Support spawning during log playback

include/ignition/gazebo/EntityComponentManager.hh

@@ -696,6 +696,12 @@ namespace ignition
           const Entity _entity, const ComponentTypeId _type,
           gazebo::ComponentState _c = ComponentState::OneTimeChange);
 
+      /// \brief All future entities will have an id that starts at _offset.
+      /// This can be used to avoid entity id collisions, such as during log
+      /// playback.
+      /// \param[in] _offset Offset value.
+      public: void SetEntityCreateOffset(uint64_t _offset);
+
       /// \brief Mark all components as not changed.
       protected: void SetAllComponentsUnchanged();
 

src/EntityComponentManager.cc

@@ -1224,3 +1224,16 @@ std::unordered_set<ComponentTypeId> EntityComponentManager::ComponentTypes(
 
   return result;
 }
+
+/////////////////////////////////////////////////
+void EntityComponentManager::SetEntityCreateOffset(uint64_t _offset)
+{
+  if (_offset < this->dataPtr->entityCount)
+  {
+    ignwarn << "Setting an entity offset of [" << _offset << "] is less than "
+     << "the current entity count of [" << this->dataPtr->entityCount << "]. "
+     << "Incorrect behavior should be expected.\n";
+  }
+
+  this->dataPtr->entityCount = _offset;
+}

src/EntityComponentManager_TEST.cc

@@ -2009,6 +2009,19 @@ TEST_P(EntityComponentManagerFixture, SetChanged)
       manager.ComponentState(e2, c2.first));
 }
 
+//////////////////////////////////////////////////
+TEST_P(EntityComponentManagerFixture, SetEntityCreateOffset)
+{
+  // First entity should have a value of 1.
+  Entity entity = manager.CreateEntity();
+  EXPECT_EQ(1u, entity);
+
+  // Apply an offset.
+  manager.SetEntityCreateOffset(1000);
+  Entity entity2 = manager.CreateEntity();
+  EXPECT_EQ(1001u, entity2);
+}
+
 // Run multiple times. We want to make sure that static globals don't cause
 // problems.
 INSTANTIATE_TEST_CASE_P(EntityComponentManagerRepeat,

src/Server.cc

@@ -68,17 +68,20 @@ struct DefaultWorld
         std::string("<plugin filename='libignition-gazebo") +
         IGNITION_GAZEBO_MAJOR_VERSION_STR + "-scene-broadcaster-system.so' "
         "name='ignition::gazebo::systems::SceneBroadcaster'></plugin>"
-      }};
+      },
+      {
+        std::string("<plugin filename='libignition-gazebo") +
+        IGNITION_GAZEBO_MAJOR_VERSION_STR + "-user-commands-system.so' " +
+        "name='ignition::gazebo::systems::UserCommands'></plugin>"
+      }
+    };
 
     // The set of default gazebo plugins.
     if (_config.LogPlaybackPath().empty())
     {
       pluginsV.push_back(std::string("<plugin filename='libignition-gazebo") +
         IGNITION_GAZEBO_MAJOR_VERSION_STR + "-physics-system.so' "
         "name='ignition::gazebo::systems::Physics'></plugin>");
-      pluginsV.push_back(std::string("<plugin filename='libignition-gazebo") +
-        IGNITION_GAZEBO_MAJOR_VERSION_STR + "-user-commands-system.so' " +
-        "name='ignition::gazebo::systems::UserCommands'></plugin>");
     }
 
     // Playback plugin

src/systems/log/LogPlayback.cc

@@ -209,6 +209,10 @@ void LogPlayback::Configure(const Entity &,
   // Prepend working directory if path is relative
   this->dataPtr->logPath = common::absPath(this->dataPtr->logPath);
 
+  // Set the entity offset.
+  // \todo This number should be included in the log file.
+  _ecm.SetEntityCreateOffset(math::MAX_I64 / 2);
+
   // If path is a file, assume it is a compressed file
   // (Otherwise assume it is a directory containing recorded files.)
   if (common::isFile(this->dataPtr->logPath))