Implements a simplistic 3D curve smoother for Unity. Depending on the intended use case, best results might be achieved by preprocessing the curve to have equally-spaced points, or using the Ramer-Douglas-Peucker algorithm to remove unnecessary points. It wasn't needed for my use case, so I didn't include that code here. YMMV.

SimplePathSmoother.cs

namespace StagPoint.Math
{
	using Unity.Collections;
	using Unity.Mathematics;

	/// <summary>
	/// Implements a simplistic 3D curve smoother
	/// </summary>
	public static class CurveSmoother
	{
		/// <summary>
		/// Performs in-place curve smoothing on a closed curve (loop)
		/// </summary>
		/// <param name="curve">A list of points to smooth.</param>
		/// <param name="iterations">The number of smoothing iterations to perform.</param>
		/// <param name="alpha">The amount of change made to point positions during each iteration.</param>
		public static void SmoothInPlaceLoop( NativeArray<float3> curve, int iterations = 1, float alpha = 0.25f )
		{
			int N = curve.Length;
			for( int iter = 0; iter < iterations; ++iter )
			{
				for( int i = 0; i < N; ++i )
				{
					int index = ( i % N );
					int iPrev = ( i == 0 ) ? N - 1 : i - 1;
					int iNext = ( i + 1 ) % N;

					var prev = curve[ iPrev ];
					var next = curve[ iNext ];
					var c = ( prev + next ) * 0.5f;

					curve[ index ] = ( 1 - alpha ) * curve[ index ] + ( alpha ) * c;
				}
			}
		}

		/// <summary>
		/// Performs in-place curve smoothing on an open curve (not looped)
		/// </summary>
		/// <param name="curve">A list of points to smooth.</param>
		/// <param name="iterations">The number of smoothing iterations to perform.</param>
		/// <param name="alpha">The amount of change made to point positions during each iteration.</param>
		public static void SmoothInPlaceOpen( NativeArray<float3> curve, int iterations = 1, float alpha = 0.25f )
		{
			for( int iter = 0; iter < iterations; ++iter )
			{
				for( int i = 1; i < curve.Length - 1; ++i )
				{
					var prev = curve[ i - 1 ];
					var next = curve[ i + 1 ];
					var c = ( prev + next ) * 0.5f;

					curve[ i ] = ( 1 - alpha ) * curve[ i ] + ( alpha ) * c;
				}
			}
		}
	}
}