Pong, in your terminal

pong.rb

require 'curses'
require 'timeout'

include Curses

PADDLE_HEIGHT = 10
PADDLE_WIDTH  = 3
SPEED = 3

def write(x, y, text, color=@color)
  Curses.attron(color_pair(color))
  Curses.setpos(y, x)
  Curses.addstr(text)
  Curses.attroff(color_pair(color))
end

def init_colors
  Curses.init_pair(COLOR_RED, COLOR_RED, COLOR_RED)
  Curses.init_pair(COLOR_CYAN, COLOR_CYAN, COLOR_CYAN)
  Curses.init_pair(COLOR_GREEN, COLOR_GREEN, COLOR_GREEN)
  Curses.init_pair(COLOR_BLACK, COLOR_BLACK, COLOR_WHITE)
  @colors = [COLOR_RED,COLOR_CYAN,COLOR_GREEN, COLOR_BLACK]
end

def init_screen
  Curses.noecho
  Curses.stdscr.nodelay = true
  Curses.curs_set(0)
  Curses.init_screen
  Curses.start_color
  init_colors
  Curses.stdscr.keypad(true)
  begin
    yield
  ensure
    Curses.close_screen
  end
end

def update
  Curses.clear

  (0..PADDLE_WIDTH).each do |w|
    (0..PADDLE_HEIGHT).each do |h|
      write(0+w, @p1+h, '*')
      write(@width-w, @p2+h, '*')
    end
  end

  write(@ball[0], @ball[1], '*', @colors[1])
  write(@width/2, 1, "#{@score[0]} | #{@score[1]}", @colors.last)

  Curses.refresh
end

def reset_ball
  @ball = [@width/2, @height/2]
  @dx = @rand.sample
  @dy = @rand.sample
end

init_screen do
  @width  = Curses.cols - 1
  @height = Curses.lines
  @p1 = @p2 = @height/2 - PADDLE_HEIGHT
  @delay = 0.05
  @last_update = Time.now
  @color = @colors.first
  @score = [0,0]
  @rand = [-2, -1, 1, 2]
  reset_ball
  update

  loop do
    case Curses.getch
      when Curses::Key::UP    then @p1 -= SPEED unless @p1 <= 0; update
      when Curses::Key::DOWN  then @p1 += SPEED unless @p1+PADDLE_HEIGHT > @height; update
      when Curses::Key::LEFT  then @p2 -= SPEED unless @p2 <= 0; update
      when Curses::Key::RIGHT then @p2 += SPEED unless @p2+PADDLE_HEIGHT > @height; update
    end

    if Time.now - @last_update > @delay
      @ball[0] += @dx
      @ball[1] += @dy
      x, y = @ball

      in_p1 = y >= @p1 && y <= @p1+PADDLE_HEIGHT
      in_p2 = y >= @p2 && y <= @p2+PADDLE_HEIGHT

      if x <= 0
        @score[1] += 1
        reset_ball
      elsif x >= @width
        @score[0] += 1
        reset_ball
      end

      @dx = -@dx if (x <= PADDLE_WIDTH && in_p1) || (x >= @width - PADDLE_WIDTH && in_p2)
      @dy = -@dy if (y <= 0 || y >= @height - 1)

      update

      @last_update = Time.now
    end
  end
end