Changelog

Version 3.6.0 (March 10, 2026)

General

Breaking API changes

1. The tendon Jacobian ten_J is now always sparse. The fields ten_J_rownnz, ten_J_rowadr, and ten_J_colind have been moved from mjData to mjModel and are no longer computed at run time by mj_tendon but at compile time.

2. Added mjs_getCompiler C API function and a compiler read-only property to all Python spec element types. This allows querying the compiler settings (e.g., meshdir) from any element, with the correct originating spec’s compiler preserved after attachment.

3. Added a new strain equality constraint type for trilinear and quadratic dofs.

4. Flexes now support collisions with SDF geoms.

5. Improved memory requirements for ten_J and ten_J_colind by reducing the upper bound for the number of non-zeros nJten.

6. Improved memory requirements for actuator_moment and moment_colind by reducing the upper bound for the number of non-zeros nJmom.

MJX

7. Add batch rendering support for MJX-Warp. See the MJX-Warp batch rendering section for details.

Bug fixes

8. Fixed a bug where mjs_attach silently dropped spatial tendons with wrapping geometries that had no sidesite attribute (issue #3119, reported by @tomstewart89).

Version 3.5.0 (February 12, 2026)

Significant new features

1. MuJoCo Warp is now officially released.

2. Added a new System Identification toolbox (Python), see README for details.
   A Colab notebook demonstrating the toolbox is available here:
   Contribution by @kevinzakka, @aftersomemath, @jonathanembleyriches, @qiayuanl, @spjardim and @gizemozd.

3. Actuators and sensors now support arbitrary delays via history buffers, and sensor values can be computed at intervals larger than the simulation timestep. Using a delay or interval introduces a new mjData.history variable to the Physics state. See Delays for details.

4. Added new flexvert equality constraints that enable cloth simulations with coarser meshes. This adds a new attribute value vert to flexcomp edge equality and the new equality type flexvert. Uses the method described in Chen, Kry and Vouga, 2019.

5. Added implicit integration support for deformable objects (flex) in implicit and implicitfast integrators. This method extracts the flex degrees of freedom and solves them as a dense block, enabling increased stability for stiff flex objects without reducing the timestep. It is compatible with the trilinear and quadratic dof types.

6. Rangefinder sensors can now be attached to a camera using the rangefinder/camera attribute. In this case, the sensor respects the camera/resolution attribute and casts multiple rays, one for each pixel.

7. Rangefinders can now report various kinds of information besides ray distances, including surface normals and intersection points.

General

Breaking API changes

8. Ray-cast functions now optionally compute the surface normal at the ray intersection. This is a breaking change due to the addition of the mjtNum normal[3] argument. The modified functions are mj_ray, mj_multiRay, mju_rayGeom, mj_rayFlex, mj_rayHfield and mj_rayMesh.

   Migration: In C/C++, pass NULL to the normal argument. In Python, in all functions except mj_multiRay, it defaults to None, so no action is required.

9. mju_rayFlex has been renamed to mj_rayFlex for consistency with other functions that take mjModel* and mjData* arguments.

10. The mjModel.cam_orthographic field has been renamed to cam_projection, with the semantic of a new enum type mjtProjection. This will allow for more projection types in the future like fisheye cameras. Relatedly, the camera/orthographic MJCF attribute for cameras has been renamed to camera/projection and now accepts the values orthographic and perspective.

    Migration: Replace orthographic = "false/true" with projection="perspective/orthographic", respectively.

11. Removed getdir from the mjpResourceProvider struct. All Resource Providers now use the same shared implementation.

12. When combining the margin or gap parameters of two geoms to obtain the parameters of a contact, the respective values are now summed rather than taking the maximum. This allows geom margins to be a proper “inflation” of the geom.

13. Camera frustum visualization is now triggered by setting resolution to values larger than 1. Relatedly, frustum visualization also works for orthographic cameras. See rangefinder for details.

14. Cameras now have an output attribute, parsed into the mjModel.cam_output bitfield. Unused by the renderer, it serves as a convenient location to store a camera’s supported output types.

15. Added mj_mountVFS and mj_unmountVFS functions for mounting a custom VFS provider. Mounting allows providers to be used to open/read/close resources dynamically at arbitrary paths.

16. The optimization whereby sequential collision sensors with identical attributes shared computation has been removed. This results in a (likely minor) performance regression for models which exploited this optimization. To recover the performance, use the fromto and compute the other values manually. If from = fromto[0:3] and to = fromto[3:6] then distance = norm(to-from) and normal = normalize(to-from).

17. OpenUSD:

    • Parsing has been moved out of experimental into a mjpDecoder plugin. (documentation pending)

    • OpenUSD can now be built with the third_party_deps/openusd CMake utility project.

    • USD_DIR is no longer used by the MuJoCo CMake project, instead use pxr_DIR if you have a pre-built USD library.

    • Users no longer have to set PXR_PLUGINPATH_NAME environment variable, MuJoCo should load USD plugins automatically.

18. Non-breaking ABI changes:

    • The type of the sig (signature) argument of mj_stateSize and related functions has been changed from unsigned int to int. Before this change, invalid negative arguments passed to this function would result in a silent implicit cast; now, negativity will trigger an error.

    • Added a depth rendering flag.

    • Allocation sizes in mjModel now use 64-bit rather than 32-bit integers to accommodate larger scenes.

MJX

19. Added actuator_length, cdof and cdof_dof fields to mjx.Data.

20. Add graph_mode argument to put_model to support multiple Warp graph capture modes.

Documentation

21. General improvements to the Programming/Simulation chapter. Notably, the main discussion of state has been moved there, and the section on mjModel changes has been expanded.

22. The usability of the MJCF schema is improved with a collapsible dropdown menu with links to elements and attributes.

23. MuJoCo version numbering is now based on Semantic Versioning, see VERSIONING.md.

Bug fixes

24. Fixed a bug in implicit integrator derivatives where actuator velocity derivatives were incorrectly computed when the force was clamped by forcerange.

25. Fixed a bug in implicit integrator derivatives where actuator velocity derivatives did not account for the actearly flag.

26. Multi-threaded mesh processing, enabled by the usethread compiler flag (on by default), was in fact disabled by the flag. Fixing this bug speeds up compilation of mesh-heavy models by (up to) the number of available cores.

27. The vertid argument of mj_rayFlex and mju_raySkin was marked as nullable but was not; it is now nullable.

28. Fixed gravcomp being ignored for bodies with no joints nested inside jointed parent bodies (issue #3066, reported by @Alex108306).

Version 3.4.0 (December 5, 2025)

General

1. Introduced a major new feature: sleeping islands. Preliminary release for early testing, see documentation for details.

2. Added “quadratic” option to flexcomp/dof. This type of fast deformable flex object is similar to the “trilinear” option, but it includes curved deformations.

3. Raise an error if there are name collisions also during parsing.

4. Increase Windows stack size to 16MB to enable models with deep nested body hierarchies.

5. Added a new pipeline component function mj_fwdKinematics that combines all kinematics-like sub-components. Relatedly, added a clarifying table at the top of the Simulation Pipeline chapter.

6. Added a new mj_extractState function that allows a subset of a state that was previously returned by mj_getState to be extracted without having to be written back into mjData first.

7. Added a new mj_copyState function that copies state components from one mjData to another.

8. Tendon paths can now be queried from Python via MjsTendon.path, the returned object is iterable and indexing it will give the MjsWrap at the given index in the path.

9. MjsWrap now exposes:

   • type -> mujoco.mjtWrap

   • target -> MjsSite|MjsJoint|MjsGeom|None

   • sidesite -> MjsSite|None

   • coef -> real

   • divisor -> real

10. Non-breaking ABI changes:

    • mjtSize is now defined as int64_t rather than uint64_t to avoid future type-promotion bugs.

    • mj_sizeModel now returns an mjtSize rather than an int.

MJX

11. warp-lang optional dependency is updated to 1.10.0. pmap now works with MuJoCo Warp from MJX.

Breaking ABI changes

• mjx.Model.tex_data is now a numpy ndarray instead of a jax.Array, to avoid vmapping over this potentially large array. This may break certain use-cases with Madrona MJX, but we are no longer supporting this codepath. We will be migrating users to a Warp-based batch renderer.

Bug fixes

12. Fixed a bug in the box-box distance computation. Reported by @nvtw.

Version 3.3.7 (October 13, 2025)

General

Breaking API changes

1. The mjSpec C API fields meshdir and texturedir have been moved to compiler.meshdir and compiler.texturedir respectively. For backwards compatibility, the old fields are still available in the Python API but will be removed in a future release.

   Migration: Replace meshdir and texturedir with compiler.meshdir and compiler.texturedir.

2. Remove _full_compat from mjx.put_data and mjx.put_model.

3. nconmax and njmax fields in mjx.make_data now default to None instead of -1. nconmax will be deprecated in favor of naconmax in a future release.

3. Joint decorators and spatial tendons which have limits defined and whose current value (angle or length) exceeds the limit, are recolored by using the constraint impedance \(d\) to mix the existing color with visual/rgba/constraint. For spatial tendons, this visualization aid is active only if no material is set and rgba is default.

4. Added mju_getXMLDependencies for computing a list of unique asset dependencies from an MJCF file.

5. Added the code sample dependencies which provides command line utility for printing the result of mju_getXMLDependencies.

6. The minimum C++ standard required to compile MuJoCo is now C++20, this has been the case within Google since 2023 but the CMake update was forgotten.

Breaking ABI changes

7. The attribute mjOption.apirate was unused and has been removed.

8. MJX nconmax and njmax fields in mjx.make_data now default to None instead of -1.

MJX

9. Fix issue #2508, qLD shapes mismatched mjModel during get_data_into.

10. Pull in MuJoCo Warp update to io.py, and use naconmax instead of nconmax to set the maximum number of contacts over all environments.

Bug fixes

11. Fix issue #2881, fitaabb was adding an offset to the mesh and applying an incorrect frame transformation. Also, unify the meaning of fitting a geom to a mesh AABB: it now means to find the smallest geom such that its AABB contains the mesh AABB.

Version 3.3.6 (September 15, 2025)

General

1. Constraint island discovery and construction, previously an experimental feature, is now documented and promoted to default; disable it with option/flag/island. We expect islanding to be a strict improvement over the monolithic constraint solver, please let us know if you experience any issues.

2. Contact sensor subtree1/subtree2 specification is now available for any body, not just direct children of the world.

Breaking API changes

3. The update of mjData.qacc_warmstart was moved from the end of the solver call (mj_fwdConstraint) to the end of mj_step, and is now updated with all other state variables. This change makes mj_forward fully idempotent.

   Before this change, calling mj_forward repeatedly would make the constraint solver converge, since each subsequent call would start from the previously updated qacc_warmstart value. Indeed, this is precisely what happened in the viewer, which calls mj_forward repeatedly in PAUSE mode.

   Migration: If your code depended on this behavior, you can recover it by updating manually after each mj_forward: qacc_warmstart ← qacc. The behavior is available in simulate by clicking the “Pause update” toggle (off by default).

   Furthermore, this change has a numerical impact on the output of the RK4 integrator. Before this change, due to the qacc_warmstart update occurring after each of the four Runge-Kutta substeps, the solver convergence of RK4 was faster, at the cost of unprincipled integration. This change makes the RK4 integration principled and well-defined. Since this change to RK4 is effectively a bug fix, migration to the previous behavior is not provided.

4. The mjDSBL_PASSIVE flag for disabling passive forces was removed and replaced by mjDSBL_SPRING and mjDSBL_DAMPER with corresponding mjcf attributes. Each flag disables only joint and tendon springs or dampers, respectively. When both flags are set, all passive forces are disabled, including gravity compensation, fluid forces, forces computed by the mjcb_passive callback, and forces computed by plugins when passed the mjPLUGIN_PASSIVE capability flag.

   Migration: Set both flags to recover the behavior of the previous flag.

Breaking ABI changes

5. Removed mjMOUSE_SELECT flag for mjtMouse as it is no longer in use.

6. The promotion of islanding to default involved removing the enable flag mjENBL_ISLAND and converting it to a disable flag mjDSBL_ISLAND.

7. Added support for shells with a curved reference configuration. See this example.

8. Added experimental option for passive contacts involving flexes.

9. Added support for assigning a default material to a mesh asset using the mesh/material attribute.

MJX

10. Promote ten_length to the public MJX API. Add Warp support for mjx.tendon.

Breaking API changes

11. ten_length was moved from mjx.Data._impl.ten_length to a public field mjx.Data.ten_length.

Bug fixes

12. Fixed a latent bug where MjData objects were not serialized correctly by the Python bindings when islanding was enabled.

Version 3.3.5 (August 8, 2025)

General

1. Added the insidesite sensor, for checking if an object is inside the volume of a site. It is useful for triggering events in surrounding environment logic.

2. Added the contact sensor, for reporting contact information according to user-defined criteria. The purpose of the contact sensor is to report contact-related information in a fixed-size array. This is useful as input to learning-based agents and in environment logic.

3. Added the tactile sensor, for measuring the penetration depth between two objects at given points and the sliding velocities in the tangent frame. The sensor reports tactile data only when colliding with SDFs.

4. Removed the SdfLib plugin and the dependency on SdfLib. SDFs are now supported natively in mjModel.

5. Removed oct_depth from mjvOption (unused).

6. Added the functionality to create a builtin meshes, see mesh/builtin.

7. Inertia computation in MuJoCo C is now performed by a new pipeline function mj_makeM, which combines the Composite Rigid Body algorithm in mj_crb and additional terms related to tendon armature. Code that uses mj_crb to compute the inertia should now use mj_makeM instead.

Breaking API changes

8. Removed the mjVIS_FLEXBVH enum value, its functionality is now provided by mjVIS_MESHBVH.

Bug fixes

9. Fixed a bug that caused object lists in the child to have missing elements after attaching an mjSpec. This was caused by adding to the lists only the objects that belong to the tree of the requested body, but this causes to skip objects that were attached, since they belong to the tree of the parent.

10. Fixed a bug where the convex hull of a collision mesh was not being computed if the mesh could only collide via a contact pair.

Python

11. On Linux, built distribution packages (wheels) now target the manylinux_2_28 platform tag. Previously MuJoCo wheels targeted manylinux2014 based on CentOS 7, which reached end-of-life in June 2024.

MJX

12. Add Warp as a backend implementation for MJX. The implementation can be specified via mjx.put_model(m, impl='warp') and mjx.make_data(m, impl='warp'). The warp implementation requires a CUDA device and warp-lang to be installed (pip install mujoco-mjx[warp]). This feature is available in “beta” and some bugs are expected.

Version 3.3.4 (July 8, 2025)

Breaking API changes

1. The functions mjs_detachBody and mjs_detachDefault have been replaced by mjs_delete.

2. The Python functions element.delete have been replaced by spec.delete(element).

3. In the mjSpec C API, directly setting an element’s name using mjs_setString has been replaced with a new function mjs_setName which allows checking for naming collisions at set-time rather than compile-time, for earlier catching of errors. Relatedly, the name attribute has been removed from all mjs elements. Known issue: the error is not raised during parsing.

4. For MJX, the mjx.Option dataclass now has private and public fields similar to mjx.Model and mjx.Data. Some fields are no longer publicly available due to differences in the underlying implementations of this data structure.

General

4. Added support for setting the initial camera in the viewer using visual/global/cameraid.

5. Added support to only sync the state in the Python passive viewer’s Sync method, this is useful to improve performance. The default behavior is unchanged and copies the entire model and data.

Bug fixes

6. Inverse dynamics were not being computed correctly when tendon armature was present, now fixed.

7. Fix bug in mjx.put_data where actuator_moment was not being copied correctly for the C implementation.

Documentation

8. Added missing item documentation and clarified the nature of breaking changes in the 3.3.3 changelog. See items 3 and 4 below.

Version 3.3.3 (June 10, 2025)

General

1. Refactored island implementation so that island data is memory-contiguous. This speeds up island processing in the solver and clears the way for the addition of the Newton and PGS solvers (currently only CG is supported).

2. Removed the shell plugin. This is now supported by flexcomp and is active depending on the elastic2d attribute (off by default).

Breaking API changes

3. Replaced the directional (boolean) field for lights with a type field (of type mjtLightType) to allow for additional lighting types.

   Migration: Replace light/directional=”false/true” with light/type=”spot/directional”, respectively.

4. Added mjtColorSpace enum and associated colorspace attribute that allows to specify the color space of textures (either linear or sRGB). Since this property is now read correctly from PNG files, textures files which use sRGB will now be rendered differently.

   Migration: Set colorspace to “linear” for all textures that should look like they did before this change.

5. Added new sub-component mj_makeM which combines the mj_crb call with additional logic to support the introduction in 3.3.1 of tendon armature. In addition to the traditional mjData.qM, mj_makeM also computes mjData.M, a CSR representation of the same matrix.

6. Added a new function mj_copyBack to copy real-valued arrays in an mjModel to a compatible mjSpec.

7. Removed the limitation of fusestatic to models which contain no references. The fusestatic flag will now fuse all bodies which are not referenced and ignore bodies which are referenced.

Simulate

8. The struct mjv_sceneState has been removed. This struct was used for partial synchronization of mjModel and mjData when the Python viewer is used in passive mode. This functionality is now provided by mjv_copyModel and mjv_copyData, which don’t copy arrays which are not required for visualization.

Python bindings

9. Added examples of procedural terrain generation to the Model Editing tutorial:

MJX

10. Added tendon armature.

Version 3.3.2 (April 28, 2025)

MJX

1. Added inverse dynamics.

2. Added tendon actuator force sensor.

3. Fix issue #2606 such that make_data copies over mocap_pos and mocap_quat from body_pos and body_quat.

Version 3.3.1 (Apr 9, 2025)

Breaking API changes

1. The default value of the flag for toggling internal flex contacts was changed from “true” to “false”. This feature has proven to be counterintuitive for users.

2. All of the attach functions (mjs_attachBody, mjs_attachFrame, mjs_attachToSite, mjs_attachFrameToSite) have been removed and replaced by a single function mjs_attach.

General

3. Added tendon armature: inertia associated with changes in tendon length.

4. Added the compiler/saveinertial flag, writing explicit inertial clauses for all bodies when saving to XML.

5. Added orientation attribute to composite. Moreover, allow the composite to be the direct child of a frame.

6. Added tendon actuator force limits and tendon actuator force sensor.

MJX

7. Added tendon actuator force limits.

Bug fixes

8. mj_jacDot was missing a term that accounts for the motion of the point with respect to which the Jacobian is computed, now fixed.

9. Fixed a bug that caused the parent frame of elements in the child worldbody to be incorrectly set when attaching an mjSpec to a frame or a site.

10. Fixed a bug that caused shadow rendering to flicker on platforms (e.g., MacOS) that do not support ARB_clip_control. Fixed in collaboration with @aftersomemath.

Python bindings

11. Added examples of procedural model creation to the Model Editing tutorial:

12. Added support for nameless mjSpec objects in the bind method, see the corresponding section in the documentation.

Version 3.3.0 (Feb 26, 2025)

Feature promotion

1. Introduced a new kind of fast deformable body, activated by setting flexcomp/dof to “trilinear”. This type of deformable flex object has the same collision geometry as a regular flex, but has far fewer degrees of freedom. Instead of 3 dofs per vertex, only the corners of the bounding box are free to move, with the positions of the interior vertices computed with trilinear interpolation of the 8 corners, for a total of 24 dofs for the entire flex object (or less, if some of the corners are pinned). This limits the types of deformation achievable by the flex, but allows for much faster simulation. For example, see the video on the right comparing full and trilinear flexes for modeling deformable gripper pads.

2. The native convex collision detection pipeline introduced in 3.2.3 and enabled by the nativeccd flag, is now the default. See the section on Convex Collision Detection for more details.

   Migration: If the new pipeline breaks your workflow, set nativeccd to “disable”.

General

3. Add support for custom plots in the MuJoCo viewer by exposing a viewport property, a set_figures method, and a clear_figures method.

4. Separate collision and deformation meshes for flex. This enables a fixed cost for the soft body computations, while preserving the fidelity of high-resolution collisions.

5. Added potential and kinetic energy sensors.

6. Improved shadow rendering in the native renderer.

7. Moved introspect to python/introspect.

Breaking API changes

8. As mentioned above, the native convex collision detection pipeline is now the default, which may break some workflows. In this case, set nativeccd to “disable” to restore the old behavior.

9. Added mjs_setDeepCopy API function. When the deep copy flag is 0, attaching a model will not copy it to the parent, so the original references to the child can be used to modify the parent after attachment. The default behavior is to perform such a shallow copy. The old behavior of creating a deep copy of the child model while attaching can be restored by setting the deep copy flag to 1.

10. Changes to inertia inference from meshes:

    Previously, in order to specify that the mass lies on the surface, geom/shellinertia could be used for any geom type. Now this attribute is ignored if the geom is a mesh; instead, inertia inference for meshes is specified in the asset, using the asset/mesh/inertia attribute.

    Previously, if the volumetric inertia computation failed (for example due to a very flat mesh), the compiler would silently fall back to surface inertia computation. Now, the compiler will throw an informative error.

11. Removed the composite type grid. Users should instead use flexcomp.

12. Removed the particle composite type. It is recommended to use the more generic replicate instead, see for example this model.

MJX

13. Added support for spatial tendons with internal sphere and cylinder wrapping.

14. Fix a bug with box-box collisions issue #2356.

Python bindings

15. Added a pedagogical colab notebook for mujoco.rollout, a Python module for multithreaded simulation rollouts. It is available here .
    Contribution by @aftersomemath.

Version 3.2.7 (Jan 14, 2025)

Python bindings

1. rollout now features native multi-threading. If a sequence of MjData instances of length nthread is passed in, rollout will automatically create a thread pool and parallelize the computation. The thread pool can be reused across calls, but then the function cannot be called simultaneously from multiple threads. To run multiple threaded rollouts simultaneously, use the new class Rollout which encapsulates the thread pool. Contribution by @aftersomemath.

2. Fix global namespace pollution when using mjpython (issue #2265).

General

Breaking API changes (minor)

3. The field mjData.qLDiagSqrtInv has been removed. This field is only required for the dual solvers. It is now computed as-needed rather than unconditionally. Relatedly, added the corresponding argument to mj_solveM2.

4. Reduced the memory footprint of the PGS solver’s A matrix. This was the last remaining dense-memory allocation in MuJoCo, allowing for a significant reduction of the dynamic memory allocation heuristic.

Bug fixes

5. Fixed a bug in the box-sphere collider, depth was incorrect for deep penetrations (issue #2206).

6. Fixed a bug in mj_mulM2 and added a test.

Version 3.2.6 (Dec 2, 2024)

General

1. Removed rope and loop from composite. The user is encouraged to instead use the cable plugin or flexcomp, respectively.

MJX

2. Added muscle actuators.

Python bindings

3. Provide prebuilt wheels for Python 3.13.

4. Added bind method and removed id attribute from mjSpec objects. Using ids is error prone in scenarios of repeated attachment and detachment. Python users are encouraged to use names for unique identification of model elements.

5. rollout can now accept sequences of MjModel of length nroll. Also removed the nroll argument because its value can always be inferred.

Bug fixes

6. Fixed issue #2212, type error in mjx.get_data.

7. Fixed bug introduced in 3.2.0 in handling of texrepeat attribute, was mistakenly cast from float to int, (fixed issue #2223).

Version 3.2.5 (Nov 4, 2024)

Feature promotion

1. The Model Editing framework afforded by mjSpec, introduced in 3.2.0 as an in-development feature, is now stable and recommended for general use.

2. The native convex collision detection pipeline introduced in 3.2.3 and enabled by the nativeccd flag, is not yet the default but is already recommended for general use. Please try it when encountering collision-related problems and report any issues you encounter.

General

3. The global compiler flag exactmeshinertia has been removed and replaced with the mesh-specific inertia attribute.

4. The not-useful convexhull compiler option (to disable computation of mesh convex hulls) has been removed.

5. Removed the deprecated mju_rotVecMat, mju_rotVecMatT and mjv_makeConnector functions.

6. Sorting now uses a faster, native sort function (fixes issue #1638).

7. The PBR texture layers introduced in 3.2.1 were refactored from separate sub-elements to a single layer sub-element.

8. The composite types box, cylinder, and sphere have been removed. Users should instead use the equivalent types available in flexcomp.

MJX

9. Added apply_ft, jac, and xfrc_accumulate as public functions.

10. Added TOUCH sensor.

11. Added support for eq_active. Fixes issue #2173.

12. Added ray intersection with ellipsoid.

Bug fixes

13. Fixed several bugs related to connect and weld constraints with site semantics (fixes issue #2179, reported by @yinfanyi). The introduction of site specification to connects and welds in 3.2.3 conditionally changed the semantics of mjData.eq_obj1id and mjData.eq_obj2id, but these changes were not properly propagated in several places leading to incorrect computations of constraint inertia, readings of affected force/torque sensors and runtime enabling/disabling of such constraints.

14. Fixed a bug in slider-crank transmission. The bug was introduced in 3.0.0.

15. Fixed a bug in flex texture coordinates that prevented the correct allocation of textures in mjModel.

Documentation

16. Function headers in the API reference now link to their source definitions in GitHub.

Version 3.2.4 (Oct 15, 2024)

General

1. The Newton solver no longer requires nv*nv memory allocation, allowing for much larger models. See e.g., 100_humanoids.xml. Two quadratic-memory allocations still remain to be fully sparsified: mjData.actuator_moment and the matrices used by the PGS solver.

2. Removed the solid and membrane plugins and moved the associated computations into the engine. See 3D example model and 2D example model for examples of flex objects that previously required these plugins.

3. Replaced the function mjs_setActivePlugins with mjs_activatePlugin.

MJX

4. Added mocap_pos and mocap_quat in kinematics.

5. Added support for spatial tendons with pulleys and external sphere and cylinder wrapping.

6. Added sphere-cylinder and sphere-ellipsoid collision functions (issue #2126).

7. Fixed a bug with frictionloss constraints.

8. Added TENDONPOS and TENDONVEL sensors.

9. Fixed a bug with the computation of tangential contact forces in _decode_pyramid.

10. Added JOINTINPARENT actuator transmission type.

Python bindings

11. Removed support for Python 3.8, now that it’s deprecated upstream.

Bug fixes

12. Fixed a bug where actuator_force was not set in MJX (issue #2068).

13. Fixed bug where MJX data tendon fields were incorrect after calling mjx.put_data.

14. The compiler now returns an error if height fields are used with collision sensors as they are not yet supported.

Version 3.2.3 (Sep 16, 2024)

General

Breaking API changes

1. The runtime options mpr_tolerance and mpr_iterations were renamed to ccd_tolerance and ccd_iterations, both in XML and in the mjOption struct. This is because the new convex collision detection pipeline (see below) does not use the MPR algorithm. The semantics of these options remain identical.

2. The functions mjs_findMesh and mjs_findKeyframe were replaced by mjs_findElement, which allows to look for any object type.

3. The experimental use of 2D/3D elasticity plugins with composite has been removed. Users should instead use flexcomp, which provides the correct collision behavior.

4. Added the nativeccd flag. When this flag is enabled, general convex collision detection is handled with a new native code path, rather than libccd. This feature is in early stages of testing, but users who’ve experienced issues related to collision detection are welcome to experiment with it and report any issues.

5. Added a new way of defining connect and weld equality constraints, using two sites. The new semantic is useful when the assumption that the constraint is satisfied in the base configuration does not hold. In this case the sites will “snap together” at the beginning of the simulation. Additionally, changing the site positions (mjModel.site_pos) and orientations ( mjModel.site_quat) at runtime will correctly modify the constraint definition. This example model using the new semantic is shown in the video on the right.

6. Introduced free joint alignment, an optimization that applies to bodies with a free joint and no child bodies (simple free-floating bodies): automatically aligning the body frame with the inertial frame. This feature can be toggled individually using the freejoint/align attribute or globally using the compiler alignfree attribute. The alignment diagonalizes the related 6x6 inertia sub-matrix, leading to both faster and more stable simulation of free bodies.

   While this optimization is a strict improvement, it changes the semantics of the joint’s degrees-of-freedom. Therefore, qpos and qvel values saved in older versions (for example, in keyframes) will become invalid. The global compiler attribute currently defaults to “false” due to this potential breakage, but could be changed to “true” in a future release. Aligned free joints are recommended for all new models.

7. Added an mjSpec option for creating a texture directly from a buffer.

8. shell (surface) inertia is now supported by all geom types.

9. When attaching sub-models, keyframes will now be correctly merged into the parent model, but only on the first attachment.

10. Added the mjtSameFrame enum which contains the possible frame alignments of bodies and their children. These alignments are used for computation shortcuts in mj_kinematics.

11. Added mj_jacDot for computing time-derivatives of kinematic Jacobians. Fixes issue #411.

MJX

12. Added efc_pos to mjx.Data (issue #1388).

13. Added position-dependent sensors: MAGNETOMETER, CAMPROJECTION, RANGEFINDER, JOINTPOS, ACTUATORPOS, BALLQUAT, FRAMEPOS, FRAMEXAXIS, FRAMEYAXIS, FRAMEZAXIS, FRAMEQUAT, SUBTREECOM, CLOCK.

14. Added velocity-dependent sensors: VELOCIMETER, GYRO, JOINTVEL, ACTUATORVEL, BALLANGVEL, FRAMELINVEL, FRAMEANGVEL, SUBTREELINVEL, SUBTREEANGMOM.

15. Added acceleration/force-dependent sensors: ACCELEROMETER, FORCE, TORQUE, ACTUATORFRC, JOINTACTFRC, FRAMELINACC, FRAMEANGACC.

16. Changed default policy to avoid placing unused (MuJoCo-only) arrays on device.

17. Added device parameter to mjx.make_data to bring it to parity with mjx.put_model and mjx.put_data.

18. Added support for implicitfast integration for all cases except fluid drag.

19. Fixed a bug where qLDiagInv had the wrong size for sparse mass matrices.

20. Added support for joint and tendon frictionloss.

21. Added support for connect equality constraints using two sites.

22. Added support for spatial tendons with site wrapping.

Bug fixes

23. Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies (issue #1875, contribution by @michael-ahn).

24. Fixed a bug wherein, for models that have both muscles and stateless actuators and used one of the implicit integrators, wrong derivatives would be computed.

25. Fixed a bug in tendon wrapping around spheres. Before this fix, tendons that wrapped around spheres with an externally-placed sidesite could jump inside the sphere instead of wrapping around it.

26. Fixed a bug that caused meshdir and texturedir to be overwritten during model attachment, preventing model attachment for models with assets in different directories.

Python bindings

27. Added support for engine plugins in mjSpec (issue #1903).

28. Better error reporting for issues with the assets dictionary, when loading models.

Version 3.2.2 (Aug 8, 2024)

General

1. Increase texture and material limit back to 1000. 3.2.0 inadvertently reduced this limit to 100, breaking some existing models (issue #1877).

Version 3.2.1 (Aug 5, 2024)

General

1. Renamed mjModel.tex_rgb to mjModel.tex_data.

2. Added a new autoreset flag to disable automatic reset when NaNs or infinities are detected.

3. Added sub-elements to the MJCF material element, to allow specification of multiple textures for rendering (e.g., occlusion, roughness, metallic). Note that the MuJoCo renderer doesn’t support these new features, and they are made available for use with external renderers.

4. Sorting (mjQUICKSORT) now calls std::sort when building with C++ (issue #1638).

MJX

5. Added more fields to mjx.Model and mjx.Data for further compatibility with the corresponding MuJoCo structs.

6. Added support for fixed tendons.

7. Added support for tendon length limits (mjCNSTR_LIMIT_TENDON in mjtConstraint).

8. Added support for tendon equality constraints (mjEQ_TENDON in mjtEq).

9. Added support for tendon actuator transmission (mjTRN_TENDON in mjtTrn).

Python bindings

10. Added support for asset dictionary argument in mujoco.spec.from_file, mujoco.spec.from_string and mujoco.spec.compile.

Bug fixes

11. Fixed a bug where implicit integrators did not take into account disabled actuators (issue #1838).

Version 3.2.0 (Jul 15, 2024)

New features

1. Introduced a major new feature: procedural model creation and editing, using a new top-level data-structure mjSpec. See the Model Editing chapter for details. Note that as of this release this feature is still in testing and subject to future breaking changes. Fixes issue #364.

General

Breaking API changes

2. Removed deprecated mj_makeEmptyFileVFS and mj_findFileVFS functions. The constants mjMAXVFS and mjMAXVFSNAME are also removed as they are no longer needed.

   Migration: Use mj_addBufferVFS to copy a buffer into a VFS file directly.

3. Calls to mj_defaultVFS may allocate memory inside VFS, and the corresponding mj_deleteVFS must be called to deallocate any internal allocated memory.

4. Deprecated mju_rotVecMat and mju_rotVecMatT in favor of mju_mulMatVec3 and mju_mulMatTVec3. These function names and argument order are more consistent with the rest of the API. The older functions have been removed from the Python bindings and will be removed from the C API in the next release.

5. Removed the actuator_actdim callback from actuator plugins. They now have the actdim attribute, which must be used with actuators that write state to the act array. This fixed a crash which happened when keyframes were used in a model with stateful actuator plugins. The PID plugin will give an error when the wrong value of actdim is provided.

6. Added attach meta-element to MJCF, which allows attaching a subtree from a different model to a body in the current model.

7. The VFS implementation has been rewritten in C++ and is now considerably more efficient in speed and memory footprint.

8. Added support for orthographic cameras. This is available for both fixed cameras and the free camera, using the camera/orthographic and global/orthographic attributes, respectively.

9. Added maxhullvert, the maximum number of vertices in a mesh’s convex hull.

10. Added mj_setKeyframe for saving the current state into a model keyframe.

11. Added support for ball joints in the URDF parser (“spherical” in URDF).

12. Replaced mjUSEDOUBLE which was previously hard-coded in mjtnum.h with the build-time flag mjUSESINGLE. If this symbol is not defined, MuJoCo will use double-precision floating point, as usual. If mjUSESINGLE is defined, MuJoCo will use single-precision floating point. See mjtNum.

    Relatedly, fixed various type errors that prevented building with single-precision.

13. Quaternions in mjData.qpos and mjData.mocap_quat are no longer normalized in-place by mj_kinematics. Instead they are normalized when they are used. After the first step, quaternions in mjData.qpos will be normalized.

14. Mesh loading in the compiler, which is usually the slowest part of the loading process, is now multi-threaded.

MJX

15. Added support for elliptic friction cones.

16. Fixed a bug that resulted in less-optimal linesearch solutions for some difficult constraint settings.

17. Fixed a bug in the Newton solver that sometimes resulted in less-optimal gradients.

Simulate

18. Added improved tutorial video.

19. Improved the Brownian noise generator.

20. Now displaying model load times if they are longer than 0.25 seconds.

Python bindings

21. Fixed a memory leak when using copy.deepcopy() on a mujoco.MjData instance (issue #1572).

Bug fixes

22. Fix an issue where mj_copyData (or copy.copy() in the Python bindings) was not copying contact information correctly (issue #1710).

23. Fix an issue with saving to XML that caused frames to be written multiple times (issue #1802).

Version 3.1.6 (Jun 3, 2024)

General

1. Added mj_geomDistance for computing the shortest signed distance between two geoms and optionally a segment connecting them. Relatedly, added the 3 sensors: distance, normal, fromto. See the function and sensor documentation for details. Fixes issue #51.

2. Improvements to position actuators:

   • Added timeconst attribute to the position actuator. When set to a positive value, the actuator is made stateful with filterexact dynamics.

   • Added dampratio to both position and intvelocity actuators. An alternative to the kv attribute, it provides a convenient way to set actuator damping using natural units. See attribute documentation for details.

MJX

3. Add height-field collision support. Fixes issue #1491.

4. Add a pre-compiled field mesh_convex to mjx.Model so that mesh properties can be vmapped over. Fixes issue #1655.

5. Fix a bug in convex mesh collisions, where erroneous edge contacts were being created even though face separating axes were found. Fixes issue #1695.

Bug fixes

6. Fixed a bug the could cause collisions to be missed when fusestatic is enabled, as is often the case for URDF imports. Fixes issue #1069, issue #1577.

7. Fixed a bug that was causing the visualization of SDF iterations to write outside the size of the vector storing them. Fixes issue #1539.

Version 3.1.5 (May 7, 2024)

General

1. Added the replicate to MJCF, a meta-element which permits to repeat a subtree with incremental translational and rotational offsets.

2. Enabled an internal cache in the MuJoCo compiler resulting in recompilation speedup. Currently, processed textures, hfields, and OBJ meshes are cached. Support for Unity environments is not yet available.

3. Added mjModel.mesh_scale: the scaling applied to asset vertices, as specified in the scale attribute.

4. Added visual properties which are ignored by the native renderer, but can be used by external renderers:

   • light/bulbradius attribute and corresponding mjModel.light_bulbradius field.

   • material/metallic attribute and corresponding mjModel.material_metallic field.

   • material/roughness attribute and corresponding mjModel.material_roughness field.

5. The type of the size argument of mj_stackAllocNum and mj_stackAllocInt was changed from int to size_t.

6. Added support for gmsh format version 2.2 surface meshes in flexcomp.

MJX

Breaking API changes

7. Removed deprecated mjx.device_get_into and mjx.device_put functions as they lack critical new functionality.

   Migration: Use mjx.get_data_into instead of mjx.device_get_into, and mjx.put_data instead of mjx.device_put.

8. Added cylinder plane collisions.

9. Added efc_type to mjx.Data and dim, efc_address to mjx.Contact.

10. Added geom to mjx.Contact and marked geom1, geom2 deprecated.

11. Added ne, nf, nl, nefc, and ncon to mjx.Data to match mujoco.MjData.

12. Given the above added fields, removed mjx.get_params, mjx.ncon, and mjx.count_constraints.

13. Changed the way meshes are organized on device to speed up collision detection when a mesh is replicated for many geoms.

14. Fixed a bug where capsules might be ignored in broadphase colliision checking.

15. Added cylinder collisions using SDFs.

16. Added support for all condim: 1, 3, 4, 6.

17. Add support functions for id2name and name2id, MJX versions of mj_id2name and mj_name2id.

18. Added support for gravcomp and actuatorgravcomp.

19. Fixed a bug in mjx.ray for sometimes allowed negative distances for ray-mesh tests.

20. Added a new differentiable physics tutorial that demonstrates training locomotion policies with analytical gradients automatically derived from the MJX physics step. Contribution by @Andrew-Luo1.

Bug fixes

21. Defaults of lights were not being saved, now fixed.

22. Prevent overwriting of frame names by body names when saving an XML. Bug introduced in 3.1.4.

23. Fixed bug in Python binding of mj_saveModel: buffer argument was documented as optional but was actually not optional.

24. Fixed bug that prevented memory allocations larger than 2.15 GB. Fixes issue #1606.

Version 3.1.4 (April 10th, 2024)

General

Breaking API changes

1. Removed the ability to natively add noise to sensors. Note that the mjModel.sensor_noise field and corresponding attribute are kept and now function as a convenient location for the user to save standard-deviation information for their own use. This feature was removed because:

   • There was no mechanism to seed the random noise generator.

   • It was not thread-safe, even if seeding would have been provided, sampling on multiple threads would lead to non-reproducible results.

   • This feature was seen as overreach by the engine. Adding noise should be the user’s responsibility.

   • We are not aware of anyone who was actually using the feature.

   Migration: Add noise to sensor values yourself.

2. Added the actuatorgravcomp joint attribute. When enabled, gravity compensation forces on the joint are treated as applied by actuators. See attribute documentation for more details. The example model refsite.xml, which demonstrates Cartesian actuation of an arm, has been updated to use this attribute.

3. Added support for gmsh format 2.2 , tetrahedral mesh, as generated by e.g. fTetwild.

4. Added mju_euler2Quat for converting an Euler-angle sequence to quaternion.

MJX

5. Improved performance of SAT for convex collisions.

6. Fixed bug for sphere/capsule-convex deep penetration.

7. Fixed bug where mjx.Data produced by mjx.put_data had different treedef than mjx.make_data.

8. Throw an error for margin/gap for convex mesh collisions, since they are not supported.

9. Added ellipsoid plane collisions.

10. Added support for userdata.

11. Added ellipsoid-ellipsoid and ellipsoid-capsule collisions using signed distance functions (SDFs).

Simulate

12. Fixed bug in order of enable flag strings. Before this change, using the simulate UI to toggle the invdiscrete or the (now removed) sensornoise flags would actually toggle the other flag.

Python bindings

13. Added the mujoco.minimize Python module for nonlinear least-squares, designed for System Identification (sysID). The sysID tutorial is work in progress, but a pedagogical colab notebook with examples, including Inverse Kinematics, is available here:
    The video on the right shows example clips from the tutorial.

Version 3.1.3 (March 5th, 2024)

General

1. Added the inheritrange attribute to position and intvelocity actuators, allowing convenient setting of the actuator’s ctrlrange or actrange (respectively), according to the range of the transmission target (joint or tendon). See position/inheritrange for details.

2. Deprecated mj_makeEmptyFileVFS in favor of mj_addBufferVFS. mjVFS now computes checksums of its internal file buffers. mj_addBufferVFS allocates an empty buffer with a given name in an mjVFS and copies the data buffer into it, combining and replacing the deprecated two-step process of calling mj_makeEmptyFileVFS followed by a direct copy into the given mjVFS internal file buffer.

3. Added mj_angmomMat which computes the 3 x nv angular momentum matrix \(H(q)\), providing the linear mapping from generalized velocities to subtree angular momentum \(h = H \dot q\). Contribution by @v-r-a.

MJX

4. Improved performance of getting and putting device data.

   • Use tobytes() for numpy array serialization, which is orders of magnitude faster than converting to tuples.

   • Avoid reallocating host mjData arrays when array shapes are unchanged.

   • Speed up calculation of mjx.ncon for models with many geoms.

   • Avoid calling mjx.ncon in mjx.get_data_into when nc can be derived from mjx.Data.

5. Fixed a bug in mjx-viewer that prevented it from running. Updated mjx-viewer to use newer mjx.get_data_into function call.

6. Fixed a bug in mjx.euler that applied incorrect damping when using dense mass matrices.

7. Fixed a bug in mjx.solve that was causing slow convergence when using mjSOL_NEWTON in mjtSolver.

8. Added support for mjOption.impratio to mjx.Model.

9. Added support for cameras in mjx.Model and mjx.Data. Fixes issue #1422.

10. Added an implementation of broadphase using top_k and bounding spheres.

Python bindings

11. Fixed incorrect data types in the bindings for the geom, vert, elem, and flex array members of the mjContact struct, and all array members of the mjrContext struct.

Version 3.1.2 (February 05, 2024)

General

1. Improved the discardvisual compiler flag, which now discards all visual-only assets. See discardvisual for details.

2. Removed the timer for midphase colllision detection, it is now folded in with the narrowphase timer. This is because timing the two phases separately required fine-grained timers inside the collision functions; these functions are so small and fast that the timer itself was incurring a measurable cost.

3. Added the flag bvactive to visual/global, allowing users to turn off visualisation of active bounding volumes (the red/green boxes in this this changelog item). For models with very high-resolution meshes, the computation required for this visualization can slow down simulation speed. Fixes issue #1279.

   • Added color of bounding volumes and active bounding volumes to visual/rgba.

4. Height-field elevation data can now be specified directly in XML with the elevation attribute (and not only with PNG files). See example model.

MJX

5. Added dyntype filterexact.

6. Added site transmission.

7. Updated MJX colab tutorial with more stable quadruped environment.

8. Added mjx.ray which mirrors mj_ray for planes, spheres, capsules, boxes, and meshes.

9. Added mjx.is_sparse which mirrors mj_isSparse and mjx.full_m which mirrors mj_fullM.

10. Added support for specifying sparse or dense mass matrices via jacobian: [dense, sparse, auto], “auto”.

11. Raise a not implemented error when nonzero frictionloss is present. Fixes issue #1344.

Python bindings

12. Improved the implementation of the rollout module. Note the changes below are breaking, dependent code will require modification.

    • Uses mjSTATE_FULLPHYSICS as state spec, enabling divergence detection by inspecting time.

    • Allows user-defined control spec for any combination of user input fields as controls.

    • Outputs are no longer squeezed and always have dim=3.

13. The sync function for the passive viewer can now pick up changes to rendering flags in user_scn, as requested in issue #1190.

Bug fixes

14. Fixed a bug that prevented the use of pins with plugins if flexes are not in the worldbody. Fixes issue #1270.

15. Fixed a bug in the muscle model that led to non-zero values outside the lower bound of the length range. Fixes issue #1342.

Version 3.1.1 (December 18, 2023)

Bug fixes

1. Fixed a bug (introduced in 3.1.0) where box-box collisions produced no contacts if one box was deeply embedded in the other.

2. Fixed a bug in simulate where the “LOADING…” message was not showing correctly.

3. Fixed a crash in the Python passive viewer, when used with models containing Flex objects.

4. Fixed a bug in MJX where site_xmat was ignored in get_data and put_data

5. Fixed a bug in MJX where efc_address was sometimes incorrectly calculated in get_data.

Version 3.1.0 (December 12, 2023)

General

1. Improved convergence of Signed Distance Function (SDF) collisions by using line search and a new objective function for the optimization. This allows to decrease the number of initial points needed for finding the contacts and is more robust for very small or large geom sizes.

2. Added frame to MJCF, a meta-element which defines a pure coordinate transformation on its direct children, without requiring a body.

3. Added the kv attribute to the position and intvelocity actuators, for specifying actuator-applied damping. This can be used to implement a PD controller with 0 reference velocity. When using this attribute, it is recommended to use the implicitfast or implicit integrators.

Plugins

4. Allow actuator plugins to use activation variables in mjData.act as their internal state, rather than mjData.plugin_state. Actuator plugins can now specify callbacks that compute activation variables, and they can be used with built-in dyntype actuator dynamics.

5. Added the pid actuator plugin, a configurable PID controller that implements the Integral term, which is not available with native MuJoCo actuators.

MJX

6. Added site_xpos and site_xmat to MJX.

7. Added put_data, put_model, get_data to replace device_put and device_get_into, which will be deprecated. These new functions correctly translate fields that are the result of intermediate calculations such as efc_J.

Bug fixes

8. Fix bug in Cartesian actuation with movable refsite, as when using body-centric Cartesian actuators on a quadruped. Before this fix such actuators could lead to non-conservation of momentum.

9. Fix bug that prevented using flex with simulate.

10. Fix bug that prevented the use of elasticity plugins in combination with pinned flex vertices.

11. Release Python wheels targeting macOS 10.16 to support x86_64 systems where SYSTEM_VERSION_COMPAT is set. The minimum supported version is still 11.0, but we release these wheels to fix compatibility for those users. See issue #1213.

12. Fixed mass computation of meshes: Use the correct mesh volume instead of approximating it using the inertia box.

Version 3.0.1 (November 15, 2023)

General

1. Added sub-terms of total passive forces in mjData.qfrc_passive to mjData: qfrc_{spring, damper, gravcomp, fluid}. The sum of these vectors equals qfrc_passive.

2. Added actuatorgroupdisable attribute and associated mjOption.disableactuator integer bitfield, which can be used to disable sets of actuators at runtime according to their group. Fixes issue #1092. See Group disable.

   • The first 6 actuator groups are toggleable in the simulate viewer. See example model and associated screen-capture on the right.

3. Increased mjMAXUIITEM (maximum number of UI elements per section in Simulate) to 200.

MJX

4. Added support for Newton solver (mjSOL_NEWTON in mjtSolver). The Newton solver significantly speeds up simulation on GPU:

   Steps-per-second, Conjugate Gradient vs. Newton on A100

   Model	CG	Newton	Speedup
   Humanoid	640,000	1,020,000	1.6 x
   Barkour v0	1,290,000	1,750,000	1.35 x
   Shadow Hand	215,000	270,000	1.25 x

   Humanoid is the standard MuJoCo humanoid, Google Barkour and the Shadow Hand are both available in the MuJoCo Menagerie.

5. Added support for joint equality constraints (mjEQ_JOINT in mjtEq).

6. Fixed bug where mixed jnt_limited joints were not being constrained correctly.

7. Made device_put type validation more verbose (fixes issue #1113).

8. Removed empty EFC rows from MJX, for joints with no limits (fixes issue #1117).

9. Fixed bug in scan.body_tree that led to incorrect smooth dynamics for some kinematic tree layouts.

Python bindings

10. Fix the macOS mjpython launcher to work with the Python interpreter from Apple Command Line Tools.

11. Fixed a crash when copying instances of mujoco.MjData for models that use plugins. Introduced a model attribute to MjData which is reference to the model that was used to create that MjData instance.

Simulate

12. simulate: correct handling of “Pause update”, “Fullscreen” and “VSync” buttons.

Documentation

13. Added cell to the tutorial colab providing an example of procedural camera control:

14. Added documentation for the User Interface framework.

15. Fixed typos and supported fields in docs (fixes issue #1105 and issue #1106).

Bug fixes

16. Fixed bug relating to welds modified with torquescale.

Version 3.0.0 (October 18, 2023)

New features

1. Added simulation on GPU and TPU via the new MuJoCo XLA (MJX) (MJX) Python module. Python users can now natively run MuJoCo simulations at millions of steps per second on Google TPU or their own accelerator hardware.

   • MJX is designed to work with on-device reinforcement learning algorithms. This Colab notebook demonstrates using MJX along with reinforcement learning to train humanoid and quadruped robots to locomote:

   • The MJX API is compatible with MuJoCo but is missing some features in this release. See the outline of MJX feature parity for more details.

2. Added new signed distance field (SDF) collision primitive. SDFs can take any shape and are not constrained to be convex. Collision points are found by minimizing the maximum of the two colliding SDFs via gradient descent.

   • Added new SDF plugin for defining implicit geometries. The plugin must define methods computing an SDF and its gradient at query points. See the documentation for more details.

3. Added new low-level model element called flex, used to define deformable objects. These simplicial complexes can be of dimension 1, 2 or 3, corresponding to stretchable lines, triangles or tetrahedra. Two new MJCF elements are used to define flexes. The top-level deformable section contains the low-level flex definition. The flexcomp element, similar to composite is a convenience macro for creating deformables, and supports the GMSH tetrahedral file format.

   • Added shell passive force plugin, computing bending forces using a constant precomputed Hessian (cotangent operator).

   Note: This feature is still under development and subject to change. In particular, deformable object functionality is currently available both via deformable and composite, and both are modifiable by the first-party elasticity plugins. We expect some of this functionality to be unified in the future.

4. Added constraint island discovery with mj_island. Constraint islands are disjoint sets of constraints and degrees-of-freedom that do not interact. The only solver which currently supports islands is CG. Island discovery can be activated using a new enable flag. If island discovery is enabled, geoms, contacts and tendons will be colored according to the corresponding island, see video. Island discovery is currently disabled for models that have deformable objects (see previous item).

5. Added mjThreadPool and mjTask which allow for multi-threaded operations within the MuJoCo engine pipeline. If engine-internal threading is enabled, the following operations will be multi-threaded:

   • Island constraint resolution, if island discovery is enabled and the CG solver is selected. The 22 humanoids model shows a 3x speedup compared to the single threaded simulation.

   • Inertia-related computations and collision detection will happen in parallel.

   Engine-internal threading is a work in progress and currently only available in first-party code via the testspeed utility, exposed with the npoolthread flag.

6. Added capability to initialize composite particles from OBJ files. Fixes issue #642 and issue #674.

General

Breaking API changes

7. Removed the macros mjMARKSTACK and mjFREESTACK.

   Migration: These macros have been replaced by new functions mj_markStack and mj_freeStack. These functions manage the mjData stack in a fully encapsulated way (i.e., without introducing a local variable at the call site).

8. Renamed mj_stackAlloc to mj_stackAllocNum. The new function mj_stackAllocByte allocates an arbitrary number of bytes and has an additional argument for specifying the alignment of the returned pointer.

   Migration: The functionality for allocating mjtNum arrays is now available via mj_stackAllocNum.

9. Renamed the nstack field in mjModel and mjData to narena. Changed narena, pstack, and maxuse_stack to count number of bytes rather than number of mjtNum⁠s.

10. Changed mjData.solver, the array used to collect solver diagnostic information. This array of mjSolverStat structs is now of length mjNISLAND * mjNSOLVER, interpreted as as a matrix. Each row of length mjNSOLVER contains separate solver statistics for each constraint island. If the solver does not use islands, only row 0 is filled.

    • The new constant mjNISLAND was set to 20.

    • mjNSOLVER was reduced from 1000 to 200.

    • Added mjData.solver_nisland: the number of islands for which the solver ran.

    • Renamed mjData.solver_iter to solver_niter. Both this member and mjData.solver_nnz are now integer vectors of length mjNISLAND.

11. Removed mjOption.collision and the associated option/collision attribute.

    Migration:

    • For models which have <option collision="all"/>, delete the attribute.

    • For models which have <option collision="dynamic"/>, delete all pair elements.

    • For models which have <option collision="predefined"/>, disable all dynamic collisions (determined via contype/conaffinity) by first deleting all contype and conaffinity attributes in the model and then setting them globally to 0 using
      <default> <geom contype="0" conaffinity="0"/> </default>.

12. Removed the rope and cloth composite objects.

    Migration: Users should use the cable and shell elasticity plugins.

13. Added mjData.eq_active user input variable, for enabling/disabling the state of equality constraints. Renamed mjModel.eq_active to mjModel.eq_active0, which now has the semantic of “initial value of mjData.eq_active”. Fixes issue #876.

    Migration: Replace uses of mjModel.eq_active with mjData.eq_active.

14. Changed the default of autolimits from “false” to “true”. This is a minor breaking change. The potential breakage applies to models which have elements with “range” defined and “limited” not set. Such models cannot be loaded since version 2.2.2 (July 2022).

15. Added a new dyntype, filterexact, which updates first-order filter states with the exact formula rather than with Euler integration.

16. Added an actuator attribute, actearly, which uses semi-implicit integration for actuator forces: using the next step’s actuator state to compute the current actuator forces.

17. Renamed actuatorforcerange and actuatorforcelimited, introduced in the previous version to actuatorfrcrange and actuatorfrclimited, respectively.

18. Added the flag eulerdamp, which disables implicit integration of joint damping in the Euler integrator. See the Numerical Integration section for more details.

19. Added the flag invdiscrete, which enables discrete-time inverse dynamics for all integrators other than RK4. See the flag documentation for more details.

20. Added ls_iterations and ls_tolerance options for adjusting linesearch stopping criteria in CG and Newton solvers. These can be useful for performance tuning.

21. Added mesh_pos and mesh_quat fields to mjModel to store the normalizing transformation applied to mesh assets. Fixes issue #409.

22. Added camera resolution attribute and camprojection sensor. If camera resolution is set to positive values, the camera projection sensor will report the location of a target site, projected onto the camera image, in pixel coordinates.

23. Added camera calibration attributes:

    • The new attributes are resolution, focal, focalpixel, principal, principalpixel and sensorsize.

    • Visualize the calibrated frustum using the mjVIS_CAMERA visualization flag when these attributes are specified. See the following example model.

    • Note that these attributes only take effect for offline rendering and do not affect interactive visualisation.

24. Implemented reversed Z rendering for better depth precision. An enum mjtDepthMap was added with values mjDEPTH_ZERONEAR and mjDEPTH_ZEROFAR, which can be used to set the new readDepthMap attribute in mjrContext to control how the depth returned by mjr_readPixels is mapped from znear to zfar. Contribution PR #978 by Levi Burner.

25. Deleted the code sample testxml. The functionality provided by this utility is implemented in the WriteReadCompare test.

26. Deleted the code sample derivative. Functionality provided by mjd_transitionFD.

Python bindings

27. Fixed issue #870 where calling update_scene with an invalid camera name used the default camera.

28. Added user_scn to the passive viewer handle, which allows users to add custom visualization geoms (issue #1023).

29. Added optional boolean keyword arguments show_left_ui and show_right_ui to the functions viewer.launch and viewer.launch_passive, which allow users to launch a viewer with UI panels hidden.

Simulate

30. Added state history mechanism to simulate and the managed Python viewer. State history can be viewed by scrubbing the History slider and (more precisely) with the left and right arrow keys. See screen capture:

31. The LOADING... label is now shown correctly. Contribution PR #1070 by Levi Burner.

Documentation

32. Added detailed documentation of fluid force modeling, and an illustrative example model showing tumbling cards using the ellipsoid-based fluid model.

Bug fixes

33. Fixed a bug that was causing geom margin to be ignored during the construction of midphase collision trees.

34. Fixed a bug that was generating incorrect values in efc_diagApprox for weld equality constraints.

Version 2.3.7 (July 20, 2023)

General

1. Added primitive collider for sphere-cylinder contacts, previously this pair used the generic convex-convex collider.

2. Added joint-actuatorforcerange for clamping total actuator force at joints and sensor-jointactuatorfrc for measuring total actuation force applied at a joint. The most important use case for joint-level actuator force clamping is to ensure that Cartesian actuator forces are realizable by individual motors at the joints. See Force limits for details.

3. Added an optional content_type attribute to hfield, texture, and mesh assets. This attribute supports a formatted Media Type (previously known as MIME type) string used to determine the type of the asset file without resorting to pulling the type from the file extension.

4. Added analytic derivatives for quaternion subtraction and integration (rotation with an angular velocity). Derivatives are in the 3D tangent space.

5. Added mjv_connector which has identical functionality to mjv_makeConnector, but with more convenient “from-to” argument parametrization. mjv_makeConnector is now deprecated.

6. Bumped oldest supported MacOS from version 10.12 to 11. MacOS 11 is the oldest version still maintained by Apple.

Python bindings

7. The passive viewer handle now exposes update_hfield, update_mesh, and update_texture methods to allow users to update renderable assets. (Issues issue #812, issue #958, issue #965).

8. Allow a custom keyboard event callback to be specified in the passive viewer (issue #766).

9. Fix GLFW crash when Python exits while the passive viewer is running (issue #790).

Models

10. Added simple car example model.

Version 2.3.6 (June 20, 2023)

Note

MuJoCo 2.3.6 is the last version to officially support Python 3.7.

Models

1. Added 3x3x3 cube example model. See README for details.

Bug fixes

2. Fixed a bug that was causing an incorrect computation of the mesh bounding box and coordinate frame if the volume was invalid. In such case, now MuJoCo only accepts a non-watertight geometry if shellinertia is equal to true.

3. Fixed the sparse Jacobian multiplication logic that is used to compute derivatives for tendon damping and fluid force, which affects the behaviour of the implicit and implicitfast integrators.

4. Fixes to mj_ray, in line with geom visualisation conventions:

   • Planes and height-fields respect the geom_group and flg_static arguments. Before this change, rays would intersect planes and height-fields unconditionally.

   • flg_static now applies to all static geoms, not just those which are direct children of the world body.

Plugins

5. Added touch-grid sensor plugin. See documentation for details, and associated touch_grid.xml example model. The plugin includes in-scene visualisation.

Simulate

6. Added Visualization tab to simulate UI, corresponding to elements of the visual MJCF element. After modifying values in the GUI, a saved XML will contain the new values. The modifiable members of mjStatistic (extent, meansize and center) are computed by the compiler and therefore do not have defaults. In order for these attributes to appear in the saved XML, a value must be specified in the loaded XML.

7. Increased text width for UI elements in the default spacing. [before / after]:

General

8. Added mj_getState and mj_setState for getting and setting the simulation state as a concatenated vector of floating point numbers. See the State section for details.

9. Added mjContact.solreffriction, allowing different solref parameters for the normal and frictional axes of contacts when using elliptic friction cones. This attribute is required for elastic frictional collisions, see associated example model mimicking the spin-bounce recoil behaviour of elastic rubber balls. This is an advanced option currently only supported by explicit contact pairs, using the solreffriction attribute.

10. Added mjd_inverseFD for finite-differenced inverse-dynamics derivatives.

11. Added functions for operations on banded-then-dense “arrowhead” matrices. Such matrices are common when doing direct trajectory optimization. See mju_cholFactorBand documentation for details.

12. Added mj_multiRay function for intersecting multiple rays emanating from a single point. This is significantly faster than calling mj_ray multiple times.

13. Ray-mesh collisions are now up to 10x faster, using a bounding volume hierarchy of mesh faces.

14. Increased mjMAXUIITEM (maximum number of UI elements per section in Simulate) to 100.

15. Added documentation for resource providers.

16. Changed the formula for mju_sigmoid, a finite-support sigmoid \(s \colon \mathbf R \rightarrow [0, 1]\). Previously, the smooth part consisted of two stitched quadratics, once continuously differentiable. It is now a single quintic, twice continuously differentiable:

    \[s(x) = \begin{cases} 0, & & x \le 0 \\ 6x^5 - 15x^4 + 10x^3, & 0 \lt & x \lt 1 \\ 1, & 1 \le & x \qquad \end{cases} \]

17. Added optional tausmooth attribute to muscle actuators. When positive, the time-constant \(\tau\) of muscle activation/deactivation uses mju_sigmoid to transition smoothly between the two extremal values given by the Millard et al. (2013) muscle model, within a range of width tausmooth. See Muscle actuators for more details. Relatedly, mju_muscleDynamics now takes 3 parameters instead of 2, adding the new smoothing-width parameter.

18. Moved public C macro definitions out of mujoco.h into a new public header file called mjmacro.h. The new file is included by mujoco.h so this change does not break existing user code.

19. Added instrumentation for the Address Sanitizer (ASAN) and Memory Sanitizer (MSAN) to detect memory bugs when allocating from the mjData stack and arena.

20. Removed pstack and parena from the output of mj_printData, since these are implementation details of the mjData allocators that are affected by diagnostic paddings in instrumented builds.

21. Removed the mj_activate and mj_deactivate functions. These had been kept around for compatibility with old user code from when MuJoCo was closed source, but have been no-op functions since open sourcing.

Version 2.3.5 (April 25, 2023)

Bug fixes

1. Fix asset loading bug that prevented OBJ and PNG files from being read from disk when mjVFS is used.

2. Fix occasional segmentation faults on macOS when mouse perturbations are applied in the Python passive viewer.

Plugins

3. The visualize callback in mjpPlugin now receives an mjvOption as an input argument.

Version 2.3.4 (April 20, 2023)

Note

This version is affected by an asset loading bug that prevents OBJ and PNG files from being read from disk when mjVFS is used. Users are advised to skip to version 2.3.5 instead.

General

1. Removed the “global” setting of the compiler/coordinate attribute. This rarely-used setting complicates the compiler logic and is blocking future improvements. In order to convert older models which used this option, load and save them in MuJoCo 2.3.3 or older.

2. Added visual-global flag ellipsoidinertia to visualize equivalent body inertias with ellipsoids instead of the default boxes.

3. Added midphase and broadphase collision statistics to mjData.

4. Added documentation for engine plugins.

5. Added struct information to the introspect module.

6. Added a new extension mechanism called resource providers. This extensible mechanism allows MuJoCo to read assets from data sources other than the local OS filesystem or the Virtual file system.

Python bindings

7. Offscreen rendering on macOS is no longer restricted to the main thread. This is achieved by using the low-level Core OpenGL (CGL) API to create the OpenGL context, rather than going via GLFW which relies on Cocoa’s NSOpenGL. The resulting context is not tied to a Cocoa window, and is therefore not tied to the main thread.

8. Fixed a race condition in viewer.launch_passive and viewer.launch_repl. These functions could previously return before an internal call to mj_forward. This allows user code to continue and potentially modify physics state concurrently with the internal mj_forward, resulting in e.g. MuJoCo stack overflow error or segmentation fault.

9. The viewer.launch_passive function now returns a handle which can be used to interact with the viewer. The passive viewer now also requires an explicit call to sync on its handle to pick up any update to the physics state. This is to avoid race conditions that can result in visual artifacts. See documentation for details.

10. The viewer.launch_repl function has been removed since its functionality is superseded by launch_passive.

11. Added a small number of missing struct fields discovered through the new introspect metadata.

Bug fixes

12. Fixed bug in the handling of ellipsoid-based fluid model forces in the new implicitfast integrator.

13. Removed spurious whole-arena copying in mj_copyData, which can considerably slow down the copying operation.

14. Make shellinertia ignore exactmeshinertia, which is

    only used for legacy volume computations (#759).

Version 2.3.3 (March 20, 2023)

General

1. Improvements to implicit integration:

   • The derivatives of the RNE algorithm are now computed using sparse math, leading to significant speed improvements for large models when using the implicit integrator.

   • A new integrator called implicitfast was added. It is similar to the existing implicit integrator, but skips the derivatives of Coriolis and centripetal forces. See the numerical integration section for a detailed motivation and discussion. The implicitfast integrator is recommended for all new models and will become the default integrator in a future version.

   The table below shows the compute cost of the 627-DoF humanoid100 model using different integrators. “implicit (old)” uses dense RNE derivatives, “implicit (new)” is after the sparsification mentioned above. Timings were measured on a single core of an AMD 3995WX CPU.

timing	Euler	implicitfast	implicit (new)	implicit (old)
one step (ms)	0.5	0.53	0.77	5.0
steps/second	2000	1900	1300	200

2. Added a collision mid-phase for pruning geoms in body pairs, see documentation for more details. This is based on static AABB bounding volume hierarchy (a BVH binary tree) in the body inertial frame. The GIF on the right is cut from this longer video.

3. The mjd_transitionFD function no longer triggers sensor calculation unless explicitly requested.

4. Corrected the spelling of the inteval attribute to interval in the mjLROpt struct.

5. Mesh texture and normal mappings are now 3-per-triangle rather than 1-per-vertex. Mesh vertices are no longer duplicated in order to circumvent this limitation as they previously were.

6. The non-zeros for the sparse constraint Jacobian matrix are now precounted and used for matrix memory allocation. For instance, the constraint Jacobian matrix from the humanoid100 model, which previously required ~500,000 mjtNum’s, now only requires ~6000. Very large models can now load and run with the CG solver.

7. Modified mju_error and mju_warning to be variadic functions (support for printf-like arguments). The functions mju_error_i, mju_error_s, mju_warning_i, and mju_warning_s are now deprecated.

8. Implemented a performant mju_sqrMatTDSparse function that doesn’t require dense memory allocation.

9. Added mj_stackAllocInt to get correct size for allocating ints on mjData stack. Reducing stack memory usage by 10% - 15%.

Python bindings

10. Fixed IPython history corruption when using viewer.launch_repl. The launch_repl function now provides seamless continuation of an IPython interactive shell session, and is no longer considered experimental feature.

11. Added viewer.launch_passive which launches the interactive viewer in a passive, non-blocking mode. Calls to launch_passive return immediately, allowing user code to continue execution, with the viewer automatically reflecting any changes to the physics state. (Note that this functionality is currently in experimental/beta stage, and is not yet described in our viewer documentation.)

12. Added the mjpython launcher for macOS, which is required for viewer.launch_passive to function there.

13. Removed efc_ fields from joint indexers. Since the introduction of arena memory, these fields now have dynamic sizes that change between time steps depending on the number of active constraints, breaking strict correspondence between joints and efc_ rows.

14. Added a number of missing fields to the bindings of mjVisual and mjvPerturb structs.

Simulate

15. Implemented a workaround for broken VSync on macOS so that the frame rate is correctly capped when the Vertical Sync toggle is enabled.

16. Added optional labels to contact visualization, indicating which two geoms are contacting (names if defined, ids otherwise). This can be useful in cluttered scenes.

Version 2.3.2 (February 7, 2023)

General

1. A more performant mju_transposeSparse has been implemented that doesn’t require dense memory allocation. For a constraint Jacobian matrix from the humanoid100.xml model, this function is 35% faster.

2. The function mj_name2id is now implemented using a hash function instead of a linear search for better performance.

3. Geom names are now parsed from URDF. Any duplicate names are ignored. mj_printData output now contains contacting geom names.

Bug fixes

4. Fixed a bug that for shellinertia equal to true caused the mesh orientation to be overwritten by the principal components of the shell inertia, while the vertex coordinates are rotated using the volumetric inertia. Now the volumetric inertia orientation is used also in the shell case.

5. Fixed misalignment bug in mesh-to-primitive fitting when using the bounding box fitting option fitaabb.

6. The launch_repl functionality in the Python viewer has been fixed.

7. Set time correctly in mjd_transitionFD, to support time-dependent user code.

8. Fixed sensor data dimension validation when user type sensors are present.

9. Fixed incorrect plugin error message when a null nsensordata callback is encountered during model compilation.

10. Correctly end the timer (TM_END) mj_fwdConstraint returns early.

11. Fixed an infinite loop in mj_deleteFileVFS.

Simulate

12. Increased precision of simulate sensor plot y-axis by 1 digit (#719).

13. Body labels are now drawn at the body frame rather than inertial frame, unless inertia is being visualised.

Plugins

14. The reset callback now receives instance-specific plugin_state and plugin_data as arguments, rather than the entire mjData. Since reset is called inside mj_resetData before any physics forwarding call has been made, it is an error to read anything from mjData at this stage.

15. The capabilities field in mjpPlugin is renamed capabilityflags to more clearly indicate that this is a bit field.

Version 2.3.1 (December 6, 2022)

Python bindings

1. The simulate GUI is now available through the mujoco Python package as mujoco.viewer. See documentation for details. (Contribution by Levi Burner.)

2. The Renderer class from the MuJoCo tutorial Colab is now available directly in the native Python bindings.

General

3. The tendon springlength attribute can now take two values. Given two non-decreasing values, springlength specifies a deadband range for spring stiffness. If the tendon length is between the two values, the force is 0. If length is outside this range, the force behaves like a regular spring, with the spring resting length corresponding to the nearest springlength value. This can be used to create tendons whose limits are enforced by springs rather than constraints, which are cheaper and easier to analyse. See tendon_springlength.xml example model.

   Attention

   This is a minor breaking API change. mjModel.tendon_lengthspring now has size ntendon x 2 rather than ntendon x 1.

4. Removed the requirement that stateless actuators come before stateful actuators.

5. Added mju_fill, mju_symmetrize and mju_eye utility functions.

6. Added gravcomp attribute to body, implementing gravity compensation and buoyancy. See balloons.xml example model.

7. Renamed the cable plugin library to elasticity.

8. Added actdim attribute to general actuators. Values greater than 1 are only allowed for dyntype user, as native activation dynamics are all scalar. Added example test implementing 2nd-order activation dynamics to engine_forward_test.cc.

9. Improved particle composite type, which now permits a user-specified geometry and multiple joints. See the two new examples: particle_free.xml and particle_free2d.xml.

10. Performance improvements for non-AVX configurations:

    • 14% faster mj_solveLD using restrict. See engine_core_smooth_benchmark_test.

    • 50% faster mju_dotSparse using manual loop unroll. See engine_util_sparse_benchmark_test.

11. Added new solid passive force plugin:

    • This is new force field compatible with the composite particles.

    • Generates a tetrahedral mesh having particles with mass concentrated at vertices.

    • Uses a piecewise-constant strain model equivalent to finite elements but expressed in a coordinate-free formulation. This implies that all quantities can be precomputed except edge elongation, as in a mass-spring model.

    • Only suitable for small strains (large displacements but small deformations). Tetrahedra may invert if subject to large loads.

12. Added API functions mj_loadPluginLibrary and mj_loadAllPluginLibraries. The first function is identical to dlopen on a POSIX system, and to LoadLibraryA on Windows. The second function scans a specified directory for all dynamic libraries file and loads each library found. Dynamic libraries opened by these functions are assumed to register one or more MuJoCo plugins on load.

13. Added an optional visualize callback to plugins, which is called during mjv_updateScene. This callback allows custom plugin visualizations. Enable stress visualization for the Cable plugin as an example.

14. Sensors of type user no longer require objtype, objname and needstage. If unspecified, the objtype is now mjOBJ_UNKNOWN. user sensors datatype default is now “real”, needstage default is now “acc”.

15. Added support for capsules in URDF import.

16. On macOS, issue an informative error message when run under Rosetta 2 translation on an Apple Silicon machine. Pre-built MuJoCo binaries make use of AVX instructions on x86-64 machines, which is not supported by Rosetta 2. (Before this version, users only get a cryptic “Illegal instruction” message.)

Bug fixes

17. Fixed bug in mj_addFileVFS that was causing the file path to be ignored (introduced in 2.1.4).

Simulate

18. Renamed the directory in which the simulate application searches for plugins from plugin to mujoco_plugin.

19. Mouse force perturbations are now applied at the selection point rather than the body center of mass.

Version 2.3.0 (October 18, 2022)

General

1. The contact array and arrays prefixed with efc_ in mjData were moved out of the buffer into a new arena memory space. These arrays are no longer allocated with fixed sizes when mjData is created. Instead, the exact memory requirement is determined during each call to mj_forward (specifically, in mj_collision and mj_makeConstraint) and the arrays are allocated from the arena space. The stack now also shares its available memory with arena. This change reduces the memory footprint of mjData in models that do not use the PGS solver, and will allow for significant memory reductions in the future. See the Memory allocation section for details.

2. Added colab notebook tutorial showing how to balance the humanoid on one leg with a Linear Quadratic Regulator. The notebook uses MuJoCo’s native Python bindings, and includes a draft Renderer class, for easy rendering in Python.
   Try it yourself:

3. Updates to humanoid model: - Added two keyframes (stand-on-one-leg and squat). - Increased maximum hip flexion angle. - Added hamstring tendons which couple the hip and knee at high hip flexion angles. - General cosmetic improvements, including improved use of defaults and better naming scheme.

4. Added mju_boxQP and allocation function mju_boxQPmalloc for solving the box-constrained Quadratic Program:

   \[x^* = \text{argmin} \; \tfrac{1}{2} x^T H x + x^T g \quad \text{s.t.} \quad l \le x \le u\]

   The algorithm, introduced in Tassa et al. 2014, converges after 2-5 Cholesky factorisations, independent of problem size.

5. Added mju_mulVecMatVec to multiply a square matrix \(M\) with vectors \(x\) and \(y\) on both sides. The function returns \(x^TMy\).

6. Added new plugin API. Plugins allow developers to extend MuJoCo’s capability without modifying core engine code. The plugin mechanism is intended to replace the existing callbacks, though these will remain for the time being as an option for simple use cases and backward compatibility. The new mechanism manages stateful plugins and supports multiple plugins from different sources, allowing MuJoCo extensions to be introduced in a modular fashion, rather than as global overrides. Note the new mechanism is currently undocumented except in code, as we test it internally. If you are interested in using the plugin mechanism, please get in touch first.

7. Added assetdir compiler option, which sets the values of both meshdir and texturedir. Values in the latter attributes take precedence over assetdir.

8. Added realtime option to visual for starting a simulation at a slower speed.

9. Added new cable composite type:

   • Cable elements are connected with ball joints.

   • The initial parameter specifies the joint at the starting boundary: free, ball, or none.

   • The boundary bodies are exposed with the names B_last and B_first.

   • The vertex initial positions can be specified directly in the XML with the parameter vertex.

   • The orientation of the body frame is the orientation of the material frame of the curve.

10. Added new cable passive force plugin:

    • Twist and bending stiffness can be set separately with the parameters twist and bend.

    • The stress-free configuration can be set to be the initial one or flat with the flag flat.

    • New cable.xml example showing the formation of plectoneme.

    • New coil.xml example showing a curved equilibrium configuration.

    • New belt.xml example showing interaction between twist and anisotropy.

    • Added test using cantilever exact solution.

Python bindings

11. Added id and name properties to named accessor objects. These provide more Pythonic API access to mj_name2id and mj_id2name respectively.

12. The length of MjData.contact is now ncon rather than nconmax, allowing it to be straightforwardly used as an iterator without needing to check ncon.

13. Fix a memory leak when a Python callable is installed as callback (#527).

Version 2.2.2 (September 7, 2022)

General

1. Added adhesion actuators mimicking vacuum grippers and adhesive biomechanical appendages.

2. Added related example model and video:

3. Added mj_jacSubtreeCom for computing the translational Jacobian of the center-of-mass of a subtree.

4. Added torquescale and anchor attributes to weld constraints. torquescale sets the torque-to-force ratio exerted by the constraint, anchor sets the point at which the weld wrench is applied. See weld for more details.

5. Increased mjNEQDATA, the row length of equality constraint parameters in mjModel.eq_data, from 7 to 11.

6. Added visualisation of anchor points for both connect and weld constraints (activated by the ‘N’ key in simulate).

7. Added weld.xml showing different uses of new weld attributes.

8. Cartesian 6D end-effector control is now possible by adding a reference site to actuators with site transmission. See description of new refsite attribute in the actuator documentation and refsite.xml example model.

9. Added autolimits compiler option. If true, joint and tendon limited attributes and actuator ctrllimited, forcelimited and actlimited attributes will automatically be set to true if the corresponding range is defined and false otherwise.

   If autolimits="false" (the default) models where a range attribute is specified without the limited attribute will fail to compile. A future release will change the default of autolimits to true, and this compilation error allows users to catch this future change of behavior.

   Attention

   This is a breaking change. In models where a range was defined but limited was unspecified, explicitly set limited to false or remove the range to maintain the current behavior of your model.

10. Added moment of inertia computation for all well-formed meshes. This option is activated by setting the compiler flag exactmeshinertia to true (defaults to false). This default may change in the future.

11. Added parameter shellinertia to geom, for locating the inferred inertia on the boundary (shell). Currently only meshes are supported.

12. For meshes from which volumetric inertia is inferred, raise error if the orientation of mesh faces is not consistent. If this occurs, fix the mesh in e.g., MeshLab or Blender.

13. Added catenary visualisation for hanging tendons. The model seen in the video can be found here.

14. Added azimuth and elevation attributes to visual/global, defining the initial orientation of the free camera at model load time.

15. Added mjv_defaultFreeCamera which sets the default free camera, respecting the above attributes.

16. simulate now supports taking a screenshot via a button in the File section or via Ctrl-P.

17. Improvements to time synchronisation in simulate, in particular report actual real-time factor if different from requested factor (if e.g., the timestep is so small that simulation cannot keep up with real-time).

18. Added a disable flag for sensors.

19. mju_mulQuat and mju_mulQuatAxis support in place computation. For example
    mju_mulQuat(a, a, b); sets the quaternion a equal to the product of a and b.

20. Added sensor matrices to mjd_transitionFD (note this is an API change).

Deleted/deprecated features

21. Removed distance constraints.

Bug fixes

22. Fixed rendering of some transparent geoms in reflection.

23. Fixed intvelocity defaults parsing.

Version 2.2.1 (July 18, 2022)

General

1. Added mjd_transitionFD to compute efficient finite difference approximations of the state-transition and control-transition matrices, see here for more details.

2. Added derivatives for the ellipsoid fluid model.

3. Added ctrl attribute to keyframes.

4. Added clock sensor which measures time.

5. Added visualisation groups to skins.

6. Added actuator visualisation for free and ball joints and for actuators with site transmission.

7. Added visualisation for actuator activations.

8. Added <actuator-intvelocity> actuator shortcut for “integrated velocity” actuators, documented here.

9. Added <actuator-damper> actuator shortcut for active-damping actuators, documented here.

10. mju_rotVecMat and mju_rotVecMatT now support in-place multiplication.

11. mjData.ctrl values are no longer clamped in-place, remain untouched by the engine.

12. Arrays in mjData’s buffer now align to 64-byte boundaries rather than 8-byte.

13. Added memory poisoning when building with Address Sanitizer (ASAN) and Memory Sanitizer (MSAN). This allows ASAN to detect reads and writes to regions in mjModel.buffer and mjData.buffer that do not lie within an array, and for MSAN to detect reads from uninitialised fields in mjData following mj_resetData.

14. Added a slider-crank example model.

Bug fixes

15. Activation clamping was not being applied in the implicit integrator.

16. Stricter parsing of orientation specifiers. Before this change, a specification that included both quat and an alternative specifier e.g., <geom ... quat=".1 .2 .3 .4" euler="10 20 30">, would lead to the quat being ignored and only euler being used. After this change a parse error will be thrown.

17. Stricter parsing of XML attributes. Before this change an erroneous XML snippet like <geom size="1/2 3 4"> would have been parsed as size="1 0 0" and no error would have been thrown. Now throws an error.

18. Trying to load a NaN via XML like <geom size="1 NaN 4">, while allowed for debugging purposes, will now print a warning.

19. Fixed null pointer dereference in mj_loadModel.

20. Fixed memory leaks when loading an invalid model from MJB.

21. Integer overflows are now avoided when computing mjModel buffer sizes.

22. Added missing warning string for mjWARN_BADCTRL.

Packaging

23. Changed MacOS packaging so that the copy of mujoco.framework embedded in MuJoCo.app can be used to build applications externally.

Version 2.2.0 (May 23, 2022)

Open Sourcing

1. MuJoCo is now fully open-source software. Newly available top level directories are:

   a. src/: All source files. Subdirectories correspond to the modules described in the Programming chapter introduction:

   • src/engine/: Core engine.

   • src/xml/: XML parser.

   • src/user/: Model compiler.

   • src/visualize/: Abstract visualizer.

   • src/ui/: UI framework.

   2. test/: Tests and corresponding asset files.

   3. dist/: Files related to packaging and binary distribution.

2. Added contributor’s guide and style guide.

General

3. Added analytic derivatives of smooth (unconstrained) dynamics forces, with respect to velocities:

   • Centripetal and Coriolis forces computed by the Recursive Newton-Euler algorithm.

   • Damping and fluid-drag passive forces.

   • Actuation forces.

4. Added implicit integrator. Using the analytic derivatives above, a new implicit-in-velocity integrator was added. This integrator lies between the Euler and Runge Kutta integrators in terms of both stability and computational cost. It is most useful for models which use fluid drag (e.g. for flying or swimming) and for models which use velocity actuators. For more details, see the Numerical Integration section.

5. Added actlimited and actrange attributes to general actuators, for clamping actuator internal states (activations). This clamping is useful for integrated-velocity actuators, see the Activation clamping section for details.

6. mjData fields qfrc_unc (unconstrained forces) and qacc_unc (unconstrained accelerations) were renamed qfrc_smooth and qacc_smooth, respectively. While “unconstrained” is precise, “smooth” is more intelligible than “unc”.

7. Public headers have been moved from /include to /include/mujoco/, in line with the directory layout common in other open source projects. Developers are encouraged to include MuJoCo public headers in their own codebase via #include <mujoco/filename.h>.

8. The default shadow resolution specified by the shadowsize attribute was increased from 1024 to 4096.

9. Saved XMLs now use 2-space indents.

Bug fixes

10. Antialiasing was disabled for segmentation rendering. Before this change, if the offsamples attribute was greater than 0 (the default value is 4), pixels that overlapped with multiple geoms would receive averaged segmentation IDs, leading to incorrect or non-existent IDs. After this change offsamples is ignored during segmentation rendering.

11. The value of the enable flag for the experimental multiCCD feature was made sequential with other enable flags. Sequentiality is assumed in the simulate UI and elsewhere.

12. Fix issue of duplicated meshes when saving models with OBJ meshes using mj_saveLastXML.

Version 2.1.5 (Apr. 13, 2022)

General

1. Added an experimental feature: multi-contact convex collision detection, activated by an enable flag. See full description here.

Bug fixes

2. GLAD initialization logic on Linux now calls dlopen to load a GL platform dynamic library if a *GetProcAddress function is not already present in the process’ global symbol table. In particular, processes that use GLFW to set up a rendering context that are not explicitly linked against libGLX.so (this applies to the Python interpreter, for example) will now work correctly rather than fail with a gladLoadGL error when mjr_makeContext is called.

3. In the Python bindings, named indexers for scalar fields (e.g. the ctrl field for actuators) now return a NumPy array of shape (1,) rather than (). This allows values to be assigned to these fields more straightforwardly.

Version 2.1.4 (Apr. 4, 2022)

General

1. MuJoCo now uses GLAD to manage OpenGL API access instead of GLEW. On Linux, there is no longer a need to link against different GL wrangling libraries depending on whether GLX, EGL, or OSMesa is being used. Instead, users can simply use GLX, EGL, or OSMesa to create a GL context and mjr_makeContext will detect which one is being used.

2. Added visualisation for contact frames. This is useful when writing or modifying collision functions, when the actual direction of the x and y axes of a contact can be important.

Binary build

3. The _nogl dynamic library is no longer provided on Linux and Windows. The switch to GLAD allows us to resolve OpenGL symbols when mjr_makeContext is called rather than when the library is loaded. As a result, the MuJoCo library no longer has an explicit dynamic dependency on OpenGL, and can be used on system where OpenGL is not present.

Simulate

4. Fixed a bug in simulate where pressing ‘[’ or ‘]’ when a model is not loaded causes a crash.

5. Contact frame visualisation was added to the Simulate GUI.

6. Renamed “set key”, “reset to key” to “save key” and “load key”, respectively.

7. Changed bindings of F6 and F7 from the not very useful “vertical sync” and “busy wait” to the more useful cycling of frames and labels.

Bug fixes

8. mj_resetData zeroes out the solver_nnz field.

9. Removed a special branch in mju_quat2mat for unit quaternions. Previously, mju_quat2mat skipped all computation if the real part of the quaternion equals 1.0. For very small angles (e.g. when finite differencing), the cosine can evaluate to exactly 1.0 at double precision while the sine is still nonzero.

Version 2.1.3 (Mar. 23, 2022)

General

1. simulate now supports cycling through cameras (with the [ and ] keys).

2. mjVIS_STATIC toggles all static bodies, not just direct children of the world.

Python bindings

3. Added a free() method to MjrContext.

4. Enums now support arithmetic and bitwise operations with numbers.

Bug fixes

5. Fixed rendering bug for planes, introduced in 2.1.2. This broke maze environments in dm_control.

Version 2.1.2 (Mar. 15, 2022)

New modules

1. Added new Python bindings, which can be installed via pip install mujoco, and imported as import mujoco.

2. Added new Unity plug-in.

3. Added a new introspect module, which provides reflection-like capability for MuJoCo’s public API, currently describing functions and enums. While implemented in Python, this module is expected to be generally useful for automatic code generation targeting multiple languages. (This is not shipped as part of the mujoco Python bindings package.)

API changes

4. Moved definition of mjtNum floating point type into a new header mjtnum.h.

5. Renamed header mujoco_export.h to mjexport.h.

6. Added mj_printFormattedData, which accepts a format string for floating point numbers, for example to increase precision.

General

7. MuJoCo can load OBJ mesh files.

   1. Meshes containing polygons with more than 4 vertices are not supported.

   2. In OBJ files containing multiple object groups, any groups after the first one will be ignored.

   3. Added (post-release, not included in the 2.1.2 archive) textured mug example model:

      

8. Added optional frame-of-reference specification to framepos, framequat, framexaxis, frameyaxis, framezaxis, framelinvel, and frameangvel sensors. The frame-of-reference is specified by new reftype and refname attributes.

9. Sizes of user parameters are now automatically inferred.

   1. Declarations of user parameters in the top-level size clause (e.g. nuser_body, nuser_jnt, etc.) now accept a value of -1, which is the default. This will automatically set the value to the length of the maximum associated user attribute defined in the model.

   2. Setting a value smaller than -1 will lead to a compiler error (previously a segfault).

   3. Setting a value to a length smaller than some user attribute defined in the model will lead to an error (previously additional values were ignored).

10. Increased the maximum number of lights in an mjvScene from 8 to 100.

11. Saved XML files only contain explicit inertial elements if the original XML included them. Inertias that were automatically inferred by the compiler’s inertiafromgeom mechanism remain unspecified.

12. User-selected geoms are always rendered as opaque. This is useful in interactive visualizers.

13. Static geoms now respect their geom group for visualisation. Until this change rendering of static geoms could only be toggled using the mjVIS_STATIC visualisation flag . After this change, both the geom group and the visualisation flag need to be enabled for the geom to be rendered.

14. Pointer parameters in function declarations in mujoco.h that are supposed to represent fixed-length arrays are now spelled as arrays with extents, e.g. mjtNum quat[4] rather than mjtNum* quat. From the perspective of C and C++, this is a non-change since array types in function signatures decay to pointer types. However, it allows autogenerated code to be aware of expected input shapes.

15. Experimental stateless fluid interaction model. As described here, fluid forces use sizes computed from body inertia. While sometimes convenient, this is very rarely a good approximation. In the new model forces act on geoms, rather than bodies, and have a several user-settable parameters. The model is activated by setting a new attribute: <geom fluidshape="ellipsoid"/>. The parameters are described succinctly here, but we leave a full description or the model and its parameters to when this feature leaves experimental status.

Bug fixes

16. mj_loadXML and mj_saveLastXML are now locale-independent. The Unity plugin should now work correctly for users whose system locales use commas as decimal separators.

17. XML assets in VFS no longer need to end in a null character. Instead, the file size is determined by the size parameter of the corresponding VFS entry.

18. Fix a vertex buffer object memory leak in mjrContext when skins are used.

19. Camera quaternions are now normalized during XML compilation.

Binary build

20. Windows binaries are now built with Clang.

Version 2.1.1 (Dec. 16, 2021)

API changes

1. Added mj_printFormattedModel, which accepts a format string for floating point numbers, for example to increase precision.

2. Added mj_versionString, which returns human-readable string that represents the version of the MuJoCo binary.

3. Converted leading underscores to trailing underscores in private instances of API struct definitions, to conform to reserved identifier directive, see C standard: Section 7.1.3.

   Attention

   This is a minor breaking change. Code which references private instances will break. To fix, replace leading underscores with trailing underscores, e.g. _mjModel → mjModel_.

General

4. Safer string handling: replaced strcat, strcpy, and sprintf with strncat, strncpy, and snprintf respectively.

5. Changed indentation from 4 spaces to 2 spaces, K&R bracing style, added braces to one-line conditionals.

Bug Fixes

6. Fixed reading from uninitialized memory in PGS solver.

7. Computed capsule inertias are now exact. Until this change, capsule masses and inertias computed by the compiler’s inertiafromgeom mechanism were approximated by a cylinder, formed by the capsule’s cylindrical middle section, extended on both ends by half the capsule radius. Capsule inertias are now computed with the Parallel Axis theorem, applied to the two hemispherical end-caps.

   Attention

   This is a minor breaking change. Simulation of a model with automatically-computed capsule inertias will be numerically different, leading to, for example, breakage of golden-value tests.

8. Fixed bug related to force and torque sensors. Until this change, forces and torques reported by F/T sensors ignored out-of-tree constraint wrenches except those produced by contacts. Force and torque sensors now correctly take into account the effects of connect and weld constraints.

   Note

   Forces generated by spatial tendons which are outside the kinematic tree (i.e., between bodies which have no ancestral relationship) are still not taken into account by force and torque sensors. This remains a future work item.

Code samples

9. testspeed: Added injection of pseudo-random control noise, turned on by default. This is to avoid settling into some fixed contact configuration and providing an unrealistic timing measure.

10. simulate:

    1. Added slower-than-real-time functionality, which is controlled via the ‘+’ and ‘-’ keys.

    2. Added sliders for injecting Brownian noise into the controls.

    3. Added “Print Camera” button to print an MJCF clause with the pose of the current camera.

    4. The camera pose is not reset when reloading the same model file.

Updated dependencies

11. TinyXML was replaced with TinyXML2 6.2.0.

12. qhull was upgraded to version 8.0.2.

13. libCCD was upgraded to version 1.4.

14. On Linux, libstdc++ was replaced with libc++.

Binary build

15. MacOS packaging. We now ship Universal binaries that natively support both Apple Silicon and Intel CPUs.

    1. MuJoCo library is now packaged as a Framework Bundle, allowing it to be incorporated more easily into Xcode projects (including Swift projects). Developers are encouraged to compile and link against MuJoCo using the -framework mujoco flag, however all header files and the libmujoco.2.1.1.dylib library can still be directly accessed inside the framework.

    2. Sample applications are now packaged into an Application Bundle called MuJoCo.app. When launched via GUI, the bundle launches the simulate executable. Other precompiled sample programs are shipped inside that bundle (in MuJoCo.app/Contents/MacOS) and can be launched via command line.

    3. Binaries are now signed and the disk image is notarized.

16. Windows binaries and libraries are now signed.

17. Link-time optimization is enabled on Linux and macOS, leading to an average of ~20% speedup when benchmarked on three test models (cloth.xml, humanoid.xml, and humanoid100.xml).

18. Linux binaries are now built with LLVM/Clang instead of GCC.

19. An AArch64 (aka ARM64) Linux build is also provided.

20. Private symbols are no longer stripped from shared libraries on Linux and MacOS.

Sample models

21. Clean-up of the model/ directory.

    1. Rearranged into subdirectories which include all dependencies.

    2. Added descriptions in XML comments, cleaned up XMLs.

    3. Deleted some composite models: grid1, grid1pin, grid2, softcylinder, softellipsoid.

22. Added descriptive animations in docs/images/models/ :

Version 2.1.0 (Oct. 18, 2021)

New features

1. Keyframes now have mocap_pos and mocap_quat fields (mpos and quat attributes in the XML) allowing mocap poses to be stored in keyframes.

2. New utility functions: mju_insertionSortInt (integer insertion sort) and mju_sigmoid (constructing a sigmoid from two half-quadratics).

General

3. The preallocated sizes in the virtual file system (VFS) increased to 2000 and 1000, to allow for larger projects.

4. The C structs in the mjuiItem union are now named, for compatibility.

5. Fixed: mjcb_contactfilter type is mjfConFilt (was mjfGeneric).

6. Fixed: The array of sensors in mjCModel was not cleared.

7. Cleaned up cross-platform code (internal changes, not visible via the API).

8. Fixed a bug in parsing of XML texcoord data (related to number of vertices).

9. Fixed a bug in simulate.cc related to nkey (the number of keyframes).

10. Accelerated collision detection in the presence of large numbers of non-colliding geoms (with contype==0 and conaffinity==0).

UI

11. Figure selection type changed from int to float.

12. Figures now show data coordinates, when selection and highlight are enabled.

13. Changed mjMAXUIMULTI to 35, mjMAXUITEXT to 300, mjMAXUIRECT to 25.

14. Added collapsible sub-sections, implemented as separators with state: mjSEPCLOSED collapsed, mjSEPCLOSED+1 expanded.

15. Added mjITEM_RADIOLINE item type.

16. Added function mjui_addToSection to simplify UI section construction.

17. Added subplot titles to mjvFigure.

Rendering

18. render_gl2 guards against non-finite floating point data in the axis range computation.

19. render_gl2 draws lines from back to front for better visibility.

20. Added function mjr_label (for text labels).

21. mjr_render exits immediately if ngeom==0, to avoid errors from uninitialized scenes (e.g. frustrum==0).

22. Added scissor box in mjr_render, so we don’t clear the entire window at every frame.

License manager

23. Removed the entire license manager. The functions mj_activate and mj_deactivate are still there for backward compatibility, but now they do nothing and it is no longer necessary to call them.

24. Removed the remote license certificate functions mj_certXXX.

Earlier versions

For changelogs of earlier versions please see roboti.us.