fix some spline bugs

Curve/CubicBezierCurve3D.cs

@@ -6,7 +6,7 @@ namespace MoonTools.Curve
     /// <summary>
     /// A 3-dimensional Bezier curve defined by 4 points.
     /// </summary>
-    public struct CubicBezierCurve3D : IEquatable<CubicBezierCurve3D>
+    public struct CubicBezierCurve3D : IEquatable<CubicBezierCurve3D>, ICurve3D
     {
         /// <summary>
         /// The start point.

Curve/Curve.csproj

@@ -13,12 +13,14 @@
     <AssemblyName>MoonTools.Curve</AssemblyName>
     <PackageLicenseExpression>LGPL-3.0-only</PackageLicenseExpression>
     <PackageProjectUrl>https://gitea.moonside.games/MoonsideGames/MoonTools.Curve</PackageProjectUrl>
+    <Platforms>x64</Platforms>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.8">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
+    <PackageReference Include="System.Collections.Immutable" Version="1.7.1" />
     <PackageReference Include="System.Numerics.Vectors" Version="4.5.0" />
     <PackageReference Include="Microsoft.Bcl.HashCode" Version="1.1.0" />
   </ItemGroup>

Curve/ICurve3D.cs

@@ -0,0 +1,10 @@
+using System.Numerics;
+
+namespace MoonTools.Curve
+{
+    public interface ICurve3D
+    {
+        Vector3 Point(float t, float startTime, float endTime);
+        Vector3 Velocity(float t, float startTime, float endTime);
+    }
+}

Curve/QuadraticBezierCurve3D.cs

@@ -6,7 +6,7 @@ namespace MoonTools.Curve
     /// <summary>
     /// A 3-dimensional Bezier curve defined by 3 points.
     /// </summary>
-    public struct QuadraticBezierCurve3D : IEquatable<QuadraticBezierCurve3D>
+    public struct QuadraticBezierCurve3D : IEquatable<QuadraticBezierCurve3D>, ICurve3D
     {
         /// <summary>
         /// The start point.

Curve/SplineCurve3D.cs

@@ -0,0 +1,60 @@
+using System.Collections.Immutable;
+using System.Numerics;
+
+namespace MoonTools.Curve
+{
+    /// <summary>
+    /// A concatenation of 3D curves with time values.
+    /// </summary>
+    public struct SplineCurve3D
+    {
+        private ICurve3D[] Curves { get; }
+        private float[] Times { get; }
+        public float TotalTime { get; }
+        public bool Loop { get; }
+
+        public SplineCurve3D(ICurve3D[] curves, 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 = incrementalTime;
+            }
+
+            return Curves[index].Point(t - startTime, 0, Times[index]);
+        }
+    }
+}