Question World Rotation to Local Rotation

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:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class TurretScriptTest : MonoBehaviour
6. {
7.  
8.  
9.  
10.     public float rotateSpeedBase = 1f;
11.     public float rotateSpeedCurr = 1f;
12.     public float yMin = 0;
13.     public float yMax = 1;
14.    
15.     public Transform target;
16.    
17.     // Start is called before the first frame update
18.     void Start()
19.     {
20.         rotateSpeedCurr = rotateSpeedBase;
21.  
22.     }
23.  
24.     // Update is called once per frame
25.     void Update()
26.     {
27.         if (target && target.gameObject.activeSelf)
28.         {
29.             // Rotate
30.             RotateWithLock();
31.  
32.         }
33.    
34.     }
35.    
36.     public virtual void RotateWithLock()
37.     {
38.  
39.         if (target)
40.         {
41.  
42.            
43.             Vector3 targetDir = target.position - transform.position;
44.            
45.             float step = rotateSpeedCurr * Time.deltaTime;
46.             Vector3 newDir = Vector3.RotateTowards(transform.forward, targetDir, step, 0.0f);
47.             newDir.y = Mathf.Clamp(newDir.y, yMin, yMax);
48.            
49.             transform.rotation = Quaternion.LookRotation(newDir);
50.            
51.         }
52.  
53.     }
54.  
55.    
56. }

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:

Code (CSharp):

1. public virtual void RotateWithLock()
2.     {
3.  
4.         if (target)
5.         {
6.  
7.            
8.             Vector3 targetDir = target.position - transform.position;
9.             float step = rotateSpeedCurr * Time.deltaTime;
10.             Vector3 newDir = Vector3.RotateTowards(transform.forward, targetDir, step, 0.0f);
11.             Vector3 newDirLocal = transform.InverseTransformDirection(newDir);
12.            
13.             newDirLocal.y = Mathf.Clamp(newDirLocal.y, yMin, yMax);
14.            
15.             transform.localRotation = Quaternion.LookRotation(newDirLocal);
16.            
17.         }
18.  
19.     }

Now the turret doesn't move at all. I can see that the rotation is changing slightly in the inspector, but not visibly in the game. When I multiply the rotation it does start to move, but still doesn't point the right direction. What am I doing wrong?

 

Well, I don't think that localRotation is what you think it is. The localRotation of an object is relative to the parent space, not to the own coordinate space. So if you use a world space direction vector, you have to transfer it into the parent space. An alternative would be to simply transform it back to world space after you clamped it. Though it makes not much sense to express the own rotation inside its own coordinate space as it would always be constant.

For turrets with certain limits it's usually easier to split the whole mechanic into seperate single axes and rotate them seperately. In many cases you usually have a seperate base that only rotates on the y axis and a separate gun barrel mounted on the base that only rotates on the local x axis. So the base would simply rotate to roughly face the target and the barrel would rotate up / down do the rest. You could clamp both individually

 

Thank you! That was the key. This code is doing what I want now.

Code (CSharp):

1.     public virtual void RotateWithLock()
2.     {
3.  
4.         if (target)
5.         {
6.  
7.             Vector3 targetDir = target.position - transform.position;
8.             float step = rotateSpeedCurr * (Time.deltaTime+1);
9.             Vector3 newDir = Vector3.RotateTowards(transform.forward, targetDir, step, 0.0f);
10.             Vector3 newDirLocal = transform.parent.transform.InverseTransformDirection(newDir);
11.             newDirLocal.y = Mathf.Clamp(newDirLocal.y, yMin, yMax);
12.             Vector3 newDir2 = transform.parent.transform.TransformDirection(newDirLocal);
13.            
14.             transform.rotation = Quaternion.LookRotation(newDir2);
15.            
16.         }
17.  
18.     }

 

You might want to check out this thread.
https://forum.unity.com/threads/quaternion-lookdirection-with-parent-rotated.1242805/
I wanted to tackle this a bit and then it turned into a complete turret implementation. Though I'm not 100% satisfied with it. In the meanwhile I learned second order dynamics, and I intend to simulate motion with that.

Edit:
I believe the most final version is in post #48