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failed_attempts/ThugRacer-v0
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injections
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process
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README.md
README.md
 
 
download
download
 
 
spec.json
spec.json
 
 

README.md

Downloading games

The download script downloads and prepares every game. It depends on jq and curl, which can be installed on Linux like so:

sudo apt-get install jq curl

or on macOS like so:

brew install jq

You should run the download script from inside this directory, like:

./download

The download script creates a directory called downloaded_games and makes a sub-directory for each game it downloads. Each game sub-directory contains an index.html file and various game-specific resource files. Each subdirectory also contains an info.json file with specific information about that game.

To download only a specific game, you can specify the game name as an argument, like in:

./download Babel-v0

The spec.json file

The spec.json file contains a JSON array of game objects. Each game object contains various information about a game. There are two general types of game objects: base objects and variant objects. A base object defines lots of information about a game, such URLs for downloading game assets. A variant object references a base object and applies some slight modifications to it. Here's what a base object might look like:

{
  "name": "SomeGame-v0",
  "base": "http://someurl",
  "top_injections": [
    "faketime.js"
  ],
  "bottom_injections": [
    "SomeGame-v0.js"
  ],
  "resources": [
    "js/game.js",
    "js/jquery-2.0.3.min.js",
    "sounds/explosion.ogg",
    "css/reset.css",
  ],
  "processors": [
    "some_script"
  ],
  "metadata": {},
  "width": 320,
  "height": 480,
  "key_whitelist": ["KeyLeft", "KeyRight"]
}

The fields in a base object have the following meaning:

  • name: a CamelCase name with a version number after it.
  • base: the base URL to fetch as index.html. Also the URL to which resource paths are relative.
  • top_injections: scripts from the injections directory to inject into the top of <head>.
  • bottom_injections: like top_injections, but for the bottom of <head>.
  • resources: a list of paths to download. All paths are relative to base. This list should be exhaustive; it should cover every resource consumed by the game.
  • processors: scripts from process to run on the downloaded game. More on this in The download process.
  • metadata: game-specific meta-data. This may be used to provide information to processor scripts.
  • width: desired browser viewport width.
  • height: desired browser viewport height.
  • key_whitelist: a list of allowed key codes.
  • options: (optional) object to be passed as an argument to window.muniverse.init(). If absent, {} is used as a default.

Variant objects define games which are derived from other games. Here's what a variant object might look like:

{
  "name": "SomeGame-v1",
  "variant_of": "SomeGame-v0",
  "options": {
    "level": 3,
    "color": "brown"
  },
  "width": 480
}

A variant object's variant_of field indicates the base object from which the variant is derived. In addition to the variant_of field, a variant object may define its own width, height, key_whitelist, and options. If one of those fields is not defined, it is inherited from the base object.

The download process

When a game is downloaded, three basic steps are taken:

  • A game directory is made and the resources are downloaded, including index.html.
  • Each script in the game's processors array is run with the game directory as an argument.
  • The index.html file is modified to include the injected scripts from top_injections and bottom_injections.

A processor script can find out information about a game by looking at the game's info.json file. The info.json file is located in the root of the game directory and contains a copy of the game object from spec.json.

All base objects in the spec.json file specify how to download a game. Variant objects, on the other hand, do not specify how to download or prepare a game. Rather, variants use the downloaded directory of their base games.

Adding a game

The first thing to do is figure out what resources the game uses. Try to build a complete list of the files loaded by the game. This way, you can build up the resources array.

Every game must expose a window.muniverse object with three functions, all of which return Promises. These functions are:

  • init(options): get the game to a logical starting point, where an agent can immediately start making actions. The game should be paused in some way so that step needn't be called immediately after init. The options argument is the same as the options object in the game spec.
  • score: get the current (numerical) score.
  • step(millis): advance the game by the given number of milliseconds. Return a boolean which is true if the game has ended.

In order to provide the above API, you will likely want to do a few things:

  • Inject the injections/faketime.js API in order to control time.
  • Inject your own script to hijack the game and implement the window.muniverse API.
  • Write a processor script to make the code easier to handle.
    • Remove unwanted content like ads or analytics.
    • Patch JS code to manipulate it more easily.