Mirra Backend

Mirra Backend is an umbrella project that contains several apps within it.

The objective is to split the project into multiple applications (modules) based on their responsibilities. This will allow us to add decoupled modules that can be used together without having a dependency between them.

Requirements

• Nix: You can install the Nix package manager by running the following command in your terminal:

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

The installer will ask you for the sudo password, and then print the details about what steps it will perform to install Nix. You have to accept this to proceed with the installation.

Make sure there weren't any errors during the installation and, if there are none, close the shell and start a new one.

To test if Nix generally works, just run GNU hello or any other package:

nix run nixpkgs#hello
> Hello, world!

For a more detailed explanation, visit the Nixcademy installation guide.

• Devenv:

After installing Nix, run the following command to install devenv:

nix-env -if https://install.devenv.sh/latest

For devenv to manage caches for you, add yourself to trusted-users in nix conf:

# Log in as super user first
sudo su -
# Open config file using Vim
vim /etc/nix/nix.custom.conf
# Add the users you want to use nix store to nix.custom.conf file
  # Press 'i' to write stuff in file using vim (insert mode).
  # Press 'esc' (exit insert mode) then type ':wq' to save changes.
trusted-users = root your-user
# If you don't know your user, you can type the following in a terminal:
whoami
# Restart nix-daemon
sudo launchctl kickstart -k system/systems.determinate.nix-daemon

Clone the repo:

git clone https://github.com/lambdaclass/mirra_backend.git

Install the last elixir package manager inside the repo folder and devenv shell:

cd mirra_backend
devenv shell
mix archive.install github hexpm/hex branch latest

• Protobuf: To serialize our websocket messages, we use Protobuf. Install running:

brew install protobuf
mix escript.install hex protobuf # Remember to add escripts folder to your $PATH. This step is not needed if you use devenv.
# JS protobuf for game_client app.
cd assets
npm install google-protobuf
npm install -g protoc-gen-js

Start applications

To build and run all the applications, run the following command:

devenv up

Then navigate to the following link to start a game: http://localhost:3000/

If you want to have access to the Elixir console, instead do:

devenv shell postgres
# Then in another terminal:
devenv shell
make start

Note you need to have ran devenv up earlier.

Applications

• Arena
• Game Client
• Gateway
• ChampionsOfMirra
• GameBackend

Arena

This app is responsible for handling the game logic and is composed of 2 parts:

• The management of the game itself, where player connections are established, their actions are received, and events are resolved. For example, in response to a player's move event, this app receives it and communicates with the 2D physics engine to execute it. It is also responsible for sending game updates to clients.
• A 2D physics engine where entity movements are handled, and collisions between them are checked.

To run this app individually, you can use the following commands:

cd apps/arena/
make deps
make start

For more information, you can read its documentation

Game Client

This app is a representation of the arena using simple 2D shapes and polygons that interact with each other. This provides a developer-friendly way to understand what is happening.

For now, this client is only connected to the Arena app, but it could be integrated with any other application.

To run this app individually, you can use the following commands:

cd apps/game_client/
make deps
make start

For more information, you can read its documentation

Gateway

Receives messages via websocket and routes them to the corresponding game's application.

ChampionsOfMirra

Application for Champions Of Mirra game. Has modules for:

• Battle - Simulates battles. For now, only allows fights between a user and a level from the campaign.
• Campaigns - Creates a campaign with customizable difficulty, in the shape of 5 units per level.
• Items - Handles logic for Items. Consumes from the Items app for general items logic.
• Units - Handles logic for Units. Consumes from the Units app for general items logic.
• Users - Handles logic for Users. Consumes from the Users app for general items logic.

GameBackend

Persistance layer and shared logic:

• Users logic that's general among all games. This module is quite incomplete for now, since users are only made of a unique username.
• Units logic that's general among all games. Defines the schemas for the characters of every game. These act like templates for Units, which are instances of them tied to a user or a campaign level.
• Items logic that's general among all games. Defines the schemas for the item templates of every game. These act like templates for Items, which are instances of them that belong to a user and can be equipped to a unit.

What's important to note is that each game's application decides how to use the functionalities these applications have. For example, take a look at how Champions of Mirra implements Champions.Units.select_unit/3 and unselect_unit/2. For the first one, we have some rules on how and when a unit can be selected, so we check they are met before calling the GameBackend app. For the second one, we don't care for the context it is called in, so we just call GameBackend.Units.unselect_unit/2 instantly. Another game might have different requirements for unit selection/unselection, and it would be handled in its own NewGame.Units module.

Configurator

This app is in charge of the configurations. Think either full game config or feature flags for A/B testing

In it you will be able to create new configurations and decide the default version to be used. Configurations are inmutable to allow rollbacks and easier A/B testing, you can always create a new one based on the default one or one in particular

Read more

Future iterations

In future iterations, we will add the following apps:

• Bots
• Matchmaking
• Marketplace
• Chat
• Inventory
• Leaderboard

And some more.