NetworkTime and ticks
LocalTime and ServerTime
Why are there two different time values and which one should be used?
Netcode for GameObjects (Netcode) uses a star topology. That means all communications happen between the clients and the server/host and never between clients directly. Messages take time to transmit over the network. That's why RPCs
and NetworkVariable
won't happen immediately on other machines. NetworkTime
allows to use time while considering those transmission delays.
LocalTime
on a client is ahead of the server. If a server RPC is sent atLocalTime
from a client it will roughly arrive atServerTime
on the server.ServerTime
on clients is behind the server. If a client RPC is sent atServerTime
from the server to clients it will roughly arrive atServerTime
on the clients.
LocalTime
- Use for player objects with client authority.
- Use if just a general time value is needed.
ServerTime
:
- For player objects with server authority (For example, by sending inputs to the server via RPCs)
- In sync with position updates of
NetworkTransform
for allNetworkObjects
where the client isn't authoritative over the transform. - For everything on non client controlled
NetworkObjects
.
Examples
Example 1: Using network time to synchronize environments
Many games have environmental objects which move in a fixed pattern. By using network time these objects can be moved without having to synchronize their positions with a NetworkTransform
.
For instance the following code can be used to create a moving elevator platform for a client authoritative game:
using Unity.Netcode;
using UnityEngine;
public class MovingPlatform : MonoBehaviour
{
public void Update()
{
// Move up and down by 5 meters and change direction every 3 seconds.
var positionY = Mathf.PingPong(NetworkManager.Singleton.LocalTime.TimeAsFloat / 3f, 1f) * 5f;
transform.position = new Vector3(0, positionY, 0);
}
}
Example 2: Using network time to create a synced event
Most of the time aligning an effect precisely to time isn't needed. But in some cases for important effects or gameplay events it can help to improve consistency especially for clients with bad network connections.
using System.Collections;
using Unity.Netcode;
using UnityEngine;
using UnityEngine.Assertions;
public class SyncedEventExample : NetworkBehaviour
{
public GameObject ParticleEffect;
// Called by the client to create a synced particle event at its own position.
public void ClientCreateSyncedEffect()
{
Assert.IsTrue(IsOwner);
var time = NetworkManager.LocalTime.Time;
CreateSyncedEffectServerRpc(time);
StartCoroutine(WaitAndSpawnSyncedEffect(0)); // Create the effect immediately locally.
}
private IEnumerator WaitAndSpawnSyncedEffect(float timeToWait)
{
// Note sometimes the timeToWait will be negative on the server or the receiving clients if a message got delayed by the network for a long time. This usually happens only in rare cases. Custom logic can be implemented to deal with that scenario.
if (timeToWait > 0)
{
yield return new WaitForSeconds(timeToWait);
}
Instantiate(ParticleEffect, transform.position, Quaternion.identity);
}
[Rpc(SendTo.Server)]
private void CreateSyncedEffectServerRpc(double time)
{
CreateSyncedEffectClientRpc(time); // Call a client RPC to also create the effect on each client.
var timeToWait = time - NetworkManager.ServerTime.Time;
StartCoroutine(WaitAndSpawnSyncedEffect((float)timeToWait)); // Create the effect on the server but wait for the right time.
}
[Rpc(SendTo.ClientsAndHost)]
private void CreateSyncedEffectClientRpc(double time)
{
// The owner already created the effect so skip them.
if (IsOwner == false)
{
var timeToWait = time - NetworkManager.ServerTime.Time;
StartCoroutine(WaitAndSpawnSyncedEffect((float)timeToWait)); // Create the effect on the client but wait for the right time.
}
}
}
Some components such as NetworkTransform
add additional buffering. When trying to align an RPC event like in this example, an additional delay would need to be added.
Network Ticks
Network ticks are run at a fixed rate. The 'Tick Rate' field on the NetworkManager
can be used to set the tick rate.
What does changing the network tick affect? Changes to NetworkVariables
aren't sent immediately. Instead during each network tick changes to NetworkVariables
are collected and sent out to other peers.
To run custom code once per network tick (before NetworkVariable
changes are collected) the Tick
event on the NetworkTickSystem
can be used.
public override void OnNetworkSpawn()
{
NetworkManager.NetworkTickSystem.Tick += Tick;
}
private void Tick()
{
Debug.Log($"Tick: {NetworkManager.LocalTime.Tick}");
}
public override void OnNetworkDespawn() // don't forget to unsubscribe
{
NetworkManager.NetworkTickSystem.Tick -= Tick;
}
When using FixedUpdate
or physics in your game, set the network tick rate to the same rate as the fixed update rate. The FixedUpdate
rate can be changed in Edit > Project Settings > Time > Fixed Timestep
Network FixedTime
Network FixedTime
can be used to get a time value representing the time during a network tick. This works similar to FixedUpdate
where Time.fixedTime
represents the time during the FixedUpdate
.
public void Update()
{
double time = NetworkManager.Singleton.LocalTime.Time; // time during this Update
double fixedTime = NetworkManager.Singleton.LocalTime.FixedTime; // time during the previous network tick
}
NetworkTime Precision
Network time values are calculated using double precisions. This allows time to stay accurate on long running servers. For game servers which run sessions for a long time (multiple hours or days) don't convert this value in a float and always use doubles for time related calculations.
For games with short play sessions casting the time to float is safe or TimeAsFloat
can be used.
NetworkTimeSystem Configuration
The properties of the NetworkTimeSystem
should be left untouched on the server/host. Changing the values on the client is sufficient to change the behavior of the time system.
The way network time gets calculated can be configured in the NetworkTimeSystem
if needed. Refer to the API docs for information about the properties which can be modified. All properties can be safely adjusted at runtime. For instance, buffer values can be increased for a player with a bad connection.