Mujoco

----------------------------

Python bindings
^^^^^^^^^^^^^^^
1. :ref:`rollout<PyRollout>` 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 :github:user:`aftersomemath`.
2. Fix global namespace pollution when using ``mjpython`` (:github:issue:`2265`).

General
^^^^^^^

.. admonition:: Breaking API changes (minor)
:class: attention

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

4. Reduced the memory footprint of the PGS solver's :ref:`A matrix<soDual>`. This was the last remaining dense-memory
allocation in MuJoCo, allowing for a significant reduction of the :ref:`dynamic memory allocation heuristic<CSize>`.

Bug fixes
^^^^^^^^^
5. Fixed a bug in the box-sphere collider, depth was incorrect for deep penetrations (:github:issue:`2206`).
6. Fixed a bug in :ref:`mj_mulM2` and added a test.

---------------------------

General
^^^^^^^
1. Removed rope and loop from :ref:`composite<body-composite>`. The user is encouraged to instead use the :at:`cable`
plugin or :ref:`flexcomp<body-flexcomp>`, respectively.

MJX
^^^
2. Added muscle actuators.

Python bindings
^^^^^^^^^^^^^^^
3. Provide prebuilt wheels for Python 3.13.
4. Added ``bind`` method and removed id attribute from :ref:`mjSpec` objects. Using ids is error prone in scenarios of
repeated attachment and detachment. Python users are encouraged to use names for unique identification of model
elements.
5. :ref:`rollout<PyRollout>` can now accept sequences of MjModel of length ``nroll``. Also removed the ``nroll``
argument because its value can always be inferred.

Bug fixes
^^^^^^^^^
6. Fixed :github:issue:`2212`, type error in ``mjx.get_data``.
7. Fixed bug introduced in 3.2.0 in handling of :ref:`texrepeat<asset-material-texrepeat>` attribute, was mistakenly
cast from ``float`` to ``int``, (fixed :github:issue:`2223`).

---------------------------

Feature promotion
^^^^^^^^^^^^^^^^^
1. The :doc:`Model Editing<programming/modeledit>` framework afforded by :ref:`mjSpec`, introduced in 3.2.0 as an
in-development feature, is now stable and recommended for general use.
2. The native convex collision detection pipeline introduced in 3.2.3 and enabled by the
:ref:`nativeccd<option-flag-nativeccd>` flag, is not yet the default but is already recommended for general use.
Please try it when encountering collision-related problems and report any issues you encounter.

General
^^^^^^^

3. The global compiler flag ``exactmeshinertia`` has been removed and replaced with the mesh-specific
:ref:`inertia<asset-mesh-inertia>` attribute.
4. The not-useful ``convexhull`` compiler option (to disable computation of mesh convex hulls) has been removed.
5. Removed the deprecated ``mju_rotVecMat``, ``mju_rotVecMatT`` and ``mjv_makeConnector`` functions.
6. Sorting now uses a faster, native sort function (fixes :github:issue:`1638`).
7. The PBR texture layers introduced in 3.2.1 were refactored from seperate sub-elements to a single
:ref:`layer<material-layer>` sub-element.
8. The composite types box, cylinder, and sphere have been removed. Users should instead use the equivalent types
available in :ref:`flexcomp<body-flexcomp>`.

MJX
^^^
9. Added ``apply_ft``, ``jac``, and ``xfrc_accumulate`` as public functions.
10. Added ``TOUCH`` sensor.
11. Added support for ``eq_active``. Fixes :github:issue:`2173`.
12. Added ray intersection with ellipsoid.

Bug fixes
^^^^^^^^^
13. Fixed several bugs related to connect and weld constraints with site semantics (fixes :github:issue:`2179`, reported
by :github:user:`yinfanyi`). The introduction of site specification to connects and welds in 3.2.3 conditionally
changed the semantics of `mjData.eq_obj1id` and `mjData.eq_obj2id`, but these changes were not properly propagated
in several places leading to incorrect computations of constraint inertia, readings of affected force/torque sensors
and runtime enabling/disabling of such constraints.
14. Fixed a bug in slider-crank :ref:`transmission<geTransmission>`. The bug was introduced in 3.0.0.
15. Fixed a bug in flex texture coordinates that prevented the correct allocation of textures in mjModel.


Documentation
^^^^^^^^^^^^^
16. Function headers in the :doc:`API reference <../APIreference/APIfunctions>` now link to their source definitions
in GitHub.

----------------------------

General
^^^^^^^

.. youtube:: e8lUuykQPGs
:align: right
:width: 240px

1. The Newton solver no longer requires ``nv*nv`` memory allocation, allowing for much larger models. See e.g.,
`100_humanoids.xml <https://github.com/google-deepmind/mujoco/blob/main/model/humanoid/100_humanoids.xml>`__.
Two quadratic-memory allocations still remain to be fully sparsified: ``mjData.actuator_moment`` and the matrices used
by the PGS solver.
2. Removed the :at:`solid` and :at:`membrane` plugins and moved the associated computations into the engine. See `3D
example model <https://github.com/google-deepmind/mujoco/blob/main/model/flex/floppy.xml>`__ and `2D example model
<https://github.com/google-deepmind/mujoco/blob/main/model/flex/trampoline.xml>`__ for examples of flex objects
that previously required these plugins.
3. Replaced the function ``mjs_setActivePlugins`` with :ref:`mjs_activatePlugin`.

MJX
^^^
4. Added ``mocap_pos`` and ``mocap_quat`` in kinematics.
5. Added support for :ref:`spatial tendons <tendon-spatial>` with pulleys and external sphere and cylinder wrapping.
6. Added sphere-cylinder and sphere-ellipsoid collision functions (:github:issue:`2126`).
7. Fixed a bug with frictionloss constraints.
8. Added ``TENDONPOS`` and ``TENDONVEL`` sensors.
9. Fixed a bug with the computation of tangential contact forces in ``_decode_pyramid``.
10. Added ``JOINTINPARENT`` actuator transmission type.

Python bindings
^^^^^^^^^^^^^^^
11. Removed support for Python 3.8, now that it's `deprecated upstream <https://devguide.python.org/versions>`__.

Bug fixes
^^^^^^^^^
12. Fixed a bug where ``actuator_force`` was not set in MJX (:github:issue:`2068`).
13. Fixed bug where MJX data tendon fields were incorrect after calling ``mjx.put_data``.
14. The compiler now returns an error if height fields are used with :ref:`collision sensors<collision-sensors>` as they
are not yet supported.

----------------------------

General
^^^^^^^

.. admonition:: Breaking API changes
:class: attention

1. The runtime options ``mpr_tolerance`` and ``mpr_iterations`` were renamed to
:ref:`ccd_tolerance<option-ccd_tolerance>` and :ref:`ccd_iterations<option-ccd_iterations>`, both in XML and in
the :ref:`mjOption` struct. This is because the new convex collision detection pipeline (see below) does not use
the MPR algorithm. The semantics of these options remain identical.
2. The functions ``mjs_findMesh`` and ``mjs_findKeyframe`` were replaced by ``mjs_findElement``, which allows to look
for any object type.
3. The experimental use of 2D/3D elasticity plugins with :ref:`composite<body-composite>` has been removed. Users
should instead use :ref:`flexcomp<body-flexcomp>`, which provides the correct collision behavior.

4. Added the :ref:`nativeccd<option-flag-nativeccd>` flag. When this flag is enabled, general convex collision
detection is handled with a new native code path, rather than `libccd <https://github.com/danfis/libccd>`__.
This feature is in early stages of testing, but users who've experienced issues related to collsion detection are
welcome to experiment with it and report any issues.

.. youtube:: kcM_oauk3ZA
:align: right
:width: 240px

5. Added a new way of defining :ref:`connect<equality-connect>` and :ref:`weld<equality-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 <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/equality_site.xml>`__ using
the new semantic is shown in the video on the right.
6. Introduced **free joint alignment**, an optimization that applies to bodies with a free joint and no child bodies
(simple free-floating bodies): automatically aligning the body frame with the inertial frame. This feature can be
toggled individually using the :ref:`freejoint/align<body-freejoint-align>` attribute or globally using the compiler
:ref:`alignfree<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 :ref:`keyframes<keyframe>`) will
become invalid. The global compiler attribute currently defaults to "false" due to this potential breakage, but could
be changed to "true" in a future release. Aligned free joints are recommended for all new models.

7. Added an :ref:`mjSpec` option for creating a texture directly from a buffer.
8. :ref:`shell (surface) inertia <body-geom-shellinertia>` is now supported by all geom types.
9. When :ref:`attaching<meAttachment>` sub-models, :ref:`keyframes<keyframe>` will now be correctly merged into the
parent model, but only on the first attachment.
10. Added the :ref:`mjtSameFrame` enum which contains the possible frame alignments of bodies and their children. These
alignments are used for computation shortcuts in :ref:`mj_kinematics`.
11. Added :ref:`mj_jacDot` for computing time-derivatives of kinematic Jacobians. Fixes :github:issue:`411`.

MJX
^^^
12. Added ``efc_pos`` to ``mjx.Data`` (:github:issue:`1388`).
13. Added position-dependent sensors: ``MAGNETOMETER``, ``CAMPROJECTION``, ``RANGEFINDER``, ``JOINTPOS``,
``ACTUATORPOS``, ``BALLQUAT``, ``FRAMEPOS``, ``FRAMEXAXIS``, ``FRAMEYAXIS``, ``FRAMEZAXIS``, ``FRAMEQUAT``,
``SUBTREECOM``, ``CLOCK``.
14. Added velocity-dependent sensors: ``VELOCIMETER``, ``GYRO``, ``JOINTVEL``, ``ACTUATORVEL``, ``BALLANGVEL``,
``FRAMELINVEL``, ``FRAMEANGVEL``, ``SUBTREELINVEL``, ``SUBTREEANGMOM``.
15. Added acceleration/force-dependent sensors: ``ACCELEROMETER``, ``FORCE``, ``TORQUE``, ``ACTUATORFRC``,
``JOINTACTFRC``, ``FRAMELINACC``, ``FRAMEANGACC``.
16. Changed default policy to avoid placing unused (MuJoCo-only) arrays on device.
17. Added ``device`` parameter to ``mjx.make_data`` to bring it to parity with ``mjx.put_model`` and ``mjx.put_data``.
18. Added support for :ref:`implicitfast integration<geIntegration>` for all cases except
:doc:`fluid drag <computation/fluid>`.
19. Fixed a bug where ``qLDiagInv`` had the wrong size for sparse mass matrices.
20. Added support for joint and tendon :ref:`frictionloss <coFriction>`.
21. Added support for :ref:`connect<equality-connect>` equality constraints using two sites.
22. Added support for :ref:`spatial tendons <tendon-spatial>` with site wrapping.

Bug fixes
^^^^^^^^^
23. Fixed a performance regression introduced in 3.1.7 in mesh Bounding Volume Hierarchies (:github:issue:`1875`,
contribution by :github:user:`michael-ahn`).
24. Fixed a bug wherein, for models that have both muscles and stateless actuators and used one of the implicit
integrators, wrong derivatives would be computed.
25. Fixed a bug in tendon wrapping around spheres. Before this fix, tendons that wrapped around spheres with an
externally-placed :ref:`sidesite<spatial-geom-sidesite>` could jump inside the sphere instead of wrapping around it.
26. Fixed a bug that caused :at:`meshdir` and :at:`texturedir` to be overwritten during model
:ref:`attachment<meAttachment>`, preventing model attachment for models with assets in different directories.

Python bindings
^^^^^^^^^^^^^^^
27. Added support for engine plugins in :ref:`mjSpec` (:github:issue:`1903`).
28. Better error reporting for issues with the assets dictionary, when loading models.

---------------------------

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