Prefab setup

In this section, we will learn how to prepare a Prefab for network replication.

1. Add `CoherenceSync` to your GameObject

For a Unity GameObject to be networked through coherence, it needs to have a CoherenceSync component attached. Currently, only Prefabs are supported. If your GameObject is not a Prefab, CoherenceSync can assist you.

First, create a new GameObject. In this example, we're going to create a Cube.

Next, let's add the CoherenceSync component to this Cube.

The CoherenceSync inspector now tells us that we need to make a Prefab out of this GameObject for it to work. We get to choose where to create it.

In this example, I'll be creating it on Assets / Resources by clicking Convert to Prefab in Resources.

1.1 (Optional) Using Prefab Variants

One way to configure your Prefab, instead of just adding CoherenceSync into it, is to fork a Prefab variant and add the component there.

In our Cube example, instead of adding CoherenceSync to Cube, you can create a Cube (Networked) and add CoherenceSync to it:

Learn how to create and use Prefab variants in the Unity Manual.

This way, you can retain the original Prefab untouched.

Another way to use Prefab variants to our advantage is to have a base Prefab using CoherenceSync, and create Prefab variants off that one with customizations. For example, Enemy (base Prefab) and Enemy 1, Enemy 2, Enemy 3... (variant Prefabs, using different models, animations, materials, etc.). In this setup, all of the enemies will share the networking settings stored in CoherenceSync, so you don't have to manually update every one of them.

2. Configure CoherenceSync

The CoherenceSync component will help you prepare an object for network synchronization during design time. It also exposes an API that allows us to manipulate the object during runtime.

CoherenceSync will query all public variables and methods on any of the attached components, for example Unity components such as Transform, Animator , etc. This will include any custom scripts such as PlayerInput and even scripts that came with the Asset Store packages that you may have downloaded.

You can find out more about CoherenceSync here.

3. (Optional) Prefabs outside of the Resources folders

In order for coherence to know which Prefab to instantiate through the network, they must be located in Resources folders or added to the Prefab Mapper. The Prefab Mapper is simply a ScriptableObject that holds Prefabs we want to sync.

When a CoherenceSync Prefab outside the Resources folder is not present in the Prefab Mapper, the Add to Prefab Mapper button appears.

The Prefab Mapper asset is located at Assets / coherence.

3.1. Addressables

If you are using the Addressables Package (1.15.0 or newer), the Prefab Mapper also supports that. The Prefab Mapper has a list for direct references and a list for addressables referenced using AddressableAssets.AssetReference. The directly referenced assets will be loaded at game start, while the addressables will be asynchronously loaded when needed.

Remember, in order for coherence to load assets as addressables, you need to follow Unity's default workflow for using Addressables which entails building the Addressables Group Bundles whenever the Prefab changes.

3.2. Prefab Mapper utilities

When adding a new Prefab to the mapper, it will automatically make sure to add it to the correct list (addressable or not), but if the Prefab already exists in the mapper and you have changed how it is loaded, simply press the Validate Mapping Lists button.

If you have a number of valid Prefabs that have not yet been added to the Prefab Mapper you can press the Add all CoherenceSync prefabs button.

If you have empty entries in the Prefab Mapper you can remove them by pressing Remove empty entries. This is optional.

4. Select variables to replicate

Select which variables you would like to sync across the network. Initially, this will probably be the Transform settings: position, rotation, scale.

Under Configure, click Variables.

In the Configuration dialog, select position, rotation and scale.

You can configure variables, methods and components on child objects in the CoherenceSync hierarchy. To do that, simply select the desired object in the Hierarchy window, and the Configuration window will show information for that specific object — similarly to how the inspector works.

Close the Configuration dialog.

5. Add an input script

This simple input script will use WASD or the Arrow keys to move the Prefab around the scene.

Click on Assets > Create > C# Script.

Name it Move.cs. Copy-paste the following content into the file.

Move.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Move : MonoBehaviour
{
    public float speed = 1f;

    void Update()
    {
        float h = Input.GetAxisRaw("Horizontal");
        float v = Input.GetAxisRaw("Vertical");
    
        var spf = speed * Time.deltaTime;

        transform.position += transform.forward * (v * spf);
        transform.position += transform.right * (h * spf);
    }
}

Wait for Unity to compile the file, then add it onto the Prefab.

6. Disable input on replicated object

We have added a Move script to the Prefab. This means that if we just run the scene, we will be able to use the keyboard to move the object around.

But what happens on another Client where this object is not authoritative, but replicated? We will want the position to be replicated over the network, but without the keyboard input interfering with it.

Under Configure, click Components.

Here you will see a list of Component Actions that you can apply to non-authoritative GameObjects that have been spawned by the network.

Selecting Disable for your Move script will make sure the Component is disabled for network instances of your Prefab.

7. Implementing your own Component Actions

By extending the ComponentAction abstract class, you can implement your own Component Actions.

ComponentAction.cs

using UnityEngine;

[System.Serializable]
public abstract class ComponentAction
{
    [SerializeField] internal Component component;
    public Component Component => component;

    public virtual void OnAuthority() { }
    public virtual void OnRemote() { }
}

Your custom Component Action must implement the following methods:

OnAuthority This method will be called when the object is spawned and you have authority over it.
OnRemote This method will be called when a remote object is spawned and you do not have authority over it.

It will also require the ComponentAction class attribute, specifying the type of Component that you want the Action to work with, and the display name.

For example, here is the implementation of the Component Action that we use to disable Components on remote objects:

ComponentAction.cs

using UnityEngine;

[ComponentAction(typeof(Behaviour), "Disable")]
public class DisableBehaviourComponentAction : ComponentAction
{
    public override void OnAuthority()
    {
        var b = component as Behaviour;
        b.enabled = true;
    }

    public override void OnRemote()
    {
        var b = component as Behaviour;
        b.enabled = false;
    }
}

8. Additional CoherenceSync settings

From the CoherenceSync component you can configure settings for Lifetime (Session-based or Persistent, Authority transfer (Request or Steal), Simulation model (Client Side, Server Side or Server Side with Client Input) and Adoption settings for when local persistent entities are orphaned.

There are also some Events that are triggered at different times.

On Before Networked Instantiation (before the GameObject is instantiated)
On Networked Instantiation (when the GameObject is instantiated)
On Networked Destruction (when the GameObject is destroyed)
On Authority Gained (when authority over the GameObject is transferred to the local client)
On Authority Lost (when authority over the GameObject is transferred to another client)
On After Authority Transfer Rejected (when GameObject's Authority transfer was requested and denied).
On Input Simulator Connected (when client with simulator is ready for Server-side with Client Input)
On Input Owner Assigned (when InputOwner was changed is ready)

Using the Coherence Hub

If you prefer, you can let the Coherence Hub guide you through your Prefab setup process. Simply select a Prefab, open the Synced Object tab in Coherence Hub and follow the instructions.

Extras

You can find more information in the SDK Fundamentals.

Helper scripts and samples can be found here.

9. Constraints

There are some constraints when setting up a Prefab with CoherenceSync, hereafter referred to as Sync Prefab.

A Sync Prefab has one, and only one CoherenceSync component in its hierarchy
The CoherenceSync component must be at the Sync Prefab root
A Sync Prefab cannot contain instances of other Sync Prefabs
A hierarchy in a scene can contain multiple Sync Prefabs. However, such a hierarchy cannot be saved as a Sync Prefab as that would break rule 1-3.