MeshDataPreserver

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

public class MeshDataPreserver : MonoBehaviour
{
    public GameObject originalSkinnedMeshObject;
    public GameObject mergedMeshObject;

    [ContextMenu("Transfer Mesh Data")]
    void TransferMeshData()
    {
        if (originalSkinnedMeshObject == null || mergedMeshObject == null)
        {
            Debug.LogError("Please assign both the original and merged mesh objects.");
            return;
        }

        SkinnedMeshRenderer originalSMR = originalSkinnedMeshObject.GetComponent<SkinnedMeshRenderer>();
        MeshFilter mergedMF = mergedMeshObject.GetComponent<MeshFilter>();

        if (originalSMR == null || mergedMF == null)
        {
            Debug.LogError("Original object must have SkinnedMeshRenderer and merged object must have MeshFilter.");
            return;
        }

        Mesh originalMesh = originalSMR.sharedMesh;
        Mesh mergedMesh = mergedMF.sharedMesh;

        // Create a new mesh to store the updated data
        Mesh newMesh = new Mesh();
        newMesh.name = "UpdatedMergedMesh";

        // Copy vertex data
        newMesh.vertices = mergedMesh.vertices;
        newMesh.normals = mergedMesh.normals;
        newMesh.uv = mergedMesh.uv;
        newMesh.tangents = mergedMesh.tangents;
        newMesh.colors = mergedMesh.colors;
        newMesh.triangles = mergedMesh.triangles;

        // Transfer bone weights
        if (originalMesh.boneWeights.Length > 0)
        {
            BoneWeight[] newBoneWeights = new BoneWeight[mergedMesh.vertexCount];
            for (int i = 0; i < mergedMesh.vertexCount; i++)
            {
                newBoneWeights[i] = originalMesh.boneWeights[i % originalMesh.vertexCount];
            }
            newMesh.boneWeights = newBoneWeights;
        }

        // Transfer bind poses
        if (originalMesh.bindposes.Length > 0)
        {
            newMesh.bindposes = originalMesh.bindposes;
        }

        // Transfer blend shapes
        if (originalMesh.blendShapeCount > 0)
        {
            for (int i = 0; i < originalMesh.blendShapeCount; i++)
            {
                string shapeName = originalMesh.GetBlendShapeName(i);
                int frameCount = originalMesh.GetBlendShapeFrameCount(i);

                for (int j = 0; j < frameCount; j++)
                {
                    Vector3[] deltaVertices = new Vector3[mergedMesh.vertexCount];
                    Vector3[] deltaNormals = new Vector3[mergedMesh.vertexCount];
                    Vector3[] deltaTangents = new Vector3[mergedMesh.vertexCount];

                    Vector3[] originalDeltaVertices = new Vector3[originalMesh.vertexCount];
                    Vector3[] originalDeltaNormals = new Vector3[originalMesh.vertexCount];
                    Vector3[] originalDeltaTangents = new Vector3[originalMesh.vertexCount];

                    originalMesh.GetBlendShapeFrameVertices(i, j, originalDeltaVertices, originalDeltaNormals, originalDeltaTangents);

                    for (int k = 0; k < mergedMesh.vertexCount; k++)
                    {
                        int originalIndex = k % originalMesh.vertexCount;
                        deltaVertices[k] = originalDeltaVertices[originalIndex];
                        deltaNormals[k] = originalDeltaNormals[originalIndex];
                        deltaTangents[k] = originalDeltaTangents[originalIndex];
                    }

                    float weight = originalMesh.GetBlendShapeFrameWeight(i, j);
                    newMesh.AddBlendShapeFrame(shapeName, weight, deltaVertices, deltaNormals, deltaTangents);
                }
            }
        }

        // Add SkinnedMeshRenderer if it doesn't exist, otherwise update the existing one
        SkinnedMeshRenderer newSMR = mergedMeshObject.GetComponent<SkinnedMeshRenderer>();
        if (newSMR == null)
        {
            newSMR = mergedMeshObject.AddComponent<SkinnedMeshRenderer>();
        }

        // Set the new mesh and bone data
        newSMR.sharedMesh = newMesh;
        newSMR.bones = originalSMR.bones;
        newSMR.rootBone = originalSMR.rootBone;

        // Keep the MeshFilter, but update its shared mesh
        mergedMF.sharedMesh = newMesh;

        // Save the new mesh as an asset
        AssetDatabase.CreateAsset(newMesh, "Assets/UpdatedMergedMesh.asset");
        AssetDatabase.SaveAssets();

        Debug.Log("Mesh data transferred and SkinnedMeshRenderer updated on merged object.");
    }
}