Prefab setup

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

1. Create a prefab and move it to Resources

Add an asset and create a prefab of it. Make sure the prefab is in a Resources folder in your Unity project.

Here is an example:

1.1 Create a simple Cube in the scene

GameObject -> 3D Object -> Cube

1.2 Convert the Cube into a prefab

Create a Resources folder in your Project. Drag the Cube into the Resources folder to turn it into a prefab.

It's important that your prefab is in a Resources folder so that Unity can load it at runtime. This is a Unity requirement, more info here.

2. Add CoherenceSync to the prefab

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 Asset Store packages you may have downloaded.

You can find out more about CoherenceSync here.

3. 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 Select fields and methods.

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

Close the Configuration dialog_._

4. 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.

5. 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 rather replicated? We will want the position to be replicated over the network, without the keyboard input interfering with it.

Open the Events section in CoherenceSync. Add a new On Network Instantiation handler by clicking on the plus sign next to it.

Pull the Cube prefab into the Runtime Only / None (Object) field.

Now click the dropdown No Function and select Move -> bool enabled.

Leave the Boolean field unchecked.

6. 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.

You can find more information in the SDK Fundamentals. There are also some Events that are triggered at different times.

• On Before Networked Instantiation (before the network 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)

  Extras

[Helper scripts](../resources/helper-scripts.md) and samples can be found here. 

7. Constraints

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

1. A Sync Prefab has one, and only one CoherenceSync component in its hierarchy

2. The CoherenceSync component must be at the Sync Prefab root

3. A Sync Prefab cannot contain instances of other Sync Prefabs

4. 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.

7.1. Examples of valid setup

The ‘Car’ gameobject has the only CoherenceSync component in the hierarchy

The ‘Car’ prefab has multiple child prefabs, but none of them are Sync Prefabs

The ‘Wheel’ Sync Prefabs are placed under the ‘Car’ in the scene, but are not part of the ‘Car’ Sync Prefab itself

7.2. Examples of disallowed setup

The ‘Car’ Sync Prefab has multiple wheels, which are Sync Prefabs themselves. This is not allowed