MoonTools.Curve/Curve/SplineCurve3D.cs

using System.Collections.Immutable;
using System.Numerics;

namespace MoonTools.Curve
{
    /// <summary>
    /// A concatenation of 3D curves with time values.
    /// </summary>
    public struct SplineCurve3D
    {
        public ImmutableArray<ICurve3D> Curves { get; }
        public ImmutableArray<float> Times { get; }
        public float TotalTime { get; }
        public bool Loop { get; }

        public SplineCurve3D(ImmutableArray<ICurve3D> curves, ImmutableArray<float> times, bool loop = false)
        {
            TotalTime = 0;

            for (int i = 0; i < times.Length; i++)
            {
                TotalTime += times[i];
            }

            Curves = curves;
            Times = times;
            Loop = loop;
        }

        public Vector3 Point(float t)
        {
            if (!Loop && t >= TotalTime)
            {
                var lastIndex = Curves.Length - 1;
                return Curves[lastIndex].Point(Times[lastIndex], 0, Times[lastIndex]);
            }

            t %= TotalTime;

            var index = 0;
            var startTime = 0f;
            var incrementalTime = 0f;

            for (int i = 0; i < Times.Length; i++)
            {
                incrementalTime += Times[i];

                if (t < incrementalTime)
                {
                    break;
                }

                index++;
                startTime = Times[i];
            }

            return Curves[index].Point(t - startTime, 0, Times[index]);
        }
    }
}