Add mjtState enum and related mj_stateSize, mj_getState and mj_setState functions.

PiperOrigin-RevId: 539667943
Change-Id: I14c34be8ce4c287e529380257b5c5bffc3ab45ce

doc/APIreference/APItypes.rst

@@ -346,6 +346,18 @@ Data
 The enums below are defined in `mjdata.h <https://github.com/deepmind/mujoco/blob/main/include/mujoco/mjdata.h>`_.
 
 
+
+.. _mjtState:
+
+mjtState
+~~~~~~~~
+
+State component elements as integer bitflags and several convenient combinations of these flags. Used by
+:ref:`mj_getState`, :ref:`mj_setState` and :ref:`mj_stateSize`.
+
+.. mujoco-include:: mjtState
+
+
 .. _mjtWarning:
 
 mjtWarning

doc/APIreference/functions.rst

@@ -151,6 +151,36 @@ These are support functions that need access to :ref:`mjModel` and :ref:`mjData`
 not need such access. Support functions are called within the simulator but some of them can also be useful for custom
 computations, and are documented in more detail below.
 
+.. _mj_stateSize:
+
+mj_stateSize
+~~~~~~~~~~~~
+
+.. mujoco-include:: mj_stateSize
+
+Returns the number of :ref:`mjtNum` |-| s required for a given state specification. The bits of the integer ``spec``
+correspond to element fields of :ref:`mjtState`.
+
+.. _mj_getState:
+
+mj_getState
+~~~~~~~~~~~
+
+.. mujoco-include:: mj_getState
+
+Copy concatenated state components specified by ``spec`` from ``d`` into ``state``. The bits of the integer
+``spec`` correspond to element fields of :ref:`mjtState`. Fails with :ref:`mju_error` if ``spec`` is invalid.
+
+.. _mj_setState:
+
+mj_setState
+~~~~~~~~~~~
+
+.. mujoco-include:: mj_setState
+
+Copy concatenated state components specified by ``spec`` from  ``state`` into ``d``. The bits of the integer
+``spec`` correspond to element fields of :ref:`mjtState`. Fails with :ref:`mju_error` if ``spec`` is invalid.
+
 .. _mj_addContact:
 
 mj_addContact

doc/APIreference/functions_override.rst

@@ -96,6 +96,21 @@ These are support functions that need access to :ref:`mjModel` and :ref:`mjData`
 not need such access. Support functions are called within the simulator but some of them can also be useful for custom
 computations, and are documented in more detail below.
 
+.. _mj_stateSize:
+
+Returns the number of :ref:`mjtNum` |-| s required for a given state specification. The bits of the integer ``spec``
+correspond to element fields of :ref:`mjtState`.
+
+.. _mj_getState:
+
+Copy concatenated state components specified by ``spec`` from ``d`` into ``state``. The bits of the integer
+``spec`` correspond to element fields of :ref:`mjtState`. Fails with :ref:`mju_error` if ``spec`` is invalid.
+
+.. _mj_setState:
+
+Copy concatenated state components specified by ``spec`` from  ``state`` into ``d``. The bits of the integer
+``spec`` correspond to element fields of :ref:`mjtState`. Fails with :ref:`mju_error` if ``spec`` is invalid.
+
 .. _mj_mulJacVec:
 
 This function multiplies the constraint Jacobian mjData.efc_J by a vector. Note that the Jacobian can be either dense or