Implementation:Google deepmind Mujoco MjSpec Header

Knowledge Sources	Google_deepmind_Mujoco
Domains	C API, Model Specification, Data Structures, Procedural Generation
Last Updated	2026-02-15 04:00 GMT

Overview

C header file that defines the MuJoCo model specification API (mjSpec) with types for programmatic model construction, mesh generation, and inertia inference.

Description

mjspec.h provides the C/C++ API for constructing MuJoCo models programmatically rather than from XML files. It defines string and array handle types (mjString, mjStringVec, mjIntVec, mjFloatVec, mjDoubleVec, mjByteVec) that are opaque in C but map to std::string and std::vector types in C++. Key enumerations include mjtGeomInertia (VOLUME, SHELL), mjtMeshInertia (CONVEX, EXACT, LEGACY, SHELL), and mjtMeshBuiltin (procedural mesh types including SPHERE, HEMISPHERE, CONE, SUPERSPHERE, SUPERTORUS). The header bridges the C and C++ APIs using conditional compilation.

Usage

This header is used when programmatically constructing or modifying MuJoCo models at runtime, for procedural scene generation, and for importing models from formats other than MJCF. It enables creating bodies, joints, geoms, and actuators through code rather than XML specification.

Code Reference

Source Location

• Repository: Google_deepmind_Mujoco
• File: include/mujoco/mjspec.h
• Lines: 1-800

Key Functions

// String and array handle types (C++ / C dual definitions)
#ifdef __cplusplus
  using mjString      = std::string;
  using mjStringVec   = std::vector<std::string>;
  using mjIntVec      = std::vector<int>;
  using mjFloatVec    = std::vector<float>;
  using mjDoubleVec   = std::vector<double>;
  using mjByteVec     = std::vector<std::byte>;
#else
  typedef void mjString;
  typedef void mjIntVec;
  // ... opaque types in C
#endif

// Inertia inference types
typedef enum mjtGeomInertia_ {
  mjINERTIA_VOLUME = 0,   // mass distributed in the volume
  mjINERTIA_SHELL,        // mass distributed on the surface
} mjtGeomInertia;

// Procedural mesh types
typedef enum mjtMeshBuiltin_ {
  mjMESH_BUILTIN_NONE = 0,
  mjMESH_BUILTIN_SPHERE,
  mjMESH_BUILTIN_HEMISPHERE,
  mjMESH_BUILTIN_CONE,
  mjMESH_BUILTIN_SUPERSPHERE,
  mjMESH_BUILTIN_SUPERTORUS,
  ...
} mjtMeshBuiltin;

Import

#include <mujoco/mjspec.h>

I/O Contract

Inputs

Name	Type	Required	Description
(header definitions)	N/A	N/A	No runtime inputs; provides type definitions for model specification API

Outputs

Name	Type	Description
mjSpec	struct	Model specification structure for programmatic model construction
mjtGeomInertia	enum	Inertia inference mode (volume or shell distribution)
mjtMeshInertia	enum	Mesh inertia computation method (convex, exact, legacy, shell)
mjtMeshBuiltin	enum	Procedural mesh generation types (sphere, hemisphere, cone, supersphere, supertorus)
Handle types	typedef	String and array handle types for cross-language compatibility

Related Pages

• Google_deepmind_Mujoco_MjModel_Header - Model data structure header included by mjspec.h
• Google_deepmind_Mujoco_MjTnum_Header - Numeric type definitions included by mjspec.h
• Google_deepmind_Mujoco_API_References_Header - Auto-generated API reference enumerations