Implementation:Google deepmind Mujoco mjx get data

Knowledge Sources	MuJoCo MJX Documentation
Domains	GPU_Computing, Physics_Simulation, JAX
Last Updated	2026-02-15 06:00 GMT

Overview

Concrete tools for retrieving MJX simulation data from a JAX device to CPU provided by the MJX I/O module.

Description

mjx.get_data_into writes device data into pre-allocated CPU MjData objects (in-place, zero allocation). mjx.get_data allocates new MjData objects and fills them. Both handle single and batched data, dispatching to the appropriate backend (JAX, C, CPP, Warp).

Usage

Use get_data_into in render loops for zero-allocation retrieval. Use get_data for one-time retrieval when allocation cost is acceptable.

Code Reference

Source Location

• Repository: mujoco
• File: mjx/mujoco/mjx/_src/io.py
• Lines (get_data_into): 1727-1753
• Lines (get_data): 1756-1770

Signature

def get_data_into(
    result: Union[mujoco.MjData, List[mujoco.MjData]],
    m: mujoco.MjModel,
    d: types.Data,
) -> None:

def get_data(
    m: mujoco.MjModel,
    d: types.Data,
) -> Union[mujoco.MjData, List[mujoco.MjData]]:

Import

import mujoco.mjx as mjx

I/O Contract

Inputs (get_data_into)

Name	Type	Required	Description
result	MjData or List[MjData]	Yes	Pre-allocated destination
m	mujoco.MjModel	Yes	CPU model
d	types.Data	Yes	Device data to retrieve

Inputs (get_data)

Name	Type	Required	Description
m	mujoco.MjModel	Yes	CPU model
d	types.Data	Yes	Device data to retrieve

Outputs

Name	Type	Description
get_data_into	None	Modifies result in-place
get_data	MjData or List[MjData]	New MjData with CPU data

Usage Examples

import mujoco
import mujoco.mjx as mjx

m = mujoco.MjModel.from_xml_path("humanoid.xml")
mx = mjx.put_model(m)
dx = mjx.make_data(mx)

# Run simulation on GPU
step_fn = jax.jit(mjx.step)
for _ in range(100):
    dx = step_fn(mx, dx)

# Retrieve to CPU for visualization
d = mujoco.MjData(m)
mjx.get_data_into(d, m, dx)

# Or allocate new
d = mjx.get_data(m, dx)

# Now use d with MuJoCo renderer
print(f"Time: {d.time}, qpos: {d.qpos[:3]}")

Related Pages

Implements Principle

• Principle:Google_deepmind_Mujoco_MJX_Data_Retrieval

Requires Environment

• Environment:Google_deepmind_Mujoco_MJX_JAX_Environment