Rigidbody Tracked Interactables lag way behind Axis Movement

Environment

• Source of VRTK: GitHub master
• Version of VRTK: v4 beta
• Version of the Unity software: 2019.1
• Hardware used: Oculus
• SDK used: UnityXR

Steps to reproduce

1. in the example scene change the hammer follow type to FollowRigidbody
2. start the scene and switch to axis control
3. grab the hammer and move with axis control

Expected behavior

The hammer should follow the controller without any lag

(see v3.3 functionality)

Current behavior

The hammer lags behind the controller considerably

[thestonefox]

Moving all of the relevant follow processes to fixed update and in the correct sequence does work (but is a clunky workaround)

This is all in the AxesToVector3 moment processor:

• Do AxesToVector3 movement first
• Then move play area to follow alias
• Then move controller alias to follow tracked controller
• Finally move tracked object to follow controller alias

[thestonefox]

The issue is a race condition in the fixed update routine.

If the Rigidbody Follow FixedUpdate processes before the AxesToVector3 FixedUpdate (via their respective MomentProcessors) then the issue occurs.

However, if the AxesToVector3 processes before the RigidbodyFollow then it works fine.

This can be confirmed by disabling the moment processor on the RigidbodyFollow and adding the MomentProcess from the RigidbodyFollow to the AxesToVector3 MomentProcessor List (in the second element slot).

This ensures the FixedUpdate processes the axis movement before processing the rigidbody follow and removes the issue.

The reason it worked in v3.3 was pure fluke of how the components in the example scene were saved so the race condition didn’t occur. but it is possible to recreate the issue in v3.3