Game Development with Ruby: Getting Started with Gosu

Alex Kholodniak Alex Kholodniak
• • 3 min read

Ruby works for games. Seriously. It is not C++ or Unity, but for 2D games and prototypes, it gets the job done fast.

Why Ruby?

You already know Ruby. That is the main reason. No need to learn a new language just to make a simple game. Ruby's syntax is clean, so your game code stays readable.

The Tools

Three libraries worth knowing:

Gosu - The go-to for 2D games. Handles windows, graphics, input, and audio. Simple API. Works on Mac, Windows, and Linux.

Chingu - Built on Gosu. Adds game states, animations, and collision detection. Good for bigger projects.

DragonRuby - Commercial toolkit. Fast, cross-platform, exports to consoles. Costs money but saves time.

We will use Gosu here. It is free and simple.

Installation

gem install gosu

That is it. On Mac you might need SDL2:

brew install sdl2

Your First Game Window

require 'gosu'

class Game < Gosu::Window
  def initialize
    super(640, 480)
    self.caption = "My Game"
  end
end

Game.new.show

Run this. You get a black window. That is your canvas.

The Game Loop

Gosu calls two methods every frame:

  • update - runs 60 times per second. Handle logic here.
  • draw - runs after update. Render your sprites here.
class Game < Gosu::Window
  def initialize
    super(640, 480)
    self.caption = "My Game"
    @x = 0
    @y = 0
  end

  def update
    # Game logic goes here
  end

  def draw
    # Rendering goes here
  end
end

Loading and Drawing Sprites

def initialize
  super(640, 480)
  @player = Gosu::Image.new("player.png")
  @x = 100
  @y = 100
end

def draw
  @player.draw(@x, @y, 0)
end

The third argument is the Z-order. Higher numbers draw on top.

Handling Input

Check for key presses in update:

def update
  @x -= 5 if Gosu.button_down?(Gosu::KB_LEFT)
  @x += 5 if Gosu.button_down?(Gosu::KB_RIGHT)
  @y -= 5 if Gosu.button_down?(Gosu::KB_UP)
  @y += 5 if Gosu.button_down?(Gosu::KB_DOWN)
end

Arrow keys now move your sprite. 5 pixels per frame at 60 FPS = 300 pixels per second.

Complete Example

Here is a working game. Player moves with arrow keys:

require 'gosu'

class Game < Gosu::Window
  def initialize
    super(640, 480)
    self.caption = "Ruby Game"

    @player = Gosu::Image.new("player.png")
    @x = 320
    @y = 240
    @speed = 5
  end

  def update
    @x -= @speed if Gosu.button_down?(Gosu::KB_LEFT)
    @x += @speed if Gosu.button_down?(Gosu::KB_RIGHT)
    @y -= @speed if Gosu.button_down?(Gosu::KB_UP)
    @y += @speed if Gosu.button_down?(Gosu::KB_DOWN)

    # Keep player on screen
    @x = @x.clamp(0, 640 - @player.width)
    @y = @y.clamp(0, 480 - @player.height)
  end

  def draw
    @player.draw(@x, @y, 1)
  end
end

Game.new.show

Save as game.rb. Drop a player.png in the same folder. Run with ruby game.rb.

No Image? Draw a Rectangle

Do not have art yet? Use draw_rect:

def draw
  Gosu.draw_rect(@x, @y, 32, 32, Gosu::Color::RED)
end

Red square. Works for prototyping.

Adding Sound

def initialize
  super(640, 480)
  @jump_sound = Gosu::Sample.new("jump.wav")
end

def button_down(id)
  if id == Gosu::KB_SPACE
    @jump_sound.play
  end
end

Use button_down for one-shot actions like jumping. Use button_down? in update for continuous actions like movement.

What Next

Start small. Make Pong. Then make a simple platformer. Then add enemies.

Gosu has good docs at libgosu.org. The wiki has tutorials for animations, tilemaps, and more.

Ruby games will not run on phones or consoles. For that, look at DragonRuby. But for desktop games and game jams, Gosu is solid.

Build something. Ship it. That is how you learn.

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