Basic Tweener for Unity3d

Test.cs

static bool initialized;
static Action staticUpdate;

public static Task Tween<T>(T startValue, T endValue, float duration, Func<T, T, float, T> function, Action<T> callback, CancellationToken? cToken = null)
{
    if (!initialized)
    {
        initialized = true;
        var playerLoop = UnityEngine.LowLevel.PlayerLoop.GetCurrentPlayerLoop();
        const int updateSubSystemIndex = 5;
        playerLoop.subSystemList[updateSubSystemIndex].updateDelegate += () => staticUpdate?.Invoke();
        UnityEngine.LowLevel.PlayerLoop.SetPlayerLoop(playerLoop);
    }

    float startTime = Time.time;
    float endTime = startTime + duration;

    var taskCompletionSource = new TaskCompletionSource<bool>();

    void Update()
    {
        if (Time.time < endTime)
        {
            if (cToken?.IsCancellationRequested ?? false)
            {
                taskCompletionSource.SetCanceled();
                staticUpdate -= Update;
                return;
            }

            float t = (Time.time - startTime) / duration;
            T currentValue = function(startValue, endValue, t);
            callback(currentValue);
        }
        else
        {
            taskCompletionSource.SetResult(true);
            staticUpdate -= Update;
            callback(endValue);
        }
    }

    staticUpdate += Update;

    return taskCompletionSource.Task;
}

public static Vector3 SmoothStepVector3(Vector3 start, Vector3 end, float t)
{
    return new Vector3(Mathf.SmoothStep(start.x, end.x, t), Mathf.SmoothStep(start.y, end.y, t), Mathf.SmoothStep(start.z, end.z, t));
}

static async void Test(VisualElement myElement)
{
    CancellationTokenSource cts = new CancellationTokenSource();

    await Task.WhenAll(
        Tween(1.0f, 0.0f, 1, Mathf.SmoothStep, value => myElement.style.opacity = value, cts.Token),
        Tween(Vector3.zero, Vector3.one, 1, SmoothStepVector3, value => myElement.transform.position = value, cts.Token),
        Tween(1.0f, 360.0f, 2, Mathf.Lerp, value => myElement.transform.rotation = Quaternion.EulerRotation(new Vector3(0, value, 0)), cts.Token)
    );

    await Tween(360.0f, 1.0f, 2, Mathf.Lerp, value => myElement.transform.rotation = Quaternion.EulerRotation(new Vector3(0, value, 0)), cts.Token);
}