Align Physics system (Edifice 5.1) (#365)

* Vendor Physics system

gazebosim/gz-sim@91e3e49

* Revert upstream PR 690

* Custom Physics features

* Add headers to CMakeLists.txt

* Disable broken test

scenario/src/plugins/Physics/CMakeLists.txt

@@ -28,6 +28,8 @@
 
 add_library(PhysicsSystem SHARED
     Physics.hh
+    EntityFeatureMap.hh
+    CanonicalLinkModelTracker.hh
     Physics.cc)
 
 target_link_libraries(PhysicsSystem

scenario/src/plugins/Physics/CanonicalLinkModelTracker.hh

@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2021 Open Source Robotics Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+*/
+#ifndef IGNITION_GAZEBO_SYSTEMS_PHYSICS_CANONICAL_LINK_MODEL_TRACKER_HH_
+#define IGNITION_GAZEBO_SYSTEMS_PHYSICS_CANONICAL_LINK_MODEL_TRACKER_HH_
+
+#include <set>
+#include <unordered_map>
+
+#include "ignition/gazebo/Entity.hh"
+#include "ignition/gazebo/EntityComponentManager.hh"
+#include "ignition/gazebo/components/CanonicalLink.hh"
+#include "ignition/gazebo/components/Model.hh"
+#include "ignition/gazebo/config.hh"
+
+namespace ignition::gazebo
+{
+inline namespace IGNITION_GAZEBO_VERSION_NAMESPACE {
+namespace systems::physics_system
+{
+  /// \brief Helper class that keeps track of which models have a particular
+  /// canonical link. This is useful in the physics system for updating model
+  /// poses - if a canonical link moved in the most recent physics step, then
+  /// all of the models that have this canonical link should be updated. It's
+  /// important to preserve topological ordering of the models in case there's
+  /// a nested model that shares the same canonical link (in a case like this,
+  /// the parent model pose needs to be updated before updating the child model
+  /// pose - see the documentation that explains how model pose updates are
+  /// calculated in PhysicsPrivate::UpdateSim to understand why nested model
+  /// poses need to be updated in topological order).
+  ///
+  /// It's possible to loop through all of the models and to update poses if the
+  /// model moved using something like EntityComponentManager::Each, but the
+  /// performance of this approach is worse than using just the moved canonical
+  /// links to determine which model poses should be updated (consider the case
+  /// where there are a lot of non-static models in a world, but only a few move
+  /// frequently - if using EntityComponentManager::Each, we still need to check
+  /// every single non-static model after a physics update to make sure that the
+  /// model did not move. If we instead use the updated canonical link
+  /// information, then we can skip iterating over/checking the models that
+  /// don't need to be updated).
+  class CanonicalLinkModelTracker
+  {
+    /// \brief Save mappings for new models and their canonical links
+    /// \param[in] _ecm EntityComponentManager
+    public: void AddNewModels(const EntityComponentManager &_ecm);
+
+    /// \brief Get a topological ordering of models that have a particular
+    /// canonical link
+    /// \param[in] _canonicalLink The canonical link
+    /// \return The models that have this link as their canonical link, in
+    /// topological order
+    public: const std::set<Entity> &CanonicalLinkModels(
+                const Entity _canonicalLink) const;
+
+    /// \brief Remove a link from the mapping. This method should be called when
+    /// a link is removed from simulation
+    /// \param[in] _link The link to remove
+    public: void RemoveLink(const Entity &_link);
+
+    /// \brief A mapping of canonical links to the models that have this
+    /// canonical link. The key is the canonical link entity, and the value is
+    /// the model entities that have this canonical link. The models in the
+    /// value are in topological order
+    private: std::unordered_map<Entity, std::set<Entity>> linkModelMap;
+
+    /// \brief An empty set of models that is returned from the
+    /// CanonicalLinkModels method for links that map to no models
+    private: const std::set<Entity> emptyModelOrdering{};
+  };
+
+  void CanonicalLinkModelTracker::AddNewModels(
+      const EntityComponentManager &_ecm)
+  {
+    _ecm.EachNew<components::Model, components::ModelCanonicalLink>(
+        [this](const Entity &_model, const components::Model *,
+          const components::ModelCanonicalLink *_canonicalLinkComp)
+        {
+          this->linkModelMap[_canonicalLinkComp->Data()].insert(_model);
+          return true;
+        });
+  }
+
+  const std::set<Entity> &CanonicalLinkModelTracker::CanonicalLinkModels(
+      const Entity _canonicalLink) const
+  {
+    auto it = this->linkModelMap.find(_canonicalLink);
+    if (it != this->linkModelMap.end())
+      return it->second;
+
+    // if an invalid entity was given, it maps to no models
+    return this->emptyModelOrdering;
+  }
+
+  void CanonicalLinkModelTracker::RemoveLink(const Entity &_link)
+  {
+    this->linkModelMap.erase(_link);
+  }
+}
+}
+}
+
+#endif