Plane Look at Camers script, help needed

Hi,

My script is fully functional, but what i want to do is, instead of allowing my billboard to face camera by completely turning, i only want it to turn a maximum of 15 degrees left and right..

Like if i am in front of the plane, the angle of plane will be eith 90 or 180 or 360, what i want is it should maximum turn left or right to 15 degrees...

how can i achieve this ?


This is my script below -

Code (csharp):

1.  
2. using UnityEngine;
3. using System.Collections;
4.  
5. public class Billboard : MonoBehaviour
6. {
7.     Camera referenceCamera;
8.  
9.     public enum Axis {up, down, left, right, forward, back};
10.     public bool reverseFace = false;
11.     public Axis axis = Axis.up;
12.  
13.     // return a direction based upon chosen axis
14.     public Vector3 GetAxis (Axis refAxis)
15.     {
16.         switch (refAxis)
17.         {
18.             case Axis.down:
19.                 return Vector3.down;
20.             case Axis.forward:
21.                 return Vector3.forward;
22.             case Axis.back:
23.                 return Vector3.back;
24.             case Axis.left:
25.                 return Vector3.left;
26.             case Axis.right:
27.                 return Vector3.right;
28.         }
29.  
30.         // default is Vector3.up
31.         return Vector3.up;     
32.     }
33.  
34.     void  Awake ()
35.     {
36.         // if no camera referenced, grab the main camera
37.         if (!referenceCamera)
38.             referenceCamera = Camera.main;
39.     }
40.  
41.     void  Update ()
42.     {
43.         // rotates the object relative to the camera
44.         Vector3 targetPos = transform.position + referenceCamera.transform.rotation * (reverseFace ? Vector3.forward : Vector3.back) ;
45.         Vector3 targetOrientation = referenceCamera.transform.rotation * GetAxis(axis);
46.         transform.LookAt (targetPos, targetOrientation);
47.     }
48. }
49.  
50.  
51.  

I mean i dont want this to happen
https://www.dropbox.com/s/e6mu7d7pypc4bv9/Screenshot 2014-01-19 12.42.53.png


I want it to turn max 15 degrees both sides from its base angle and only in the X - AXIS

 

I think i can do it if i can change this line

Code (csharp):

1.  
2. transform.LookAt (targetPos, targetOrientation);
3.  

to something like

Code (csharp):

1.  
2. transform.LookAt(Vector3(targetPos.x,targetPos.y,targetPos.z),targetOrientation);
3.  

but this line gives me error, i think this way i can reduce the percentage of turning for my x axis

what do you think ?