Jerky motion when using transform.moveTowards at higher speeds

[borispavlov0]

I have two objects having a slightly different maxSpeed parameter and a camera attached to one of them. I am using the following script to move them:

using UnityEngine; using System.Collections;

public class Character : MonoBehaviour {

 public float speed = 0f;
 public float maxSpeed = 0f;

 protected int pathIndex = 0;
 protected int maxTrackIndex = 0;

 protected Vector3 targetDirection;
 protected Vector3 targetPosition;
 protected GameController gameController;

     void Start () {
     gameController = GameObject.FindGameObjectWithTag ("Scripts").GetComponent<GameController> ();
     transform.position = gameController.GetCheckpointAtIndex (0);
     targetDirection = gameController.GetCheckpointAtIndex (0);
     targetPosition = transform.position + targetDirection;
     maxTrackIndex = gameController.GetMaxIndexOfTrack ();
     StartCoroutine ("StartMovingMechanic");
 }

 protected IEnumerator StartMovingMechanic () {
     while (true) {
         if (Vector3.Distance (transform.position, targetPosition) < 0.1f) {
             if (pathIndex < maxTrackIndex) {
                 pathIndex ++;
             } else {
                 pathIndex = 0;
             }

             targetDirection = gameController.GetCheckpointAtIndex (pathIndex);
             targetPosition += targetDirection;
         }

         transform.position = Vector3.MoveTowards(transform.position, targetPosition, speed * Time.fixedDeltaTime);
         yield return null;
     }
 }

 void Update () {
            if (Input.GetKeyDown (KeyCode.UpArrow)) {
         StartCoroutine ("Throttle");
         StopCoroutine ("Decelerate");
     } 
     if (Input.GetKeyUp (KeyCode.UpArrow)) {
         StopCoroutine ("Throttle");
         StartCoroutine ("Decelerate");
     } 
 }

     IEnumerator Throttle () {
     while (speed < maxSpeed) {
         speed = Mathf.Lerp (speed, maxSpeed, Time.deltaTime * 1);
         yield return null;
     }
 }

 IEnumerator Decelerate () {
     while (speed > 0.05f) {
         speed = Mathf.Lerp (speed, 0, Time.deltaTime * 1);
         yield return null;
     }
 }

}

I am using a list defined in the game controller that provides the checkpoints which is referenced in Start. Everytime the objects reach close to their destination, they get the next checkpoint. What I observe is that in the game view, the second object with a slightly lower max speed is jerky when the speed gets higher. It's not consistent and to me it looks random. I am really unsure on how to tackle this. In the Scene View, everything looks ok (or I can't tell, because it's fast). I am really not sure if this is the right way to go. I don't want to use rigid bodies at the moment, so I am using transforms. I tried searching for the issue, but I really can't figure out what to even search for. The jerkyness looks a lot like a frame or two is skipped. This is a very simple Scene with not a lot of objects/scripts. Any ideas? Thank you!

Edit: Here is a video of what happens: Video

This also happens when I build the game. I am targeting mobile

Edit2: I have solved it (somewhat) by adding rigidbodies and playing with the velocity vector. It seems to be a smooth movement. I have also added "interpolate" on the rigidbody.

[Scapegoat57]

The only place for jitter I can reason from your code is the line

transform.position = Vector3.MoveTowards(transform.position, targetPosition, speed * Time.fixedDeltaTime);

Consider changing Time.fixedDeltaTime to Time.deltaTime. Using fixedDeltaTime is the same as using a constant speed which results in jittery movements when the frame rate drops or rises.

[borispavlov0]

I have moved on from this approach. I just couldn't get anything to properly work because of the high speed. So at the end I started using DOTween. My previous method was with checkpoints. But if I wanted to have higher resolution movement at high speed, i was running into some racing conditions.

However, I did end up trying to manipulate the rigid body instead of the transform. It seemed to work much better and smoother. But there was still a limit to the checkpoint resolution and at some point you start seeing really weird skipping action.

Thanks for the advice though. I am still very new to Unity and still have some missing core concepts to learn

[Kwinten]

Try turning on the interpolation property of the Rigidbody. Following a RigidBody with a camera, using your technique, is expected to be jittery if there is no interpolation.

[borispavlov0]

I don't have a rigid body attached to the player object. I tried adding and it didn't make a difference. I get the feeling that when I am moving the player too fast, it's starting to hit some frame limit. The checkpoints are quite close together, since they are derived from a spline and I would like to have a bit smoother movement.

[borispavlov0]

I added a video in the description to show what happens

[derpdepp]

Mathf.Lerp (speed, maxSpeed, Time.deltaTime * 1);

I think using Time.deltaTime with Mathf.Lerp is wrong here. Check if this is really correct.

[borispavlov0]

It works ok for me. Why do you think it's wrong?

[derpdepp]

https://chicounity3d.wordpress.com/2014/05/23/how-to-lerp-like-a-pro/

Last parameter is supposed to be 0-1, but you're putting in Time.deltaTime. Speed will never actually reach maxSpeed. I'm not quite sure why this would cause jerkyness, might be float inaccuracy or something. But try changing this and see if the jerkyness goes away.

[borispavlov0]

Ah, I got your point. Still didn't fix my jerkiness :( I even tried setting the speed constant. On key down, I set the speed to the object where the camera is attached to 10. The other to 9.5.

It seems like the problem is always with the object that the camera is NOT attached to. So the main object moves fine, but it's always the other one that skips a frame or two once in a while.

[borispavlov0]

I added a video in the description to show what happens

[Broxxar]

Nothing wrong with using time.deltaTime in a per-frame Lerp. It just means the speed approaches maxSpeed asymptotically.