static void SerializeGltfSkin(Skin &skin, json &o) {
  // required
  SerializeNumberArrayProperty<int>("joints", skin.joints, o);

  if (skin.inverseBindMatrices >= 0) {
    SerializeNumberProperty("inverseBindMatrices", skin.inverseBindMatrices, o);
  }

  if (skin.skeleton >= 0) {
    SerializeNumberProperty("skeleton", skin.skeleton, o);
  }

  if (skin.name.size()) {
    SerializeStringProperty("name", skin.name, o);
  }
}
static void SerializeGltfSkin(Skin &skin, json &o) {
   
  SerializeNumberArrayProperty<int>("joints", skin.joints, o);

  if (skin.inverseBindMatrices >= 0) {
    SerializeNumberProperty("inverseBindMatrices", skin.inverseBindMatrices, o);
  }

  if (skin.skeleton >= 0) {
    SerializeNumberProperty("skeleton", skin.skeleton, o);
  }

  if (skin.name.size()) {
    SerializeStringProperty("name", skin.name, o);
  }
}