Implementation:Google deepmind Mujoco XML Native Writer

Knowledge Sources	Google_deepmind_Mujoco
Domains	Physics Simulation, XML Serialization, MJCF Format
Last Updated	2026-02-15 04:00 GMT

Overview

Implements the native MJCF XML writer that serializes MuJoCo model specifications back to XML format.

Description

xml_native_writer.cc converts MuJoCo model specification data structures back into MJCF XML documents using tinyxml2. It provides a custom mj_XMLPrinter class that overrides the default indentation to use 2 spaces instead of 4, and a WriteDoc function that serializes the document and inserts blank lines between top-level MJCF sections (actuator, asset, compiler, contact, custom, default, equality, extension, keyframe, option, sensor, size, statistic, tendon, visual, worldbody). The writer handles all MJCF elements and their attributes, including plugin configurations.

Usage

Called when saving models via mj_saveXML, mj_saveXMLString, or mj_saveLastXML to produce well-formatted MJCF XML output.

Code Reference

Source Location

• Repository: Google_deepmind_Mujoco
• File: src/xml/xml_native_writer.cc
• Lines: 1-2469

Key Functions

class mj_XMLPrinter : public tinyxml2::XMLPrinter {
 public:
  void PrintSpace(int depth);  // 2-space indentation
};

static string WriteDoc(XMLDocument& doc, char* error, size_t error_sz);

Import

#include "xml/xml_native_writer.h"
#include "user/user_model.h"
#include "user/user_objects.h"
#include "xml/xml_util.h"
#include "tinyxml2.h"

I/O Contract

Inputs

Name	Type	Required	Description
doc	XMLDocument&	Yes	TinyXML2 document to serialize
s	const mjSpec*	Yes	Model specification to write
error	char*	No	Buffer for error messages
error_sz	size_t	No	Size of error buffer

Outputs

Name	Type	Description
string	std::string	Serialized MJCF XML content with 2-space indentation
int	int	Return code (0 on success, -1 on failure)

Related Pages

• Environment:Google_deepmind_Mujoco_C_Build_Environment