chunky math

private void OnDrawGizmos()
    {
        if (!enabled)
            return;

        if (samplePoint != null)
        {
            Gizmos.color = Color.red;
            var samplePos = samplePoint.position;
            Gizmos.DrawWireSphere(samplePos, .05f);

            //super advanced
            var xform = transform;
            var localUp = xform.up;

            Vector3 hitPoint = samplePos - localUp
                               * Vector3.Dot(
                                   samplePos - xform.position,
                                   localUp);

            //the hit point in local terrain space
            var hitPointLocal = transform.InverseTransformPoint(hitPoint);

            //what point was hit in the overall terrain
            var flooredHit = new Vector2Int(
                Mathf.FloorToInt(hitPointLocal.x / size.x * TerrainSubdivs * chunkSubdivs),
                Mathf.FloorToInt(hitPointLocal.z / size.y * TerrainSubdivs * chunkSubdivs));

            //what point was hit inside the chunk
            var flooredHitChunk = new Vector2Int(flooredHit.x % chunkSubdivs,flooredHit.y % chunkSubdivs);

            // the 2d position of the chunk
            Vector2Int chunkPosition = new Vector2Int(
                flooredHit.x / chunkSubdivs,
                flooredHit.y / chunkSubdivs
            );

            var ChunkArray1DIndex = chunkPosition.x + chunkPosition.y * TerrainSubdivs;

            Debug.Log($"flooredHit: {flooredHit.ToString()} " +
                      $"flooredHitChunk: {flooredHitChunk.ToString()} " +
                      $"chunkPosition: {chunkPosition.ToString()} " +
                      $"chunkArrayIndex: {ChunkArray1DIndex.ToString()}");

            chunks[chunkPosition.x, chunkPosition.y].DrawPointGizmo(flooredHitChunk);

            Gizmos.DrawLine(samplePos, hitPoint);


        }

        if (chunks == null) return;

        Gizmos.matrix = transform.localToWorldMatrix;
        foreach (var chunk in chunks) chunk.DrawGizmo(settings.pointSize, quad);
    }