code: public void copy(VertexData data) {
          clear();
          indices.addAll(data.indices);
          final TIntObjectIterator<VertexAttribute> iterator = data.attributes.iterator();
          while (iterator.hasNext()) {
              iterator.advance();
              attributes.put(iterator.key(), iterator.value().clone());
          }
          nameToIndex.putAll(data.nameToIndex);
      }
docs: Replaces the contents of this vertex data by the provided one. This is a deep copy. The vertex attribute are each individually cloned.
  
  @param data The data to copy.