Implementation:Google deepmind Mujoco Engine Ray

Knowledge Sources	Google_deepmind_Mujoco
Domains	Physics Simulation, Ray Casting, Collision Detection
Last Updated	2026-02-15 04:00 GMT

Overview

Implements ray casting against all MuJoCo geometry types for distance queries, sensor simulation, and selection.

Description

engine_ray.c provides a comprehensive ray casting system that can test rays against all MuJoCo geometry primitives (plane, sphere, capsule, ellipsoid, cylinder, box), as well as triangle meshes, height fields, flex elements, and skins. Rays are mapped to local geometry frames for intersection testing, with analytic solutions for quadric surfaces and iterative methods for SDFs. The system supports body exclusion, geometry group filtering, static body filtering, and bounding volume hierarchy (BVH) acceleration via mju_rayTree and mju_raySlab. Multi-ray batched queries are supported for efficient sensor simulation (e.g., LIDAR), with a preparation phase that precomputes BVH traversal data shared across rays.

Usage

Called via mj_ray() for single ray queries against the full scene, or via mj_multiRay() for batched ray queries from a common origin. Individual geometry tests are available through mju_rayGeom(). Used internally by rangefinder sensors and externally for mouse picking and distance queries.

Code Reference

Source Location

Repository: Google_deepmind_Mujoco
File: src/engine/engine_ray.c
Lines: 1-1570

Key Functions

// single ray cast against all geoms in the scene
mjtNum mj_ray(const mjModel* m, const mjData* d, const mjtNum pnt[3],
              const mjtNum vec[3], const mjtByte* geomgroup,
              mjtByte flg_static, int bodyexclude, int geomid[1]);

// batched multi-ray queries from common origin
void mj_multiRay(const mjModel* m, mjData* d, const mjtNum pnt[3],
                 const mjtNum* vec, const mjtByte* geomgroup,
                 mjtByte flg_static, int bodyexclude,
                 int* geomid, mjtNum* dist, int nray, mjtNum cutoff);

// prepare shared data for multi-ray
void mju_multiRayPrepare(const mjModel* m, const mjData* d,
                         const mjtNum pnt[3], const mjtByte* geomgroup,
                         mjtByte flg_static, int bodyexclude, ...);

// ray-geom intersection for a single primitive
mjtNum mju_rayGeom(const mjtNum pos[3], const mjtNum mat[9],
                   const mjtNum size[3], const mjtNum pnt[3],
                   const mjtNum vec[3], int geomtype);

// ray-mesh intersection using BVH
mjtNum mj_rayMesh(const mjModel* m, const mjData* d, int id,
                  const mjtNum pnt[3], const mjtNum vec[3]);

// ray-heightfield intersection
mjtNum mj_rayHfield(const mjModel* m, const mjData* d, int geomid,
                    const mjtNum pnt[3], const mjtNum vec[3]);

// ray-BVH intersection (AABB slab test)
int mju_raySlab(const mjtNum aabb[6], const mjtNum xpos[3],
                const mjtNum xmat[9], const mjtNum pnt[3],
                const mjtNum vec[3], mjtNum* t);

// ray-BVH tree traversal
mjtNum mju_rayTree(const mjModel* m, const mjData* d, int id,
                   const mjtNum pnt[3], const mjtNum vec[3]);

// ray-flex intersection
mjtNum mj_rayFlex(const mjModel* m, const mjData* d, int flex_layer,
                  int flexid, int exclude_bodyid,
                  const mjtNum pnt[3], const mjtNum vec[3]);

// ray-skin intersection
mjtNum mju_raySkin(int nface, int nvert, const int* face,
                   const float* vert, const mjtNum pnt[3],
                   const mjtNum vec[3], int vertid[1]);

Import

#include "engine/engine_ray.h"

I/O Contract

Inputs

Name	Type	Required	Description
m	const mjModel*	Yes	Physics model with geometry data
d	const mjData*	Yes	Simulation state with geometry poses
pnt	const mjtNum[3]	Yes	Ray origin point
vec	const mjtNum[3]	Yes	Ray direction vector
geomgroup	const mjtByte*	No	Group inclusion mask (NULL for all)
flg_static	mjtByte	Yes	Include static (world-welded) geoms
bodyexclude	int	Yes	Body ID to exclude (-1 for none)
nray	int	Yes (multiRay)	Number of rays in batch
cutoff	mjtNum	Yes (multiRay)	Maximum ray distance

Outputs

Name	Type	Description
return (mj_ray)	mjtNum	Distance to nearest intersection (-1 if no hit)
geomid	int[1]	ID of intersected geom (-1 if no hit)
dist	mjtNum*	Per-ray distances (multiRay)

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Principle

Implementation

Heuristic

Environment