Unity3D: World Rotation to Local Rotation - unity3d

Question

I'm really struggling with this. I have a turret that is mounted on a spaceship. It's a child object of the ship. The turret is allowed to point left, right, up, but not down, because that would be pointing through the spaceship.
So, I need to limit the rotation of the turret so it won't point down. I started with this code:
`
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class TurretScriptTest : MonoBehaviour
{
public float rotateSpeedBase = 1f;
public float rotateSpeedCurr = 1f;
public float yMin = 0;
public float yMax = 1;
public Transform target;
// Start is called before the first frame update
void Start()
{
rotateSpeedCurr = rotateSpeedBase;
}
// Update is called once per frame
void Update()
{
if (target && target.gameObject.activeSelf)
{
// Rotate
RotateWithLock();
}
}
public virtual void RotateWithLock()
{
if (target)
{
Vector3 targetDir = target.position - transform.position;
float step = rotateSpeedCurr * Time.deltaTime;
Vector3 newDir = Vector3.RotateTowards(transform.forward, targetDir, step, 0.0f);
newDir.y = Mathf.Clamp(newDir.y, yMin, yMax);
transform.rotation = Quaternion.LookRotation(newDir);
}
}
}
`
This works great except for one thing. The spaceship is also rotating all over the place. As soon as the parent spaceship goes off its original axis the above code is worthless. The turret will point through the spaceship or whatever else is in the way.
I'm assuming that what I need to do is convert everything to local rotation and position so that "down" for the turret will always be its base, not "down" in world space. So I try this code:
`
public virtual void RotateWithLock()
{
if (target)
{
Vector3 targetDir = target.position - transform.position;
float step = rotateSpeedCurr * Time.deltaTime;
Vector3 newDir = Vector3.RotateTowards(transform.forward, targetDir, step, 0.0f);
Vector3 newDirLocal = transform.InverseTransformDirection(newDir);
newDirLocal.y = Mathf.Clamp(newDirLocal.y, yMin, yMax);
transform.localRotation = Quaternion.LookRotation(newDirLocal);
}
}
`
Now the turret doesn't move at all. What to do?

Answer 1

If your turret's gun is a child of the turret's base, then you can just use "transform.localRotation" to get the rotation relative to the base.
If not, then try this:
If you have the Transform of the base, then you can use "Quaternion.Inverse" to get the inverse of the base's rotation. Then just take the LookRotation and multiply it by this inverse (Quaternion1 * Quaternion2 just adds them together). To convert that to a Direction Vector for the clamp calculations, just do "Quaternion * new Vector3(0, 0, 1)"
Vector3 targetDir = target.position - transform.position;
//Gets rotation to the target
Quaternion rotToTarget = Quaternion.LookRotation(newDirLocal);
float step = rotateSpeedCurr * Time.deltaTime;
//Gets new rotation
Quaternion newRot = Quaternion.RotateTowards(transform.rotation, rotToTarget, step);
//Gets the local rotation by adding (yes adding) the inverse of the base rotation
//Make sure to set the turretBase variable to the turret base's GameObject
newRot = newRot * Quaternion.Inverse(turretBase.transform.rotation);
//Gets a vector that points to the direction
Vector3 dirFromRot = newRot * new Vector3(0, 0, 1);
//This sets the y-limit. The yLimit should be less than 1.
//I am using your code, but a more effective way would be to limit the angle of the quaternion.
dirFromRot.y = Mathf.Clamp(dirFromRot.y, -yLimit, yLimit);
//Gets the LookRotation of this clamped Vector3 and sets the result.
transform.localRotation = Quaternion.LookRotation(dirFromRot.normalized);