mjxml 0.1.3

Utilities to programatically create MuJoCo XML configuration files

mjxml

Programmatic, type-checked helpers for composing MuJoCo XML. Define assets and worldbody elements in Python (with Pydantic validation), serialize to XML, and write files you can load in MuJoCo.

Highlights

• Strong typing and validation via Pydantic v2.
• Easy XML serialization: to_xml(), to_xml_str(), write().
• Assets: TextureAsset, MeshAsset, HFieldAsset, ModelAsset.
• Bodies: Geom (with many MuJoCo attributes), WorldBody base.
• Utilities: Defaults blocks, rotation helpers, and runtime type protocols.

Requirements

• Python >= 3.13
• Runtime deps: numpy, pydantic

Install

From a checkout of this repository:

pip install -e .

For development (tests and linting):

pip install pytest ruff

If you run examples or tests without installing, set PYTHONPATH to include src.

export PYTHONPATH=src

Quickstart

Below are minimal examples showing how to construct elements and serialize them.

Texture asset

from asset.texture import TextureAsset

tex = TextureAsset(
		name="tex_grid",
		file="albedo.png",
		type="2d",
		colorspace="srgb",
		content_type="image/png",
		nchannel=3,
)

# ElementTree element
elem = tex.to_xml()

# Pretty string
print(tex.to_xml_str())

# Write to a file
tex.write("texture.xml")

Generated <texture> will include only attributes you set and perform validation (e.g., nchannel must be 1, 3, or 4; random in [0,1]).

Mesh asset

from asset.mesh import MeshAsset

mesh = MeshAsset(
		name="m_cube",
		file="cube.obj",
		content_type="model/obj",
		scale=[1.0, 1.0, 1.0],
		inertia="exact",
)

print(mesh.to_xml_str())

MeshAsset supports inline data (vertex/normal/texcoord/face), reference poses (refpos/refquat), and procedural builtin shapes.

Height field asset

from asset.hfield import HFieldAsset

hfield = HFieldAsset(
		name="terrain",
		file="height.png",
		content_type="image/png",
		nrow=256,
		ncol=256,
		size=[5.0, 5.0, 1.0, 0.0],  # required
)

print(hfield.to_xml_str())

size is required and encodes (radius_x, radius_y, elevation_z, base_z).

Geom

from body.geom import Geom

g = Geom(
		name="box1",
		type="box",
		size=[0.5, 0.5, 0.5],
		rgba=[0.8, 0.2, 0.2, 1.0],
		friction=[0.5, 0.1, 0.01],
)

print(g.to_xml_str())

If friction is provided, condim is emitted as its length, matching MuJoCo’s behavior.

Testing

Run the unit tests with pytest.

pytest -q -s

Status

This repository is under active development; expect minor API adjustments. A high-level MujocoModel aggregator is planned but not yet included.

Roadmap

• [✅] High-level Wrapper: MujocoModel class to aggregate assets, worldbody, and other sections.
• [✅] Body Elements: Support for joint, site, camera.
• [=] Sections: Support for actuator, sensor, equality, contact, tendon.
• [❌] IO: Parsing existing XML files for round-trip editing.
• [❌] Docs: Comprehensive API documentation and more examples.