feat: add a mjcf loader

.github/workflows/rapier-ci-build.yml

@@ -23,7 +23,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Cargo doc
-        run: cargo doc --features parallel,simd-stable,serde-serialize,debug-render -p rapier3d -p rapier2d -p rapier3d-meshloader -p rapier3d-urdf
+        run: cargo doc --features parallel,simd-stable,serde-serialize,debug-render -p rapier3d -p rapier2d -p rapier3d-meshloader -p rapier3d-urdf && cargo doc -p mjcf-rs --features msh && cargo doc -p rapier3d-mjcf --features stl,wavefront,msh
   build-native:
     runs-on: ubuntu-latest
     env:
@@ -37,6 +37,10 @@ jobs:
         run: cargo clippy -p rapier-examples-2d --features parallel,simd-stable
       - name: Clippy rapier3d
         run: cargo clippy -p rapier-examples-3d --features parallel,simd-stable
+      - name: Clippy mjcf-rs
+        run: cargo clippy -p mjcf-rs --all-targets --features msh
+      - name: Clippy rapier3d-mjcf
+        run: cargo clippy -p rapier3d-mjcf --all-targets --features stl,wavefront,msh
       - name: Build rapier2d
         run: cargo build --verbose -p rapier2d;
       - name: Build rapier3d
@@ -51,6 +55,10 @@ jobs:
         run: cd crates/rapier3d; cargo build --verbose --features simd-stable --features parallel;
       - name: Run tests
         run: cargo test
+      - name: Test mjcf-rs
+        run: cargo test -p mjcf-rs --features msh
+      - name: Test rapier3d-mjcf
+        run: cargo test -p rapier3d-mjcf --features stl,wavefront,msh
       - name: Check rapier_testbed2d
         run: cargo check --verbose -p rapier_testbed2d;
       - name: Check rapier_testbed3d

.typos.toml

@@ -18,6 +18,10 @@ extend-ignore-re = [
 [default.extend-identifiers]
 anc_color = "anc_color"
 rady = "rady"
+iit_softfoot = "iit_softfoot"
+FoV = "FoV"
+# Shepperd's method: named after S. W. Shepperd (quaternion extraction).
+Shepperd = "Shepperd"
 
 # Case insensitive, matches inside word.
 [default.extend-words]

CHANGELOG.md

@@ -56,7 +56,7 @@
 - Update `glamx` to 0.3.
 - Updated `wide` version to `1` ([#902](https://github.com/dimforge/rapier/issues/902)).
 
-## v0.31.0 (09 Jan. 2026)
+## v0.32.0 (09 Jan. 2026)
 
 ### Modified
 

Cargo.toml

@@ -13,6 +13,8 @@ members = [
     "examples3d-f64",
     "crates/rapier3d-urdf",
     "crates/rapier3d-meshloader",
+    "crates/mjcf-rs",
+    "crates/rapier3d-mjcf",
 ]
 resolver = "2"
 

README.md

@@ -49,6 +49,21 @@ The easiest way to get started with Rapier is to:
    Their source code are available on the `examples2d/` and `examples3d/` directory.
 3. Don't hesitate to ask for help on [Discord](https://discord.gg/vt9DJSW), or by opening an issue on GitHub.
 
+## AI coding disclaimer and policy
+
+AI coding is extensively used for the implementation and maintenance of the following crates: `mjcf-rs`, `rapier3d-mjcf`.
+
+We actively use AI assistance (with human reviews) for the following tasks:
+    - Documentation generation.
+    - Changelogs generation.
+    - Tests generation.
+    - CI configuration and scripts.
+
+We accept contributions involving AI coding as long as:
+    - They are verified to work properly by a human.
+    - The code quality is up to human-written code standards.
+    - Include non-regression tests whenever applicable (which itself can be AI-generated).
+
 ## Resources and discussions
 
 - [Dimforge](https://dimforge.com): See all the open-source projects we are working on! Follow our announcements

assets/3d/agility_cassie/scene.xml

@@ -0,0 +1,23 @@
+<mujoco model="cassie scene">
+  <include file="cassie.xml"/>
+
+  <statistic center="0 0 0.55" extent="1.1"/>
+
+  <visual>
+    <headlight diffuse="0.6 0.6 0.6" ambient="0.3 0.3 0.3" specular="0 0 0"/>
+    <rgba haze="0.15 0.25 0.35 1"/>
+    <global azimuth="150" elevation="-20"/>
+  </visual>
+
+  <asset>
+    <texture type="skybox" builtin="gradient" rgb1="0.3 0.5 0.7" rgb2="0 0 0" width="512" height="3072"/>
+    <texture type="2d" name="groundplane" builtin="checker" mark="edge" rgb1="0.2 0.3 0.4" rgb2="0.1 0.2 0.3"
+      markrgb="0.8 0.8 0.8" width="300" height="300"/>
+    <material name="groundplane" texture="groundplane" texuniform="true" texrepeat="5 5" reflectance="0.2"/>
+  </asset>
+
+  <worldbody>
+    <light pos="0 0 3" dir="0 0 -1" directional="false"/>
+    <geom name="floor" size="0 0 .125" type="plane" material="groundplane" conaffinity="15" condim="3"/>
+  </worldbody>
+</mujoco>

crates/mjcf-rs/Cargo.toml

@@ -0,0 +1,32 @@
+[package]
+name = "mjcf-rs"
+version = "0.1.0"
+authors = ["Sébastien Crozet <sebcrozet@dimforge.com>"]
+description = "Pure-Rust parser for the MuJoCo MJCF XML format."
+documentation = "https://docs.rs/mjcf-rs"
+homepage = "https://rapier.rs"
+repository = "https://github.com/dimforge/rapier"
+readme = "README.md"
+categories = [
+    "parser-implementations",
+    "science",
+    "simulation",
+]
+keywords = ["mjcf", "mujoco", "robotics", "parser", "xml"]
+license = "Apache-2.0"
+edition = "2024"
+
+[features]
+default = []
+## Enable parsing MuJoCo's custom binary `.msh` mesh format.
+msh = ["dep:byteorder"]
+
+[dependencies]
+roxmltree = "0.20"
+thiserror = "2"
+log = "0.4"
+byteorder = { version = "1", optional = true }
+glamx = { workspace = true, features = ["std", "f64"] }
+
+[dev-dependencies]
+tempfile = "3"

crates/mjcf-rs/README.md

@@ -0,0 +1,22 @@
+## MJCF parser for Rust
+
+> **Disclaimer.** Most of this crate — source, tests, and documentation — was
+> produced by an AI coding assistant working iteratively from MJCF reference
+> scenes (primarily the [MuJoCo Menagerie](https://github.com/google-deepmind/mujoco_menagerie)),
+> under human direction and review.
+
+`mjcf-rs` is a pure-Rust parser for the [MuJoCo XML format (MJCF)](https://mujoco.readthedocs.io/en/stable/XMLreference.html).
+
+It produces a typed AST that mirrors MJCF 1:1 in element names, with all
+preprocessing (`<include>` resolution, `<default>` class inheritance, angle
+unit normalization) already done — so consumers don't need to revisit the
+spec for any of those.
+
+This crate has **no dependency** on `rapier3d` or any physics engine. Pair
+it with [`rapier3d-mjcf`](../rapier3d-mjcf) to actually simulate MJCF
+models.
+
+### Status
+
+See [`rapier3d-mjcf`'s feature matrix](../rapier3d-mjcf/README.md) for an
+up-to-date, phase-by-phase list of what's supported.

crates/mjcf-rs/src/assets.rs

@@ -0,0 +1,146 @@
+//! `<asset>` library: meshes, hfields, textures, materials.
+
+use crate::Pose;
+
+/// Container for all assets defined in a model (and its includes).
+#[derive(Default, Clone, Debug)]
+pub struct Assets {
+    /// `<mesh>` definitions, keyed by name.
+    pub meshes: Vec<Mesh>,
+    /// `<hfield>` definitions, keyed by name.
+    pub hfields: Vec<Hfield>,
+    /// `<texture>` definitions (recorded only — not loaded).
+    pub textures: Vec<Texture>,
+    /// `<material>` definitions (recorded only).
+    pub materials: Vec<Material>,
+}
+
+impl Assets {
+    /// Looks up a `<mesh>` by name.
+    pub fn mesh(&self, name: &str) -> Option<&Mesh> {
+        self.meshes.iter().find(|m| m.name.as_deref() == Some(name))
+    }
+
+    /// Looks up a `<hfield>` by name.
+    pub fn hfield(&self, name: &str) -> Option<&Hfield> {
+        self.hfields
+            .iter()
+            .find(|h| h.name.as_deref() == Some(name))
+    }
+
+    /// Looks up a `<material>` by name.
+    pub fn material(&self, name: &str) -> Option<&Material> {
+        self.materials
+            .iter()
+            .find(|m| m.name.as_deref() == Some(name))
+    }
+
+    /// Looks up a `<texture>` by name.
+    pub fn texture(&self, name: &str) -> Option<&Texture> {
+        self.textures
+            .iter()
+            .find(|t| t.name.as_deref() == Some(name))
+    }
+}
+
+/// `<mesh>` asset. Either references a file or carries inline vertex/face data.
+#[derive(Default, Clone, Debug)]
+pub struct Mesh {
+    /// Asset name.
+    pub name: Option<String>,
+    /// Class for default lookup.
+    pub class: Option<String>,
+    /// Mesh file path (relative to `meshdir` / model dir).
+    pub file: Option<String>,
+    /// Per-axis scale (default `[1, 1, 1]`).
+    pub scale: [f64; 3],
+    /// Reference pose applied to the source mesh before use.
+    pub refpose: Pose,
+    /// Inline vertex array (alternative to `file`). Flat `[x0, y0, z0, x1, …]`.
+    pub inline_vertices: Option<Vec<f64>>,
+    /// Inline normals. Optional even when `inline_vertices` is set.
+    pub inline_normals: Option<Vec<f64>>,
+    /// Inline triangle indices.
+    pub inline_faces: Option<Vec<u32>>,
+    /// `inertia` attribute: `"shell"`, `"convex"` (default), or `"exact"`.
+    pub inertia: MeshInertia,
+    /// Maximum number of vertices when computing the convex hull.
+    pub max_hull_vert: Option<u32>,
+    /// `smoothnormal` (visualisation only — recorded).
+    pub smoothnormal: f64,
+}
+
+/// `<mesh inertia>` selector.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
+pub enum MeshInertia {
+    /// Surface integral.
+    Shell,
+    /// Convex-hull interior (default).
+    #[default]
+    Convex,
+    /// Tetrahedral integration over all triangles.
+    Exact,
+    /// Treat as a point mass at the geometric centre.
+    Legacy,
+}
+
+/// `<hfield>` heightfield asset.
+#[derive(Default, Clone, Debug)]
+pub struct Hfield {
+    /// Asset name.
+    pub name: Option<String>,
+    /// Class.
+    pub class: Option<String>,
+    /// Number of grid rows.
+    pub nrow: u32,
+    /// Number of grid columns.
+    pub ncol: u32,
+    /// `(radius_x, radius_y, elevation_z, base_z)`.
+    pub size: [f64; 4],
+    /// File path (PNG / `.hfield`).
+    pub file: Option<String>,
+    /// Inline elevation data (`nrow * ncol` values, row-major).
+    pub elevation: Option<Vec<f64>>,
+}
+
+/// `<texture>` asset (recorded only).
+#[derive(Default, Clone, Debug)]
+pub struct Texture {
+    /// Asset name.
+    pub name: Option<String>,
+    /// Asset class.
+    pub class: Option<String>,
+    /// Texture type (`2d`, `cube`, `skybox`).
+    pub type_: Option<String>,
+    /// File path.
+    pub file: Option<String>,
+    /// `builtin` (`"none"`, `"gradient"`, `"checker"`, `"flat"`).
+    pub builtin: Option<String>,
+    /// Primary RGB.
+    pub rgb1: Option<[f64; 3]>,
+    /// Secondary RGB.
+    pub rgb2: Option<[f64; 3]>,
+}
+
+/// `<material>` asset (recorded only).
+#[derive(Default, Clone, Debug)]
+pub struct Material {
+    /// Asset name.
+    pub name: Option<String>,
+    /// Asset class.
+    pub class: Option<String>,
+    /// Texture reference.
+    pub texture: Option<String>,
+    /// `rgba`.
+    pub rgba: Option<[f64; 4]>,
+    /// `emission`.
+    pub emission: f64,
+    /// `specular`.
+    pub specular: f64,
+    /// `shininess`.
+    pub shininess: f64,
+    /// `roughness`.
+    pub roughness: f64,
+    /// `metallic`.
+    pub metallic: f64,
+}