Fix examples in migration plugins tutorial (#543)

Signed-off-by: Nick Lamprianidis <[email protected]>

tutorials/migration_plugins.md

@@ -1,6 +1,6 @@
 \page migrationplugins
 
-# Migration from Gazebo-classic: Plugins
+# Migration from Gazebo Classic: Plugins
 
 Classic Gazebo supports
 [6 different C++ plugin types](http://gazebosim.org/tutorials?tut=plugins_hello_world&cat=write_plugin),
@@ -75,7 +75,7 @@ class MyPlugin : public ModelPlugin
     this->link = _model->GetLink(linkName);
 
     // Register callback to be called at every iteration
-    this->connection = event::Events::ConnectWorldUpdateBegin(
+    this->updateConnection = event::Events::ConnectWorldUpdateBegin(
             std::bind(&MyPlugin::OnUpdate, this));
   }
 
@@ -103,6 +103,11 @@ On Ignition Gazebo, that would be implemented as follows:
 #include <ignition/gazebo/Model.hh>
 #include <ignition/gazebo/Util.hh>
 #include <ignition/gazebo/System.hh>
+#include <ignition/plugin/Register.hh>
+
+using namespace ignition;
+using namespace gazebo;
+using namespace systems;
 
 // Inherit from System and 2 extra interfaces:
 // ISystemConfigure and ISystemPostUpdate
@@ -113,25 +118,25 @@ class MyPlugin
 {
   // Implement Configure callback, provided by ISystemConfigure
   // and called once at startup.
-  void MyPlugin::Configure(const Entity &_entity,
-      const std::shared_ptr<const sdf::Element> &_sdf,
-      EntityComponentManager &_ecm,
-      EventManager &/*_eventMgr*/)
+  virtual void Configure(const Entity &_entity,
+                         const std::shared_ptr<const sdf::Element> &_sdf,
+                         EntityComponentManager &_ecm,
+                         EventManager &/*_eventMgr*/) override
   {
     // Read property from SDF
     auto linkName = _sdf->Get<std::string>("link_name");
 
-    // Create model object, to access convenient functions
+    // Create model object to access convenient functions
     auto model = Model(_entity);
 
     // Get link entity
-    auto linkEntity = model->LinkByName(_ecm, linkName);
+    this->linkEntity = model.LinkByName(_ecm, linkName);
   }
 
   // Implement PostUpdate callback, provided by ISystemPostUpdate
   // and called at every iteration, after physics is done
-  void MyPlugin::PostUpdate(const UpdateInfo &/*_info*/,
-      const EntityComponentManager &_ecm)
+  virtual void PostUpdate(const UpdateInfo &/*_info*/,
+                          const EntityComponentManager &_ecm) override
   {
     // Get link pose and print it
     std::cout << worldPose(this->linkEntity, _ecm) << std::endl;
@@ -149,7 +154,7 @@ IGNITION_ADD_PLUGIN(MyPlugin,
 
 // Add plugin alias so that we can refer to the plugin without the version
 // namespace
-IGNITION_ADD_PLUGIN_ALIAS(MyPlugin,"ignition::gazebo::systems::MyPlugin")
+IGNITION_ADD_PLUGIN_ALIAS(MyPlugin, "ignition::gazebo::systems::MyPlugin")
 ```
 
 The example above uses headers like `Model.hh` and `Util.hh`, which offer
@@ -161,6 +166,15 @@ the ECM's API:
 ```cpp
 #include <ignition/gazebo/EntityComponentManager.hh>
 #include <ignition/gazebo/System.hh>
+#include <ignition/gazebo/components/Link.hh>
+#include <ignition/gazebo/components/Name.hh>
+#include <ignition/gazebo/components/ParentEntity.hh>
+#include <ignition/gazebo/components/Pose.hh>
+#include <ignition/plugin/Register.hh>
+
+using namespace ignition;
+using namespace gazebo;
+using namespace systems;
 
 // Inherit from System and 2 extra interfaces:
 // ISystemConfigure and ISystemPostUpdate
@@ -169,43 +183,43 @@ class MyPlugin
         public ISystemConfigure,
         public ISystemPostUpdate
 {
-  void MyPlugin::Configure(const Entity &_entity,
-      const std::shared_ptr<const sdf::Element> &_sdf,
-      EntityComponentManager &_ecm,
-      EventManager &/*_eventMgr*/)
+  virtual void Configure(const Entity &_entity,
+                         const std::shared_ptr<const sdf::Element> &_sdf,
+                         EntityComponentManager &_ecm,
+                         EventManager &/*_eventMgr*/) override
   {
+    // Read property from SDF
     auto linkName = _sdf->Get<std::string>("link_name");
 
-    // Create link entity by querying for an entity that has a specific set of
+    // Get link entity by querying for an entity that has a specific set of
     // components
     this->linkEntity = _ecm.EntityByComponents(
-        components::ParentEntity(this->dataPtr->id),
-        components::Name(_name),
-        components::Link());
+        components::ParentEntity(_entity),
+        components::Name(linkName), components::Link());
   }
 
-  void MyPlugin::PostUpdate(const UpdateInfo &/*_info*/,
-      const EntityComponentManager &_ecm)
+  virtual void PostUpdate(const UpdateInfo &/*_info*/,
+                          const EntityComponentManager &_ecm) override
   {
     // Get link's local pose
     auto pose = _ecm.Component<components::Pose>(this->linkEntity)->Data();
 
     // Get link's parent entity
-    auto p = _ecm.Component<components::ParentEntity>(this->linkEntity);
+    auto parent = _ecm.Component<components::ParentEntity>(this->linkEntity);
 
     // Iterate over parents until world is reached
-    while (p)
+    while (parent)
     {
       // Get parent entity's pose
-      auto parentPose = _ecm.Component<components::Pose>(p->Data());
+      auto parentPose = _ecm.Component<components::Pose>(parent->Data());
       if (!parentPose)
         break;
 
       // Add pose
-      pose = pose + parentPose->Data();
+      pose = parentPose->Data() * pose;
 
       // keep going up the tree
-      p = _ecm.Component<components::ParentEntity>(p->Data());
+      parent = _ecm.Component<components::ParentEntity>(parent->Data());
     }
 
     std::cout << pose << std::endl;
@@ -220,7 +234,7 @@ IGNITION_ADD_PLUGIN(MyPlugin,
                     MyPlugin::ISystemConfigure,
                     MyPlugin::ISystemPostUpdate)
 
-IGNITION_ADD_PLUGIN_ALIAS(MyPlugin,"ignition::gazebo::systems::MyPlugin")
+IGNITION_ADD_PLUGIN_ALIAS(MyPlugin, "ignition::gazebo::systems::MyPlugin")
 ```
 
 In summary, the key differences between classic and Igntion Gazebo are:
@@ -234,7 +248,7 @@ In summary, the key differences between classic and Igntion Gazebo are:
 
 * Plugins don't have direct access to physics objects such as `physics::Model`.
   Instead, they can either deal directly with entities and their components by
-  calling functions in the ECM, or use convenient objects such as
+  calling functions of the ECM, or use convenient objects such as
   `ignition::gazebo::Model` which wrap the ECM interface.
 
 All these changes are meant to give plugin developers more flexibility to