NetworkObject parenting inside Boss Room

note

Required reading: NetworkObject Parenting

Before detailing Boss Room's approach to NetworkObject parenting, it's important to highlight a limitation of Netcode: A dynamically-spawned NetworkObject can't contain another NetworkObject in its hierarchy. If you spawn such a NetworkObject, you can't spawn children NetworkObjects. You can only add children NetworkObject components to a NetworkObject that is part of a scene.

Boss Room leverages NetworkObject parenting through the server-driven PickUp action (see PickUpAction.cs), where a character has the ability to pick up a specially-tagged, in-scene placed NetworkObject (see PickUpPot prefab].

At its root, PickUpPot has a NetworkObject, a NetworkTransform, and a PositionConstraint component. AutoObjectParentSync is enabled on its NetworkTransform (as is by default) so that:

1. The NetworkObject can verify server-side if parenting a Heavy object to another NetworkObject is allowed.
2. The NetworkObject can notify us when the parent has successfully been modified server-side.

To accommodate the limitation highlighted at the beginning of this document, Boss Room leverages the PositionConstraint component to simulate an object following a character's position.

A special hand bone has been added to our Character's avatar. Upon a character's successful parenting attempt, this special bone is set as the PickUpPot's PositonConstraint target. So while the PickUpPot is technically parented to a player, the PositionConstraint component allows the PickUpPot to follow a bone's position, presenting the illusion that the PickUpPot is parented to the player's hand bone itself.

Once the PickUpPot is parented, local space simulation is enabled on its NetworkTransform component.