code: def save(self):
      # check validity of mesh
      if (
          self.mesh.verts_packed() is None
          or self.mesh.faces_packed() is None
      ):
          raise ValueError(
              "invalid mesh to save, verts or face indices are empty"
          )
  
      # accessors for positions, texture uvs and face indices
      pos_byte, pos_data = self._write_accessor_json("positions")
      idx_byte, idx_data = self._write_accessor_json("indices")
      include_textures = False
      if self.mesh.textures is not None:
          if hasattr(self.mesh.textures, "verts_features_list"):
              tex_byte, tex_data = self._write_accessor_json(
                  "texvertices"
              )
              include_textures = True
              texcoords = False
          elif self.mesh.textures.verts_uvs_list()[0] is not None:
              tex_byte, tex_data = self._write_accessor_json(
                  "texcoords"
              )
              include_textures = True
              texcoords = True
  
      # bufferViews for positions, texture coords and indices
      byte_offset = 0
      self._write_bufferview(
          "positions", byte_length=pos_byte, offset=byte_offset
      )
      byte_offset += pos_byte
  
      self._write_bufferview(
          "indices", byte_length=idx_byte, offset=byte_offset
      )
      byte_offset += idx_byte
  
      if include_textures:
          if texcoords:
              self._write_bufferview(
                  "texcoords", byte_length=tex_byte, offset=byte_offset
              )
          else:
              self._write_bufferview(
                  "texvertices",
                  byte_length=tex_byte,
                  offset=byte_offset,
              )
          byte_offset += tex_byte
  
      # image bufferView
      include_image = False
      if self.mesh.textures is not None and hasattr(
          self.mesh.textures, "maps_list"
      ):
          include_image = True
          image_byte, image_data = self._write_image_buffer(
              offset=byte_offset
          )
          byte_offset += image_byte
  
      # buffers
      self._json_data["buffers"].append(
          {"byteLength": int(byte_offset)}
      )
  
      # organize into a glb
      json_bytes = bytes(
          json.dumps(self._json_data, cls=OurEncoder), "utf-8"
      )
      json_length = len(json_bytes)
  
      # write header
      version = 2
      total_header_length = (
          28  # (file header = 12) + 2 * (chunk header = 8)
      )
      file_length = json_length + byte_offset + total_header_length
      header = struct.pack("<III", _GLTF_MAGIC, version, file_length)
      self.buffer_stream.write(header)
  
      # write json
      self.buffer_stream.write(
          struct.pack("<II", json_length, _JSON_CHUNK_TYPE)
      )
      self.buffer_stream.write(json_bytes)
  
      # write binary data
      self.buffer_stream.write(
          struct.pack("<II", byte_offset, _BINARY_CHUNK_TYPE)
      )
      self.buffer_stream.write(pos_data)
      self.buffer_stream.write(idx_data)
      if include_textures:
          self.buffer_stream.write(tex_data)
      if include_image:
          self.buffer_stream.write(image_data)
  
imports: import json
  import struct
  import warnings
  from base64 import b64decode
  from collections import defaultdict, deque
  from enum import IntEnum
  from io import BytesIO
  from typing import Any, BinaryIO, cast, Dict, List, Optional, Tuple, Union
  import numpy
  import torch
  from iopath.common.file_io import PathManager
  from PIL import Image
  from pytorch3d.io.utils import _open_file, PathOrStr
  from pytorch3d.renderer.mesh import TexturesBase, TexturesUV, TexturesVertex
  from pytorch3d.structures import join_meshes_as_scene, Meshes
  from pytorch3d.transforms import quaternion_to_matrix, Transform3d
  from .pluggable_formats import endswith, MeshFormatInterpreter
label_desc: Use image node_id 5 for calling the _GLTFWriter obj's underlying member method code with example usage: obj.save() without return types