Split API reference pages into Data Structures and Functions pages.

PiperOrigin-RevId: 510422950
Change-Id: I6b2eebab0c0020b80fec83094aa65c6a412e277e

doc/APIreference/APIfunctions.rst

@@ -0,0 +1,94 @@
+.. _API:
+
+=========
+Functions
+=========
+
+The main header `mujoco.h <https://github.com/deepmind/mujoco/blob/main/include/mujoco/mujoco.h>`_ exposes a very large
+number of functions. However the functions that most users are likely to need are a small fraction. For example,
+:ref:`simulate.cc <saSimulate>` which is as elaborate as a MuJoCo application is likely to get, calls around 40 of these
+functions, while ``basic.cc`` calls around 20. The rest are explosed just in case someone has a use for them. This
+includes us as users of MuJoCo -- we do our own work with the public library instead of relying on internal builds.
+
+.. include:: functions.rst
+
+.. _Macros:
+
+Macros
+^^^^^^
+
+.. _mjMARKSTACK:
+
+mjMARKSTACK
+~~~~~~~~~~~
+
+.. code-block:: C
+
+   #define mjMARKSTACK int _mark = d->pstack;
+
+This macro is helpful when using the MuJoCo stack in custom computations. It works together with the next macro and the
+:ref:`mj_stackAlloc` function, and assumes that mjData\* d is defined. The use pattern is this:
+
+::
+
+       mjMARKSTACK
+       mjtNum* temp = mj_stackAlloc(d, 100);
+       // ... use temp as needed
+       mjFREESTACK
+
+.. _mjFREESTACK:
+
+mjFREESTACK
+~~~~~~~~~~~
+
+.. code-block:: C
+
+   #define mjFREESTACK d->pstack = _mark;
+
+Reset the MuJoCo stack pointer to the variable \_mark, normally saved by mjMARKSTACK.
+
+.. _mjDISABLED:
+
+mjDISABLED
+~~~~~~~~~~
+
+.. code-block:: C
+
+   #define mjDISABLED(x) (m->opt.disableflags & (x))
+
+Check if a given standard feature has been disabled via the physics options, assuming mjModel\* m is defined. x is of
+type :ref:`mjtDisableBit`.
+
+.. _mjENABLED:
+
+mjENABLED
+~~~~~~~~~
+
+.. code-block:: C
+
+   #define mjENABLED(x) (m->opt.enableflags & (x))
+
+Check if a given optional feature has been enabled via the physics options, assuming mjModel\* m is defined. x is of
+type :ref:`mjtEnableBit`.
+
+.. _mjMAX:
+
+mjMAX
+~~~~~
+
+.. code-block:: C
+
+   #define mjMAX(a,b) (((a) > (b)) ? (a) : (b))
+
+Return maximum value. To avoid repeated evaluation with mjtNum types, use the function :ref:`mju_max`.
+
+.. _mjMIN:
+
+mjMIN
+~~~~~
+
+.. code-block:: C
+
+   #define mjMIN(a,b) (((a) < (b)) ? (a) : (b))
+
+Return minimum value. To avoid repeated evaluation with mjtNum types, use the function :ref:`mju_min`.