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Draco

Draco is an Entity Component System for DragonRuby GTK.

An Entity Component System is an architectural framework that decouples game objects from game logic. An allows you to build game objects through composition. This allows you to easily share small logic components between different game objects.

Table of Contents

  1. Sample Application
  2. Installation
  3. Support
  4. Versioning
  5. Usage
    1. Components
    2. Entities
    3. Systems
    4. Worlds
  6. Plugins
  7. Resources
  8. Commercial License

Sample Application

This repository includes sample applications in the samples/ directory.

  • teeny-tiny - A 20 second space shooter created during the DragonRuby TeenyTiny Game Jam
  • gorillas-basic - A recreation of the gorillas_basic sample game that comes with DragonRuby

Running the sample application

  1. Download the latest release of this repository.
  2. Create a copy of DragonRuby GTK in a new folder.
  3. Copy the teeny-tiny directory from draco into your new DragonRuby GTK folder. cp -r draco/samples/ dragonruby/.
  4. Run them using ./dragonruby teeny-tiny or ./dragonruby gorillas-basic.

Installation

  1. Create a lib directory inside your game's app directory.
  2. Copy lib/draco.rb into your new lib directory.
  3. In your main.rb file, require app/lib/draco.rb.

Support

Versioning

Draco uses [https://semver.org/].

  • Major (X.y.z) - Incremented for any backwards incompatible public API changes.
  • Minor (x.Y.z) - Incremented for new, backwards compatible, public API enhancements/fixes.
  • Patch (x.y.Z) - Incremented for small, backwards compatible, bug fixes.

Usage

Components

Components represent small atomic bits of state. It's better to use many small components than few large components. These can be shared across many different types of game objects.

class Visible < Draco::Component; end

Visible is an example of a tag component. An entity either has it, or it doesn't. We can also associate data with our components.

class Position < Draco::Component
  attribute :x, default: 0
  attribute :y, default: 0
end

component = Position.new

The component's attributes add a getter and setter on the component for ease of use.

component.x = 110

component.x
# => 110

Tag Components

The Visible class above is an example of a tag component. These are common enough that we don't necessarily want to define a bunch of empty component classes. Draco provides a way to generate these classes at runtime.

Draco::Tag(:visible)
# => Visible

Entities

Entities are independant game objects. They consist of a unique id and a list of components.

entity = Draco::Entity.new
entity.components << Position.new(x: 50, y: 50)

Often we have types of entities that are reused throughout the game. We can define our own subclass in order to automate creating these entities.

class Goblin < Draco::Entity
  component Position, x: 50, y: 50
  component Tag(:visible)
end

goblin = Goblin.new

We can override the default values for the given components when initializing a new entity.

goblin = Goblin.new(position: {x: 100, y: 100})

In order to access the data within our entity's components, the entity has a method named after that component. This is generated based on the underscored name of the component's class (e.g. MapLayer would be map_layer).

goblin.position.x
# => 100

Systems

Systems encapsulate all of the logic of your game. The system runs on every tick and it's job is to update the state of the entities.

Filters

Each system can set a default filter by passing in a list of components. When the world runs the system, it will set the system's entities to the entities that include all of the given components.

class RenderSpriteSystem < Draco::System
  filter Tag(:visible), Position, Sprite

  def tick(args)
    # You can also access the world that called the system.
    camera = world.filter([Camera]).first

    sprites = entities.select { |e| entity_in_camera?(e, camera) }.map do |entity|
       {
        x: entity.position.x - camera.position.x,
        y: entity.position.y - camera.position.y,
        w: entity.sprite.w,
        h: entity.sprite.h,
        path: entity.sprite.path
      }
    end

    args.outputs.sprites << sprites
  end

  def entity_in_camera?(entity, camera)
    camera_rect = {x: camera.x, y: camera.y, w: camera.w, h: camera.h}
    entity_rect = {x: entity.position.x, y: entity.position.y, w: entity.sprite.w, h: entity.sprite.h}

    entity_rect.intersect_rect?(camera_rect)
  end
end

Worlds

A world keeps track of all current entities and runs all of the systems on every tick.

world = Draco::World.new
world.entities << goblin
world.systems << RenderSpriteSystem

world.tick(args)

Just like with entities, we can define a subclassed template for our world.

class Overworld < Draco::World
  entity Goblin
  entity Player, position: { x: 50, y: 50 }, as: :player
  systems RenderSpriteSystem, InputSystem
end

world = Overworld.new

Named Entities

If there are entities that are frequently accessed in our systems, we can give these a name. In the above example, our player entity has been given the name player. We can now access this directly from our world:

world.player

Fetching entities by id

In some cases you'll want to keep track of entities by their id, such as when you want to keep track of another entity in a component.

entity = Player.new
entity.id
# => 12

world.entities[12] == entity
# => true

Plugins

  • Draco::Events - On demand system dispatch and component observers.
  • Draco::Scenes - Quickly switch out entities and systems in a world.
  • Draco::State - Define a set of components on an entity that are mutually exclusive.
  • Draco::Periodic - Make a system run every n ticks instead of every tick.

Learn More

Here are some good resources to learn about Entity Component Systems

Commercial License

Draco is licensed under AGPL. You can purchase the right to use Draco under the commercial license.

Each purchase comes with free upgrades for the current major version of Draco.

Purchase Commercial License

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Before submitting a pull request, please read the contribution guidelines.

Bug reports and pull requests are welcome on GitHub at https://github.com/guitsaru/draco. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

Code of Conduct

Everyone interacting in the Draco project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.