How do I combine meshes in code?

Question

So let's say I have six separate sides that I created that represents a cube. But I'll need to mash all six side meshes into one mesh that would represent a cube. And to be even more efficient, I need to take all cube meshes within a 16x16x256 area and combine them into a chunk mesh, which will then be attached to a GameObject. So I know how to create all the different sides (right, left, top, bottom, front, back) but I just can't figure out to combine the meshes together. I also need to have multiple materials for the same mesh if that is possible. The code below demonstrates how I go about creating a side.

 public Mesh CreateSide(Vector3[] vertices, int[] triangles){
     Mesh mesh = new Mesh ();
     mesh.vertices = vertices;
     mesh.triangles = triangles;
     mesh.uv = standardMeshUV;
     MeshUtility.Optimize (mesh);
     mesh.RecalculateNormals ();
     return mesh;
 }
 public Mesh CreateFrontSide(){
     Vector3[] vertices = new Vector3[] {
         new Vector3 (-1, 1, 1),
         new Vector3 (1, 1, 1),
         new Vector3 (-1, -1, 1),
         new Vector3 (1, -1, 1)
     };
     int[] triangles = new int[] {
         0, 2, 3,
         3, 1, 0,
     };
     return CreateSide (meshFilter, vertices, triangles);
 }

Answer 1

Apparently, the simplest option is to just store all the meshes in GameObjects, combine them using mesh.CombineMeshes, and then delete all the GameObjects that were created. I'm sure there is a better option in terms of taking up fewer resources, but it seems to work alright.

     public GameObject CreateChunk(short chunkX, short chunkY){
         
         List<GameObject> physicalBlocks = new List<GameObject> ();
 
         for (short y = 0; y < height; y++) {
             for (short x = (short)(chunkX * chunkSize); x < (short)(chunkX * chunkSize) + chunkSize; x++) {
                 for (short z = (short)(chunkY * chunkSize); z < (short)(chunkY * chunkSize) + chunkSize; z++) {
                     GameObject physicalBlock = CreatePhysicalBlock (blocks [x, y, z]);
                     if (physicalBlock != null) {
                         physicalBlocks.Add (physicalBlock);
                         physicalBlock.name = x + "," + y + "," + z;
                     }
                 }
             }
         }
         //Merge physical blocks into one chunk.
         CombineInstance[] combine = new CombineInstance[physicalBlocks.Count];
 
         for(int i = 0; i < physicalBlocks.Count; i++){
             combine[i].mesh = physicalBlocks[i].GetComponent<MeshFilter> ().sharedMesh;
             combine[i].transform = physicalBlocks[i].transform.localToWorldMatrix;
         }
 
         GameObject chunk = new GameObject ();
         chunk.AddComponent<MeshCollider> ();
         chunk.AddComponent<MeshFilter> ();
         chunk.AddComponent<MeshRenderer> ();
         chunk.transform.GetComponent<MeshFilter> ().mesh = new Mesh ();
         chunk.transform.GetComponent<MeshFilter> ().mesh.CombineMeshes (combine, true);
         chunk.GetComponent<MeshCollider> ().sharedMesh = chunk.GetComponent<MeshFilter> ().sharedMesh;
         chunk.GetComponent<MeshRenderer>().material = atlasMaterial;
         chunk.transform.GetComponent<MeshFilter> ().mesh.RecalculateBounds ();
         chunk.transform.GetComponent<MeshFilter> ().mesh.RecalculateNormals ();
         MeshUtility.Optimize (chunk.GetComponent<MeshFilter> ().mesh);
 
         for (int i = physicalBlocks.Count; i > 0; i--) {
             Destroy (physicalBlocks[i - 1]);
         }
 
         chunk.name = "Chunk_" + chunkX + "_" + chunkY;
         return chunk;
     }

How do I combine meshes in code?

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