Add mjModel.tendon_type and the mjtTendon enum.

PiperOrigin-RevId: 1009752952
Change-Id: I3c3bc2564593e41af7b0ff0b0c0c80c8dab94653

Author: yuvaltassa

doc/APIreference/APItypes.rst

@@ -297,6 +297,16 @@ Equality constraint types. These values are used in ``m->eq_type``.
 .. mujoco-include:: mjtEq
 
 
+.. _mjtTendon:
+
+mjtTendon
+~~~~~~~~~
+
+Tendon types. These values are used in ``m->tendon_type``.
+
+.. mujoco-include:: mjtTendon
+
+
 .. _mjtWrap:
 
 mjtWrap

doc/changelog.rst

@@ -64,6 +64,8 @@ General
 - Added a :ref:`castshadow<body-geom-castshadow>` attribute to :ref:`geom<body-geom>` (``mjsGeom.castshadow``,
   ``mjModel.geom_castshadow``, ``mjvGeom.castshadow``; default ``true``) to disable shadow casting per geom in both the
   classic OpenGL and Filament renderers.
+- Added ``mjModel.tendon_type`` with values from the new :ref:`mjtTendon` enum, distinguishing fixed and spatial
+  tendons. Previously, the type was implied by whether the first path element was a joint.
 
 Engine
 ^^^^^^

doc/includes/references.h

@@ -1105,6 +1105,7 @@ typedef struct mjModel_ {
   mjtNum*   eq_data;              // numeric data for constraint              (neq x mjNEQDATA)
 
   // tendons
+  int*      tendon_type;          // type of tendon (mjtTendon)               (ntendon x 1)
   int*      tendon_adr;           // address of first object in tendon's path (ntendon x 1)
   int*      tendon_num;           // number of objects in tendon's path       (ntendon x 1)
   int*      tendon_matid;         // material id for rendering                (ntendon x 1)
@@ -2607,6 +2608,10 @@ typedef enum mjtEq {              // type of equality constraint
   mjEQ_FLEXSTRAIN,                // constrain strain of a trilinear/quadratic flex (B-bar)
   mjEQ_DISTANCE                   // unsupported, will cause an error if used
 } mjtEq;
+typedef enum mjtTendon {          // type of tendon
+  mjTENDON_FIXED      = 0,        // linear combination of joint coordinates
+  mjTENDON_SPATIAL                // path through sites, around geoms
+} mjtTendon;
 typedef enum mjtWrap {            // type of tendon wrap object
   mjWRAP_NONE         = 0,        // null object
   mjWRAP_JOINT,                   // constant moment arm

include/mujoco/mjmodel.h

@@ -738,6 +738,7 @@ typedef struct mjModel_ {
   mjtNum*   eq_data;              // numeric data for constraint              (neq x mjNEQDATA)
 
   // tendons
+  int*      tendon_type;          // type of tendon (mjtTendon)               (ntendon x 1)
   int*      tendon_adr;           // address of first object in tendon's path (ntendon x 1)
   int*      tendon_num;           // number of objects in tendon's path       (ntendon x 1)
   int*      tendon_matid;         // material id for rendering                (ntendon x 1)

include/mujoco/mjtype.h

@@ -223,6 +223,12 @@ typedef enum mjtEq {              // type of equality constraint
 } mjtEq;
 
 
+typedef enum mjtTendon {          // type of tendon
+  mjTENDON_FIXED      = 0,        // linear combination of joint coordinates
+  mjTENDON_SPATIAL                // path through sites, around geoms
+} mjtTendon;
+
+
 typedef enum mjtWrap {            // type of tendon wrap object
   mjWRAP_NONE         = 0,        // null object
   mjWRAP_JOINT,                   // constant moment arm

include/mujoco/mjxmacro.h

@@ -646,6 +646,7 @@
     X   ( mjtNum,  eq_data,               neq,           mjNEQDATA            )
 
 #define MJMODEL_POINTERS_TENDON                                                 \
+    X   ( int,     tendon_type,           ntendon,       1                    ) \
     X   ( int,     tendon_adr,            ntendon,       1                    ) \
     X   ( int,     tendon_num,            ntendon,       1                    ) \
     X   ( int,     tendon_matid,          ntendon,       1                    ) \
@@ -996,6 +997,7 @@
     X( eq_obj2id,            0,          mjSC_IN,    0,          0          ) \
     X( eq_objtype,           0,          mjSC_IN,    0,          0          ) \
     X( eq_data,              0,          mjSC_INOUT, 0,          0          ) \
+    X( tendon_type,          mjSC_IN,    mjSC_IN,    mjSC_IN,    mjSC_IN    ) \
     X( tendon_adr,           mjSC_IN,    mjSC_IN,    mjSC_IN,    mjSC_IN    ) \
     X( tendon_num,           mjSC_IN,    mjSC_IN,    mjSC_IN,    mjSC_IN    ) \
     X( tendon_actuatorid,    mjSC_OUT,   0,          mjSC_IN,    0          ) \

mjx/mujoco/mjx/_src/io.py

@@ -406,6 +406,7 @@ def _put_model_jax(
       (m.actuator_trntype, types.TrnType, mujoco.mjtTrn),
       (m.eq_type, types.EqType, mujoco.mjtEq),
       (m.sensor_type, types.SensorType, mujoco.mjtSensor),
+      (m.tendon_type, types.TendonType, mujoco.mjtTendon),
       (m.wrap_type, types.WrapType, mujoco.mjtWrap),
   ):
     missing = set(enum_field) - set(enum_type)

mjx/mujoco/mjx/_src/io_test.py

@@ -208,6 +208,7 @@ def assert_not_weak_type(x):
     np.testing.assert_allclose(mx.actuator_biastype, m.actuator_biastype)
     np.testing.assert_allclose(mx.actuator_trnid, m.actuator_trnid)
 
+    np.testing.assert_equal(mx.tendon_type, m.tendon_type)
     np.testing.assert_equal(mx.wrap_type, m.wrap_type)
     np.testing.assert_equal(mx.wrap_objid, m.wrap_objid)
     np.testing.assert_almost_equal(mx.wrap_prm, m.wrap_prm)

mjx/mujoco/mjx/_src/smooth.py

@@ -31,6 +31,7 @@
 from mujoco.mjx._src.types import Model
 from mujoco.mjx._src.types import ModelJAX
 from mujoco.mjx._src.types import ObjType
+from mujoco.mjx._src.types import TendonType
 from mujoco.mjx._src.types import TrnType
 from mujoco.mjx._src.types import WrapType
 # pylint: enable=g-importing-member
@@ -892,7 +893,7 @@ def tendon(m: Model, d: Data) -> Data:
 
   # process joint tendons
   (wrap_id_jnt,) = np.nonzero(m.wrap_type == WrapType.JOINT)
-  (tendon_id_jnt,) = np.nonzero(np.isin(m.tendon_adr, wrap_id_jnt))
+  (tendon_id_jnt,) = np.nonzero(m.tendon_type == TendonType.FIXED)
 
   ntendon_jnt = tendon_id_jnt.size
   wrap_objid_jnt = m.wrap_objid[wrap_id_jnt]

mjx/mujoco/mjx/_src/types.py

@@ -237,6 +237,18 @@ class EqType(enum.IntEnum):
   # unsupported: DISTANCE
 
 
+class TendonType(enum.IntEnum):
+  """Type of tendon.
+
+  Attributes:
+    FIXED: linear combination of joint coordinates
+    SPATIAL: path through sites, around geoms
+  """
+
+  FIXED = mujoco.mjtTendon.mjTENDON_FIXED  # pyrefly: ignore[bad-assignment]
+  SPATIAL = mujoco.mjtTendon.mjTENDON_SPATIAL  # pyrefly: ignore[bad-assignment]
+
+
 class WrapType(enum.IntEnum):
   """Type of tendon wrap object.
 
@@ -828,6 +840,7 @@ class Model(PyTreeNode):
   eq_solref: jax.Array
   eq_solimp: jax.Array
   eq_data: jax.Array
+  tendon_type: np.ndarray
   tendon_adr: np.ndarray
   tendon_num: np.ndarray
   tendon_limited: np.ndarray