All static elements in place

my-first-ray.rb

require 'rubygems'
require 'ray'

WIDTH             = 800
HEIGHT            = 800
PADDLE_X_OFFSET   = 40
PADDLE_WIDTH      = 40
BALL_RADIUS       = 20
SCORE_TEXT_X_OFFSET = 40

def paddle(paddle_x_coord, paddle_y_coord)
  arguments_array = [paddle_x_coord, paddle_y_coord, PADDLE_WIDTH, HEIGHT / 3]
  Ray::Polygon.rectangle(arguments_array, Ray::Color.white)
end

def ball
  Ray::Polygon.circle([WIDTH/2, HEIGHT/2], BALL_RADIUS, Ray::Color.white)
end

def center_x_pos
  WIDTH / 2
end

def pixels_left_of_center(num_pixels)
  center_x_pos - num_pixels
end

def pixels_right_of_center(num_pixels)
  center_x_pos + num_pixels
end

def middle_line
  line_width = 5
  line_x_pos = center_x_pos
  Ray::Polygon.line([line_x_pos, 0], [line_x_pos, HEIGHT], line_width, Ray::Color.white)
end

Ray.game 'Pong', :size => [WIDTH, HEIGHT] do
  register { add_hook(:quit, method(:exit!)) }

  scene :start do
    @left_paddle  = paddle(PADDLE_X_OFFSET, 100)
    @right_paddle = paddle(WIDTH - (PADDLE_X_OFFSET + PADDLE_WIDTH), 100)
    @ball         = ball
    @left_score   = text "left", :at => [pixels_left_of_center(SCORE_TEXT_X_OFFSET), 20],  :size => 20
    @right_score  = text "right", :at => [pixels_right_of_center(SCORE_TEXT_X_OFFSET), 20], :size => 20
    @scores = [@left_score, @right_score]
    @middle_line  = middle_line

    # Exit when q is pressed
    on :key_press, key(:q){ exit! }

    render do |win|
      win.draw @left_paddle
      win.draw @right_paddle
      win.draw @ball
      win.draw @middle_line

      @scores.each{|score| win.draw score }
    end
  end

  scenes << :start
end