Script that lets me rotate player towards velocity direction only in y axis

So, i have recenlty change my Symmetrical spherical player to a semi symmetrical crystal like player who is quite tall. Before the direction the player faced was the direction it was going but now i can't do that as it would just look silly. I just want it to rotate in one axis (i think the y) to face towards where it is going. With my limited knowledge of quaternions i tried to do this but failed, the player seems to sort of rotate all over the place.

Heres a script that i wrote to try and do this, doesn't work so well:

1. void FixedUpdate()
2. {
3. if(doInput == true)
4. {
5. float moveHor = Input.GetAxis ("Horizontal");
6. float moveVer = Input.GetAxis ("Vertical");
7. Vector3 movement = new Vector3(moveHor, 0.0f, moveVer);
8. 
   
9. if(Input.GetButtonDown("Jump") && isGrounded == true)
10. {
11. Jump();
12. }
13. 
    
14. Move (movement);
15. 
    
16. if (rigidbody.velocity != Vector3.zero)
17. {
18. temp = new Vector3(0 , rigidbody.velocity.y, 0);
19. Quaternion rotation = Quaternion.LookRotation (temp, Vector3.up);
20. Quaternion newRotation = Quaternion.Lerp (rigidbody.rotation, rotation, 8 * Time.deltaTime);
21. rigidbody.MoveRotation (newRotation);
22. }
23. }
24. }

 

Something like this should be roughly what you want. Depending on the co-ordinates, heading will be the rotation around the y-axis. You might need to multiply by Mathf.Rad2Deg before making the rotation.

Code (csharp):

1. float heading = Mathf.Atan2(rigidbody.velocity.x, rigidbody.velocity.z);
2. Quaternion rotation = Quaternion.Euler(0, heading, 0);

 

I tried out your code and it sort of works, but i'm so confused by it so i made a video about the problem (Sorry for croaky voice i have cold);

 

The purpose of atan2 is to give you the angle of a right triangle when you know the sides. Using atan2 is preferable to using atan(z/x) because it avoids the case where you divide by zero. The angle value that it returns would be in radians. Depending on your co-ordinates you may need to use atan2(y, x) or atan2(x, z), etc.


Euler angles are rotations about the x, y, z axes respectively. These are what you are normally using in the editor panel in Unity. Using Euler angles in a script is expecially useful when you want to control rotation about one axis only.



Unity takes Euler angles in degrees, so if you have a value from a trig function like atan2, you need to convert it from radians. For example

Code (csharp):

1. transform.localEulerAngles = new Vector3(
2.   0f,
3.   Mathf.Rad2Deg * Mathf.Atan2(x, z),
4.   0f);

In your specific case, you have extra rotations on your object and it might be worth making a parent transform so that you have two nested sets of rotations, eg (90, 0, 90) and (0, y, 0).

 

I just sorta clicked how quaternions work a little bit. So just to clarify on the actual code would i do something like this:

1. Put my player object under a new transform.
2. Attach this script:

float heading = Mathf.Atan2(rigidbody.velocity.x, rigidbody.velocity.z) * Mathf.Rad2Deg;
Quaternion rotation = Quaternion.Euler(0, heading, 0);

3. Celebrate my success.

 

Tried that, and it didn't seem to work additionally would rad2deg just be multiplying it by 180?

Well, actualyl i just lied. It did work but doesn't produce very satisfactory results, there is not any smooth transition between the movement, and when i use lerp it gives strange results.