Sensors of type user no longer require objtype and objname. If unspecified, the objtype will be mjOBJ_UNKNOWN. Also, `user sensors datatype default is now "real"`.

PiperOrigin-RevId: 489652972
Change-Id: I0a8f21ee1a2f5292e6bbcfe3785536cfd1498b85

doc/XMLreference.rst

@@ -3913,7 +3913,7 @@ at a specified body, in global coordinates.
 .. _sensor-clock:
 
 :el-prefix:`sensor/` **clock** (*)
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 This element creates sensor that returns the simulation time.
 
@@ -3934,12 +3934,12 @@ bodies whose center of mass is of interest.
 
 :at:`name`, :at:`noise`, :at:`cutoff`, :at:`user`
    See :ref:`CSensor`.
-:at:`objtype`: :at-val:`(any element type that can be named), required`
+:at:`objtype`: :at-val:`(any element type that can be named), optional`
    Type of the MuJoCo object to which the sensor is attached. This together with the objname attribute determines the
-   actual object.
+   actual object. If unspecified, will be :ref:`mjOBJ_UNKNOWN<mjtObj>`.
-:at:`objname`: :at-val:`string, required`
+:at:`objname`: :at-val:`string, optional`
    Name of the MuJoCo object to which the sensor is attached.
-:at:`datatype`: :at-val:`[real, positive, axis, quaternion], required`
+:at:`datatype`: :at-val:`[real, positive, axis, quaternion], "real"`
    The type of output generated by this sensor. "axis" means a unit-length 3D vector. "quat" means a unit quaternion.
    These need to be declared because when MuJoCo adds noise, it must respect the vector normalization. "real" means a
    generic array (or scalar) of real values to which noise can be added independently.
@@ -3952,7 +3952,7 @@ bodies whose center of mass is of interest.
 .. _keyframe:
 
 **keyframe** (*)
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~
 
 This is a grouping element for keyframe definitions. It does not have attributes. Keyframes can be used to create a
 library of states that are of interest to the user, and to initialize the simulation state to one of the states in the

doc/changelog.rst

@@ -54,6 +54,8 @@ General
   ``dlopen`` on a POSIX system, and to ``LoadLibraryA`` on Windows. The second function scans a specified directory for
   all dynamic libraries file and loads each library found. Dynamic libraries opened by these functions are assumed to
   register one or more MuJoCo plugins on load.
+- Sensors of type :ref:`user<sensor-user>` no longer require :at:`objtype` and :at:`objname`. If unspecified, the
+  objtype will be :ref:`mjOBJ_UNKNOWN<mjtObj>`. ``user`` sensors :at:`datatype` default is now :at-val:`"real"`.
 
 Simulate
 ^^^^^^^^

src/user/user_objects.cc

@@ -3697,7 +3697,7 @@ void mjCSensor::Compile(void) {
 
     // get sensorized object id
     objid = pobj->id;
-  } else if (type != mjSENS_CLOCK && type != mjSENS_PLUGIN) {
+  } else if (type != mjSENS_CLOCK && type != mjSENS_PLUGIN && type != mjSENS_USER) {
     throw mjCError(this, "invalid type in sensor '%s' (id = %d)", name.c_str(), id);
   }
 
@@ -3779,7 +3779,7 @@ void mjCSensor::Compile(void) {
                      "joint must be slide or hinge in sensor '%s' (id = %d)", name.c_str(), id);
     }
 
-    //set
+    // set
     dim = 1;
     datatype = mjDATATYPE_REAL;
     if (type==mjSENS_JOINTPOS) {

src/xml/xml_native_reader.cc

@@ -3147,16 +3147,23 @@ void mjXReader::Sensor(XMLElement* section) {
     // user-defined sensor
     else if (type=="user") {
       psen->type = mjSENS_USER;
-      ReadAttrTxt(elem, "objtype", text, true);
+      bool objname_given = ReadAttrTxt(elem, "objname", psen->objname);
-      psen->objtype = (mjtObj)mju_str2Type(text.c_str());
+      if (ReadAttrTxt(elem, "objtype", text)) {
-      ReadAttrTxt(elem, "objname", psen->objname, true);
+        if (!objname_given) {
+          throw mjXError(elem, "objtype '%s' given but objname is missing", text.c_str());
+        }
+        psen->objtype = (mjtObj)mju_str2Type(text.c_str());
+      } else if (objname_given) {
+        throw mjXError(elem, "objname '%s' given but objtype is missing", psen->objname.c_str());
+      }
       ReadAttrInt(elem, "dim", &psen->dim, true);
 
       // keywords
       MapValue(elem, "needstage", &n, stage_map, stage_sz, true);
       psen->needstage = (mjtStage)n;
-      MapValue(elem, "datatype", &n, datatype_map, datatype_sz, true);
+      if (MapValue(elem, "datatype", &n, datatype_map, datatype_sz)) {
-      psen->datatype = (mjtDataType)n;
+       psen->datatype = (mjtDataType)n;
+      }
     }
 
     else if (type=="plugin") {

src/xml/xml_native_writer.cc

@@ -1768,7 +1768,7 @@ void mjXWriter::Sensor(XMLElement* root) {
     // user-defined sensor
     case mjSENS_USER:
       elem = InsertEnd(section, "user");
-      WriteAttrTxt(elem, "objtype", mju_type2Str(psen->objtype));
+      if (mju_type2Str(psen->objtype)) WriteAttrTxt(elem, "objtype", mju_type2Str(psen->objtype));
       WriteAttrTxt(elem, "objname", psen->objname);
       WriteAttrInt(elem, "dim", psen->dim);
       WriteAttrKey(elem, "needstage", stage_map, stage_sz, (int)psen->needstage);

test/user/user_objects_test.cc

@@ -202,6 +202,29 @@ TEST_F(RelativeFrameSensorParsingTest, BadRefType) {
   EXPECT_THAT(error.data(), HasSubstr("reference frame object must be"));
 }
 
+// ------------- sensor compilation --------------------------------------------
+
+using SensorTest = MujocoTest;
+TEST_F(SensorTest, OjbtypeParsedButNotRequired) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <sensor>
+      <user dim="3" needstage="vel" datatype="axis"/>
+      <user dim="2" needstage="pos" objtype="body" objname="world"/>
+    </sensor>
+  </mujoco>
+  )";
+  mjModel* model = LoadModelFromString(xml, 0, 0);
+  ASSERT_THAT(model, NotNull());
+  EXPECT_EQ(model->sensor_datatype[0], mjDATATYPE_AXIS);
+  EXPECT_EQ(model->sensor_objtype[0], mjOBJ_UNKNOWN);
+  EXPECT_EQ(model->sensor_dim[0], 3);
+  EXPECT_EQ(model->sensor_datatype[1], mjDATATYPE_REAL);
+  EXPECT_EQ(model->sensor_objtype[1], mjOBJ_BODY);
+  EXPECT_EQ(model->sensor_objid[1], 0);
+  mj_deleteModel(model);
+}
+
 // ------------- test capsule inertias -----------------------------------------
 
 static const char* const kCapsuleInertiaPath =

test/xml/xml_native_reader_test.cc

@@ -935,6 +935,38 @@ TEST_F(ActuatorParseTest, ActdimDefaultsPropagate) {
   mj_deleteModel(model);
 }
 
+// ------------- test sensor parsing -------------------------------------------
+
+using SensorParseTest = MujocoTest;
+
+TEST_F(SensorParseTest, UserObjTypeNoName) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <sensor>
+      <user dim="1" needstage="vel" objtype="site"/>
+    </sensor>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("objtype 'site' given but"));
+}
+
+TEST_F(SensorParseTest, UserObjNameNoType) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <sensor>
+      <user dim="1" needstage="vel" objname="kevin"/>
+    </sensor>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("objname 'kevin' given but"));
+}
+
 // ------------- test general parsing ------------------------------------------
 
 TEST_F(XMLReaderTest, ZnearZeroNotAllowed) {

test/xml/xml_native_writer_test.cc

@@ -129,6 +129,24 @@ TEST_F(XMLWriterTest, SavesDisableSensor) {
   mj_deleteModel(model);
 }
 
+TEST_F(XMLWriterTest, EmptyUserSensor) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <sensor>
+      <user dim="2" needstage="vel"/>
+    </sensor>
+  </mujoco>
+  )";
+  mjModel* model = LoadModelFromString(xml);
+  std::string saved_xml = SaveAndReadXml(model);
+  EXPECT_THAT(saved_xml, HasSubstr("dim=\"2\""));
+  EXPECT_THAT(saved_xml, HasSubstr("needstage=\"vel\""));
+  EXPECT_THAT(saved_xml, HasSubstr("datatype=\"real\""));
+  EXPECT_THAT(saved_xml, Not(HasSubstr("objtype")));
+  EXPECT_THAT(saved_xml, Not(HasSubstr("objname")));
+  mj_deleteModel(model);
+}
+
 TEST_F(XMLWriterTest, KeepsEmptyClasses) {
   static constexpr char xml[] = R"(
   <mujoco>