public void MergeMeshes()
        {
            var submesh = new ObjMesh(this);

            submesh.PositionFaces   = Meshes.SelectMany(i => i.PositionFaces).ToList();
            submesh.NormalFaces     = Meshes.SelectMany(i => i.NormalFaces)  .ToList();
            submesh.TexCoordFaces   = Meshes.SelectMany(i => i.TexCoordFaces).ToList();

            Meshes.Clear();
            Meshes.Add(submesh);
        }
        private ObjMesh NewMesh()
        {
            if(CurrentMesh != null && CurrentMesh.IsEmpty)
                return CurrentMesh;

            CurrentMesh     = new ObjMesh(CurrentGroup);

            CurrentGroup.Meshes.Add(CurrentMesh);

            return CurrentMesh;
        }