Trail Renderer SetPosition isn't setting positions properly

Questions & Answers
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1

Hey everybody,

I’m been trying to get a trail renderer to work with a floating origin system I’m implementing and pretty sure I’ve come across a bug in SetPosition. My Unity Version is 2022.3.14f.

Whenever I call SetPosition(), the trail renderer seems to be correctly setting the positions of all the vertices, but the visual trail itself doesn’t seem to be correctly displaced. I think the trail renderer is still rendering the trail at the previous position, making it incorrectly renderer a line at that point to its new position. You can see the effect on the image below:

trailrendererbug
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I debugged this by spawning an object at each of the trail vertices after SetPosition() and they’re in the right place.

trailrendererbug2.JPG
trailrendererbug2.JPG907×492 261 KB

Here’s a picture of the trail renderer’s visuals after SetPosition is called. They’re in their original position - i.e. not having been shifted along with the vertices.

trailrendererbug3
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Here’s my offset function:

void TrailOffset(Vector3 offsetPosition)
{
    foreach (TrailRenderer trailRenderer in trails)
    {
        int trailSize = trailRenderer.positionCount;
        Vector3[] positions = new Vector3[trailSize];
        trailRenderer.GetPositions(positions);
        if (positions.Length > 0)
        {
            for (int i = 0; i < positions.Length; ++i)
            {
                positions[i] -= offsetPosition;
            }
        }
        trailRenderer.SetPositions(positions);
 
        trailRenderer.GetPositions(positions);
        //DEBUG
        for (int i = 0; i < positions.Length; ++i)
        {
            Instantiate(debugObject, positions[i], Quaternion.identity);
        }
    }
}

Has anybody run into something similar or knows if this is intended behaviour? Really would appreciate any help there is, as this is the last thing I need to fix up before a floating point implementation is good to go.

Thanks!

2

Where / when do you actually update the TrailRenderer’s own gameobject? Where is that even attached to? Have you tried calling Clear in between GetPositions and SetPositions?

3

Hey buddy, the trail renderer’s gameobject is a child of the plane itself, so moves with the plane. The trail is offset whenever the plane moves too far away from the origin I call a function to shift everything in the scene to move the plane back to the origin to avoid floating point error. During this function, I invoke a UnityEvent which a controller is subscribed to to update the trail renderers which is the function in my first post.

private void LateUpdate()
{
    FloatingOriginUpdate(); //this does not work with trail renderers 
}

void FloatingOriginUpdate()
{
    if (GameManager.PlayerAircraft.transform.position.magnitude > floatingPointResetThreshold)
    {
        sceneObjects = SceneManager.GetActiveScene().GetRootGameObjects();
        origin -= GameManager.PlayerAircraft.transform.position;
        Vector3 offset = -GameManager.PlayerAircraft.transform.position;
        if (FloatingOriginEvent != null)
        {
            FloatingOriginEvent.Invoke(GameManager.PlayerAircraft.transform.position);
        }
        AltosSkyDirector.Instance.SetOrigin(origin);
        for (int i = 0; i < sceneObjects.Length;  i++)
        {
            sceneObjects[i].transform.position += offset;
        }
    }
}

I can’t clear the trail because I need the contrail to hang around for a while for a realistic effect.

4

same issue here, unity havent implemented a function to shift the line renderer points yet i think