Multi-Material Mesh Merge Snippet

For this video

public void AdvancedMerge()
 {
  // All our children (and us)
  MeshFilter[] filters = GetComponentsInChildren (false);

  // All the meshes in our children (just a big list)
  List materials = new List();
  MeshRenderer[] renderers = GetComponentsInChildren (false); // <-- you can optimize this
  foreach (MeshRenderer renderer in renderers)
  {
   if (renderer.transform == transform)
    continue;
   Material[] localMats = renderer.sharedMaterials;
   foreach (Material localMat in localMats)
    if (!materials.Contains (localMat))
     materials.Add (localMat);
  }

  // Each material will have a mesh for it.
  List submeshes = new List();
  foreach (Material material in materials)
  {
   // Make a combiner for each (sub)mesh that is mapped to the right material.
   List combiners = new List ();
   foreach (MeshFilter filter in filters)
   {
    if (filter.transform == transform) continue;
    // The filter doesn't know what materials are involved, get the renderer.
    MeshRenderer renderer = filter.GetComponent ();  // <-- (Easy optimization is possible here, give it a try!)
    if (renderer == null)
    {
     Debug.LogError (filter.name + " has no MeshRenderer");
     continue;
    }

    // Let's see if their materials are the one we want right now.
    Material[] localMaterials = renderer.sharedMaterials;
    for (int materialIndex = 0; materialIndex < localMaterials.Length; materialIndex++)
    {
     if (localMaterials [materialIndex] != material)
      continue;
     // This submesh is the material we're looking for right now.
     CombineInstance ci = new CombineInstance();
     ci.mesh = filter.sharedMesh;
     ci.subMeshIndex = materialIndex;
     ci.transform = Matrix4x4.identity;
     combiners.Add (ci);
    }
   }
   // Flatten into a single mesh.
   Mesh mesh = new Mesh ();
   mesh.CombineMeshes (combiners.ToArray(), true);
   submeshes.Add (mesh);
  }

  // The final mesh: combine all the material-specific meshes as independent submeshes.
  List finalCombiners = new List ();
  foreach (Mesh mesh in submeshes)
  {
   CombineInstance ci = new CombineInstance ();
   ci.mesh = mesh;
   ci.subMeshIndex = 0;
   ci.transform = Matrix4x4.identity;
   finalCombiners.Add (ci);
  }
  Mesh finalMesh = new Mesh();
  finalMesh.CombineMeshes (finalCombiners.ToArray(), false);
  myMeshFilter.sharedMesh = finalMesh;
  Debug.Log ("Final mesh has " + submeshes.Count + " materials.");
 }