Merge pull request #3223 from pleroy/Serialization

Only write the number of dense points if downsampling is enabled

Author: pleroy

physics/discrete_trajectory_body.hpp

@@ -879,6 +879,7 @@ void DiscreteTrajectory<Frame>::ReadFromPreHamiltonMessage(
           downsampling_parameters.max_dense_intervals);
       downsampling_parameters.tolerance.WriteToMessage(
           serialized_downsampling_parameters->mutable_tolerance());
+      serialized_segment.set_number_of_dense_points(0);  // Overridden later.
     }
     *sit = DiscreteTrajectorySegment<Frame>::ReadFromMessage(serialized_segment,
                                                              self);

physics/discrete_trajectory_segment_body.hpp

@@ -300,14 +300,17 @@ DiscreteTrajectorySegment<Frame>::ReadFromMessage(
   }
 
   // Finally, restore the downsampling information.
+  CHECK_EQ(message.has_downsampling_parameters(),
+           message.has_number_of_dense_points())
+      << message.DebugString();
   if (message.has_downsampling_parameters()) {
     segment.downsampling_parameters_ = DownsamplingParameters{
         .max_dense_intervals =
             message.downsampling_parameters().max_dense_intervals(),
         .tolerance = Length::ReadFromMessage(
             message.downsampling_parameters().tolerance())};
+    segment.number_of_dense_points_ = message.number_of_dense_points();
   }
-  segment.number_of_dense_points_ = message.number_of_dense_points();
 
   return segment;
 }
@@ -542,11 +545,11 @@ void DiscreteTrajectorySegment<Frame>::WriteToMessage(
         downsampling_parameters_->max_dense_intervals);
     downsampling_parameters_->tolerance.WriteToMessage(
         serialized_downsampling_parameters->mutable_tolerance());
+    message->set_number_of_dense_points(std::min(
+        timeline_size,
+        std::max<std::int64_t>(
+            0, number_of_dense_points_ - number_of_points_to_skip_at_end)));
   }
-  message->set_number_of_dense_points(std::min(
-      timeline_size,
-      std::max<std::int64_t>(
-          0, number_of_dense_points_ - number_of_points_to_skip_at_end)));
 
   // Convert the |exact| vector into a set, and add the extremities.  This
   // ensures that we don't have redundancies.  The set is sorted by time to

serialization/physics.proto

@@ -136,7 +136,7 @@ message DiscreteTrajectorySegment {
     required int32 timeline_size = 4;
   }
   optional DownsamplingParameters downsampling_parameters = 1;
-  required int32 number_of_dense_points = 2;
+  optional int32 number_of_dense_points = 2;
   repeated InstantaneousDegreesOfFreedom exact = 3;
   required Zfp zfp = 4;
 }