off, replace this monstrosity:

Code (CSharp):

1. var bulletRotation = new Quaternion(player.transform.rotation.x, player.transform.rotation.y, player.transform.rotation.z, player.transform.rotation.w);

With this equivalent but much more readable code:

Code (CSharp):

1. Quaternion bulletRotation = player.transform.rotation;

Next, if you want to add some rotation on the Y axis for example, you can compose quaternions. Try this to add spread:

Code (CSharp):

1. Quaternion bulletRotation = player.transform.rotation;
2. // Our spread is just a simple Y-axis-only rotation.
3. Quaternion spreadToAdd = Quaternion.Euler(0, nextShotSpread, 0);
4. // Using the '*' operator we can"compose" quaternions.
5. bulletRotation = bulletRotation * spreadToAdd;
6.  
7. Instantiate(AssaultRifleProjectile, transform.position, bulletRotation);

 

The Quaternion class is designed so that you never have to interact with its base components, and if you're trying to interact with WXYZ in any way and don't have a math degree, you're almost certainly going about using Quaternions the wrong way.

In your last code sample you've also mixed up Euler angles with Quaternion values, which are not compatible at all.

Video with more detailed stuff about rotations

So don't ever touch any Quaternion's WXYZ components. Instead, use the many helper functions in Quaternion as well as the * operator to combine them as needed. Something like:

Code (csharp):

1. Quaternion bulletRotation = player.transform.rotation * Quaternion.AngleAxis(nextShotSpread, Vector3.up);

 

Thank you! i was stuck on this problem for a very long time.