Quick Start Guide

Setting up Gosu with Baku

First, follow the instructions to install Gosu, then set up an empty Gosu game window in quick_start.rb like so:

require 'gosu'

class QuickStart < Gosu::Window
  def initialize
    super 640, 480
    self.caption = "Quick Start"
    
  end
  
  def update

  end
  
  def draw

  end
end

QuickStart.new.show

Try running it from the command line to make sure nothing is wrong:

$ ruby quick_start.rb

Next, install Baku by following the installation instructions on the repository's README. Add require 'baku' to the top of quick_start.rb and you should be good to go!

Your First Components

Components represent all the data that make up an Entity. Create a Component by overriding Baku::Component and calling super() in the constructor. In a pure ECS approach, Components should contain only data and possibly helper methods to shape the data where necessary. The TransformComponent and VelocityComponent examples below store the x and y position and velocity of an Entity in a 2D space. See the Components section for more details.

class TransformComponent < Baku::Component
  attr_accessor :x, :y

  def initialize(x, y)
    super()

    @x = x
    @y = y
  end
end

class VelocityComponent < Baku::Component
  attr_accessor :x, :y

  def initialize(x, y)
    super()

    @x = x
    @y = y
  end
end

Systems contain your game logic. Each system operates on all Entities that have the specified set of Components. Create a System by overriding Baku::System and calling super() to specify the Components that an entity must possess in order for it to be processed by the System. The example MovementSystem below will only process entities that possess both a TransformComponent and a VelocityComponent. You will also need to specify whether the System should be run during the :update or :draw loop. See the Systems section for more details.

class MovementSystem < Baku::System
  def initialize
    super([TransformComponent, VelocityComponent], :update)
  end

  def process_entity(entity, transform, velocity)
    transform.x += velocity.x
    transform.y += velocity.y
  end
end

The World is the glue that ties the ECS ecosystem together. It contains all of your Entities and the Systems that process them. In your game initialization logic, create a Baku::World instance and register any systems you want to use. In the below example, we register our example MovementSystem from above and create an Entity with both a TransformComponent and a VelocityComponent so that it will be processed by the MovementSystem. See the World section for more details.

def game_initialization
  @world = Baku::World.new
  @world.add_system(MovementSystem.new)

  entity = @world.create_entity
  entity.add_component(TransformComponent)
  entity.add_component(VelocityComponent)
end

In your game's update and draw loops, call the Baku::World instance's #update and #draw methods. If possible, you'll likely want to keep track of the milliseconds between frames and pass that to the #update method if you're planning to use the ECS for anything that needs it, such as smoothing out frame progression on sprite animations.

def game_update_loop
  current_ms = Gosu::milliseconds()
  delta_ms = current_ms - @prev_ms
  @prev_ms = current_ms

  @world.update(delta_ms)
end

def game_draw_loop
  @world.draw
end

That should be enough to get you started with an entity that has a position and velocity in your game! Now hook it up to an InputSystem to make it move or add a SpriteRenderSystem to draw it on the screen. Check out the Asteroids example in the Baku example repository for a more complete example of what Baku can do.