Animation Clip

animation-clip.cs

public interface IAnimationCurve
{
    double this[double t] { get; }
    double Duration { get; }
}

public class AnimationClip<T> : IAnimationClip<T>
{
    public AnimationClip(IAnimationCurve curve, T from, T to, Func<T, T, double, T> lerp)
        => (Curve, From, To, Lerp) = (curve, from, to, lerp);

    public IAnimationCurve Curve { get; set; }
    public Func<T, T, double, T> Lerp { get; }
    public T From { get; set; }
    public T To { get; set; }
    public bool Started { get; private set; } = false;
    public bool Stopped { get; private set; } = false;
    public double StartTime { get; private set; }
    public double StopTime { get; private set; }

    public void Start(double t)
    {
        StartTime = t;
        Started = true;
        Stopped = false;
    }

    public void Update(double t)
    {
        if (!Started || Stopped) return;
        OnUpdate?.Invoke(this, Evaluate(t));
        if (Elapsed(t) > Curve.Duration)
            Stop(t);
    }

    public void Continue(double t)
    {
        if (!Stopped) return;
        StartTime += t - StopTime;
    }

    public void Stop(double t)
    {
        Stopped = true;
        StopTime = t;
    }

    public double Elapsed(double t)
        => Started ? t - StartTime : StopTime - StartTime;

    public T Evaluate(double t)
        => Lerp(From, To, Curve[Elapsed(t)]);

    public event EventHandler<T> OnUpdate;
}