Our vision: write Ruby code and run your game on desktop, mobile, and in-browser. We do this by providing a "standard" Ruby interface, and generating equivalent code for various platforms through various back-ends (like webruby for web support).

Our current methodology is to use high-velocity stacks instead of a common code-base. This means we use CraftyJS (web) and libGDX (desktop/android) even though we could use mruby with SDL everywhere.

To start, main.rb looks like this:

# ... some requires and other notes ...

class MainGame < Game

  def initialize
    super(800, 600)
  end

  def create
    super

    load_content({
      :images => ['content/images/fox.png', 'content/images/background.jpg'],
      :audio => ['content/audio/noise.ogg']
    }, lambda {
      Entity.new(TwoDComponent.new, ImageComponent.new).image('content/images/background.jpg')

      e = Entity.new(ImageComponent.new, KeyboardComponent.new, TwoDComponent.new, TouchComponent.new, AudioComponent.new)
      e.image('content/images/fox.png')
      e.move_with_keyboard

      touches = 0
      t = Entity.new(TextComponent.new, TwoDComponent.new)
      t.text('Touches: 0')
      t.move(8, 8)

      e.touch(lambda {
        e.play('content/audio/noise.ogg')
        touches += 1
        t.text("Touches: #{touches}")
      })
    })
  end
end

Game.launch(MainGame)

This sample creates a new 800x600 game with a fox sprite on a space background. The fox moves with the arrow keys (or WASD). Clicking the fox with the mouse (or touching it on Android) plays a sound and increments the touch count, which is displayed as text. The sample also pre-loads all the necessary images and audio files.

To run your game in-browser, run rake or rake build:web. This will generate the HTML5 version under bin/web-craftyjs. To play the game, open bin/web-craftyjs/index.html in your browser.

To run your game on your desktop, run rake build:desktop. This will generate a main_game.rb file under bin/desktop-libgdx. Run it with JRuby to launch your game.

To run your game on android, run rake build:android. Provided you have Ruboto installed and setup correctly, this will generate a Libgdx-Debug.apk file under bin/android-libgdx/bin which you can deploy and test via adb.

A summary of the main components and their methods:

• TwoDComponent: Anything in 2D space. Has move(x, y), x, y
• ImageComponent: An image! Has image(filename); you can get the width and height.
• KeyboardComponent: Responds to keyboard input. Has move_with_keyboard().
• TouchComponent: Receives touches. Has touch(callback)
• AudioComponent: Can play a sound. Has play(filename, { :loop => true/false })
• TextComponent: Displays text. Can move, and set text(display_text).

Two pieces make up terrace:

• A common Ruby-agnostic platform (eg. our entity class)
• Target-specific code (eg. ImageComponent for the web target).

Terrace supports the following targets:

• web-craftyjs: OpalRB (Ruby to JS converter) with CraftyJS (HTML5 game engine)
• desktop-libgdx: JRuby (Ruby in Java) and with libGDX (cross-platform game engine)
• android-libgdx: Same as above, with Ruboto (JRuby on Android)

The meaning of backticks also changes per platform:

• Web: backticks execute raw Javascript
• Desktop: backticks execute local commands
• Android: backticks execute android commands

When you run rake build:<target>, it uses mrubymix to combine both the common Rby code with the specified target (platform-specific) code (this is why we use #= require instead of require).

All the code (including common and target code) libs in lib, while templates (eg. HTML templates for web, Android project templates) live in templates.

To build your application in release mode, add release to the end of the command-line, eg. ruby build.rb desktop-gosu release. What this does changes by platform:

• Desktop: TBD: Release mode builds compiled, self-contained binaries.
• Android: TBD: Release mode builds the APK in release mode, which uses the key file.

To use Terrace, you need Ruby (1.9.3 or newer), along with platform-specific pieces:

To build binaries for the web, you need:

• The opal gem (0.8.0)

To run the desktop target, you also need:

• JRuby 1.7.13 or newer

Arguably the most complex target setup-wise, you need to set up a lot of things. Thankfully, Ruboto covers it.

• Install the ruboto gem (1.3.0)
• Run ruboto setup -y. This will install the Android SDK, Java, Ant, and any other necessities.