What is MMO?

MMO (massively multiplayer online) is a type of video game with a large number of players on the same server. MMO games enable players to cooperate and compete with each other.

Multiplayer mode makes a game more replayable, but in the past it was hard for creators to design an MMO system. You need to build a matchmaking system, a broadcast system, a sync system, and so on.

Why use Simple MMO?

Making an MMO game in Scratch is extremely hard because of the cloud variables. For example:

1. A cloud variable doesn't accept strings, so you must encode and decode.
2. Usually, you need to share more than one project to build multiple servers for more players.

To simplify the development of MMO games, Gandi IDE built this extension.

Best Practices

How to Make a Multiplayer Game and Sync Its State in Scratch? - Gandi IDE

In this article, you will learn how to realize the most common scenario in MMO games. Create an online game room where everyone could join and sync positions with each other. You will know how to use Simple MMO and Dolly extensions.

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Video Guide

Episode 1 - Connection & Message

Episode 2 - Online Players

Episode 3 - Matching System

Modules

Functions and Definitions

🚥 Connection and Basic info

Connect to a room

Connect to an online room with server ID and extra data.

The following stack block is similar with the first one, but will wait until the player has joined the room successfully.

Disconnect

Use the following stack block to disconnect from a room.

Get the data from a room

This reporter block will return the Internet lag of the current player in the room in ms.

The value of lag is related to the experience of the player.

Use the following reporter blocks to get the data.

Set and get extra data on the current room

Set extra data to a room. Each player in the room will obtain it.

Get extra data from the current room.

Changes in a room

When the extra data or the player’s information changes, the event will be triggered.

Example value of room state:

{
    "onlineCount":1,
    "players":{
        "w0ZHUA0iX":{
            "name":"Jamin",
            "scale":0,
            "direction":0,
            "sessionId":"w0ZHUA0iX",
            "uuid":"18270013",
            "extra":"data",
            "connected":true
        }
    }
}

Example value of changes when a new player joins the room:

[
    {
        "op":128,
        "field":"onlineCount",
        "value":2,
        "previousValue":1
    }
]

Test

Normally, MMO game developers can't test the game by themself because one user can get only one session ID in a game.

Use the following stack block to enable or disable multi-IDs for one player.

With multi-IDs, developers can create several characters in an MMO game by themselves.

🗺 Game Lobby

Get data of match rooms in the lobby

There can be several match rooms in a lobby. A player can obtain some basic data from each match room in the lobby.

Use the following reporter block to obtain states of a match room in the lobby.

The match room numbers start from 0. The player can obtain the following data.

Example value of metadata:

{
    "locked":false,
    "gid":"62dcbecb55e9663ece47846b-test02"
}

Example value of all data in JSON:

{
    "clients":1,
    "createdAt":"2022-07-24T04:30:12.387Z",
    "maxClients":5,
    "metadata":{
        "locked":false,
        "gid":"62dcbecb55e9663ece47846b-test02"
    },
    "name":"match",
    "processId":"LoAOMOAlm",
    "roomId":"Y4_eGxDG3"
}

This event will be triggered when a match room changes in the lobby.

Example value of rooms:

[
    {
        "clients":1,
        "createdAt":"2022-07-21T05:06:51.304Z",
        "maxClients":4,
        "metadata":{
            "locked":true,
            "gid":"62d42391e189602916172fec-test01",
            "extra":"{\"inGame\":0,\"winner\":\"default\"}"
        },
        "name":"match",
        "processId":"vdXjfoyKm",
        "roomId":"8D_cGWbDW"
    }
]

Use this reporter block to get the match room count in the lobby.

Use the following stack block to fill the state of match rooms in the lobby into a list. To use this block, you must make a list first.

Use this reporter block to get states of match rooms in the lobby.

Example of the return value:

[
    {
        "clients":1,
        "createdAt":"2022-07-24T04:55:18.150Z",
        "maxClients":5,
        "metadata":{
            "locked":false,
            "gid":"62dcbecb55e9663ece47846b-test02"
        },
        "name":"match",
        "processId":"LoAOMOAlm",
        "roomId":"lleCilflR"
    },
    {
        "clients":1,
        "createdAt":"2022-07-24T04:55:20.471Z",
        "maxClients":5,
        "metadata":{
            "locked":false,
            "gid":"62dcbecb55e9663ece47846b-test02"
        },
        "name":"match",
        "processId":"LoAOMOAlm",
        "roomId":"vWVfV-lqW"
    }
]

🎾 Match Game

Join or create a match room in a lobby

Use the following stack blocks to join or create a match room in a lobby.

The server ID should be the same as the server ID of the lobby.

Use the following stack blocks to join a particular room in the lobby.

Lock or unlock a match room

Use the following stack block to lock or unlock a room.

✉️ Message

Broadcast messages

Use the following block to broadcast a message to other players in the room.

Receive a message

This event will be triggered when the player receives a message from others.

😽 Player

Get states of players in the room

This reporter block will return players' data in the room.

The players' data can be shown in two formats:

default: In this format, the value will contain all players' session IDs, user IDs, and user names.

For example, there are two players in the room.

w1wHX6sDi,196572628,Jamin;ShbK_dKmG,18270013,Shawn;

JSON: The value will be in JSON format. The players will be in a list, and each player is treated as an object that contains several properties. You can process JSON files with other extensions like Gandi Data Utils.

[
    {
        "name":"Jamin test",
        "scale":0,
        "direction":0,
        "sessionId":"YjUOIes3M",
        "uuid":"196572628",
        "extra":"{\"ready\":0}",
        "connected":true
    },
    {
        "name":"Jamin test",
        "scale":0,
        "direction":0,
        "sessionId":"Csj2Bjnp6",
        "uuid":"196572628",
        "extra":"{\"ready\":0}",
        "connected":true
    }
]

This reporter block will return the online player count of a room.

Use the following reporter block to get the data of a player with the session ID.

Example value of all data in JSON:

{
    "name":"Jamin test",
    "scale":0,
    "direction":0,
    "sessionId":"4MWHoPRRO",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Set the value of states

Use the following stack blocks to set the states of the player.

🙀 Player Event

When I connect to a room

This event will be triggered when the player has just joined or created a room and will get all data in the room.

When a new player connects to the room

This event will be triggered when a new player connects to the room.

Example value of data:

{
    "name":"Jamin",
    "scale":0,
    "direction":0,
    "sessionId":"an3r2W7bb",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Use the following reporter block to get the data of the last connected player.

Example value of all data in JSON:

{
    "name":"Jamin test",
    "scale":0,
    "direction":0,
    "sessionId":"4MWHoPRRO",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

When a player is disconnected

This event will be dispatched when a player is disconnected.

The example value of data:

{
    "name":"Jamin",
    "scale":0,
    "direction":0,
    "sessionId":"an3r2W7bb",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Use the following reporter block to get the data of the last disconnected player.

Example value of all data in JSON:

{
    "name":"Jamin test",
    "scale":0,
    "direction":0,
    "sessionId":"4MWHoPRRO",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Unexpected situation

This event will be triggered when a player is disconnected abnormally because of network failure or similar issues.

When a player's state changes

This event will be triggered when a player's state changes.

Example value of data:

{
    "name":"Jamin",
    "scale":0,
    "direction":0,
    "sessionId":"an3r2W7bb",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Use the following reporter block to get the data of the last state-changed player.

Returns the data of a particular player. Count from 0.

Example value of all data in JSON:

{
    "name":"Jamin test",
    "scale":0,
    "direction":0,
    "sessionId":"4MWHoPRRO",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

Create a clone of a player

In MMO games, we recommend you create clones to generate characters for each player.

Use the following block to create a clone of a player with a session ID.

This stack block will create a clone of the sprite with the session ID as a clone ID.

Use the following reporter block to get the data from a clone.

Example value of all data in JSON:

{
    "name":"Jamin test",
    "scale":0,
    "direction":0,
    "sessionId":"4MWHoPRRO",
    "uuid":"196572628",
    "extra":"data",
    "connected":true
}

🛠 Utils

Use the following boolean block to determine whether the sprite is a clone.

Use the following boolean block to determine whether the clone represents yourself.

Use the following boolean block to determine whether the clone's session ID is the value in the block.