Authority transfer

Overview

The state of network entities that are currently not simulated locally (either because they are being simulated on another game client or on a simulator) cannot be affected directly.

Network commands can help us affect state indirectly, but for anything more involved, an authority transfer might be necessary.

Types of Authority Transfer

In the design phase, CoherenceSync objects can be configured to handle authority transfer in different ways:

• Request. Authority transfer may be requested, but it may be rejected by the receiving party.

• Steal. Authority will always be given to the requesting party on a FCFS ("first come first serve") basis.

• Not transferable. Authority cannot be transferred.

Note also that you need to set up Auto-adopt Orphan if you wan't orphans to be adopted automatically by nearest player.

When using Request, an optional callback OnAuthorityRequestedByConnection can be set on the CoherenceSync behaviour. If the callback is set, then the results of the callback will override the Approve Requests setting in the behaviour.

The request can be approved or rejected in the callback.

// connectionID is the network connection ID of the requesting client.
// sync is the CoherenceSync behaviour of the object the other client is
// requesting authority over.
public bool OnRequest(ushort connectionID, CoherenceSync sync)
{
    return (sync == theRightSync && connectionID == goodConnectionID);
}

Requesting Authority in Code

Requesting authority is very straight-forward.

var coherenceSync = target.GetComponent<CoherenceSync>();
coherenceSync.RequestAuthority();

As the transfer is asynchronous, we have to subscribe to one or more Unity Events in CoherenceSync to learn the result.

The request will first go to the replication server and be passed onto the receiving simulator or game client, so it may take a few frames to get a response.

// There Unity Events in CoherenceSync help us understand 
// what happened with authority requests and act accordingly.

// called when the CoherenceSync entity becomes the simulation authority
public UnityEvent OnAuthorityGained;

// called when the CoherenceSync entity loses simulatino authority
public UnityEvent OnAuthorityLost;

// called when a request to assume authority over the CoherenceSync entity
// is rejected
public UnityEvent OnAuthorityTransferRejected;

These events are also exposed to the Unity inspector in the Events on authority transfer section of the CoherenceSync behaviour.