General

1. eb18d77ca The .mjz encoder now writes the root file as model.xml in the archive as this is less susceptible to breakage due to file renaming.

2. 4affbb64a Site geometries can now also be associated with meshes (type="mesh" with mesh="name"), supporting visualization, the insidesite sensor, and the new mj_insideSite function.

3. b59b07fae Added support for Python 3.15 (GIL and Free-Threading).

Engine

1. 5660353ec Added a new integrator discrete: the constraint solve and the implicit velocity update merge into one operation, performed in the effective metric widehat{M} = M + hD + h^2K, which incorporates both implicit damping hD and implicit position stiffness h^2 K. Under this integrator mjData.qacc is the discrete step map (v^+ - v)/h, and joint, tendon and actuator stiffness and damping join the solver's metric, making passive springs and actuator position gains stable at timesteps far beyond the explicit stability limit. Constraint rows are treated implicitly as well: solref spring--dampers are evaluated at the end of the step, so constraints are stable at any timeconst; under this integrator the refsafe flag replaces contact and limit rows stiffer than the timestep can resolve by the stiffest zero-restitution row instead of clamping timeconst. The actuator-gain treatment resolves the stiff-servo timestep limitation of 3443 (analysis contributed by qiayuanl). See the integrator documentation for semantics and current limitations.

   Breaking API changes

   Removed the implicit flex effective-metric special case under implicit/implicitfast with the CG solver, introduced in 3.11.0. This behavior now requires integrator="discrete" (with a primal solver: CG or Newton), which additionally treats joint damping and stiffness implicitly inside the solve. Models relying on the old behavior should set integrator to discrete; models with flex elasticity or passive flex contact under implicit/implicitfast now raise a runtime error carrying this migration note.

2. 0b4e17747 Restored clamping of non-positive pivots in the sparse inertia factorization, along with the associated mjWARN_INERTIA warning. The guard was inadvertently dropped in the 3.3.0 conversion of qLD to CSR format; since then, models with singular mass matrices silently produced non-finite accelerations, typically surfacing as divergence warnings and automatic resets.

3. c9d997610 Added single-shot multicontact for collisions with cylinder geoms.

4. 10eeb8289 The Newton solver with elliptic cones now rebuilds the cone-augmented Hessian factor with a single refactorization instead of per-contact rank-1 updates when a flop-count model predicts this is faster. Scenes with many simultaneously sliding contacts speed up by 1.4-2x on average and 3-4x on the slowest steps. Contribution by kevinzakka.

Compiler

1. 2a3957558 Custom text fields (custom/text) in MJCF now accept their values inside a <![CDATA[ ... ]]> block in addition to the data attribute. When saving a model via mj_saveXML, custom text containing newlines or XML characters is exported as CDATA.

2. 47ebfe48a Added cutoff attribute to sensor/tactile.

Samples

1. 834983fbb Added render.cc: a headless offscreen rendering sample that saves an image to a PNG image. Supports both the Filament and classic OpenGL backends, with command-line options for camera, resolution, keyframe, simulation steps, geom/site groups, visualization and rendering flags, labels, and frames.

Bug fixes

1. 67562d95f Rewrote the Plane-Mesh collider to fix bugs and improve performance. Fixes 3524.

Models

1. f6c1004b7 Added house of cards example model and three free-standing arch models: roman, gothic, and hyperbolic. Inspired by Song et al.

Rendering

Breaking API changes

1. cb57b526f For materials with physically-based rendering parameters that do not provide a metallic texture the fallback is now white. Previously the fallback was black, which caused scalar metallic values to be discarded when multiplied in the PBR shader.

Engine

1. 4787c809 Added geom/surfacevel: the velocity of a geom's surface as seen by contacts, given as a velocity field with a constant component and a rotational component about the geom frame origin. This allows conveyor belts, treadmills and turntables to be modeled with static geoms and no degrees of freedom: friction drives touching bodies along the motion of the surface, with the field projected onto each contact's tangent plane. Surface velocities compose correctly with each other and with body motion. Note that the contact rows of mjData.efc_vel, and the constraint-state sensors that read them, report the velocity relative to the moving surface rather than to the geom, since that is the quantity the constraint acts on; for geoms without surfacevel the two are identical. Contact-point visualization draws an arrow along the surface velocity at contacts with moving surfaces.

1. a264d0bc Added geom/adhesion and pair/adhesion: an adhesive force associated with a contact, useful for modeling sticky materials. Contacts can pull with up to the given force before breaking, and the friction budget becomes mu(f_N + text{adhesion}). Combined with gap, adhesive contacts apply "adhesion at a distance", useful for modeling magnets. Resting penetration is unaffected by adhesion. mj_contactForce reports the net interface force, whose normal component can now be negative.

2. f0fa3d82 Replaced midpoint integration of free bodies with gyroscopic derivatives in the implicitfast integrator: the bias-force derivative of every standalone free body is applied via a local unsymmetric solve of its decoupled block, making implicitfast identical to implicit for such bodies. Unlike midpoint integration, which required vacuum and no constraints, this applies in all environments (contacts, fluid, constraints), and is compatible with discrete-time inverse dynamics. Spinning free bodies no longer gain energy, but tumbling motion is now mildly damped; models requiring long-horizon energy conservation of tumbling bodies in vacuum should use RK4. The invdiscrete flag no longer has any effect on forward dynamics.

3. 5618666a Added body/simple attribute ("false"/"auto") to disable the simple body mass matrix optimization. This is useful for domain randomization, where model parameters may change post-compilation.

4. 14c0b0c9 mj_setConst now recomputes the mjModel.{body,geom,site}_sameframe flags, to account for changes in body/geom/site frames after compilation.

5. 2444defc Added support for multiccd with arbitrarily large meshes.

6. a04b0c5b Added flg_gravcomp and flg_surfacevel boolean flags to mjModel. These flags replace the fast-path checks as originally guarded by ngravcomp. Since the engine uses these integers as flags (zero vs. non-zero), the new flags are honest boolean properties, writeable from the Python bindings at runtime. The field ngravcomp is deprecated and will be removed in a future release.

7. a1f38c8e Replaced quadratic scratch in DFS flood-fill island discovery with a linear-memory Union-Find (disjoint set). Contribution by teerthsharma.

Breaking API changes

1. ff629889 Changed the default value of sleep_tolerance from 1e-4 to 1e-3 (1mm/sec in SI units).

2. 315bcfbf Removed the legacy sparse ancestor-walk inertia matrix mjData.qM. The joint-space inertia matrix is now stored exclusively in the compressed sparse row (CSR) format mjData.M.

3. 7e9ac58f Switched mjd_inverseFD to use the CSR-format mjData.M representation instead of the legacy mjData.qM for the mass matrix derivative. This changes the shape of the DmDq parameter from (nv x nM) to (nv x nC).

4. 1ea2d884 mju_round now breaks ties away from zero rather than towards +infty. This only affects negative half-integers, e.g. mju_round(-2.5) now returns -3 rather than -2.

5. fa36015b Removed unneeded mjvScene argument from mjv_moveCamera.

6. ba9a6503 Split up mjrfMeshData into mjrfMeshData and mjrfMeshConfig to allow reuploading of mesh data without having to recreate the mesh object. Introduces mjrf_defaultMeshConfig and mjrf_setMeshData functions.

7. ba9a6503 Removed bytes field from mjrVertexAttribute.

Breaking ABI changes

1. 072e963f mjModel gained the actuator_ctrlspec field (input signature of each actuator), and mjsActuator gained ctrlspec, changing their size and layout. The mjtGain and mjtBias enums gained so3 members, shifting the values of mjGAIN_USER and mjBIAS_USER.

2. d43c3ed4 Added texid, texuniform and texrepeat fields to mjvGeom.

3. a264d0bc The mjContact struct gained an adhesion member, changing its size and layout.

Bug fixes

1. dddb2767 Fixed a bug where body_margin excluded gap, causing the mid-phase collision filter to incorrectly prune in-gap contacts on multi-geom bodies.

Actuation

1. d507e921 Refactored actuator infrastructure in preparation for MIMO (multi-input multi-output) actuator support. Each actuator now has ctrlnum (number of controls) and outnum (number of force outputs). The total counts nu = sum(ctrlnum) and nout = sum(outnum) dimension mjData.ctrl and mjData.actuator_force, respectively, nactuator is the number of actuators. For existing actuators ctrnum = outnum = 1, so nactuator == nu == nout and existing code is unaffected.

2. 56a93979 Setpoints of position and intvelocity servos acting on 3D rotational transmissions (ball joints, or site transmissions with a refsite and purely rotational gear) are now interpreted on the circle: the force uses the setpoint representative nearest the current angle, so targets winding beyond half a turn are tracked continuously instead of slipping by full turns. Behavior is identical whenever the error does not exceed π. Relatedly, intvelocity actuators now expose actlimited, which was previously hardcoded to "true": as for general actuators it defaults to "auto", so activation clamping is enabled by specifying actrange. Unclamped integrated setpoints are well-behaved on rotational transmissions, where they wrap.

1. 072e963f Added the orientation actuator: a geodesic servo on a new SO(3) transmission (ball joints, or a site with a refsite), acting jointly on the full relative orientation with an exact equilibrium at every commanded orientation. This is the first actuator with multiple force outputs (3), and, with input="quat", the first with different input and output dimensions (4 controls, 3 outputs). The input signature is recorded in the new mjModel.actuator_ctrlspec, exposed as the input attribute.

2. 072e963f Added mj_actuatorInputName, returning the name of an actuator input (e.g. "qw" for the first control of a quaternion-commanded orientation actuator). The control sliders in simulate and MuJoCo Studio are now generated per control and labeled with the actuator name plus the input name suffix.

3. 072e963f Viewer control sliders now use a defined ctrlrange even when ctrllimited is "false": the range sets the slider span, while clamping remains controlled by ctrllimited.

4. 072e963f Added mj_resetCtrl, setting controls to neutral values: zero, except quaternion inputs which reset to the identity quaternion. Called by mj_resetData and the viewers' "Clear All".

Solvers

1. ea230a95 Flex elasticity (stretch, bending, interpolation stiffness) is now integrated implicitly inside the CG constraint solver via an effective metric: the mass matrix is augmented with the stiffness Hessian, so contact and elastic forces are solved against one consistent metric. This replaces the previous post-hoc CG correction, which modified qacc after the constraint solve. The gate is solver="CG" with an implicit integrator and flex stiffness present; Newton and PGS are unaffected. Bending-only models pay zero per-step factorization cost (the factor is precomputed in mj_setConst). Inverse dynamics (mj_inverse) is now discrete-consistent with forward dynamics for gated models.

2. c499f7f2 Added Nesterov momentum extrapolation with adaptive gradient restart (O'Donoghue-Candès) to the PGS solver, significantly improving convergence. Overall PGS now requires ~2x fewer iterations.

3. 1e66efd1 Added the Newton decrement -- the quadratic model's predicted cost improvement of the next iteration -- as a third early-termination criterion of the Newton solver, alongside cost improvement and gradient norm. This reduces iteration counts at no accuracy cost. Proposed by adenzler-nvidia in MJWarp pull request 1520.

4. c69ef030 The CG and Newton solvers now terminate with zero iterations when a duality-gap certificate proves that the warmstarted solution already satisfies the tolerance. The certificate requires only the existing mass-matrix factorization, so quiescent scenes skip Hessian construction, factorization and the line search entirely. Newton zero-iteration exits additionally require the gradient criterion, preserving Newton's characteristic force-level accuracy. See Warmstart in the Computation chapter for details.

Compiler

1. 4e1795b9 mj_encode now supports encoding of MJB and TXT files.

2. c6c3ec31 The attach element now supports self-attachment (attaching elements of the current model to itself) by omitting the model attribute. It also supports attaching a frame via the new frame attribute, which is mutually exclusive with body.

3. 040872fd Fixed loading of .mjz archives in simulate: the archive was unmounted before model compilation, so assets failed to load. Failures in the mjz decoder now emit a warning with the underlying error instead of the generic "could not decode content" message.

4. ebd4abae The mjz decoder now searches for model.xml and <stem>/model.xml as a fallback if <stem>.xml and <stem>/<stem>.xml are not found.

5. dc7581ac Added support for resource writing via mju_writeResource and the write callback in mjpResourceProvider.

Breaking API changes

1. d83ef0b6 The return type of mj_encode and the mjfEncode callback changed from int to mjtSize (64-bit).

Bug fixes

1. f5f9d9ef Fixed a bug in the mesh compiler where normals were scaled as vectors rather than covectors.

Python bindings

1. a07ae6f8 The bindings now support free threading (PEP 703) for Python 3.14.

Documentation

1. 1f1bfa9e Expanded documentation for spec.encode workflows and added detailed documentation for the MJZ Archive format (.mjz / .zip).

General

b935d415 Added mju_threadpool , a new function for creating a thread pool on an mjData instance. When a thread pool is initialized, parts of the simulation pipeline, such as collision detection and constraint solving across islands, are parallelized. The thread pool is automatically destroyed when the mjData is freed.

58f6d524 Added a unified logging API :

All errors, warnings, and informational messages are now routed through a single mjfLogHandler callback receiving a structured mjLogMessage .

Users can install a custom handler via mju_setLogHandler , configure the default handler’s behavior (console/file output, topic filtering) via mju_setLogConfig .

Messages can be emitted via mju_info and mju_message .

New types: mjtLogLevel , mjtLogTopic , mjLogMessage , mjLogConfig .

The legacy callbacks mju_user_error and mju_user_warning are deprecated but remain functional.

6f8bb5ef Added mjs_numWarnings and mjs_getWarning for retrieving all warnings accumulated during model compilation and attachment. Deprecated mjs_isWarning in favor of mjs_numWarnings(s) > 0 .

410c7316 Added the compiler/conflict attribute for controlling how conflicting global attributes are resolved during attachment . Possible values are “warning” (default: parent values take precedence, warnings emitted on conflicts), “merge” (per-field min/max/error strategy), and “error” (any conflict raises an error). See Attribute Merging for details.

Future breaking API changes

The current default conflict resolution policy “warn” (ignore the child model) is backward compatible. However, the default policy will change to “merge” in a future release.

cd6db9eb Improved primal solver convergence under float32. Improvements initially proposed by @n3b in issue #2313 and @adenzler-nvidia in MJWarp pull request 1374 .

828052e6 The CG solver now uses the Hager-Zhang conjugate direction update instead of the Polak-Ribiere-Plus formula. This improves convergence and leads to a significant speedup under float32.

4c381635 Added mjs_makeFlex , a new C API function equivalent to the flexcomp element for programmatically creating flex objects with auto-generated bodies, joints, and equality constraints. Exposed as body.make_flex() in Python.

7a7dc7cc Added support for loading 1D flex components from OBJ line segments

ea2d785e Significantly improved the quality of coarse convex hulls produced by the maxhullvert attribute by invoking Qhull’s Q9 option.

Breaking API changes

b935d415 The header file mjthread.h was removed along with the old engine threading API.

Migration: Use mju_threadpool to set number of worker threads for the engine.

96bf8aea Moved island sparse matrix construction from mj_island (single threaded) into mj_fwdConstraint (multi-threaded). The island-specific matrices iM, iLD, iefc_J were removed from the arena and are now allocated on the stack.

4548e81e Following the introduction of the diagexact flag, the mjData field efc_diagApprox was renamed to efc_diagA , as it can now be either the exact or approximate diagonal of the (A) (“Delassus”) matrix.

062b0f1e The deprecated functions mju_{error,warning}_{i,s} have been removed.

7b9b8806 Changed the signature of mj_fullM from mj_fullM(m, dst, M) to mj_fullM(m, d, dst) as part of the planned deprecation of mjData.qM in favor of the CSR-format mjData.M .

Migration: For inertia matrix conversion, replace mj_fullM(m, dst, d->qM) with mj_fullM(m, d, dst) or mju_sym2dense(dst, d->M, m->nv, m->M_rownnz, m->M_rowadr, m->M_colind) .

Bug fixes

a8eaccd2 Fixed a vulnerability in the System Identification toolbox where loading a trajectory or time series called np.load with allow_pickle=True , allowing arbitrary code execution from a malicious .npz file. Signal metadata is now serialized as JSON and loaded with allow_pickle=False .

b9fb817a Fixed a bug in the mjz decoder where unnormalized paths would fail to be read.

986d73c0 Fixed a bug where the mesh compiler would produce non-unit convex hull polygon normals.

General

1. b935d415 Added mju_threadpool, a new function for creating a thread pool on an mjData instance. When a thread pool is initialized, parts of the simulation pipeline, such as collision detection and constraint solving across islands, are parallelized. The thread pool is automatically destroyed when the mjData is freed.

2. 58f6d524 Added a unified logging API:

   • All errors, warnings, and informational messages are now routed through a single mjfLogHandler callback receiving a structured mjLogMessage.

   • Users can install a custom handler via mju_setLogHandler, configure the default handler's behavior (console/file output, topic filtering) via mju_setLogConfig.

   • Messages can be emitted via mju_info and mju_message.

   • New types: mjtLogLevel, mjtLogTopic, mjLogMessage, mjLogConfig.

   • The legacy callbacks mju_user_error and mju_user_warning are deprecated but remain functional.

3. 6f8bb5ef Added mjs_numWarnings and mjs_getWarning for retrieving all warnings accumulated during model compilation and attachment. Deprecated mjs_isWarning in favor of mjs_numWarnings(s) > 0.

4. 410c7316 Added the compiler/conflict attribute for controlling how conflicting global attributes are resolved during attachment. Possible values are "warning" (default: parent values take precedence, warnings emitted on conflicts), "merge" (per-field min/max/error strategy), and "error" (any conflict raises an error). See Attribute Merging for details.

   Future breaking API changes

   The current default conflict resolution policy "warn" (ignore the child model) is backward compatible. However, the default policy will change to "merge" in a future release.

5. cd6db9eb Improved primal solver convergence under float32. Improvements initially proposed by n3b in 2313 and adenzler-nvidia in MJWarp pull request 1374.

6. 828052e6 The CG solver now uses the Hager-Zhang conjugate direction update instead of the Polak-Ribiere-Plus formula. This improves convergence and leads to a significant speedup under float32.

7. 4c381635 Added mjs_makeFlex, a new C API function equivalent to the flexcomp element for programmatically creating flex objects with auto-generated bodies, joints, and equality constraints. Exposed as body.make_flex() in Python.

8. 7a7dc7cc Added support for loading 1D flex components from OBJ line segments

9. ea2d785e Significantly improved the quality of coarse convex hulls produced by the maxhullvert attribute by invoking Qhull's Q9 option.

Breaking API changes

1. b935d415 The header file mjthread.h was removed along with the old engine threading API. |br| Migration: Use mju_threadpool to set number of worker threads for the engine.

2. 96bf8aea Moved island sparse matrix construction from mj_island (single threaded) into mj_fwdConstraint (multi-threaded). The island-specific matrices iM, iLD, iefc_J were removed from the arena and are now allocated on the stack.

3. 4548e81e Following the introduction of the diagexact flag, the mjData field efc_diagApprox was renamed to efc_diagA, as it can now be either the exact or approximate diagonal of the A ("Delassus") matrix.

4. 062b0f1e The deprecated functions mju_{error,warning}_{i,s} have been removed.

5. 7b9b8806 Changed the signature of mj_fullM from mj_fullM(m, dst, M) to mj_fullM(m, d, dst) as part of the planned deprecation of mjData.qM in favor of the CSR-format mjData.M.

   Migration: For inertia matrix conversion, replace mj_fullM(m, dst, d->qM) with mj_fullM(m, d, dst) or mju_sym2dense(dst, d->M, m->nv, m->M_rownnz, m->M_rowadr, m->M_colind).

Bug fixes

1. a8eaccd2 Fixed a vulnerability in the System Identification toolbox where loading a trajectory or time series called np.load with allow_pickle=True, allowing arbitrary code execution from a malicious .npz file. Signal metadata is now serialized as JSON and loaded with allow_pickle=False.

2. b9fb817a Fixed a bug in the mjz decoder where unnormalized paths would fail to be read.

3. 986d73c0 Fixed a bug where the mesh compiler would produce non-unit convex hull polygon normals.

General

71d1014e Added mjData.efc_Y , the whitened constraint Jacobian (Y = J M^{-1/2}) , allocated in the arena when dual solvers (PGS or NoSlip) are used or when diagexact is enabled.

71d1014e Added the diagexact enable flag, which computes the exact diagonal of the constraint-space inertia matrix at the current configuration, replacing the default compile-time approximation. This improves solver quality for models with anisotropic inertias or complex kinematic coupling. See Exact diagonal for details.

7bfdbad8 The pseudo-random constraint visitation order in the PGS solver , introduced in the previous release, now uses a fixed seed. The previous implementation seeded with mjData.time , which introduced subtle yet undesirable time dependence.

f712eed4 Flexes are now allowed to sleep, with the exception of completely passive (constraint-free) flexes.

bdf00966 Added compiler timing diagnostics via the new mjtCTimer enum and the mjs_getTimer C API. After mj_compile , per-category timings (total, assets, mesh loading, convex hull, normals, inertia, BVH, octree, textures) are available via mjs_getTimer(spec) . The compile sample prints a detailed timing breakdown when run without an output file.

393c1e42 Added mjtBool to represent boolean variables, replacing mjtByte across all boolean fields in mjModel , mjData , and public C API function signatures.

Breaking API changes

a4e49f2d The semantics of the contact margin and gap parameters have been redesigned for conceptual clarity and consistency with Newton . See the new margin and gap documentation section for details.

Previously, margin controlled the detection threshold (contacts exist when dist < margin ) and gap was subtracted from it to produce the force threshold (forces generated when dist < margin - gap ). This was unintuitive: users expected margin to mean geometric inflation and gap to mean a spatial gap.

Under the new semantics, margin is the geometric inflation of the geom surface and gap is an additional detection buffer beyond the inflated surface:

Detection : contacts are created when dist < margin + gap .

Force generation : constraint forces are applied when dist < margin .

Inactive contacts : contacts with margin < dist ≤ margin + gap are included in mjData.contact but generate no force ( efc_address = -1 ). This is useful for adhesion actuators and custom callbacks.

With the default values margin = 0 , gap = 0 , the behavior is unchanged.

Migration: Models that use the default gap="0" (the vast majority) require no changes. For models with gap > 0 , apply the following transformation to preserve identical behavior:

margin_new = margin_old - gap_old gap_new = gap_old

For example, a geom with the old attributes margin="0.1" gap="0.1" should be changed to margin="0" gap="0.1" .

Negative margin values are now permitted (corresponding to gap > margin under the old semantics). The constraint margin + gap >= 0 should be maintained to ensure valid collision detection.

7174d33f The mjfCollision functions now populate the mjPreContact struct instead of the mjContact struct. The mjPreContact only contains the necessary fields needed for the narrowphase collision detection.

2810edd2 The header file mjtnum.h was renamed to mjtype.h https://github.com/google-deepmind/mujoco/blob/main/include/mujoco/mjtype.h and now includes all enum type definitions.

f6cd0234 The tactile sensor now reports raw depth instead of an estimated pressure.

072125c4 MJX: Removed the deprecated nconmax argument from mjx.make_data and mjx.put_data in favor of naconmax .

15d27b36 Maybe-breaking: Added mjassert.h , a new header containing compile-time assertions that verify the sizes of MuJoCo’s public types for ABI stability. This is a first step towards replacing int with strongly-typed enums in the public API. If these assertions fail on your compiler or platform, please report the issue on GitHub.

General

1. 71d1014e Added mjData.efc_Y, the whitened constraint Jacobian Y = J M^{-1/2}, allocated in the arena when dual solvers (PGS or NoSlip) are used or when diagexact is enabled.

2. 71d1014e Added the diagexact enable flag, which computes the exact diagonal of the constraint-space inertia matrix at the current configuration, replacing the default compile-time approximation. This improves solver quality for models with anisotropic inertias or complex kinematic coupling. See Exact diagonal for details.

3. 7bfdbad8 The pseudo-random constraint visitation order in the PGS solver, introduced in the previous release, now uses a fixed seed. The previous implementation seeded with mjData.time, which introduced subtle yet undesirable time dependence.

4. f712eed4 Flexes are now allowed to sleep, with the exception of completely passive (constraint-free) flexes.

5. bdf00966 Added compiler timing diagnostics via the new mjtCTimer enum and the mjs_getTimer C API. After mj_compile, per-category timings (total, assets, mesh loading, convex hull, normals, inertia, BVH, octree, textures) are available via mjs_getTimer(spec). The compile sample prints a detailed timing breakdown when run without an output file.

6. 393c1e42 Added mjtBool to represent boolean variables, replacing mjtByte across all boolean fields in mjModel, mjData, and public C API function signatures.

Breaking API changes

1. a4e49f2d The semantics of the contact margin and gap parameters have been redesigned for conceptual clarity and consistency with Newton. See the new margin and gap documentation section for details.

   Previously, margin controlled the detection threshold (contacts exist when dist < margin) and gap was subtracted from it to produce the force threshold (forces generated when dist < margin - gap). This was unintuitive: users expected margin to mean geometric inflation and gap to mean a spatial gap.

   Under the new semantics, margin is the geometric inflation of the geom surface and gap is an additional detection buffer beyond the inflated surface:

   • Detection: contacts are created when dist < margin + gap.

   • Force generation: constraint forces are applied when dist < margin.

   • Inactive contacts: contacts with margin < dist ≤ margin + gap are included in mjData.contact but generate no force (efc_address = -1). This is useful for adhesion actuators and custom callbacks.

   With the default values margin = 0, gap = 0, the behavior is unchanged.

   
   

   Migration: Models that use the default gap="0" (the vast majority) require no changes. For models with gap > 0, apply the following transformation to preserve identical behavior:

   margin_new = margin_old - gap_old
   gap_new    = gap_old

   For example, a geom with the old attributes margin="0.1" gap="0.1" should be changed to margin="0" gap="0.1".

   Negative margin values are now permitted (corresponding to gap > margin under the old semantics). The constraint margin + gap >= 0 should be maintained to ensure valid collision detection.

2. 7174d33f The mjfCollision functions now populate the mjPreContact struct instead of the mjContact struct. The mjPreContact only contains the necessary fields needed for the narrowphase collision detection.

3. 2810edd2 The header file mjtnum.h was renamed to mjtype.h <https://github.com/google-deepmind/mujoco/blob/main/include/mujoco/mjtype.h> and now includes all enum type definitions.

4. f6cd0234 The tactile sensor now reports raw depth instead of an estimated pressure.

5. 072125c4 MJX: Removed the deprecated nconmax argument from mjx.make_data and mjx.put_data in favor of naconmax.

6. 15d27b36 Maybe-breaking: Added mjassert.h, a new header containing compile-time assertions that verify the sizes of MuJoCo's public types for ABI stability. This is a first step towards replacing int with strongly-typed enums in the public API. If these assertions fail on your compiler or platform, please report the issue on GitHub.

General

647af382 Added island support for the PGS solver .

4ed69b5c The PGS solver now iterates over constraints in pseudo-random order, improving performance by ~20%.

b9c1877e Added support for elastic2d for trilinear and quadratic flex dofs .

910b3336 Midpoint integration is now restricted to the implicitfast integrator and is disabled when fluid forces are active (nonzero density or viscosity ). Midpoint integration treats external forces as zero-order-hold constants, which causes energy gain in the presence of contacts and in fluid media.

ec50260e Added mjs_getOriginSpec , returning the spec that originally defined an element, prior to attachment. This is in contrast to mjs_getSpec which returns the spec currently owning the element. If the element is not the result of an attach operation, the functions are identical.

767c607f Added mju_sym2dense , converting a lower-triangular, implicitly symmetric CSR matrix to a dense symmetric matrix. The inertia matrix mjData.M is an example of such a matrix.

Future breaking API changes

767c607f The introduction of mju_sym2dense is a step towards the removal of the legacy-format mjData.qM in favor of the CSR-format mjData.M . This removal will involve a future breaking change to mj_fullM (which currently accepts a qM -like matrix as an argument). To prevent a future breakage, replace mj_fullM(m, dst, d->qM) with

mju_sym2dense(dst, d->M, m->nv, m->M_rownnz, m->M_rowadr, m->M_colind) .

Bug fixes

3e960ba3 Fixed default for multiccd in mjcPhysics .

Python

d92fe081 Added MjSpec.encode method, wrapping mj_encode .

723b8b1e Added mujoco.MjVfs Python binding to interact with the Virtual File System directly from Python. See Virtual File System for usage details.

Warning

The previous way of passing assets via a dictionary mapping asset names to bytes is deprecated and will be removed in an upcoming release. You cannot specify both the assets dictionary and the vfs argument at the same time. MjVfs should be used as a drop-in replacement.

General

1. 647af382 Added island support for the PGS solver.

2. 4ed69b5c The PGS solver now iterates over constraints in pseudo-random order, improving performance by ~20%.

3. b9c1877e Added support for elastic2d for trilinear and quadratic flex dofs.

4. 910b3336 Midpoint integration is now restricted to the implicitfast integrator and is disabled when fluid forces are active (nonzero density or viscosity). Midpoint integration treats external forces as zero-order-hold constants, which causes energy gain in the presence of contacts and in fluid media.

5. ec50260e Added mjs_getOriginSpec, returning the spec that originally defined an element, prior to attachment. This is in contrast to mjs_getSpec which returns the spec currently owning the element. If the element is not the result of an attach operation, the functions are identical.

6. 767c607f Added mju_sym2dense, converting a lower-triangular, implicitly symmetric CSR matrix to a dense symmetric matrix. The inertia matrix mjData.M is an example of such a matrix.

Future breaking API changes

1. 767c607f The introduction of mju_sym2dense is a step towards the removal of the legacy-format mjData.qM in favor of the CSR-format mjData.M. This removal will involve a future breaking change to mj_fullM (which currently accepts a qM-like matrix as an argument). To prevent a future breakage, replace mj_fullM(m, dst, d->qM) with |br| mju_sym2dense(dst, d->M, m->nv, m->M_rownnz, m->M_rowadr, m->M_colind).

Bug fixes

1. 3e960ba3 Fixed default for multiccd in mjcPhysics.

Python

1. d92fe081 Added MjSpec.encode method, wrapping mj_encode.

2. 723b8b1e Added mujoco.MjVfs Python binding to interact with the Virtual File System directly from Python. See Virtual File System for usage details.

   Warning

   The previous way of passing assets via a dictionary mapping asset names to bytes is deprecated and will be removed in an upcoming release. You cannot specify both the assets dictionary and the vfs argument at the same time. MjVfs should be used as a drop-in replacement.

General

a04cf1b2 Added support for Python 3.14.

2f2d00da Added multi-cell support for trilinear and quadratic flexes. Note that the implicit integrator uses a dense solver for the flex degrees of freedom, which can be slow for multi-cell flexes.

3d45a331 Refactored strain flex equality constraints to be instantiated per cell instead of per flex object, reducing the number of degrees of freedom per constraint row. The equality can be associated with a specific cell with the new attribute cell

33259718 Added new mj_maxContact function to get the maximum number of possible contacts returned by colliding two geoms.

4cfebcc3 Added mj_containsBufferVFS and mj_containsFileVFS to check for existence of buffers and files in VFS.

Breaking API changes

6cb6e5a9 The multiccd option (multiple contacts returned from the convex collision detection pipeline) is now enabled by default. The new implementation (as opposed to the legacy pipeline) has little performance overhead and improves stability.

Migration: Disable multiccd to recover the previous behavior.

Documentation

2f5e5d3d Added documentation for mjpDecoder plugins.

Bug fixes

da01bd37 Asset paths in attached child specs are now resolved relative to the model file directory of the child spec, rather than the parent spec. This prevents the origin of the parent spec to affect the resolution of asset paths in the child spec.

General

1. a04cf1b2 Added support for Python 3.14.

2. 2f2d00da Added multi-cell support for trilinear and quadratic flexes. Note that the implicit integrator uses a dense solver for the flex degrees of freedom, which can be slow for multi-cell flexes.

3. 3d45a331 Refactored strain flex equality constraints to be instantiated per cell instead of per flex object, reducing the number of degrees of freedom per constraint row. The equality can be associated with a specific cell with the new attribute cell

4. 33259718 Added new mj_maxContact function to get the maximum number of possible contacts returned by colliding two geoms.

5. 4cfebcc3 Added mj_containsBufferVFS and mj_containsFileVFS to check for existence of buffers and files in VFS.

Breaking API changes

1. 6cb6e5a9 The multiccd option (multiple contacts returned from the convex collision detection pipeline) is now enabled by default. The new implementation (as opposed to the legacy pipeline) has little performance overhead and improves stability.

   Migration: Disable multiccd to recover the previous behavior.

Documentation

1. 2f5e5d3d Added documentation for mjpDecoder plugins.

Bug fixes

1. da01bd37 Asset paths in attached child specs are now resolved relative to the model file directory of the child spec, rather than the parent spec. This prevents the origin of the parent spec to affect the resolution of asset paths in the child spec.

General

70a7647a Added the dcmotor actuator for modeling DC motors. Supports optional electrical dynamics (inductance), cogging torque, thermal resistance variation, and LuGre friction. See the technical note for more details.

510d75f4 Actuators with joint or tendon transmissions can now contribute damping and armature to their transmission target. These are applied during the passive force and inertia computations, respectively, and are scaled by gear 2 (“reflected” damping/inertia).

efae9157 Stiffness in joints and tendons and damping in joints and tendons now support nonlinear polynomial force profiles . New mjModel arrays ( jnt_stiffnesspoly , tendon_stiffnesspoly , dof_dampingpoly , tendon_dampingpoly ) hold higher-order coefficients. The existing scalar arrays ( jnt_stiffness , dof_damping , etc.) continue to hold the linear coefficient and are unchanged. The polynomial order is defined by the new constant mjNPOLY . A future breaking C-API change may unify the linear and higher-order coefficients into a single array.

0c337799 Added midpoint integration for standalone free bodies in implicit and implicitfast integrators . This applies the implicit midpoint rule to the rotational dynamics of free bodies with no children, conserving kinetic energy to machine precision in the absence of external torques. The invdiscrete flag now also disables midpoint integration, providing an opt-out mechanism.

412cee20 Added the centripetal/Coriolis acceleration term (\dot{J}v) to the constraint solver bias for connect and weld equality constaints. This significantly improves the stability of constrained mechanisms like four-bar linkages. See Dual problem for details.

f5d3ce34 Introduced mjpEncoder , the counterpart to mjpDecoder for encoding of mjSpec and mjModel into mjResource .

f5d3ce34 Added mj_encode , mjp_registerEncoder , mjp_defaultEncoder , and mjp_findEncoder .

Breaking API changes

efae9157 The mjs layer fields stiffness and damping in mjsJoint and mjsTendon have been widened from mjtNum scalars to mjtNum[mjNPOLY+1] arrays. The first element is the linear coefficient (previously the scalar), and subsequent elements are the higher-order polynomial coefficients.

Migration: Replace assignments like joint.stiffness = val with joint.stiffness[0] = val .

15ca42ff .obj and .stl decoders are now included as source when building MuJoCo with CMake. This fixes the behaviour from the previous release where it required downstream code to load these plugins explicitly.

4b1667e4 The vertcollide field in mjsFlex has been removed. It is no longer required since MuJoCo Warp supports native flex collisions.

f2461f9c mjPLUGIN_LIB_INIT macro now requires a name argument to avoid initialization function name collisions. When building with MSVC, we now use the C runtime initialization section to initialize plugins instead of DllMain . See plugin registration for more details.

0e04436d The mjtWarning enum value mjWARN_VGEOMFULL is removed. Exhaustion of visual geoms is now handled internally by the mjvScene .

7ae07d81 URDF parsing no longer hardcodes strippath to “true”. The setting is now respected and the default is “false”. Setting this is attribute is now the responsibility of the user.

Migration: Set strippath to “true” in MJCF or programmatically using

spec = mujoco . MjSpec . from_file ( "path/to/model.urdf" ) spec . compiler . strippath = True

Bug fixes

ecc22667 The compiler now correctly accounts for negative scaling when loading user specified mesh data.

General

1. 70a7647a Added the dcmotor actuator for modeling DC motors. Supports optional electrical dynamics (inductance), cogging torque, thermal resistance variation, and LuGre friction. See the technical note for more details.

2. 510d75f4 Actuators with joint or tendon transmissions can now contribute damping and armature to their transmission target. These are applied during the passive force and inertia computations, respectively, and are scaled by gear2 ("reflected" damping/inertia).

1. efae9157 Stiffness in joints and tendons and damping in joints and tendons now support nonlinear polynomial force profiles. New mjModel arrays (jnt_stiffnesspoly, tendon_stiffnesspoly, dof_dampingpoly, tendon_dampingpoly) hold higher-order coefficients. The existing scalar arrays (jnt_stiffness, dof_damping, etc.) continue to hold the linear coefficient and are unchanged. The polynomial order is defined by the new constant mjNPOLY. A future breaking C-API change may unify the linear and higher-order coefficients into a single array.

2. 0c337799 Added midpoint integration for standalone free bodies in implicit and implicitfast integrators. This applies the implicit midpoint rule to the rotational dynamics of free bodies with no children, conserving kinetic energy to machine precision in the absence of external torques. The invdiscrete flag now also disables midpoint integration, providing an opt-out mechanism.

3. 412cee20 Added the centripetal/Coriolis acceleration term dot{J}v to the constraint solver bias for connect and weld equality constaints. This significantly improves the stability of constrained mechanisms like four-bar linkages. See Dual problem for details.

4. f5d3ce34 Introduced mjpEncoder, the counterpart to mjpDecoder for encoding of mjSpec and mjModel into mjResource.

5. f5d3ce34 Added mj_encode, mjp_registerEncoder, mjp_defaultEncoder, and mjp_findEncoder.

Breaking API changes

1. efae9157 The mjs layer fields stiffness and damping in mjsJoint and mjsTendon have been widened from mjtNum scalars to mjtNum[mjNPOLY+1] arrays. The first element is the linear coefficient (previously the scalar), and subsequent elements are the higher-order polynomial coefficients.

   Migration: Replace assignments like joint.stiffness = val with joint.stiffness[0] = val.

2. 15ca42ff .obj and .stl decoders are now included as source when building MuJoCo with CMake. This fixes the behaviour from the previous release where it required downstream code to load these plugins explicitly.

3. 4b1667e4 The vertcollide field in mjsFlex has been removed. It is no longer required since MuJoCo Warp supports native flex collisions.

4. f2461f9c mjPLUGIN_LIB_INIT macro now requires a name argument to avoid initialization function name collisions. When building with MSVC, we now use the C runtime initialization section to initialize plugins instead of DllMain. See plugin registration for more details.

5. 0e04436d The mjtWarning enum value mjWARN_VGEOMFULL is removed. Exhaustion of visual geoms is now handled internally by the mjvScene.

6. 7ae07d81 URDF parsing no longer hardcodes strippath to "true". The setting is now respected and the default is "false". Setting this is attribute is now the responsibility of the user.

   Migration: Set strippath to "true" in MJCF or programmatically using

   spec = mujoco.MjSpec.from_file("path/to/model.urdf")
   spec.compiler.strippath = True

Bug fixes

1. ecc22667 The compiler now correctly accounts for negative scaling when loading user specified mesh data.

General

Breaking API changes

9efe41c0 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.

6890e133 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.

713b5524 Added a new strain equality constraint type for trilinear and quadratic dofs .

bf74d01d Flexes now support collisions with SDF geoms.

5903d482 Improved memory requirements for ten_J and ten_J_colind by reducing the upper bound for the number of non-zeros nJten .

37e993f6 Improved memory requirements for actuator_moment and moment_colind by reducing the upper bound for the number of non-zeros nJmom .

MJX

62a32386 Add batch rendering support for MJX-Warp. See the MJX-Warp batch rendering section for details.

Bug fixes

6ec808e2 Fixed a bug where mjs_attach silently dropped spatial tendons with wrapping geometries that had no sidesite attribute ( issue #3119 , reported by @tomstewart89 ).

General

Breaking API changes

1. 9efe41c0 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.

1. 6890e133 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.

2. 713b5524 Added a new strain equality constraint type for trilinear and quadratic dofs.

3. bf74d01d Flexes now support collisions with SDF geoms.

4. 5903d482 Improved memory requirements for ten_J and ten_J_colind by reducing the upper bound for the number of non-zeros nJten.

5. 37e993f6 Improved memory requirements for actuator_moment and moment_colind by reducing the upper bound for the number of non-zeros nJmom.

MJX

1. 62a32386 Add batch rendering support for MJX-Warp. See the MJX-Warp batch rendering section for details.

Bug fixes

1. 6ec808e2 Fixed a bug where mjs_attach silently dropped spatial tendons with wrapping geometries that had no sidesite attribute (3119, reported by tomstewart89).

Significant new features

b64b527e MuJoCo Warp is now officially released.

146a5c08 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 .

6419534b 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.

7da271c6 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 .

0041fdcb 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.

9d646e65 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.

ed15493a Rangefinders can now report various kinds of information besides ray distances, including surface normals and intersection points.

General

Breaking API changes

218226fc 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.

218226fc mju_rayFlex has been renamed to mj_rayFlex for consistency with other functions that take mjModel* and mjData* arguments.

b8a4ac5d 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.

cb9a9c15 Removed getdir from the mjpResourceProvider struct. All Resource Providers now use the same shared implementation.

6af0d4c8 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.

c7f57663 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.

608115ab 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.

37762e3f 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.

1d2d0b1c 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) .

a5dc57c0 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.

1ff74ba8 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

1483aefe Added actuator_length , cdof and cdof_dof fields to mjx.Data .

d07f39b4 Add graph_mode argument to put_model to support multiple Warp graph capture modes.

Documentation

b77977a9 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.

c5925e7b The usability of the MJCF schema is improved with a collapsible dropdown menu with links to elements and attributes.

c54f1fe3 MuJoCo version numbering is now based on Semantic Versioning, see VERSIONING.md .

Bug fixes

b4668294 Fixed a bug in implicit integrator derivatives where actuator velocity derivatives were incorrectly computed when the force was clamped by forcerange .

7f74487a Fixed a bug in implicit integrator derivatives where actuator velocity derivatives did not account for the actearly flag.

64a2345c 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.

223ba99e The vertid argument of mj_rayFlex and mju_raySkin was marked as nullable but was not; it is now nullable.

c1b3b306 Fixed gravcomp being ignored for bodies with no joints nested inside jointed parent bodies ( issue #3066 , reported by @Alex108306 ).

Significant new features

1. b64b527e MuJoCo Warp is now officially released.

2. 146a5c08 Added a new System Identification toolbox (Python), see README for details. |br| A Colab notebook demonstrating the toolbox is available here: |br| Contribution by kevinzakka, aftersomemath, jonathanembleyriches, qiayuanl, spjardim and gizemozd.

1. 6419534b 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.

1. 7da271c6 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.

2. 0041fdcb 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.

1. 9d646e65 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.

2. ed15493a Rangefinders can now report various kinds of information besides ray distances, including surface normals and intersection points.

General

Breaking API changes

1. 218226fc 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.

2. 218226fc mju_rayFlex has been renamed to mj_rayFlex for consistency with other functions that take mjModel* and mjData* arguments.

3. b8a4ac5d 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.

4. cb9a9c15 Removed getdir from the mjpResourceProvider struct. All Resource Providers now use the same shared implementation.

5. 6af0d4c8 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.

1. c7f57663 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.

2. 608115ab 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.

3. 37762e3f 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.

4. 1d2d0b1c 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).

5. a5dc57c0 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.

6. 1ff74ba8 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

1. 1483aefe Added actuator_length, cdof and cdof_dof fields to mjx.Data.

2. d07f39b4 Add graph_mode argument to put_model to support multiple Warp graph capture modes.

Documentation

1. b77977a9 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.

2. c5925e7b The usability of the MJCF schema is improved with a collapsible dropdown menu with links to elements and attributes.

3. c54f1fe3 MuJoCo version numbering is now based on Semantic Versioning, see VERSIONING.md.

Bug fixes

1. b4668294 Fixed a bug in implicit integrator derivatives where actuator velocity derivatives were incorrectly computed when the force was clamped by forcerange.

2. 7f74487a Fixed a bug in implicit integrator derivatives where actuator velocity derivatives did not account for the actearly flag.

3. 64a2345c 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.

4. 223ba99e The vertid argument of mj_rayFlex and mju_raySkin was marked as nullable but was not; it is now nullable.

5. c1b3b306 Fixed gravcomp being ignored for bodies with no joints nested inside jointed parent bodies (3066, reported by Alex108306).

General

8734cab3 Introduced a major new feature: sleeping islands . Preliminary release for early testing, see documentation for details.

3a7aa84e Added “quadratic” option to flexcomp/dof . This type of fast deformable flex object is similar to the “trilinear” option, but it includes curved deformations.

b6f25ca6 Raise an error if there are name collisions also during parsing.

b6f25ca6 Increase Windows stack size to 16MB to enable models with deep nested body hierarchies.

19e2d0ae 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.

2f65e237 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.

888d3a7b Added a new mj_copyState function that copies state components from one mjData to another.

ac2cd5df 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.

ac2cd5df MjsWrap now exposes:

type -> mujoco.mjtWrap

target -> MjsSite|MjsJoint|MjsGeom|None

sidesite -> MjsSite|None

coef -> real

divisor -> real

86a77ff8 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

c34ac712 warp-lang optional dependency is updated to 1.10.0. pmap now works with MuJoCo Warp from MJX.

Breaking ABI changes

d0f32a7f 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

88383684 Fixed a bug in the box-box distance computation. Reported by @nvtw .

General

1. 8734cab3 Introduced a major new feature: sleeping islands. Preliminary release for early testing, see documentation for details.

2. 3a7aa84e 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. b6f25ca6 Raise an error if there are name collisions also during parsing.

4. b6f25ca6 Increase Windows stack size to 16MB to enable models with deep nested body hierarchies.

5. 19e2d0ae 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. 2f65e237 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. 888d3a7b Added a new mj_copyState function that copies state components from one mjData to another.

8. ac2cd5df 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. ac2cd5df MjsWrap now exposes:

   • type -> mujoco.mjtWrap

   • target -> MjsSite|MjsJoint|MjsGeom|None

   • sidesite -> MjsSite|None

   • coef -> real

   • divisor -> real

10. 86a77ff8 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

1. c34ac712 warp-lang optional dependency is updated to 1.10.0. pmap now works with MuJoCo Warp from MJX.

Breaking ABI changes

1. d0f32a7f 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

1. 88383684 Fixed a bug in the box-box distance computation. Reported by nvtw.

General

Breaking API changes

77e025ea 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 .

192da874 Remove _full_compat from mjx.put_data and mjx.put_model .

b56cf98e 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.

fe8384b6 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.

6320b959 Added mju_getXMLDependencies for computing a list of unique asset dependencies from an MJCF file.

e4704cd2 Added the code sample dependencies which provides command line utility for printing the result of mju_getXMLDependencies .

bd68f0c6 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

431f9657 The attribute mjOption.apirate was unused and has been removed.

b56cf98e MJX nconmax and njmax fields in mjx.make_data now default to None instead of -1.

MJX

6ae9cc80 Fix issue #2508 , qLD shapes mismatched mjModel during get_data_into .

b56cf98e 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

98682ae2 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.

General

Breaking API changes

1. 77e025ea 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. 192da874 Remove _full_compat from mjx.put_data and mjx.put_model.

3. b56cf98e 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.

1. fe8384b6 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.

2. 6320b959 Added mju_getXMLDependencies for computing a list of unique asset dependencies from an MJCF file.

3. e4704cd2 Added the code sample dependencies which provides command line utility for printing the result of mju_getXMLDependencies.

4. bd68f0c6 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

1. 431f9657 The attribute mjOption.apirate was unused and has been removed.

2. b56cf98e MJX nconmax and njmax fields in mjx.make_data now default to None instead of -1.

MJX

1. 6ae9cc80 Fix 2508, qLD shapes mismatched mjModel during get_data_into.

2. b56cf98e 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

1. 98682ae2 Fix 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.

General

ec94bb49 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.

7443e685 Contact sensor subtree1/subtree2 specification is now available for any body, not just direct children of the world.

Breaking API changes

6ec5f8b9 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.

b092563c 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

ed6fa7fe Removed mjMOUSE_SELECT flag for mjtMouse as it is no longer in use.

ec94bb49 The promotion of islanding to default involved removing the enable flag mjENBL_ISLAND and converting it to a disable flag mjDSBL_ISLAND .

b66175eb Added support for shells with a curved reference configuration. See this example .

8acd83f3 Added experimental option for passive contacts involving flexes.

1fb1810b Added support for assigning a default material to a mesh asset using the mesh/material attribute.

MJX

1763fa53 Promote ten_length to the public MJX API. Add Warp support for mjx.tendon .

Breaking API changes

1763fa53 ten_length was moved from mjx.Data._impl.ten_length to a public field mjx.Data.ten_length .

Bug fixes

ec94bb49 Fixed a latent bug where MjData objects were not serialized correctly by the Python bindings when islanding was enabled.

General

e6c57159 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.

d0e4771c 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.

51babec9 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.

0b11e3e3 Removed the SdfLib plugin and the dependency on SdfLib . SDFs are now supported natively in mjModel.

5e666635 Removed oct_depth from mjvOption (unused).

89f47890 Added the functionality to create a builtin meshes, see mesh/builtin .

ad0dc0de 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

5e666635 Removed the mjVIS_FLEXBVH enum value, its functionality is now provided by mjVIS_MESHBVH .

Bug fixes

6e7aaacb 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.

3434f5d9 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

2e60d058 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

47bc16a3 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.

General

1. e6c57159 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. d0e4771c 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. 51babec9 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. 0b11e3e3 Removed the SdfLib plugin and the dependency on SdfLib. SDFs are now supported natively in mjModel.

5. 5e666635 Removed oct_depth from mjvOption (unused).

6. 89f47890 Added the functionality to create a builtin meshes, see mesh/builtin.

7. ad0dc0de 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

1. 5e666635 Removed the mjVIS_FLEXBVH enum value, its functionality is now provided by mjVIS_MESHBVH.

Bug fixes

1. 6e7aaacb 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.

2. 3434f5d9 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

1. 2e60d058 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

1. 47bc16a3 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.

Breaking API changes

18d5d5d0 The functions mjs_detachBody and mjs_detachDefault have been replaced by mjs_delete .

0488d9f4 The Python functions element.delete have been replaced by spec.delete(element) .

564c51dd 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.

47bc16a3 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

14dc7c2a Added support for setting the initial camera in the viewer using visual/global/cameraid .

09f7154e 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

4ce62932 Inverse dynamics were not being computed correctly when tendon armature was present, now fixed.

45d4cacc Fix bug in mjx.put_data where actuator_moment was not being copied correctly for the C implementation.

Documentation

7548d370 Added missing item documentation and clarified the nature of breaking changes in the 3.3.3 changelog. See items 3 and 4 below.

Breaking API changes

1. 18d5d5d0 The functions mjs_detachBody and mjs_detachDefault have been replaced by mjs_delete.

2. 0488d9f4 The Python functions element.delete have been replaced by spec.delete(element).

3. 564c51dd 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. 47bc16a3 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

1. 14dc7c2a Added support for setting the initial camera in the viewer using visual/global/cameraid.

2. 09f7154e 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

1. 4ce62932 Inverse dynamics were not being computed correctly when tendon armature was present, now fixed.

2. 45d4cacc Fix bug in mjx.put_data where actuator_moment was not being copied correctly for the C implementation.

Documentation

1. 7548d370 Added missing item documentation and clarified the nature of breaking changes in the 3.3.3 changelog. See items 3 and 4 below.

General

ecb769fc 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).

7edbdd0a Removed the shell plugin. This is now supported by flexcomp and is active depending on the elastic2d attribute (off by default).

Breaking API changes

74cc904e 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.

3e9bc79b 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.

89e39dc0 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.

84ad22a5 Added a new function mj_copyBack to copy real-valued arrays in an mjModel to a compatible mjSpec.

b8768aa1 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

ced63018 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

3a4b6e6c Added examples of procedural terrain generation to the Model Editing tutorial:

MJX

caaf7b3a Added tendon armature.

General

1. ecb769fc 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. 7edbdd0a Removed the shell plugin. This is now supported by flexcomp and is active depending on the elastic2d attribute (off by default).

Breaking API changes

1. 74cc904e 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.

2. 3e9bc79b 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.

1. 89e39dc0 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.

2. 84ad22a5 Added a new function mj_copyBack to copy real-valued arrays in an mjModel to a compatible mjSpec.

3. b8768aa1 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

1. ced63018 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

1. 3a4b6e6c Added examples of procedural terrain generation to the Model Editing tutorial: |mjspec_colab|

MJX

1. caaf7b3a Added tendon armature.

MJX

51c489fc Added inverse dynamics.

f317bd17 Added tendon actuator force sensor.

421c487d Fix issue #2606 such that make_data copies over mocap_pos and mocap_quat from body_pos and body_quat .

MJX

1. 51c489fc Added inverse dynamics.

2. f317bd17 Added tendon actuator force sensor.

3. 421c487d Fix 2606 such that make_data copies over mocap_pos and mocap_quat from body_pos and body_quat.

Breaking API changes

f25fc63f 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.

a02a27d4 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

d05251af Added tendon armature : inertia associated with changes in tendon length.

f96f3e1c Added the compiler/saveinertial flag, writing explicit inertial clauses for all bodies when saving to XML.

e8c67ca5 Added orientation attribute to composite . Moreover, allow the composite to be the direct child of a frame.

96dda6ea Added tendon actuator force limits and tendon actuator force sensor .

MJX

8fc616bf Added tendon actuator force limits.

Bug fixes

de48f417 mj_jacDot was missing a term that accounts for the motion of the point with respect to which the Jacobian is computed, now fixed.

1bf24e9f 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.

40393f46 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

16e49f27 Added examples of procedural model creation to the Model Editing tutorial:

ebd30493 Added support for nameless mjSpec objects in the bind method, see the corresponding section in the documentation.

Breaking API changes

1. f25fc63f 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. a02a27d4 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

1. d05251af Added tendon armature: inertia associated with changes in tendon length.

2. f96f3e1c Added the compiler/saveinertial flag, writing explicit inertial clauses for all bodies when saving to XML.

3. e8c67ca5 Added orientation attribute to composite. Moreover, allow the composite to be the direct child of a frame.

4. 96dda6ea Added tendon actuator force limits and tendon actuator force sensor.

MJX

1. 8fc616bf Added tendon actuator force limits.

Bug fixes

1. de48f417 mj_jacDot was missing a term that accounts for the motion of the point with respect to which the Jacobian is computed, now fixed.

2. 1bf24e9f 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.

3. 40393f46 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

1. 16e49f27 Added examples of procedural model creation to the Model Editing tutorial:

2. ebd30493 Added support for nameless mjSpec objects in the bind method, see the corresponding section in the documentation.

Feature promotion

7cdf1806 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.

ed16f2da 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

37d7591c Add support for custom plots in the MuJoCo viewer by exposing a viewport property, a set_figures method, and a clear_figures method.

7cdf1806 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.

240a7afd Added potential and kinetic energy sensors.

ac2a324f Improved shadow rendering in the native renderer.

b0e9d086 Moved introspect to python/introspect .

Breaking API changes

ed16f2da 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.

c2138c3f 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.

89253d95 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.

0fcd20f0 Removed the composite type grid . Users should instead use flexcomp .

c52d1b39 Removed the particle composite type. It is recommended to use the more generic replicate instead, see for example this model .

MJX

f4096bca Added support for spatial tendons with internal sphere and cylinder wrapping.

e0664b1b Fix a bug with box-box collisions issue #2356 .

Python bindings

7a2ad8fd Added a pedagogical colab notebook for mujoco.rollout , a Python module for multithreaded simulation rollouts. It is available here .

Contribution by @aftersomemath .

Feature promotion

1. 7cdf1806 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.

1. ed16f2da 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

1. 37d7591c Add support for custom plots in the MuJoCo viewer by exposing a viewport property, a set_figures method, and a clear_figures method.

2. 7cdf1806 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.

3. 240a7afd Added potential and kinetic energy sensors.

4. ac2a324f Improved shadow rendering in the native renderer.

5. b0e9d086 Moved introspect to python/introspect.

Breaking API changes

1. ed16f2da 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.

2. c2138c3f 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.

3. 89253d95 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.

4. 0fcd20f0 Removed the composite type grid. Users should instead use flexcomp.

5. c52d1b39 Removed the particle composite type. It is recommended to use the more generic replicate instead, see for example this model.

MJX

1. f4096bca Added support for spatial tendons with internal sphere and cylinder wrapping.

2. e0664b1b Fix a bug with box-box collisions 2356.

Python bindings

1. 7a2ad8fd Added a pedagogical colab notebook for mujoco.rollout, a Python module for multithreaded simulation rollouts. It is available here . |br| Contribution by aftersomemath.

Python bindings

a7eb6efd 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 .

40ef08c8 Fix global namespace pollution when using mjpython ( issue #2265 ).

General

Breaking API changes (minor)

69c9ac07 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 .

d4ca66a4 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

0e7d2ef6 Fixed a bug in the box-sphere collider, depth was incorrect for deep penetrations ( issue #2206 ).

ec322641 Fixed a bug in mj_mulM2 and added a test.

Python bindings

1. a7eb6efd 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. 40ef08c8 Fix global namespace pollution when using mjpython (2265).

General

Breaking API changes (minor)

1. 69c9ac07 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.

1. d4ca66a4 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

1. 0e7d2ef6 Fixed a bug in the box-sphere collider, depth was incorrect for deep penetrations (2206).

2. ec322641 Fixed a bug in mj_mulM2 and added a test.

General

300450f8 Removed rope and loop from composite . The user is encouraged to instead use the cable plugin or flexcomp , respectively.

MJX

0f381a9e Added muscle actuators.

Python bindings

74dcd51d Provide prebuilt wheels for Python 3.13.

3a12db9a 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.

943eb6bc rollout can now accept sequences of MjModel of length nroll . Also removed the nroll argument because its value can always be inferred.

Bug fixes

f9569cda Fixed issue #2212 , type error in mjx.get_data .

5c23ae11 Fixed bug introduced in 3.2.0 in handling of texrepeat attribute, was mistakenly cast from float to int , (fixed issue #2223 ).

General

1. 300450f8 Removed rope and loop from composite. The user is encouraged to instead use the cable plugin or flexcomp, respectively.

MJX

1. 0f381a9e Added muscle actuators.

Python bindings

1. 74dcd51d Provide prebuilt wheels for Python 3.13.

2. 3a12db9a 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.

3. 943eb6bc rollout can now accept sequences of MjModel of length nroll. Also removed the nroll argument because its value can always be inferred.

Bug fixes

1. f9569cda Fixed 2212, type error in mjx.get_data.

2. 5c23ae11 Fixed bug introduced in 3.2.0 in handling of texrepeat attribute, was mistakenly cast from float to int, (fixed 2223).

Feature promotion

b6037d17 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.

298ce31e 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

b598d79b The global compiler flag exactmeshinertia has been removed and replaced with the mesh-specific inertia attribute.

7dc8aef8 The not-useful convexhull compiler option (to disable computation of mesh convex hulls) has been removed.

d8494fef Removed the deprecated mju_rotVecMat , mju_rotVecMatT and mjv_makeConnector functions.

2b0629d7 Sorting now uses a faster, native sort function (fixes issue #1638 ).

61cb552f The PBR texture layers introduced in 3.2.1 were refactored from separate sub-elements to a single layer sub-element.

831d9881 The composite types box, cylinder, and sphere have been removed. Users should instead use the equivalent types available in flexcomp .

MJX

680fb3e5 Added apply_ft , jac , and xfrc_accumulate as public functions.

b00a7c67 Added TOUCH sensor.

f24de91c Added support for eq_active . Fixes issue #2173 .

3c21abc0 Added ray intersection with ellipsoid.

Bug fixes

864b805a 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.

7620aef5 Fixed a bug in slider-crank transmission . The bug was introduced in 3.0.0.

831d9881 Fixed a bug in flex texture coordinates that prevented the correct allocation of textures in mjModel.

Documentation

1d58576d Function headers in the API reference now link to their source definitions in GitHub.

Feature promotion

1. b6037d17 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. 298ce31e 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

1. b598d79b The global compiler flag exactmeshinertia has been removed and replaced with the mesh-specific inertia attribute.

2. 7dc8aef8 The not-useful convexhull compiler option (to disable computation of mesh convex hulls) has been removed.

3. d8494fef Removed the deprecated mju_rotVecMat, mju_rotVecMatT and mjv_makeConnector functions.

4. 2b0629d7 Sorting now uses a faster, native sort function (fixes 1638).

5. 61cb552f The PBR texture layers introduced in 3.2.1 were refactored from separate sub-elements to a single layer sub-element.

6. 831d9881 The composite types box, cylinder, and sphere have been removed. Users should instead use the equivalent types available in flexcomp.

MJX

1. 680fb3e5 Added apply_ft, jac, and xfrc_accumulate as public functions.

2. b00a7c67 Added TOUCH sensor.

3. f24de91c Added support for eq_active. Fixes 2173.

4. 3c21abc0 Added ray intersection with ellipsoid.

Bug fixes

1. 864b805a Fixed several bugs related to connect and weld constraints with site semantics (fixes 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.

2. 7620aef5 Fixed a bug in slider-crank transmission. The bug was introduced in 3.0.0.

3. 831d9881 Fixed a bug in flex texture coordinates that prevented the correct allocation of textures in mjModel.

Documentation

1. 1d58576d Function headers in the API reference now link to their source definitions in GitHub.

General

2dd51873 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.

4998e7b3 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.

6832df30 Replaced the function mjs_setActivePlugins with mjs_activatePlugin .

MJX

1a9d3070 Added mocap_pos and mocap_quat in kinematics.

160ed9bf Added support for spatial tendons with pulleys and external sphere and cylinder wrapping.

fa22e6d0 Added sphere-cylinder and sphere-ellipsoid collision functions ( issue #2126 ).

22e4f7fc Fixed a bug with frictionloss constraints.

ac91a763 Added TENDONPOS and TENDONVEL sensors.

19459263 Fixed a bug with the computation of tangential contact forces in _decode_pyramid .

096853e1 Added JOINTINPARENT actuator transmission type.

Python bindings

6881ce24 Removed support for Python 3.8, now that it’s deprecated upstream .

Bug fixes

ab3954d8 Fixed a bug where actuator_force was not set in MJX ( issue #2068 ).

5838f847 Fixed bug where MJX data tendon fields were incorrect after calling mjx.put_data .

8d84b5f6 The compiler now returns an error if height fields are used with collision sensors as they are not yet supported.

General

1. 2dd51873 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. 4998e7b3 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. 6832df30 Replaced the function mjs_setActivePlugins with mjs_activatePlugin.

MJX

1. 1a9d3070 Added mocap_pos and mocap_quat in kinematics.

2. 160ed9bf Added support for spatial tendons with pulleys and external sphere and cylinder wrapping.

3. fa22e6d0 Added sphere-cylinder and sphere-ellipsoid collision functions (2126).

4. 22e4f7fc Fixed a bug with frictionloss constraints.

5. ac91a763 Added TENDONPOS and TENDONVEL sensors.

6. 19459263 Fixed a bug with the computation of tangential contact forces in _decode_pyramid.

7. 096853e1 Added JOINTINPARENT actuator transmission type.

Python bindings

1. 6881ce24 Removed support for Python 3.8, now that it's deprecated upstream.

Bug fixes

1. ab3954d8 Fixed a bug where actuator_force was not set in MJX (2068).

2. 5838f847 Fixed bug where MJX data tendon fields were incorrect after calling mjx.put_data.

3. 8d84b5f6 The compiler now returns an error if height fields are used with collision sensors as they are not yet supported.

General

Breaking API changes

088079ef 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.

d3dfa6f9 The functions mjs_findMesh and mjs_findKeyframe were replaced by mjs_findElement , which allows to look for any object type.

4862b9e7 The experimental use of 2D/3D elasticity plugins with composite has been removed. Users should instead use flexcomp , which provides the correct collision behavior.

0bffd744 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.

60a1921b 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.

8954a088 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.

851bb6ee Added an mjSpec option for creating a texture directly from a buffer.

466368ef shell (surface) inertia is now supported by all geom types.

afd7c73f When attaching sub-models, keyframes will now be correctly merged into the parent model, but only on the first attachment.

8b03daa0 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 .

2d3d5415 Added mj_jacDot for computing time-derivatives of kinematic Jacobians. Fixes issue #411 .

MJX

a74c184f Added efc_pos to mjx.Data ( issue #1388 ).

6a12787a Added position-dependent sensors: MAGNETOMETER , CAMPROJECTION , RANGEFINDER , JOINTPOS , ACTUATORPOS , BALLQUAT , FRAMEPOS , FRAMEXAXIS , FRAMEYAXIS , FRAMEZAXIS , FRAMEQUAT , SUBTREECOM , CLOCK .

9805df61 Added velocity-dependent sensors: VELOCIMETER , GYRO , JOINTVEL , ACTUATORVEL , BALLANGVEL , FRAMELINVEL , FRAMEANGVEL , SUBTREELINVEL , SUBTREEANGMOM .

9d732117 Added acceleration/force-dependent sensors: ACCELEROMETER , FORCE , TORQUE , ACTUATORFRC , JOINTACTFRC , FRAMELINACC , FRAMEANGACC .

390bce23 Changed default policy to avoid placing unused (MuJoCo-only) arrays on device.

390bce23 Added device parameter to mjx.make_data to bring it to parity with mjx.put_model and mjx.put_data .

a68141ee Added support for implicitfast integration for all cases except fluid drag .

494e166f Fixed a bug where qLDiagInv had the wrong size for sparse mass matrices.

49711fa1 Added support for joint and tendon frictionloss .

cd8ff440 Added support for connect equality constraints using two sites.

e3d3a24b Added support for spatial tendons with site wrapping.

Bug fixes

39896f80 Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies ( issue #1875 , contribution by @michael-ahn ).

0bcaa856 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.

3e701b21 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.

567793c2 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

cfc7dc98 Added support for engine plugins in mjSpec ( issue #1903 ).

9a27fc14 Better error reporting for issues with the assets dictionary, when loading models.

General

Breaking API changes

1. 088079ef 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. d3dfa6f9 The functions mjs_findMesh and mjs_findKeyframe were replaced by mjs_findElement, which allows to look for any object type.

3. 4862b9e7 The experimental use of 2D/3D elasticity plugins with composite has been removed. Users should instead use flexcomp, which provides the correct collision behavior.

1. 0bffd744 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.

1. 60a1921b 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.

2. 8954a088 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.

3. 851bb6ee Added an mjSpec option for creating a texture directly from a buffer.

4. 466368ef shell (surface) inertia is now supported by all geom types.

5. afd7c73f When attaching sub-models, keyframes will now be correctly merged into the parent model, but only on the first attachment.

6. 8b03daa0 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.

7. 2d3d5415 Added mj_jacDot for computing time-derivatives of kinematic Jacobians. Fixes 411.

MJX

1. a74c184f Added efc_pos to mjx.Data (1388).

2. 6a12787a Added position-dependent sensors: MAGNETOMETER, CAMPROJECTION, RANGEFINDER, JOINTPOS, ACTUATORPOS, BALLQUAT, FRAMEPOS, FRAMEXAXIS, FRAMEYAXIS, FRAMEZAXIS, FRAMEQUAT, SUBTREECOM, CLOCK.

3. 9805df61 Added velocity-dependent sensors: VELOCIMETER, GYRO, JOINTVEL, ACTUATORVEL, BALLANGVEL, FRAMELINVEL, FRAMEANGVEL, SUBTREELINVEL, SUBTREEANGMOM.

4. 9d732117 Added acceleration/force-dependent sensors: ACCELEROMETER, FORCE, TORQUE, ACTUATORFRC, JOINTACTFRC, FRAMELINACC, FRAMEANGACC.

5. 390bce23 Changed default policy to avoid placing unused (MuJoCo-only) arrays on device.

6. 390bce23 Added device parameter to mjx.make_data to bring it to parity with mjx.put_model and mjx.put_data.

7. a68141ee Added support for implicitfast integration for all cases except fluid drag.

8. 494e166f Fixed a bug where qLDiagInv had the wrong size for sparse mass matrices.

9. 49711fa1 Added support for joint and tendon frictionloss.

10. cd8ff440 Added support for connect equality constraints using two sites.

11. e3d3a24b Added support for spatial tendons with site wrapping.

Bug fixes

1. 39896f80 Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies (1875, contribution by michael-ahn).

2. 0bcaa856 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.

3. 3e701b21 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.

4. 567793c2 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

1. cfc7dc98 Added support for engine plugins in mjSpec (1903).

2. 9a27fc14 Better error reporting for issues with the assets dictionary, when loading models.

General

9db9df73 Increase texture and material limit back to 1000. 3.2.0 inadvertently reduced this limit to 100, breaking some existing models ( issue #1877 ).

General

e92af73c Renamed mjModel.tex_rgb to mjModel.tex_data .

24a55506 Added a new autoreset flag to disable automatic reset when NaNs or infinities are detected.

33e59606 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.

82c27165 Sorting ( mjQUICKSORT ) now calls std::sort when building with C++ ( issue #1638 ).

MJX

dbe18f57 Added more fields to mjx.Model and mjx.Data for further compatibility with the corresponding MuJoCo structs.

2d24c588 Added support for fixed tendons .

2d24c588 Added support for tendon length limits ( mjCNSTR_LIMIT_TENDON in mjtConstraint ).

2d24c588 Added support for tendon equality constraints ( mjEQ_TENDON in mjtEq ).

2d24c588 Added support for tendon actuator transmission ( mjTRN_TENDON in mjtTrn ).

Python bindings

70ac76bb Added support for asset dictionary argument in mujoco.spec.from_file , mujoco.spec.from_string and mujoco.spec.compile .

Bug fixes

a4bd2bec Fixed a bug where implicit integrators did not take into account disabled actuators ( issue #1838 ).

General

1. e92af73c Renamed mjModel.tex_rgb to mjModel.tex_data.

2. 24a55506 Added a new autoreset flag to disable automatic reset when NaNs or infinities are detected.

3. 33e59606 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. 82c27165 Sorting (mjQUICKSORT) now calls std::sort when building with C++ (1638).

MJX

1. dbe18f57 Added more fields to mjx.Model and mjx.Data for further compatibility with the corresponding MuJoCo structs.

2. 2d24c588 Added support for fixed tendons.

3. 2d24c588 Added support for tendon length limits (mjCNSTR_LIMIT_TENDON in mjtConstraint).

4. 2d24c588 Added support for tendon equality constraints (mjEQ_TENDON in mjtEq).

5. 2d24c588 Added support for tendon actuator transmission (mjTRN_TENDON in mjtTrn).

Python bindings

1. 70ac76bb Added support for asset dictionary argument in mujoco.spec.from_file, mujoco.spec.from_string and mujoco.spec.compile.

Bug fixes

1. a4bd2bec Fixed a bug where implicit integrators did not take into account disabled actuators (1838).

New features

e13ddfa2 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

e66b9a36 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.

57e6760e Calls to mj_defaultVFS may allocate memory inside VFS, and the corresponding mj_deleteVFS must be called to deallocate any internal allocated memory.

60670485 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.

393895bb 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.

27b9ddda Added attach meta-element to MJCF, which allows attaching a subtree from a different model to a body in the current model.

57e6760e The VFS implementation has been rewritten in C++ and is now considerably more efficient in speed and memory footprint.

07fc95ca 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.

ace0c8f0 Added maxhullvert , the maximum number of vertices in a mesh’s convex hull.

c9bcf837 Added mj_setKeyframe for saving the current state into a model keyframe.

5ed464b4 Added support for ball joints in the URDF parser (“spherical” in URDF).

3f3b39bb 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.

22a10fd2 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.

3d1d1d07 Mesh loading in the compiler, which is usually the slowest part of the loading process, is now multi-threaded.

MJX

4c3d9461 Added support for elliptic friction cones .

4c3d9461 Fixed a bug that resulted in less-optimal linesearch solutions for some difficult constraint settings.

4c3d9461 Fixed a bug in the Newton solver that sometimes resulted in less-optimal gradients.

Simulate

1eb70864 Added improved tutorial video.

f37f8408 Improved the Brownian noise generator.

3d1d1d07 Now displaying model load times if they are longer than 0.25 seconds.

Python bindings

2188cba4 Fixed a memory leak when using copy.deepcopy() on a mujoco.MjData instance ( issue #1572 ).

Bug fixes

e7301edd Fix an issue where mj_copyData (or copy.copy() in the Python bindings) was not copying contact information correctly ( issue #1710 ).

8e827d0d Fix an issue with saving to XML that caused frames to be written multiple times ( issue #1802 ).

New features

1. e13ddfa2 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 364.

General

Breaking API changes

1. e66b9a36 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.

2. 57e6760e Calls to mj_defaultVFS may allocate memory inside VFS, and the corresponding mj_deleteVFS must be called to deallocate any internal allocated memory.

3. 60670485 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.

4. 393895bb 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.

1. 27b9ddda Added attach meta-element to MJCF, which allows attaching a subtree from a different model to a body in the current model.

2. 57e6760e The VFS implementation has been rewritten in C++ and is now considerably more efficient in speed and memory footprint.

1. 07fc95ca 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.

2. ace0c8f0 Added maxhullvert, the maximum number of vertices in a mesh's convex hull.

3. c9bcf837 Added mj_setKeyframe for saving the current state into a model keyframe.

4. 5ed464b4 Added support for ball joints in the URDF parser ("spherical" in URDF).

5. 3f3b39bb 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.

6. 22a10fd2 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.

7. 3d1d1d07 Mesh loading in the compiler, which is usually the slowest part of the loading process, is now multi-threaded.

MJX

1. 4c3d9461 Added support for elliptic friction cones.

2. 4c3d9461 Fixed a bug that resulted in less-optimal linesearch solutions for some difficult constraint settings.

3. 4c3d9461 Fixed a bug in the Newton solver that sometimes resulted in less-optimal gradients.

Simulate

1. 1eb70864 Added improved tutorial video.

2. f37f8408 Improved the Brownian noise generator.

3. 3d1d1d07 Now displaying model load times if they are longer than 0.25 seconds.

Python bindings

1. 2188cba4 Fixed a memory leak when using copy.deepcopy() on a mujoco.MjData instance (1572).

Bug fixes

1. e7301edd Fix an issue where mj_copyData (or copy.copy() in the Python bindings) was not copying contact information correctly (1710).

2. 8e827d0d Fix an issue with saving to XML that caused frames to be written multiple times (1802).

General

02d01545 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 .

2830a407 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

c511d022 Add height-field collision support. Fixes issue #1491 .

c511d022 Add a pre-compiled field mesh_convex to mjx.Model so that mesh properties can be vmapped over. Fixes issue #1655 .

c511d022 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

96844db9 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 .

1d181786 Fixed a bug that was causing the visualization of SDF iterations to write outside the size of the vector storing them. Fixes issue #1539 .

General

26f23066 Added the replicate to MJCF, a meta-element which permits to repeat a subtree with incremental translational and rotational offsets.

ad045968 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.

6481a838 Added mjModel.mesh_scale : the scaling applied to asset vertices, as specified in the scale attribute.

caf215e3 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.

546a27ca The type of the size argument of mj_stackAllocNum and mj_stackAllocInt was changed from int to size_t .

131b1745 Added support for gmsh format version 2.2 surface meshes in flexcomp .

MJX

Breaking API changes

718e079c 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 .

0cd28d24 Added cylinder plane collisions.

71333938 Added efc_type to mjx.Data and dim , efc_address to mjx.Contact .

71333938 Added geom to mjx.Contact and marked geom1 , geom2 deprecated.

3b64217b Added ne , nf , nl , nefc , and ncon to mjx.Data to match mujoco.MjData .

a4df9120 Given the above added fields, removed mjx.get_params , mjx.ncon , and mjx.count_constraints .

a4df9120 Changed the way meshes are organized on device to speed up collision detection when a mesh is replicated for many geoms.

a4df9120 Fixed a bug where capsules might be ignored in broadphase colliision checking.

c2d0c5dd Added cylinder collisions using SDFs.

71333938 Added support for all condim : 1, 3, 4, 6.

d15db545 Add support functions for id2name and name2id , MJX versions of mj_id2name and mj_name2id .

e9709900 Added support for gravcomp and actuatorgravcomp .

719476c2 Fixed a bug in mjx.ray for sometimes allowed negative distances for ray-mesh tests.

24bc1c8b 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

0cd28d24 Defaults of lights were not being saved, now fixed.

4b6c07cd Prevent overwriting of frame names by body names when saving an XML. Bug introduced in 3.1.4.

2b497581 Fixed bug in Python binding of mj_saveModel : buffer argument was documented as optional but was actually not optional.

546a27ca Fixed bug that prevented memory allocations larger than 2.15 GB. Fixes issue #1606 .

General

1. 26f23066 Added the replicate to MJCF, a meta-element which permits to repeat a subtree with incremental translational and rotational offsets.

2. ad045968 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. 6481a838 Added mjModel.mesh_scale: the scaling applied to asset vertices, as specified in the scale attribute.

4. caf215e3 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. 546a27ca The type of the size argument of mj_stackAllocNum and mj_stackAllocInt was changed from int to size_t.

6. 131b1745 Added support for gmsh format version 2.2 surface meshes in flexcomp.

MJX

Breaking API changes

1. 718e079c 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.

1. 0cd28d24 Added cylinder plane collisions.

2. 71333938 Added efc_type to mjx.Data and dim, efc_address to mjx.Contact.

3. 71333938 Added geom to mjx.Contact and marked geom1, geom2 deprecated.

4. 3b64217b Added ne, nf, nl, nefc, and ncon to mjx.Data to match mujoco.MjData.

5. a4df9120 Given the above added fields, removed mjx.get_params, mjx.ncon, and mjx.count_constraints.

6. a4df9120 Changed the way meshes are organized on device to speed up collision detection when a mesh is replicated for many geoms.

7. a4df9120 Fixed a bug where capsules might be ignored in broadphase colliision checking.

8. c2d0c5dd Added cylinder collisions using SDFs.

9. 71333938 Added support for all condim: 1, 3, 4, 6.

10. d15db545 Add support functions for id2name and name2id, MJX versions of mj_id2name and mj_name2id.

11. e9709900 Added support for gravcomp and actuatorgravcomp.

12. 719476c2 Fixed a bug in mjx.ray for sometimes allowed negative distances for ray-mesh tests.

13. 24bc1c8b 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

1. 0cd28d24 Defaults of lights were not being saved, now fixed.

2. 4b6c07cd Prevent overwriting of frame names by body names when saving an XML. Bug introduced in 3.1.4.

3. 2b497581 Fixed bug in Python binding of mj_saveModel: buffer argument was documented as optional but was actually not optional.

4. 546a27ca Fixed bug that prevented memory allocations larger than 2.15 GB. Fixes 1606.

General

Breaking API changes

5d26b50f 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.

47ba72ea 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.

4f0293c6 Added support for gmsh format 2.2 , tetrahedral mesh, as generated by e.g. fTetwild .

5a365603 Added mju_euler2Quat for converting an Euler-angle sequence to quaternion.

MJX

22cd96fb Improved performance of SAT for convex collisions.

f2e107f7 Fixed bug for sphere/capsule-convex deep penetration.

02c62c11 Fixed bug where mjx.Data produced by mjx.put_data had different treedef than mjx.make_data .

2386353b Throw an error for margin/gap for convex mesh collisions, since they are not supported.

2b3f336b Added ellipsoid plane collisions.

b4419235 Added support for userdata.

2b3f336b Added ellipsoid-ellipsoid and ellipsoid-capsule collisions using signed distance functions (SDFs).

Simulate

bb42ff16 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

adc4b92c 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.

General

Breaking API changes

1. 5d26b50f 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.

1. 47ba72ea 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.

2. 4f0293c6 Added support for gmsh format 2.2 , tetrahedral mesh, as generated by e.g. fTetwild.

3. 5a365603 Added mju_euler2Quat for converting an Euler-angle sequence to quaternion.

MJX

1. 22cd96fb Improved performance of SAT for convex collisions.

2. f2e107f7 Fixed bug for sphere/capsule-convex deep penetration.

3. 02c62c11 Fixed bug where mjx.Data produced by mjx.put_data had different treedef than mjx.make_data.

4. 2386353b Throw an error for margin/gap for convex mesh collisions, since they are not supported.

5. 2b3f336b Added ellipsoid plane collisions.

6. b4419235 Added support for userdata.

7. 2b3f336b Added ellipsoid-ellipsoid and ellipsoid-capsule collisions using signed distance functions (SDFs).

Simulate

1. bb42ff16 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

1. adc4b92c 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: |br| The video on the right shows example clips from the tutorial.

General

05150546 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.

a4a621f6 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.

6b7d7142 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

4933a2c7 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 .

e77c3cb2 Fixed a bug in mjx-viewer that prevented it from running. Updated mjx-viewer to use newer mjx.get_data_into function call.

47bb4a82 Fixed a bug in mjx.euler that applied incorrect damping when using dense mass matrices.

47bb4a82 Fixed a bug in mjx.solve that was causing slow convergence when using mjSOL_NEWTON in mjtSolver .

6a346c42 Added support for mjOption.impratio to mjx.Model .

2067e208 Added support for cameras in mjx.Model and mjx.Data . Fixes issue #1422 .

419be4c6 Added an implementation of broadphase using top_k and bounding spheres.

Python bindings

abf6d41b 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.

General

1. 05150546 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. a4a621f6 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. 6b7d7142 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

1. 4933a2c7 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.

2. e77c3cb2 Fixed a bug in mjx-viewer that prevented it from running. Updated mjx-viewer to use newer mjx.get_data_into function call.

3. 47bb4a82 Fixed a bug in mjx.euler that applied incorrect damping when using dense mass matrices.

4. 47bb4a82 Fixed a bug in mjx.solve that was causing slow convergence when using mjSOL_NEWTON in mjtSolver.

5. 6a346c42 Added support for mjOption.impratio to mjx.Model.

6. 2067e208 Added support for cameras in mjx.Model and mjx.Data. Fixes 1422.

7. 419be4c6 Added an implementation of broadphase using top_k and bounding spheres.

Python bindings

1. abf6d41b 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.

General

e0864ab7 Improved the discardvisual compiler flag, which now discards all visual-only assets. See discardvisual for details.

2feefbc5 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.

fea7c10b 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 .

e143b3db 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

80f50c94 Added dyntype filterexact .

8ce2c920 Added site transmission.

feb92bf5 Updated MJX colab tutorial with more stable quadruped environment.

a02fc405 Added mjx.ray which mirrors mj_ray for planes, spheres, capsules, boxes, and meshes.

0a7be173 Added mjx.is_sparse which mirrors mj_isSparse and mjx.full_m which mirrors mj_fullM .

0a7be173 Added support for specifying sparse or dense mass matrices via jacobian: [dense, sparse, auto], “auto” .

508669a9 Raise a not implemented error when nonzero frictionloss is present. Fixes issue #1344 .

Python bindings

aceb52bd 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.

7bb0ce42 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

1e2e0b30 Fixed a bug that prevented the use of pins with plugins if flexes are not in the worldbody. Fixes issue #1270 .

a14a584f Fixed a bug in the muscle model that led to non-zero values outside the lower bound of the length range. Fixes issue #1342 .

General

1. e0864ab7 Improved the discardvisual compiler flag, which now discards all visual-only assets. See discardvisual for details.

2. 2feefbc5 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. fea7c10b 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 1279.

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

4. e143b3db 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

1. 80f50c94 Added dyntype filterexact.

2. 8ce2c920 Added site transmission.

3. feb92bf5 Updated MJX colab tutorial with more stable quadruped environment.

4. a02fc405 Added mjx.ray which mirrors mj_ray for planes, spheres, capsules, boxes, and meshes.

5. 0a7be173 Added mjx.is_sparse which mirrors mj_isSparse and mjx.full_m which mirrors mj_fullM.

6. 0a7be173 Added support for specifying sparse or dense mass matrices via option-jacobian.

7. 508669a9 Raise a not implemented error when nonzero frictionloss is present. Fixes 1344.

Python bindings

1. aceb52bd 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.

2. 7bb0ce42 The sync function for the passive viewer can now pick up changes to rendering flags in user_scn, as requested in 1190.

Bug fixes

1. 1e2e0b30 Fixed a bug that prevented the use of pins with plugins if flexes are not in the worldbody. Fixes 1270.

2. a14a584f Fixed a bug in the muscle model that led to non-zero values outside the lower bound of the length range. Fixes 1342.

Bug fixes

d39ed1d3 Fixed a bug (introduced in 3.1.0) where box-box collisions produced no contacts if one box was deeply embedded in the other.

dc0d0c59 Fixed a bug in simulate where the “LOADING…” message was not showing correctly.

d39ed1d3 Fixed a crash in the Python passive viewer , when used with models containing Flex objects.

0915d69c Fixed a bug in MJX where site_xmat was ignored in get_data and put_data

d39ed1d3 Fixed a bug in MJX where efc_address was sometimes incorrectly calculated in get_data .

Bug fixes

1. d39ed1d3 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. dc0d0c59 Fixed a bug in simulate where the "LOADING..." message was not showing correctly.

3. d39ed1d3 Fixed a crash in the Python passive viewer, when used with models containing Flex objects.

4. 0915d69c Fixed a bug in MJX where site_xmat was ignored in get_data and put_data

5. d39ed1d3 Fixed a bug in MJX where efc_address was sometimes incorrectly calculated in get_data.

General

8ca51b53 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.

eb9568a4 Added frame to MJCF, a meta-element which defines a pure coordinate transformation on its direct children, without requiring a body .

762371c3 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

f2025c6a 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.

ca046cbf Added the pid actuator plugin, a configurable PID controller that implements the Integral term, which is not available with native MuJoCo actuators.

MJX

35c90844 Added site_xpos and site_xmat to MJX.

67fa7c1d 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

cd56a41f 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.

cd56a41f Fix bug that prevented using flex with simulate .

7d8d4d39 Fix bug that prevented the use of elasticity plugins in combination with pinned flex vertices.

3c05f9fa 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 .

49ddb7ca Fixed mass computation of meshes: Use the correct mesh volume instead of approximating it using the inertia box.

General

1. 8ca51b53 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. eb9568a4 Added frame to MJCF, a meta-element which defines a pure coordinate transformation on its direct children, without requiring a body.

3. 762371c3 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

1. f2025c6a 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.

2. ca046cbf Added the pid actuator plugin, a configurable PID controller that implements the Integral term, which is not available with native MuJoCo actuators.

MJX

1. 35c90844 Added site_xpos and site_xmat to MJX.

2. 67fa7c1d 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

1. cd56a41f 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.

2. cd56a41f Fix bug that prevented using flex with simulate.

3. 7d8d4d39 Fix bug that prevented the use of elasticity plugins in combination with pinned flex vertices.

4. 3c05f9fa 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 1213.

5. 49ddb7ca Fixed mass computation of meshes: Use the correct mesh volume instead of approximating it using the inertia box.

General

a89412bb 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 .

893c4042 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.

7e419276 Increased mjMAXUIITEM (maximum number of UI elements per section in Simulate) to 200.

MJX

3c0a56c1 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 .

70699765 Added support for joint equality constraints ( mjEQ_JOINT in mjtEq ).

f6ed57e9 Fixed bug where mixed jnt_limited joints were not being constrained correctly.

e4a9f535 Made device_put type validation more verbose (fixes issue #1113 ).

843360b7 Removed empty EFC rows from MJX , for joints with no limits (fixes issue #1117 ).

c8146372 Fixed bug in scan.body_tree that led to incorrect smooth dynamics for some kinematic tree layouts.

Python bindings

4c24be9e Fix the macOS mjpython launcher to work with the Python interpreter from Apple Command Line Tools.

084facc9 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

f6ed57e9 simulate : correct handling of “Pause update”, “Fullscreen” and “VSync” buttons.

Documentation

8d5966ee Added cell to the tutorial colab providing an example of procedural camera control:

2bb8652b Added documentation for the User Interface framework.

dc8bac2f Fixed typos and supported fields in docs (fixes issue #1105 and issue #1106 ).

Bug fixes

86d9c84e Fixed bug relating to welds modified with torquescale .

General

1. a89412bb 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.

1. 893c4042 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 1092. See CActDisable.

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

2. 7e419276 Increased mjMAXUIITEM (maximum number of UI elements per section in Simulate) to 200.

MJX

1. 3c0a56c1 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.

2. 70699765 Added support for joint equality constraints (mjEQ_JOINT in mjtEq).

3. f6ed57e9 Fixed bug where mixed jnt_limited joints were not being constrained correctly.

4. e4a9f535 Made device_put type validation more verbose (fixes 1113).

5. 843360b7 Removed empty EFC rows from MJX, for joints with no limits (fixes 1117).

6. c8146372 Fixed bug in scan.body_tree that led to incorrect smooth dynamics for some kinematic tree layouts.

Python bindings

1. 4c24be9e Fix the macOS mjpython launcher to work with the Python interpreter from Apple Command Line Tools.

2. 084facc9 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

1. f6ed57e9 simulate: correct handling of "Pause update", "Fullscreen" and "VSync" buttons.

Documentation

1. 8d5966ee Added cell to the tutorial colab providing an example of procedural camera control:

2. 2bb8652b Added documentation for the UI framework.

3. dc8bac2f Fixed typos and supported fields in docs (fixes 1105 and 1106).

Bug fixes

1. 86d9c84e Fixed bug relating to welds modified with torquescale.

New features

1. 8f9c690c Added simulation on GPU and TPU via the new 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.

1. fdb04158 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.

1. 139a8ae2 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.

1. 3e034e38 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).

2. 62251869 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.

3. 139a8ae2 Added capability to initialize composite particles from OBJ files. Fixes 642 and 674.

General

Breaking API changes

1. ba66bd4f 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).

2. 9902b735 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.

3. 49290772 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 mjtNum |-| s.

4. 86d8b912 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.

5. 9cf1f6eb 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 |br| <default> <geom contype="0" conaffinity="0"/> </default>.

6. d3d46e16 Removed the rope and cloth composite objects.

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

7. ee78b8f7 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 876.

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

8. d88675a0 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).

1. 2c3297b3 Added a new dyntype, filterexact, which updates first-order filter states with the exact formula rather than with Euler integration.

2. 2c3297b3 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.

3. a276c49c Renamed actuatorforcerange and actuatorforcelimited, introduced in the previous version to actuatorfrcrange and actuatorfrclimited, respectively.

4. b7cf479a Added the flag eulerdamp, which disables implicit integration of joint damping in the Euler integrator. See the Numerical Integration section for more details.

5. 819b5cb9 Added the flag invdiscrete, which enables discrete-time inverse dynamics for all integrators other than RK4. See the flag documentation for more details.

6. 1a3215e3 Added ls_iterations and ls_tolerance options for adjusting linesearch stopping criteria in CG and Newton solvers. These can be useful for performance tuning.

7. ccda87aa Added mesh_pos and mesh_quat fields to mjModel to store the normalizing transformation applied to mesh assets. Fixes 409.

8. 8064ad59 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.

9. 36d2ffe4 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.

10. 59164702 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 978 by Levi Burner.

11. fb4cf472 Deleted the code sample testxml. The functionality provided by this utility is implemented in the WriteReadCompare test.

12. a1b6026b Deleted the code sample derivative. Functionality provided by mjd_transitionFD.

Python bindings

1. 631b16e7 Fixed 870 where calling update_scene with an invalid camera name used the default camera.

2. 2e15574b Added user_scn to the passive viewer handle, which allows users to add custom visualization geoms (1023).

3. a1d0cbd6 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

1. 3e12f0d5 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:

2. 93d1c3c9 The LOADING... label is now shown correctly. Contribution 1070 by Levi Burner.

Documentation

1. 18e4e101 Added detailed documentation of fluid force modeling, and an illustrative example model showing tumbling cards using the ellipsoid-based fluid model.

Bug fixes

1. b0077e40 Fixed a bug that was causing geom margin to be ignored during the construction of midphase collision trees.

2. 1bd6c94e Fixed a bug that was generating incorrect values in efc_diagApprox for weld equality constraints.

General

a7021df6 Added primitive collider for sphere-cylinder contacts, previously this pair used the generic convex-convex collider.

51aa375a 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.

5fcdae77 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.

5cfbb6ac Added analytic derivatives for quaternion subtraction and integration (rotation with an angular velocity). Derivatives are in the 3D tangent space.

c50c92cc Added mjv_connector which has identical functionality to mjv_makeConnector , but with more convenient “from-to” argument parametrization. mjv_makeConnector is now deprecated.

242aea93 Bumped oldest supported MacOS from version 10.12 to 11. MacOS 11 is the oldest version still maintained by Apple.

Python bindings

0ccfef73 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 ).

06b70832 Allow a custom keyboard event callback to be specified in the passive viewer ( issue #766 ).

f7847ba7 Fix GLFW crash when Python exits while the passive viewer is running ( issue #790 ).

Models

51aa375a Added simple car example model.

Note

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

Models

3d71b160 Added 3x3x3 cube example model. See README for details.

Bug fixes

41a70499 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 .

55c7f45d 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 .

c66d7940 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

b397b312 Added touch-grid sensor plugin. See documentation for details, and associated touch_grid.xml example model. The plugin includes in-scene visualisation .

Simulate

d40c3959 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.

d40c3959 Increased text width for UI elements in the default spacing. [before / after]:

General

f67e3595 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.

d82f5ce5 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.

c50177d3 Added mjd_inverseFD for finite-differenced inverse-dynamics derivatives.

49efa9cc 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.

2ad82d59 Added mj_multiRay function for intersecting multiple rays emanating from a single point. This is significantly faster than calling mj_ray multiple times.

9d1a21f9 Ray-mesh collisions are now up to 10x faster, using a bounding volume hierarchy of mesh faces.

3d82d2a4 Increased mjMAXUIITEM (maximum number of UI elements per section in Simulate) to 100.

67f0f515 Added documentation for resource providers.

49efa9cc 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}

]

770b4b36 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.

• f887c1e9 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.

• f887c1e9 Added instrumentation for the Address Sanitizer (ASAN) and Memory Sanitizer (MSAN) to detect memory bugs when allocating from the mjData stack and arena.

• f887c1e9 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.

• 466c9aca 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.

Bug fixes

d23c5e78 Fix asset loading bug that prevented OBJ and PNG files from being read from disk when mjVFS is used.

d23c5e78 Fix occasional segmentation faults on macOS when mouse perturbations are applied in the Python passive viewer.

Plugins

d23c5e78 The visualize callback in mjpPlugin now receives an mjvOption as an input argument.

Bug fixes

1. d23c5e78 Fix asset loading bug that prevented OBJ and PNG files from being read from disk when mjVFS is used.

2. d23c5e78 Fix occasional segmentation faults on macOS when mouse perturbations are applied in the Python passive viewer.

Plugins

1. d23c5e78 The visualize callback in mjpPlugin now receives an mjvOption as an input argument.

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

7cc42ecf 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.

7cc42ecf Added visual-global flag ellipsoidinertia to visualize equivalent body inertias with ellipsoids instead of the default boxes.

5f132af6 Added midphase and broadphase collision statistics to mjData .

01b84089 Added documentation for engine plugins .

2e23594f Added struct information to the introspect module.

fe3dccfd 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

6d63e046 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.

34226bf5 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 .

0db9a453 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.

b362cb49 The viewer.launch_repl function has been removed since its functionality is superseded by launch_passive .

2e23594f Added a small number of missing struct fields discovered through the new introspect metadata.

Bug fixes

101c647a Fixed bug in the handling of ellipsoid-based fluid model forces in the new implicitfast integrator.

• 0db9a453 Removed spurious whole-arena copying in mj_copyData , which can considerably slow down the copying operation.

• 2d69b158 Make shellinertia ignore exactmeshinertia , which is only used for legacy volume computations ( #759 ).

General

1. 8c7f6ce5 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

1. 70959c1a 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.

2. 49c939ea The mjd_transitionFD function no longer triggers sensor calculation unless explicitly requested.

3. c57a588a Corrected the spelling of the inteval attribute to interval in the mjLROpt struct.

4. 9756ed0d 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.

5. 50bebcb4 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.

6. d3d789cf 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.

7. 056e8492 Implemented a performant mju_sqrMatTDSparse function that doesn't require dense memory allocation.

8. 8696247f Added mj_stackAllocInt to get correct size for allocating ints on mjData stack. Reducing stack memory usage by 10% - 15%.

Python bindings

1. e58d53e7 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.

2. 7a0def97 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.)

3. 7a0def97 Added the mjpython launcher for macOS, which is required for viewer.launch_passive to function there.

4. 71c5f179 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.

5. e20ab6c9 Added a number of missing fields to the bindings of mjVisual and mjvPerturb structs.

Simulate

1. 2f0fb1e4 Implemented a workaround for broken VSync on macOS so that the frame rate is correctly capped when the Vertical Sync toggle is enabled.

1. 2607e67f Added optional labels to contact visualization, indicating which two geoms are contacting (names if defined, ids otherwise). This can be useful in cluttered scenes.

|br|

General

c741dfce 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.

f1007df0 The function mj_name2id is now implemented using a hash function instead of a linear search for better performance.

929e09f8 Geom names are now parsed from URDF. Any duplicate names are ignored. mj_printData output now contains contacting geom names.

Bug fixes

6ba4d6f0 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.

19b6c70e Fixed misalignment bug in mesh-to-primitive fitting when using the bounding box fitting option fitaabb .

d022cd1a The launch_repl functionality in the Python viewer has been fixed.

06557c14 Set time correctly in mjd_transitionFD , to support time-dependent user code.

6b80b010 Fixed sensor data dimension validation when user type sensors are present.

093125c2 Fixed incorrect plugin error message when a null nsensordata callback is encountered during model compilation.

e9869d3b Correctly end the timer ( TM_END ) mj_fwdConstraint returns early.

436fc6e7 Fixed an infinite loop in mj_deleteFileVFS .

Simulate

bc0184d6 Increased precision of simulate sensor plot y-axis by 1 digit ( #719 ).

79fffdc0 Body labels are now drawn at the body frame rather than inertial frame, unless inertia is being visualised.

Plugins

5c021d04 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.

• 30b4309a The capabilities field in mjpPlugin is renamed capabilityflags to more clearly indicate that this is a bit field.

Python bindings

0846f38c The simulate GUI is now available through the mujoco Python package as mujoco.viewer . See documentation for details. (Contribution by Levi Burner .)

ef695bb8 The Renderer class from the MuJoCo tutorial Colab is now available directly in the native Python bindings.

General

893942a7 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 .

0eb7f871 Removed the requirement that stateless actuators come before stateful actuators.

f905c7fb Added mju_fill , mju_symmetrize and mju_eye utility functions.

23092a11 Added gravcomp attribute to body , implementing gravity compensation and buoyancy. See balloons.xml example model.

36b30e45 Renamed the cable plugin library to elasticity .

0b45129c 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 .

3b89b0fd 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 .

7b0fbc63 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 .

d0b1a973 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.

9ecade07 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.

0d52feaa 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.

dee1d602 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” .

638c9a69 Added support for capsules in URDF import.

df25d7d6 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

89185b4a Fixed bug in mj_addFileVFS that was causing the file path to be ignored (introduced in 2.1.4).

Simulate

2ebc5f09 Renamed the directory in which the simulate application searches for plugins from plugin to mujoco_plugin .

165e72f7 Mouse force perturbations are now applied at the selection point rather than the body center of mass.

General

1. 58fd72f5 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. f151e84a 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. |br| Try it yourself:

3. 04d44e1e 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. 89579766 Added mju_boxQP and allocation function mju_boxQPmalloc for solving the box-constrained Quadratic Program:

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

5. f4e7fa97 Added mju_mulVecMatVec to multiply a square matrix M with vectors x and y on both sides. The function returns x^TMy.

6. 1e2a9a53 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. cce35e18 Added assetdir compiler option, which sets the values of both meshdir and texturedir. Values in the latter attributes take precedence over assetdir.

8. 84d16844 Added realtime option to visual for starting a simulation at a slower speed.

9. e250ff0d 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. e250ff0d 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

1. c13979cd Added id and name properties to named accessor objects. These provide more Pythonic API access to mj_name2id and mj_id2name respectively.

2. 58fd72f5 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.

3. ec6ea6a6 Fix a memory leak when a Python callable is installed as callback (#527).

General

3d77eb1e Added adhesion actuators mimicking vacuum grippers and adhesive biomechanical appendages.

3d77eb1e Added related example model and video:

fcf41317 Added mj_jacSubtreeCom for computing the translational Jacobian of the center-of-mass of a subtree.

d26501c0 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.

d26501c0 Increased mjNEQDATA , the row length of equality constraint parameters in mjModel.eq_data , from 7 to 11.

d26501c0 Added visualisation of anchor points for both connect and weld constraints (activated by the ‘N’ key in simulate ).

8ca5887c Added weld.xml showing different uses of new weld attributes.

46da1285 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.

a693a2d9 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.

8ca5887c 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.

5c5449bf Added parameter shellinertia to geom , for locating the inferred inertia on the boundary (shell). Currently only meshes are supported.

833dc740 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.

ae0ac86e Added catenary visualisation for hanging tendons. The model seen in the video can be found here .

b966a378 Added azimuth and elevation attributes to visual/global , defining the initial orientation of the free camera at model load time.

b966a378 Added mjv_defaultFreeCamera which sets the default free camera, respecting the above attributes.

80b4ffdd simulate now supports taking a screenshot via a button in the File section or via Ctrl-P .

834e8dd5 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).

090fe2db Added a disable flag for sensors.

fdbbc8bb 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 .

e3a82247 Added sensor matrices to mjd_transitionFD (note this is an API change).

Deleted/deprecated features

c8ff7b3d Removed distance constraints.

Bug fixes

f71daed6 Fixed rendering of some transparent geoms in reflection.

0b2f19bb Fixed intvelocity defaults parsing.

General

228264c9 Added mjd_transitionFD to compute efficient finite difference approximations of the state-transition and control-transition matrices, see here for more details.

373cc894 Added derivatives for the ellipsoid fluid model.

09a5efc0 Added ctrl attribute to keyframes .

c14a7ef4 Added clock sensor which measures time .

2d0995b4 Added visualisation groups to skins.

6ead1461 Added actuator visualisation for free and ball joints and for actuators with site transmission.

d3a86bb7 Added visualisation for actuator activations.

d3a86bb7 Added <actuator-intvelocity> actuator shortcut for “integrated velocity” actuators, documented here .

d3a86bb7 Added <actuator-damper> actuator shortcut for active-damping actuators, documented here .

ec7133b0 mju_rotVecMat and mju_rotVecMatT now support in-place multiplication.

d3a86bb7 mjData.ctrl values are no longer clamped in-place, remain untouched by the engine.

d3a86bb7 Arrays in mjData’s buffer now align to 64-byte boundaries rather than 8-byte.

f887c1e9 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 .

373cc894 Added a slider-crank example model .

Bug fixes

d3a86bb7 Activation clamping was not being applied in the implicit integrator .

d3a86bb7 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.

f3453cf8 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.

d3a86bb7 Trying to load a NaN via XML like <geom size="1 NaN 4"> , while allowed for debugging purposes, will now print a warning.

d5672639 Fixed null pointer dereference in mj_loadModel .

dbef8e6c Fixed memory leaks when loading an invalid model from MJB.

d3a86bb7 Integer overflows are now avoided when computing mjModel buffer sizes.

d3a86bb7 Added missing warning string for mjWARN_BADCTRL .

Packaging

d3a86bb7 Changed MacOS packaging so that the copy of mujoco.framework embedded in MuJoCo.app can be used to build applications externally.

Open Sourcing

1913a02b 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.

test/ : Tests and corresponding asset files.

dist/ : Files related to packaging and binary distribution.

1913a02b Added contributor’s guide and style guide .

General

64bc6d27 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.

64bc6d27 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.

1913a02b 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.

1913a02b 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”.

1913a02b 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> .

1913a02b The default shadow resolution specified by the shadowsize attribute was increased from 1024 to 4096.

1913a02b Saved XMLs now use 2-space indents.

Bug fixes

1913a02b 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.

• 1913a02b 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.

1913a02b Fix issue of duplicated meshes when saving models with OBJ meshes using mj_saveLastXML.

General

90dea1bd 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.

90dea1bd 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

90dea1bd 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

90dea1bd Fixed a bug in simulate where pressing ‘[’ or ‘]’ when a model is not loaded causes a crash.

90dea1bd Contact frame visualisation was added to the Simulate GUI.

90dea1bd Renamed “set key”, “reset to key” to “save key” and “load key”, respectively.

90dea1bd 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

90dea1bd mj_resetData zeroes out the solver_nnz field.

90dea1bd 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.

General

df048e54 simulate now supports cycling through cameras (with the [ and ] keys).

df048e54 mjVIS_STATIC toggles all static bodies, not just direct children of the world.

Python bindings

df048e54 Added a free() method to MjrContext .

df048e54 Enums now support arithmetic and bitwise operations with numbers.

Bug fixes

df048e54 Fixed rendering bug for planes, introduced in 2.1.2. This broke maze environments in dm_control .

General

1. df048e54 simulate now supports cycling through cameras (with the [ and ] keys).

2. df048e54 mjVIS_STATIC toggles all static bodies, not just direct children of the world.

Python bindings

1. df048e54 Added a free() method to MjrContext.

2. df048e54 Enums now support arithmetic and bitwise operations with numbers.

Bug fixes

1. df048e54 Fixed rendering bug for planes, introduced in 2.1.2. This broke maze environments in dm_control.