Add mjs_getParent to retrieve the parent body of an object.

PiperOrigin-RevId: 715794859
Change-Id: Ib9792787cdb966f579938dde3f94ebabca8ef1fc

doc/APIreference/functions.rst

@@ -4175,6 +4175,15 @@ Find element in spec by name.
 
 Find child body by name.
 
+.. _mjs_getParent:
+
+`mjs_getParent <#mjs_getParent>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. mujoco-include:: mjs_getParent
+
+Get parent body.
+
 .. _mjs_findFrame:
 
 `mjs_findFrame <#mjs_findFrame>`__

doc/includes/references.h

@@ -3607,6 +3607,7 @@ mjSpec* mjs_findSpec(mjSpec* spec, const char* name);
 mjsBody* mjs_findBody(mjSpec* s, const char* name);
 mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name);
 mjsBody* mjs_findChild(mjsBody* body, const char* name);
+mjsBody* mjs_getParent(mjsElement* element);
 mjsFrame* mjs_findFrame(mjSpec* s, const char* name);
 mjsDefault* mjs_getDefault(mjsElement* element);
 const mjsDefault* mjs_findDefault(mjSpec* s, const char* classname);

doc/python.rst

@@ -591,6 +591,8 @@ Recursive search:
   ``body.find_all(mujoco.mjtObj.mjOBJ_SITE)`` or ``body.find_all('site')`` will return a list of all sites under the
   body.
 
+Additionally, the parent body of a given element - including bodies and frames - can be accessed via the ``parent``
+property. For example, the parent of a site can be accessed via ``site.parent``.
 
 Relationship to ``PyMJCF``
 --------------------------

include/mujoco/mujoco.h

@@ -1546,6 +1546,9 @@ MJAPI mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name);
 // Find child body by name.
 MJAPI mjsBody* mjs_findChild(mjsBody* body, const char* name);
 
+// Get parent body.
+MJAPI mjsBody* mjs_getParent(mjsElement* element);
+
 // Find frame by name.
 MJAPI mjsFrame* mjs_findFrame(mjSpec* s, const char* name);
 

introspect/functions.py

@@ -9828,6 +9828,22 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
          ),
          doc='Find child body by name.',
      )),
+    ('mjs_getParent',
+     FunctionDecl(
+         name='mjs_getParent',
+         return_type=PointerType(
+             inner_type=ValueType(name='mjsBody'),
+         ),
+         parameters=(
+             FunctionParameterDecl(
+                 name='element',
+                 type=PointerType(
+                     inner_type=ValueType(name='mjsElement'),
+                 ),
+             ),
+         ),
+         doc='Get parent body.',
+     )),
     ('mjs_findFrame',
      FunctionDecl(
          name='mjs_findFrame',

python/mujoco/specs.cc

@@ -680,6 +680,12 @@ PYBIND11_MODULE(_specs, m) {
         return mjs_getSpec(self.element);
       },
       py::return_value_policy::reference_internal);
+  mjsBody.def_property_readonly(
+      "parent",
+      [](raw::MjsBody& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsBody.def(
       "attach_frame",
       [](raw::MjsBody& self, raw::MjsFrame& frame,
@@ -713,6 +719,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsFrame.def("set_frame", [](raw::MjsFrame& self, raw::MjsFrame& frame) {
     mjs_setFrame(self.element, &frame);
   });
+  mjsFrame.def_property_readonly(
+      "parent",
+      [](raw::MjsFrame& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsFrame.def(
       "attach_body",
       [](raw::MjsFrame& self, raw::MjsBody& body,
@@ -760,6 +772,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsGeom.def("set_default", [](raw::MjsGeom& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
   });
+  mjsGeom.def_property_readonly(
+      "parent",
+      [](raw::MjsGeom& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsGeom.def(
       "default",
       [](raw::MjsGeom& self) -> raw::MjsDefault* {
@@ -775,6 +793,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsJoint.def("set_default", [](raw::MjsJoint& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
   });
+  mjsJoint.def_property_readonly(
+      "parent",
+      [](raw::MjsJoint& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsJoint.def(
       "default",
       [](raw::MjsJoint& self) -> raw::MjsDefault* {
@@ -790,6 +814,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsSite.def("set_default", [](raw::MjsSite& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
   });
+  mjsSite.def_property_readonly(
+      "parent",
+      [](raw::MjsSite& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsSite.def(
       "default",
       [](raw::MjsSite& self) -> raw::MjsDefault* {
@@ -845,6 +875,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsCamera.def("set_default", [](raw::MjsCamera& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
   });
+  mjsCamera.def_property_readonly(
+      "parent",
+      [](raw::MjsCamera& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsCamera.def(
       "default",
       [](raw::MjsCamera& self) -> raw::MjsDefault* {
@@ -860,6 +896,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsLight.def("set_default", [](raw::MjsLight& self, raw::MjsDefault& def) {
     mjs_setDefault(self.element, &def);
   });
+  mjsLight.def_property_readonly(
+      "parent",
+      [](raw::MjsLight& self) -> raw::MjsBody* {
+        return mjs_getParent(self.element);
+      },
+      py::return_value_policy::reference_internal);
   mjsLight.def(
       "default",
       [](raw::MjsLight& self) -> raw::MjsDefault* {

python/mujoco/specs_test.py

@@ -646,6 +646,10 @@ class SpecsTest(absltest.TestCase):
     self.assertEqual(spec.bodies[2].name, 'body2')
     self.assertEqual(spec.bodies[3].name, 'body3')
     self.assertEqual(spec.bodies[4].name, 'body4')
+    self.assertEqual(spec.bodies[1].parent, spec.worldbody)
+    self.assertEqual(spec.bodies[2].parent, spec.worldbody)
+    self.assertEqual(spec.bodies[3].parent, spec.bodies[1])
+    self.assertEqual(spec.bodies[4].parent, spec.bodies[3])
     self.assertLen(spec.worldbody.find_all(bodytype), 4)
     self.assertLen(spec.bodies[1].find_all(bodytype), 2)
     self.assertLen(spec.bodies[3].find_all(bodytype), 1)
@@ -671,6 +675,11 @@ class SpecsTest(absltest.TestCase):
     self.assertEqual(spec.bodies[3].sites[2].name, 'site3')
     self.assertEqual(spec.bodies[3].sites[3].name, 'site4')
     self.assertEqual(spec.bodies[4].sites[0].name, 'site5')
+    self.assertEqual(spec.bodies[3].sites[0].parent, spec.bodies[3])
+    self.assertEqual(spec.bodies[3].sites[1].parent, spec.bodies[3])
+    self.assertEqual(spec.bodies[3].sites[2].parent, spec.bodies[3])
+    self.assertEqual(spec.bodies[3].sites[3].parent, spec.bodies[3])
+    self.assertEqual(spec.bodies[4].sites[0].parent, spec.bodies[4])
     with self.assertRaises(ValueError) as cm:
       spec.worldbody.find_all('actuator')
     self.assertEqual(

src/user/user_api.cc

@@ -649,6 +649,30 @@ mjsBody* mjs_findChild(mjsBody* bodyspec, const char* name) {
 
 
 
+// get parent body
+mjsBody* mjs_getParent(mjsElement* element) {
+  switch (element->elemtype) {
+    case mjOBJ_BODY:
+      return &(static_cast<mjCBody*>(element)->GetParent()->spec);
+    case mjOBJ_FRAME:
+      return &(static_cast<mjCFrame*>(element)->GetParent()->spec);
+    case mjOBJ_JOINT:
+      return &(static_cast<mjCJoint*>(element)->GetParent()->spec);
+    case mjOBJ_GEOM:
+      return &(static_cast<mjCGeom*>(element)->GetParent()->spec);
+    case mjOBJ_SITE:
+      return &(static_cast<mjCSite*>(element)->GetParent()->spec);
+    case mjOBJ_CAMERA:
+      return &(static_cast<mjCCamera*>(element)->GetParent()->spec);
+    case mjOBJ_LIGHT:
+      return &(static_cast<mjCLight*>(element)->GetParent()->spec);
+    default:
+      return nullptr;
+  }
+}
+
+
+
 // find frame by name
 mjsFrame* mjs_findFrame(mjSpec* s, const char* name) {
   mjsElement* frame = mjs_findElement(s, mjOBJ_FRAME, name);

src/user/user_api.h

@@ -201,6 +201,9 @@ MJAPI mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name);
 // Find child body by name.
 MJAPI mjsBody* mjs_findChild(mjsBody* body, const char* name);
 
+// Get parent body.
+MJAPI mjsBody* mjs_getParent(mjsElement* element);
+
 // Find frame by name.
 MJAPI mjsFrame* mjs_findFrame(mjSpec* s, const char* name);
 

src/user/user_objects.h

@@ -347,6 +347,7 @@ class mjCBody : public mjCBody_, private mjsBody {
 
   // set parent of this body
   void SetParent(mjCBody* _body) { parent = _body; }
+  mjCBody* GetParent() const { return parent; }
 
  private:
   mjCBody(const mjCBody& other, mjCModel* _model);  // copy constructor
@@ -411,6 +412,7 @@ class mjCFrame : public mjCFrame_, private mjsFrame {
   void CopyFromSpec(void);
   void PointToLocal(void);
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
 
   mjCFrame& operator+=(const mjCBody& other);
 
@@ -462,6 +464,7 @@ class mjCJoint : public mjCJoint_, private mjsJoint {
 
   void CopyFromSpec(void);
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
 
   // used by mjXWriter and mjCModel
   const std::vector<double>& get_userdata() const { return userdata_; }
@@ -543,6 +546,7 @@ class mjCGeom : public mjCGeom_, private mjsGeom {
   bool IsVisual(void) const { return visual_; }
   void SetNotVisual(void) { visual_ = false; }
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
   mjtGeom Type() const { return type; }
 
   // Compute all coefs modeling the interaction with the surrounding fluid.
@@ -608,6 +612,7 @@ class mjCSite : public mjCSite_, private mjsSite {
   // site's body
   mjCBody* Body() const { return body; }
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
 
   // use strings from mjCBase rather than mjStrings from mjsSite
   using mjCBase::name;
@@ -661,6 +666,7 @@ class mjCCamera : public mjCCamera_, private mjsCamera {
   const std::vector<double>& get_userdata() const { return userdata_; }
 
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
 
  private:
   void Compile(void);                     // compiler
@@ -701,6 +707,7 @@ class mjCLight : public mjCLight_, private mjsLight {
   const std::string& get_targetbody() const { return targetbody_; }
 
   void SetParent(mjCBody* _body) { body = _body; }
+  mjCBody* GetParent() const { return body; }
 
  private:
   void Compile(void);                     // compiler