Implementation:Google deepmind Mujoco Engine Name
| Knowledge Sources | |
|---|---|
| Domains | Physics Simulation, Name Resolution |
| Last Updated | 2026-02-15 04:00 GMT |
Overview
Implements name-to-id and id-to-name lookup functions for all named MuJoCo model objects, using hash-based name resolution.
Description
This file provides the name resolution system for MuJoCo models, allowing bidirectional mapping between human-readable string names and integer IDs for all object types (bodies, joints, geoms, sites, cameras, lights, tendons, actuators, sensors, flexes, meshes, skins, materials, textures, pairs, excludes, equalities, numerics, texts, tuples, keys, plugins). The internal _getnumadr function uses a switch statement with explicit fallthrough to compute hash map addresses for each object type, traversing the type hierarchy to find the correct offset into the names map. mj_name2id performs hash-based lookup using the djb2 hash function (mj_hashString) with linear probing for collision resolution. mj_id2name performs direct array-based reverse lookup. The hash map uses a load factor of 0.5 (controlled by mjLOAD_MULTIPLE).
Usage
Called by user code and internal engine functions whenever an object needs to be referenced by name (e.g., mj_name2id(m, mjOBJ_BODY, "torso")) or when an object's name needs to be displayed (e.g., for visualization labels).
Code Reference
Source Location
- Repository: Google_deepmind_Mujoco
- File: src/engine/engine_name.c
- Lines: 1-283
Key Functions
// Internal: get number of objects and name address array for a given type
static int _getnumadr(const mjModel* m, mjtObj type, int** padr, int* mapadr);
// Hash function (djb2 variant)
uint64_t mj_hashString(const char* s, uint64_t n);
// Name-to-ID lookup (returns -1 if not found)
int mj_name2id(const mjModel* m, int type, const char* name);
// ID-to-name lookup (returns NULL if not found)
const char* mj_id2name(const mjModel* m, int type, int id);
Import
#include "engine/engine_name.h"
I/O Contract
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| m | const mjModel* | Yes | Model containing name arrays and hash maps |
| type | int (mjtObj) | Yes | Object type enum (mjOBJ_BODY, mjOBJ_JOINT, etc.) |
| name | const char* | Yes (for name2id) | String name to look up |
| id | int | Yes (for id2name) | Integer ID to look up |
Outputs
| Name | Type | Description |
|---|---|---|
| return value (mj_name2id) | int | Object ID, or -1 if name not found |
| return value (mj_id2name) | const char* | Object name string, or NULL if ID invalid or unnamed |
| return value (mj_hashString) | uint64_t | Hash value modulo table size |