Unity3D Slerp rotation speed

Question

I'm using Unity3D. I'd like to rotate an object to face the direction of the mouse pointer, but allow a maximum rotation speed, like "max 100 degrees per second".

There is an example in the doc, but it does not do what I want.
I think the Time.time should be Time.deltaTime, and I can't really understand what the last parameter does. Is it supposed to be the number that gets summed to the start vector?
http://docs.unity3d.com/Documentation/ScriptReference/Quaternion.Slerp.html

Also, I can't really understand what the last parameter does. Is it a time for the rotation?

The code I'm using now

Plane plane = new Plane(Vector3.up, 0);
float dist;
void Update () {
    //cast ray from camera to plane (plane is at ground level, but infinite in space)
    Ray ray = Camera.mainCamera.ScreenPointToRay(Input.mousePosition);
    if (plane.Raycast(ray, out dist)) {
        Vector3 point = ray.GetPoint(dist);

        //find the vector pointing from our position to the target
        Vector3 direction = (point - transform.position).normalized;

        //create the rotation we need to be in to look at the target
        Quaternion lookRotation = Quaternion.LookRotation(direction);

        //rotate towards a direction, but not immediately (rotate a little every frame)
        transform.rotation = Quaternion.Slerp(transform.rotation, lookRotation, Time.deltaTime * rotationSpeed);
    }
}

I think the weak spot is in the third parameter of the Slerp, but I can't figure out what to put there.

The parameters are: the starting rotation, the ending rotation, and the fraction of the rotation that has been completed so far. When using `Time.deltaTime` and using the current transform instead of the transform when the rotation first started, then the third parameter is basically how much of the rotation should be done this frame. Is the code you have now working? — jonhopkins, Dec 02 '13 at 13:40

Agostino · Accepted Answer · 2013-12-02T19:12:58.110

This code works, but I'm not sure it's 100% correct.

Plane plane = new Plane(Vector3.up, 0);
float dist;
void Update () {
    //cast ray from camera to plane (plane is at ground level, but infinite in space)
    Ray ray = Camera.mainCamera.ScreenPointToRay(Input.mousePosition);
    if (plane.Raycast(ray, out dist)) {
        Vector3 point = ray.GetPoint(dist);

        //find the vector pointing from our position to the target
        Vector3 direction = (point - transform.position).normalized;

        //create the rotation we need to be in to look at the target
        Quaternion lookRotation = Quaternion.LookRotation(direction);

        float angle = Quaternion.Angle(transform.rotation, lookRotation);
        float timeToComplete = angle / rotationSpeed;
        float donePercentage = Mathf.Min(1F, Time.deltaTime / timeToComplete);

        //rotate towards a direction, but not immediately (rotate a little every frame)
        //The 3rd parameter is a number between 0 and 1, where 0 is the start rotation and 1 is the end rotation
        transform.rotation = Quaternion.Slerp(transform.rotation, lookRotation, donePercentage);
    }
}

I know you should usually avoid comments that just say "Thanks" or whatever, but I have spent days looking for a solution, and although I found many answers... none of them worked right. this worked perfectly, so thank you! — Asher, May 08 '20 at 20:29

score 3 · Answer 2 · answered Dec 02 '13 at 17:59

3

You need to maintain a separate variable for the interpolation and update that every frame. Otherwise your Time.deltaTime * rotationSpeed will keep going up forever past the 0-1 range.

private float _RawLerp;
private float _Lerp;
public float _Speed;
public transform _Source;
public transform _Target;

private transform _TransformCache; // the transform for my game object, set in the Awake method

public void Update()
{
    _RawLerp += Time.deltaTime * _Speed;
     _Lerp = Mathf.Min(_RawLerp, 1); 
   _TransformCache.rotation = Quaternion.Slerp(
         _Source.TargetRotation(),
         _Target.TargetRotation(), 
         _Lerp);
}

answered Dec 02 '13 at 17:59

theodox

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Thanks, the point was understanding that the 3rd parameter must be in the 0-1 range. I'll post the fixed code. – Agostino Dec 02 '13 at 18:59
@user1600770 If theodox answered your question you should accept this answer. – Jerdak Dec 02 '13 at 20:54
@Jerdak He gave me the right tip, but it's not exactly what I need. I can't keep a fixed target rotation because I need to change it every frame to follow the muouse. I'll give a +1, but I accept the fixed code below. Theodox, is this fair enough for you? – Agostino Dec 03 '13 at 08:10

Unity3D Slerp rotation speed

2 Answers2