MeshMerger

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

public class MeshMerger : MonoBehaviour
{
    public GameObject[] meshesToMerge;

    [ContextMenu("Merge Meshes")]
    void MergeMeshes()
    {
        if (meshesToMerge.Length != 4)
        {
            Debug.LogError("Please assign exactly 5 meshes to merge.");
            return;
        }

        List<CombineInstance> combine = new List<CombineInstance>();
        MeshFilter[] meshFilters = new MeshFilter[meshesToMerge.Length];

        for (int i = 0; i < meshesToMerge.Length; i++)
        {
            meshFilters[i] = meshesToMerge[i].GetComponent<MeshFilter>();
            if (meshFilters[i] == null)
            {
                Debug.LogError($"MeshFilter component not found on GameObject {i}");
                return;
            }
        }

        for (int i = 0; i < meshFilters.Length; i++)
        {
            CombineInstance ci = new CombineInstance();
            ci.mesh = meshFilters[i].sharedMesh;
            ci.transform = meshFilters[i].transform.localToWorldMatrix;
            combine.Add(ci);
        }

        Mesh combinedMesh = new Mesh();
        combinedMesh.CombineMeshes(combine.ToArray());

        GameObject mergedObject = new GameObject("MergedMesh");
        MeshFilter mergedMeshFilter = mergedObject.AddComponent<MeshFilter>();
        mergedMeshFilter.sharedMesh = combinedMesh;

        MeshRenderer mergedMeshRenderer = mergedObject.AddComponent<MeshRenderer>();
        mergedMeshRenderer.sharedMaterial = meshesToMerge[0].GetComponent<MeshRenderer>().sharedMaterial;

        // Save the combined mesh as an asset
        AssetDatabase.CreateAsset(combinedMesh, "Assets/MergedMesh.asset");
        AssetDatabase.SaveAssets();
    }
}