27. Record and Playback

Note

This is an experimental feature meaning it may be changed in the future with no guaranteed backwards compatibility.

AGX Dynamics for Unreal offers some functionality that enables recording and playback of some aspects of a Simulation. This can be useful when for example recording the movements of a machine controlled by user inputs for later playback.

The Play Record Component is responsible for handling the record and playback functionality. During recording it writes data to a Play Record Asset which is stored permanently for later playback.

27.1. Record

  1. Create a Play Record Asset. This is where the recorded data will be stored.

Create a Play Record Asset.

  1. Add a Play Record Component (AGX Play Record) to your Blueprint and assign the Play Record Asset created from step 1 to it, in the Details Panel.

Assign Play Record Asset.

3. Call one of the Record <> functions. Currently only either Constraint positions or Rigid Body positions are supported, see Limitations.

Call record function recording Constraints.
Call record function recording Rigid Bodies.

Notice that we use a AGX Simulation Step Forward event for triggering the recording instead of Unreal Engines Tick event. This is important for determinism. See Events and Delegates for more information.

4. Play the Simulation and stop it once done. The recorded data is now present in the Play Record Asset and can be used for future playback. Remember to disconnect the Record <> function route node in your Blueprint to avoid overwriting the data in subsequent Simulations.

27.2. Playback

Here it is assumed that the steps in Record has been followed.

  1. Assign a Play Record Asset containing recorded data to the Play Record Component in the Details Panel.

Assign Play Record Asset.

  1. Call one of the Play Back <> functions, either Constraint Positions or Rigid Body Positions. See Limitations.

Call playback function for Constraints.
Call playback function for Rigid Bodies.

It is important that the array of Constraints or Rigid Bodies match those used during recording to get a correct result.

3. Play the Simulation. The Constraints or Rigid Bodies will now move according to the recorded data. Note that the Play Record Component does position control internally and does not guarantee equal Constraint forces/torques during playback as during recording. While playing back Rigid Body trajectories the bodies temporarily have their Motion Control set to Kinematics.

27.3. Limitations

Currently only one of Constraint positions or Rigid Body trajectories can be recorded and played back when using the Play Record Component. The Play Record Component strictly uses position control of Constraints during playback meaning forces, torques and trajectories are not guaranteed to be the same as during recording.