Initial work for a subspace clone written on top of a game engine I'm working out that hasn't been released yet.

subspace.rb

class Game
  attr_accessor :_

  def default_ship x, y, heading
    _.new(:ship) do |s|
      s.x       = x
      s.y       = y
      s.dy      = 0
      s.dx      = 0
      s.heading = heading
    end
  end

  def defaults
    _.particles ||= []
    _.stars ||= 100.times.map do |i|
      [rand * _.screen.w_half * [1, -1].sample,
       rand * _.screen.h_half * [1, -1].sample, 1, 1, 255 * rand, 255, 255]
    end

    _.ship_1 ||= default_ship(-400, 0, 0)
    _.ship_2 ||= default_ship( 400, 0, 180)

    _.origin_x = 640
    _.origin_y = 360
    _.pos_y_direction = -1
    _.pos_x_direction =  1
  end

  def render_background
    _.solids << [-_.screen.w, -_.screen.h, _.screen.w * 2, _.screen.h * 2, 0, 0, 0]
    _.solids += _.stars
  end

  def render_ship
    _.sprites << ['ship_1.png', _.ship_1.x - 16, _.ship_1.y - 16, 33, 33, _.ship_1.heading]
    _.sprites << ['ship_2.png', _.ship_2.x - 16, _.ship_2.y - 16, 33, 33, _.ship_2.heading]
  end

  def render_thrusts
    _.solids += _.particles.map do |p|
      [-1 + p.x, -1 + p.y, 3, 3, 255, 128, 0, 255 * p.lifetime.minus(p.__elapsed_ticks_since_creation__) / p.lifetime]
    end
  end

  def calc_wrap_location location
    location.x = _.screen.w_half * -1 if location.x > _.screen.w_half
    location.x = _.screen.w_half      if location.x < _.screen.w_half * -1
    location.y = _.screen.h_half * -1 if location.y > _.screen.h_half
    location.y = _.screen.h_half      if location.y < _.screen.h_half * -1
  end

  def calc_thrusts
    _.particles.each do |p|
      p.speed *= 0.9
      p.y += p.speed * p.heading.y_vector
      p.x += p.speed * p.heading.x_vector
      calc_wrap_location p
    end

    _.particles.reject! { |p| p.__elapsed_ticks_since_creation__ >= p.lifetime }
  end

  def calc_ship_for ship
    ship.x += ship.dx
    ship.y += ship.dy
    calc_wrap_location ship
  end

  def calc_ship
    calc_ship_for _.ship_1
    calc_ship_for _.ship_2
  end

  def input_particles ship
    _.particles << _.new(:ship_thruster) do |s|
      s.heading = ship.heading + 180 + [1, -1].sample.mult(rand * 20)
      s.speed = 10 * rand
      s.lifetime = 30
      s.x = ship.x
      s.y = ship.y
    end
  end

  def input_accelerate_ship should_move_ship, ship
    if should_move_ship
      input_particles ship
      ship.dx += 0.025 * ship.heading.x_vector
      ship.dy += 0.025 * ship.heading.y_vector
    else
      ship.dx *= 0.99
      ship.dy *= 0.99
    end
  end

  def input_accelerate
    input_accelerate_ship _.player_1_r1_key_held, _.ship_1
    input_accelerate_ship _.player_2_r1_key_held, _.ship_2
  end

  def input_turn_ship direction, ship
    ship.heading += 2 * direction
  end

  def input_turn
    input_turn_ship( 1, _.ship_1) if _.player_1_left_key_held
    input_turn_ship(-1, _.ship_1) if _.player_1_right_key_held
    input_turn_ship( 1, _.ship_2) if _.player_2_left_key_held
    input_turn_ship(-1, _.ship_2) if _.player_2_right_key_held
  end

  def tick
    defaults
    render_background
    render_ship
    render_thrusts
    calc_thrusts
    calc_ship
    input_accelerate
    input_turn
  end
end

$game = Game.new

def tick game_state
  $game._ = game_state
  $game.tick
end

Reddit discussion: https://www.reddit.com/r/ruby/comments/ava1ey/game_dev_with_ruby_130_lines_two_32x32_pngs/