Building on "Hello World"

In this guide we will build on the work we have already done in Hello World and add in a few more features, we will be covering the following:

Adding scripts to your objects
Adding editor modes inside your game (Host Server and Client)
Basic Player Movement
Permissions
Basic RPC use

Requirements#

This tutorial requires an MLAPI-supported version of Unity (2019.4+).

We recommend that you complete the Your First Networking Game "Hello World" guide before starting this one.

Adding Scripts to Hello World#

This section will add some scripts to Hello World which will contain the new features we will be covering in the tutorial.

Click the Assets folder.
Create a new Folder and call it Scripts.
Create an empty GameObject rename it HelloWorldManager.
Create a script called HelloWorldManager.
Add the HelloWorldManager script as a component.
Open the HelloWorldManager.cs script.
Edit the HelloWorldManager.cs script to match the following.

tip

You can copy the script from here and paste it into your file.

Select the code sample.
Click Copy in the top right corner.
Paste it into your code editor.

Click to show/hide the Code.

using MLAPI;
using UnityEngine;

namespace HelloWorld
{
    public class HelloWorldManager : MonoBehaviour
    {
        void OnGUI()
        {
            GUILayout.BeginArea(new Rect(10, 10, 300, 300));
            if (!NetworkManager.Singleton.IsClient && !NetworkManager.Singleton.IsServer)
            {
                StartButtons();
            }
            else
            {
                StatusLabels();

                SubmitNewPosition();
            }

            GUILayout.EndArea();
        }

        static void StartButtons()
        {
            if (GUILayout.Button("Host")) NetworkManager.Singleton.StartHost();
            if (GUILayout.Button("Client")) NetworkManager.Singleton.StartClient();
            if (GUILayout.Button("Server")) NetworkManager.Singleton.StartServer();
        }

        static void StatusLabels()
        {
            var mode = NetworkManager.Singleton.IsHost ?
                "Host" : NetworkManager.Singleton.IsServer ? "Server" : "Client";

            GUILayout.Label("Transport: " +
                NetworkManager.Singleton.NetworkConfig.NetworkTransport.GetType().Name);
            GUILayout.Label("Mode: " + mode);
        }

        static void SubmitNewPosition()
        {
            if (GUILayout.Button(NetworkManager.Singleton.IsServer ? "Move" : "Request Position Change"))
            {
                if (NetworkManager.Singleton.ConnectedClients.TryGetValue(NetworkManager.Singleton.LocalClientId,
                    out var networkedClient))
                {
                    var player = networkedClient.PlayerObject.GetComponent<HelloWorldPlayer>();
                    if (player)
                    {
                        player.Move();
                    }
                }
            }
        }
    }
}

Adding Editor Modes to Hello World#

Inside the HelloWorldManager.cs script, we define two methods which mimic the editor buttons inside of NetworkManager during Play mode.

Click to show/hide the Code.

        static void StartButtons()
        {
            if (GUILayout.Button("Host")) NetworkManager.Singleton.StartHost();
            if (GUILayout.Button("Client")) NetworkManager.Singleton.StartClient();
            if (GUILayout.Button("Server")) NetworkManager.Singleton.StartServer();
        }

        static void StatusLabels()
        {
            var mode = NetworkManager.Singleton.IsHost ?
                "Host" : NetworkManager.Singleton.IsServer ? "Server" : "Client";

            GUILayout.Label("Transport: " +
                NetworkManager.Singleton.NetworkConfig.NetworkTransport.GetType().Name);
            GUILayout.Label("Mode: " + mode);
        }

NetworkManager implements the singleton pattern as it declares its singleton named Singleton. This is defined when the MonoBehaviour is enabled. This component also contains very useful properties, such as IsClient, IsServer, and IsLocalClient. The first two dictate the connection state we have currently established that you will use shortly.

We call these methods inside of OnGUI().

Click to show/hide the Code.

void OnGUI()
        {
            GUILayout.BeginArea(new Rect(10, 10, 300, 300));
            if (!NetworkManager.Singleton.IsClient && !NetworkManager.Singleton.IsServer)
            {
                StartButtons();
            }
            else
            {
                StatusLabels();

                SubmitNewPosition();
            }

            GUILayout.EndArea();
        }

note

You will notice the introduction of a new method, SubmitNewPosition(); which we will be using later.

Adding basic movement to the Player object#

This script adds some basic movement to the Hello World player.

Create a new script HelloWorldPlayer.
Open the HelloWorldPlayer.cs script.
Edit the HelloWorldPlayer.cs script to match the following.

Click to show/hide the Code.

using MLAPI;
using MLAPI.Messaging;
using MLAPI.NetworkVariable;
using UnityEngine;

namespace HelloWorld
{
    public class HelloWorldPlayer : NetworkBehaviour
    {
        public NetworkVariableVector3 Position = new NetworkVariableVector3(new NetworkVariableSettings
        {
            WritePermission = NetworkVariablePermission.ServerOnly,
            ReadPermission = NetworkVariablePermission.Everyone
        });

        public override void NetworkStart()
        {
            Move();
        }

        public void Move()
        {
            if (NetworkManager.Singleton.IsServer)
            {
                var randomPosition = GetRandomPositionOnPlane();
                transform.position = randomPosition;
                Position.Value = randomPosition;
            }
            else
            {
                SubmitPositionRequestServerRpc();
            }
        }

        [ServerRpc]
        void SubmitPositionRequestServerRpc(ServerRpcParams rpcParams = default)
        {
            Position.Value = GetRandomPositionOnPlane();
        }

        static Vector3 GetRandomPositionOnPlane()
        {
            return new Vector3(Random.Range(-3f, 3f), 1f, Random.Range(-3f, 3f));
        }

        void Update()
        {
            transform.position = Position.Value;
        }
    }
}

Select the Player prefab.
Add the script HelloWorldPlayer script as a component.

This class will inherit from NetworkBehaviour instead of MonoBehaviour.

Click to show/hide the Code.

public class HelloWorldPlayer : NetworkBehaviour

Inside this class we now define a NetworkVariable to represent this player's networked position.

Click to show/hide the Code.

        public NetworkVariableVector3 Position = new NetworkVariableVector3(new NetworkVariableSettings
        {
            WritePermission = NetworkVariablePermission.ServerOnly,
            ReadPermission = NetworkVariablePermission.Everyone
        });

Introducing permissions#

In the HelloWorldPlayer.cs script we introduce read and write permissions on a NetworkVariable . For the purposes of this demo, the server will be authoritative on the NetworkVariable representing position. All clients are able to read the value, however.

HelloWorldPlayer overrides NetworkStart.

Click to show/hide the Code.

        public override void NetworkStart()
        {
            Move();
        }

Any MonoBehaviour implementing NetworkBehaviour can override the MLAPI method NetworkStart(). This method is fired when message handlers are ready to be registered and the networking is setup. We override NetworkStart since a client and a server will run different logic here.

note

This can be overriden on any NetworkBehaviour.

On both client and server instances of this player, we call the Move() method, which will simply do the following.

Click to show/hide the Code.

        public void Move()
        {
            if (NetworkManager.Singleton.IsServer)
            {
                var randomPosition = GetRandomPositionOnPlane();
                transform.position = randomPosition;
                Position.Value = randomPosition;
            }
            else
            {
                SubmitPositionRequestServerRpc();
            }
        }

Some simple RPC use#

If this player is a server-owned player, at NetworkStart() we can immediately move this player, as suggested in the following code.

Click to show/hide the Code.

            if (NetworkManager.Singleton.IsServer)
            {
                var randomPosition = GetRandomPositionOnPlane();
                transform.position = randomPosition;
                Position.Value = randomPosition;
            }

If we are a client, we call a ServerRpc. A ServerRpc can be invoked by a client to be executed on the server.

Click to show/hide the Code.

            else
            {
                SubmitPositionRequestServerRpc();
            }

This ServerRpc simply sets the position NetworkVariable on the server's instance of this player by just picking a random point on the plane.

Click to show/hide the Code.

        [ServerRpc]
        void SubmitPositionRequestServerRpc(ServerRpcParams rpcParams = default)
        {
            Position.Value = GetRandomPositionOnPlane();
        }

The server instance of this player has just modified the Position NetworkVariable, meaning that if we are a client, we need to apply this position locally inside of our Update loop.

Click to show/hide the Code.

        void Update()
        {
            transform.position = Position.Value;
        }

We can now go back to HelloWorldManager.cs and define the contents of SubmitNewPosition().

Click to show/hide the Code.

        static void SubmitNewPosition()
        {
            if (GUILayout.Button(NetworkManager.Singleton.IsServer ? "Move" : "Request Position Change"))
            {
                if (NetworkManager.Singleton.ConnectedClients.TryGetValue(NetworkManager.Singleton.LocalClientId,
                    out var networkedClient))
                {
                    var player = networkedClient.PlayerObject.GetComponent<HelloWorldPlayer>();
                    if (player)
                    {
                        player.Move();
                    }
                }
            }
        }

Whenever you press the GUI button (which is contextual depending on if you are server or a client), you find your local player and simply call Move().

You can now create a build which will demonstrate the concepts outlined above.

tip

Make sure SampleScene is included in BuildSettings.

One build instance can create a host. Another client can join the host's game. Both are able to press a GUI button to move. Server will move immediately and be replicated on client. Client can request a new position, which will instruct the server to modify that server instance's position NetworkVariable. That client will apply that NetworkVariable position inside of it's Update() method.

Congrats!

Congratulations you have learned the basics of a networked game

Special Thanks

This guide would not have been possible without the hard work and support of Fernando Cortez, Unity.