Crystal framework for making games
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README.md

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Glove

Glove is a framework for making games. It is implemented in Crystal.

⚠ Caution! ⚠ Glove is experimental. Expect breaking changes. There are few tests. Do not use this for your own projects (yet). (Or do, and contribute back to Glove? That’d be cool. I’ll give you commit access. You can be one of the first people to write a proper game engine in Crystal.)

Usage

To use this shard, add the following lines to your shard.yml:

dependencies:
  glove:
    git: git@github.com:ddfreyne/glove.git

Glove comes with shaders in its shaders/ directory, which needs to be copied to where the executable is located. For example, the following will create a target/ directory that contains the executable and the shaders directory:

rm -rf target/
mkdir -p target

crystal build -o target/mygame src/mygame.cr

cp -r lib/glove/src/shaders target/shaders

It is useful to let the executable cd to the directory it is located in, before doing anything else, so that it can find the shaders easily:

if full_path = Process.executable_path
  Dir.cd(File.dirname(full_path))
end

The target/ directory should also include any assets that the game needs to run; a more complete build script could therefore look as follows:

rm -rf target/
mkdir -p target

crystal build -o target/mygame src/mygame.cr

cp -r lib/glove/src/shaders target/shaders
cp -r assets target/assets # <- added

Example code

Here is a trivial example that renders a card (from assets/card.png):

require "glove"

if full_path = Process.executable_path
  Dir.cd(File.dirname(full_path))
end

card =
  Glove::Entity.new.tap do |e|
    e << Glove::Components::Texture.new("assets/card.png")
    e << Glove::Components::Transform.new.tap do |t|
      t.width = 140_f32
      t.height = 190_f32
      t.translate_x = 400_f32
      t.translate_y = 300_f32
    end
  end

scene =
  Glove::Scene.new.tap do |scene|
    scene.spaces << Glove::Space.new.tap do |space|
      space.entities << card
    end
  end

game = Glove::EntityApp.new(800, 600, "Inari")
game.clear_color = Glove::Color::WHITE
game.replace_scene(scene)
game.run

Architecture

  • Glove::EntityApp is a generic game superclass that provides functionality for handling entities, and everything associated with it. Here is how a typical game would build an instance and run the game:

    game = Glove::EntityApp.new(800, 600, "Inari")
    game.clear_color = Glove::Color::WHITE
    scene = Glove::Scene.new.tap do |scene|
      # … build scene here …
    end
    game.replace_scene(scene)
    game.run
  • Glove::Entity is a game object that is visible and/or reacts to user input.

  • Glove::Component is a property of an entity. A common component is Glove::Components::Transform, which adds width, height, rotation, scale, … to an entity. Another common component is Glove::Components::Camera, which marks an entity as being a camera, and defines which part of a space (see below) will be rendered, with what rotation, etc.

  • Glove::Action defines a change to an entity. It can either be instant (e.g. remove entity) or act over time (e.g. move).

  • Glove::Space groups entities in a scene that logically belong together and can interact with each other. Entities in different spaces never interact. For example, one space might contain the game entities, and another space might contain UI elements.

  • Glove::Scene describes a scene (such as the main menu, credits, or in-game screen). It contains one or more spaces.

  • Glove::System describes logic for making changes to a space. A common system is a physics system, which would calculate velocities and update positions.

There are also a handful of simple data classes:

  • Glove::Color
  • Glove::Point
  • Glove::Quad
  • Glove::Rect
  • Glove::Size
  • Glove::Vector

Acknowledgements

This project started out by playing with crystal-gl by Gustavo Giráldez.