Making a Sprite Follow a Unity Spline Over Time

Unity Engine
,
1

Hello, I would like to understand and create a simple script to make a sprite (in 2D only) follow a Unity spline over time.

I have some early code working but I am getting caught up with quaternions and rotation as the 2D sprite isn’t rotating and pointing forward where it should and to be honest this part is way over my head at this point.

I understand and have successfully used Unity’s built-in Spline Animate component but I would like to achieve a simplified implementation that only does this singular thing well and is something that I can understand and build off of in future.

Thank you kindly in advance for any guidance you could provide.

Edit: Here is the code I have (partially) working so far:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Splines;

public class splineMoveWorks : MonoBehaviour
{
    [SerializeField]
    private SplineContainer splineContainer;
    public float Speed = 1;
    private void Update(){
       

        var localPoint = splineContainer.transform.InverseTransformPoint(transform.position);

        SplineUtility.GetNearestPoint(splineContainer.Spline, localPoint, out var nearest, out var ratio, 10, 10);
        var tangent = SplineUtility.EvaluateTangent(splineContainer.Spline, ratio);
        var rotation = Quaternion.LookRotation(tangent);
        transform.rotation = rotation;

        Debug.Log(rotation);
        var globalNearest = splineContainer.transform.TransformPoint(nearest);
        var perpendicular = Vector3.Cross(tangent, Vector3.up);
        var position = globalNearest + perpendicular.normalized;
        transform.position = position;
        transform.Translate(Vector3.forward * Speed * Time.deltaTime, Space.Self);

    }
}
2

Quaternion.LookRotation will create a quaternion to cause the “forward” vector of an object to face Vector defined in the first parameter. Unfortunately for 2D sprites, “forward” is the z axis pointing into the screen.

I have had luck with using Quaternion.LookRotation on sprites by setting the forward parameter to (0, 0, 1) and specifying the desired “up” direction in the second parameter. Perhaps something like this could work for you:

var upVector = SplineUtility.EvaluateUpVector(splineContainer.Spline, ratio);
var rotation = Quaternion.LookRotation(new Vector3(0, 0, 1), upVector);
transform.rotation = rotation;
3

Sounds great, thank you @dstears ! I will give this a try and report back.