Random improvements and cleanups done while investigating #2519

ksp_plugin/interface_part.cpp

@@ -71,11 +71,11 @@ void __cdecl principia__PartApplyIntrinsicTorque(
   return m.Return();
 }
 
-QPRW __cdecl principia__PartGetActualDegreesOfFreedom(
+QPRW __cdecl principia__PartGetActualRigidMotion(
     Plugin const* const plugin,
     PartId const part_id,
     Origin const origin) {
-  journal::Method<journal::PartGetActualDegreesOfFreedom> m(
+  journal::Method<journal::PartGetActualRigidMotion> m(
       {plugin, part_id, origin});
   CHECK_NOTNULL(plugin);
   RigidMotion<RigidPart, World> const part_motion = plugin->GetPartActualMotion(

ksp_plugin/pile_up.cpp

@@ -119,6 +119,7 @@ Status PileUp::DeformAndAdvanceTime(Instant const& t) {
 }
 
 void PileUp::RecomputeFromParts() {
+  absl::MutexLock l(lock_.get());
   mass_ = Mass();
   intrinsic_force_ = Vector<Force, Barycentric>();
   intrinsic_torque_ = Bivector<Torque, NonRotatingPileUp>();

ksp_plugin/plugin.cpp

@@ -461,8 +461,8 @@ void Plugin::InsertOrKeepLoadedPart(
           main_body_frame.ToThisFrameAtTime(previous_time).orthogonal_map() *
               Δplanetarium_rotation.Inverse() *
               renderer_->WorldToBarycentric(PlanetariumRotation())},
-          (renderer_->BarycentricToWorld(PlanetariumRotation()) *
-                Δplanetarium_rotation)(-angular_velocity_of_world_),
+      (renderer_->BarycentricToWorld(PlanetariumRotation()) *
+          Δplanetarium_rotation)(-angular_velocity_of_world_),
       main_body_degrees_of_freedom.velocity()};
   RigidMotion<World, Barycentric> const world_to_barycentric_motion =
       main_body_frame.FromThisFrameAtTime(previous_time) *

ksp_plugin_adapter/ksp_plugin_adapter.cs

@@ -444,7 +444,7 @@ private void UpdateVessel(Vessel vessel, double universal_time) {
           // TODO(egg): check that the vessel is moved *after* this.  Shouldn't
           // we be calling vessel.orbitDriver.updateFromParameters() after
           // setting the orbit anyway?
-          QPRW part_actual_motion = plugin_.PartGetActualDegreesOfFreedom(
+          QPRW part_actual_motion = plugin_.PartGetActualRigidMotion(
               part.flightID,
               new Origin{
                   reference_part_is_at_origin = true,
@@ -1294,7 +1294,7 @@ private System.Collections.IEnumerator WaitedForFixedUpdate() {
         }
         foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
           QPRW part_actual_motion =
-              plugin_.PartGetActualDegreesOfFreedom(
+              plugin_.PartGetActualRigidMotion(
                   part.flightID,
                   new Origin{
                       reference_part_is_at_origin  =
@@ -1541,11 +1541,11 @@ private void JaiFailliAttendre() {
                     physical_parent,
                     new Part.ForceHolder {
                       force = -part.dragVectorDir * part.dragScalar,
-                      pos = (physical_parent != part &&
-                             PhysicsGlobals.ApplyDragToNonPhysicsPartsAtParentCoM)
+                      pos = (physical_parent != part && PhysicsGlobals.
+                                 ApplyDragToNonPhysicsPartsAtParentCoM)
                                 ? physical_parent.rb.worldCenterOfMass
                                 : part.partTransform.TransformPoint(
-                                      part.CoPOffset)});
+                                    part.CoPOffset)});
           }
         }
       }

mathematica/mathematica.hpp

@@ -8,6 +8,7 @@
 #include "astronomy/orbital_elements.hpp"
 #include "geometry/grassmann.hpp"
 #include "geometry/point.hpp"
+#include "geometry/quaternion.hpp"
 #include "geometry/r3_element.hpp"
 #include "numerics/fixed_arrays.hpp"
 #include "physics/degrees_of_freedom.hpp"
@@ -18,7 +19,9 @@ namespace principia {
 namespace mathematica {
 namespace internal_mathematica {
 
+using geometry::Bivector;
 using geometry::Point;
+using geometry::Quaternion;
 using geometry::R3Element;
 using geometry::Vector;
 using numerics::FixedVector;
@@ -55,9 +58,14 @@ std::string ToMathematica(FixedVector<T, size> const& fixed_vector);
 template<typename T>
 std::string ToMathematica(R3Element<T> const& r3_element);
 
+std::string ToMathematica(Quaternion const& quaternion);
+
 template<typename D>
 std::string ToMathematica(Quantity<D> const& quantity);
 
+template<typename S, typename F>
+std::string ToMathematica(Bivector<S, F> const& bivector);
+
 template<typename S, typename F>
 std::string ToMathematica(Vector<S, F> const& vector);
 

mathematica/mathematica_body.hpp

@@ -49,8 +49,9 @@ inline std::string Apply(
   result += "[";
   for (int i = 0; i < arguments.size(); ++i) {
     result += arguments[i];
-    result += (i + 1 == arguments.size() ? "]" : ",");
+    result += (i + 1 < arguments.size() ? "," : "");
   }
+  result += "]";
   return result;
 }
 
@@ -105,6 +106,11 @@ inline std::string ToMathematica(double const& real) {
   }
 }
 
+inline std::string ToMathematica(Quaternion const& quaternion) {
+  return ToMathematica<double, R3Element<double>>(
+      {quaternion.real_part(), quaternion.imaginary_part()});
+}
+
 template<typename T, int size>
 std::string ToMathematica(FixedVector<T, size> const & fixed_vector) {
   std::vector<std::string> expressions;
@@ -137,6 +143,11 @@ std::string ToMathematica(Quantity<D> const& quantity) {
       {Apply("Quantity", {number, units}), "$MachinePrecision"});
 }
 
+template<typename S, typename F>
+std::string ToMathematica(Bivector<S, F> const& bivector) {
+  return ToMathematica(bivector.coordinates());
+}
+
 template<typename S, typename F>
 std::string ToMathematica(Vector<S, F> const & vector) {
   return ToMathematica(vector.coordinates());

serialization/journal.proto

@@ -1587,9 +1587,9 @@ message PartApplyIntrinsicTorque {
   optional In in = 1;
 }
 
-message PartGetActualDegreesOfFreedom {
+message PartGetActualRigidMotion {
   extend Method {
-    optional PartGetActualDegreesOfFreedom extension = 5116;
+    optional PartGetActualRigidMotion extension = 5116;
   }
   message In {
     required fixed64 plugin = 1 [(pointer_to) = "Plugin const",