Consolidate entity creation. (#2452)

* Resolve failing tests

Signed-off-by: Nate Koenig <natekoenig@gmail.com>

* Cleanup

Signed-off-by: Nate Koenig <natekoenig@gmail.com>

* Update src/EntityComponentManager.cc

Co-authored-by: Ian Chen <ichen@openrobotics.org>
Signed-off-by: Nate Koenig <natekoenig@gmail.com>

* Incorrect else

Signed-off-by: Nate Koenig <natekoenig@gmail.com>

---------

Signed-off-by: Nate Koenig <natekoenig@gmail.com>
Co-authored-by: Ian Chen <ichen@openrobotics.org>

include/gz/sim/EntityComponentManager.hh

@@ -675,6 +675,14 @@ namespace gz
       /// \return True if there are components marked for removal.
       public: bool HasRemovedComponents() const;
 
+      /// \brief Get an Entity based on a name component that is associated
+      /// with the entity.
+      /// \param[in] _name Name associated with the Entity
+      /// \return The Entity, if an Entity with the given name exists,
+      /// otherwise return std::nullopt.
+      public: std::optional<Entity> EntityByName(
+                  const std::string &_name) const;
+
       /// \brief Clear the list of newly added entities so that a call to
       /// EachAdded after this will have no entities to iterate. This function
       /// is protected to facilitate testing.

include/gz/sim/SdfEntityCreator.hh

@@ -93,6 +93,13 @@ namespace gz
       /// \return World entity.
       public: Entity CreateEntities(const sdf::World *_world);
 
+      /// \brief Create all entities that exist in the sdf::World object and
+      /// load their plugins.
+      /// \param[in] _world SDF world object.
+      /// \param[in] _worldEntity The world entity object.
+      public: void CreateEntities(const sdf::World *_world,
+                  Entity _worldEntity);
+
       /// \brief Create all entities that exist in the sdf::Model object and
       /// load their plugins. Also loads plugins of child sensors.
       /// \param[in] _model SDF model object.
@@ -186,6 +193,9 @@ namespace gz
       private: Entity CreateEntities(const sdf::Model *_model,
                                      bool _staticParent);
 
+      /// \brief Load plugins for all models
+      private: void LoadModelPlugins();
+
       /// \brief Pointer to private data.
       private: std::unique_ptr<SdfEntityCreatorPrivate> dataPtr;
     };

include/gz/sim/components/Performer.hh

@@ -17,6 +17,7 @@
 #ifndef GZ_SIM_COMPONENTS_PERFORMER_HH_
 #define GZ_SIM_COMPONENTS_PERFORMER_HH_
 
+#include <string>
 #include <gz/sim/config.hh>
 #include <gz/sim/Export.hh>
 
@@ -34,6 +35,11 @@ namespace components
   /// \brief This component identifies an entity as being a performer.
   using Performer = Component<NoData, class PerformerTag>;
   GZ_SIM_REGISTER_COMPONENT("gz_sim_components.Performer", Performer)
+
+  /// \brief This component contains the performer reference name.
+  using PerformerRef = Component<std::string, class PerformerRefTag,
+      serializers::StringSerializer>;
+  GZ_SIM_REGISTER_COMPONENT("gz_sim_components.PerformerRef", PerformerRef)
 }
 }
 }

src/EntityComponentManager.cc

@@ -2314,3 +2314,15 @@ void EntityComponentManager::ResetTo(const EntityComponentManager &_other)
   tmpCopy.ApplyEntityDiff(*this, ecmDiff);
   this->CopyFrom(tmpCopy);
 }
+
+/////////////////////////////////////////////////
+std::optional<Entity> EntityComponentManager::EntityByName(
+    const std::string &_name) const
+{
+  std::optional<Entity> entity;
+   Entity entByName = EntityByComponents(components::Name(_name));
+  if (entByName != kNullEntity)
+    entity = entByName;
+
+  return entity;
+}

src/EntityComponentManager_TEST.cc

@@ -3421,6 +3421,23 @@ TEST_P(EntityComponentManagerFixture,
   EXPECT_EQ(321, comp->Data());
 }
 
+//////////////////////////////////////////////////
+TEST_P(EntityComponentManagerFixture, EntityByName)
+{
+  // Create an entity, and give it a name
+  Entity entity = manager.CreateEntity();
+  manager.CreateComponent(entity, components::Name("entity_name_a"));
+
+  // Try to get an entity that doesn't exist
+  std::optional<Entity> entityByName = manager.EntityByName("a_bad_name");
+  EXPECT_FALSE(entityByName);
+
+  entityByName = manager.EntityByName("entity_name_a");
+  EXPECT_TRUE(entityByName);
+  CompareEntityComponents<components::Name>(manager, entity,
+    *entityByName, true);
+}
+
 // Run multiple times. We want to make sure that static globals don't cause
 // problems.
 INSTANTIATE_TEST_SUITE_P(EntityComponentManagerRepeat,