Quick and dirty Pong clone written in Ruby.

pong.rb

#!/usr/bin/env ruby
# 
# Pong clone written in Ruby.
#
# 2014, Mihail Szabolcs
# Released into the Public Domain.
#
# Keys:
#
# Escape - quit
# Up Arrow - move up
# Down Arrow - move down
#
# That's all folks :)
#
#
require 'curses'

module Pong
  FPS = 33 # 30 fps = 1000.0 / 30.0 =~ 33 ms
  BLOCK = 254 # block character
  ESC = 27 # escape ascii code

  class Shape
    attr_reader :w, :h

    def initialize
      @shape = yield.map { |l| l.split('') }
      @w = @shape.map(&:length).max
      @h = @shape.count
    end

    def draw(x, y)
      @shape.each_with_index do |line, j|
        line.each_with_index do |col, i|
          if col != ' '
            Curses.setpos(y + j, x + i)
            Curses.addch(BLOCK)
          end
        end
      end
    end
  end

  class Logo
    def initialize
      @logo = Shape.new do
        [ "0000000  0000000  00    0  0000000",
          "0     0  0     0  0 0   0  0      ",
          "0  0000  0     0  0  0  0  0 0000 ",
          "0  0     0     0  0   0 0  0     0",
          "0000     0000000  0    00  0000000" ]
      end

      @x = ((Curses.cols - @logo.w) / 2.0).ceil
      @y = ((Curses.lines - @logo.h) / 2.0).ceil
    end

    def draw
      @logo.draw(@x, @y)
    end
  end

  class Digits
    attr_reader :x, :y

    def initialize
      @digits = []
      @digits << Shape.new do
        [ "0000000",
          "0     0",
          "0     0",
          "0     0",
          "0000000"]
      end
      @digits << Shape.new do
        [ "   00  ",
          "  000  ",
          " 0000  ",
          "   00  ",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0000000",
          "    00 ",
          "  00   ",
          " 00    ",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0000000",
          "      0",
          "  00000",
          "      0",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0     0",
          "0     0",
          "0000000",
          "      0",
          "      0"]
      end
      @digits << Shape.new do
        [ "0000000",
          "0     ",
          "0000000",
          "      0",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0000000",
          "0      ",
          "0000000",
          "0     0",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0000000",
          "     00",
          "    00 ",
          "   00  ",
          "   00  "]
      end
      @digits << Shape.new do
        [ "0000000",
          "0     0",
          "0000000",
          "0     0",
          "0000000"]
      end
      @digits << Shape.new do
        [ "0000000",
          "0     0",
          "0000000",
          "      0",
          "0000000"]
      end
      
      @w = @digits.first.w
      @h = @digits.first.h
    end

    def draw(x, y, n)
      @digits[n].draw(x, y)
    end
  end

  class Score
    def initialize(x, y)
      @x = x
      @y = y
      @digits = Digits.new
      @score = 0
    end

    def draw
      @digits.draw(@x, @y, @score)
    end

    def inc
      @score += 1
      self
    end

    def won?
      @score > 9
    end
  end

  class Separator
    def initialize
      @x = ((Curses.cols - 1) / 2).ceil
      @y = 0
    end

    def draw
      (0..Curses.lines-1).each do |i|
        if i % 2 == 1 
          Curses.setpos(@y + i, @x)
          Curses.addch(BLOCK)
        end
      end
    end
  end

  class Ball
    attr_reader :x, :y

    def initialize
      reset!
    end

    def reset!
      @x = ((Curses.cols - 1) / 2).ceil
      @y = ((Curses.lines - 1) / 2).ceil
      @dx = rand(10) < 5 ? 1 : -1
      @dy = rand(10) < 5 ? 1 : -1
      @c = @x.ceil
    end

    def draw
      Curses.setpos(@y, @x)
      Curses.addch(BLOCK)
    end

    def coming_to_right?
      @x > @c and @dx == 1
    end

    def is_out_left?
      @x == 0
    end

    def is_out_right?
      @x == Curses.cols - 1
    end

    def update
#      if @x == 0 || @x == Curses.cols - 1
#        @dx = -@dx
#      end

      if @y == 0 || @y == Curses.lines - 1
        @dy = -@dy
      end

      if (x = @x - 1) == 0 || (x = @x + 1) == Curses.cols - 1
        Curses.setpos(@y, x)
        
        if Curses.inch == BLOCK
          @dx = -@dx
          Curses.setpos(@y - 1, x)
          if Curses.inch != BLOCK
            @dy = -1
          else
            Curses.setpos(@y + 1, x)
            if Curses.inch != BLOCK
              @dy = 1
            end
          end
        end

        Curses.setpos(@y, @x)
      end

      @x += @dx
      @y += @dy
    end
  end

  class Player
    attr_reader :score

    def initialize
      @n = 4
      @h = (@n / 2).ceil
      @x ||= 0
      @y = ((Curses.lines - @n) / 2).ceil
      @score = Score.new((Curses.cols / 2.0).ceil + (@x == 0 ? -(@n * 3) : @n), 1)
    end

    def cy
      @y + @h
    end

    def draw
      (0..@n-1).each do |i|
        Curses.setpos(@y + i, @x)
        Curses.addch(BLOCK)
      end

      @score.draw
    end

    def up(n)
      @y -= n if @y > 0
    end

    def down(n)
      @y += n if @y + @n < Curses.lines
    end
  end

  class Computer < Player
    def initialize
      @x = Curses.cols - 1
      super
    end

    def can_move?
      rand(66).to_i < 60
    end
  end

  class Main
    def initialize
      srand(Time.now.to_f)

      Curses.init_screen()
      Curses.noecho()
      Curses.nonl()
      Curses.cbreak()
      Curses.curs_set(0)
      Curses.stdscr.keypad(true)
    end

    def run
      Curses.stdscr.nodelay = false

      Curses.clear()
      Logo.new.draw
      Curses.refresh()

      case Curses.getch
      when ESC
        return
      end

      Curses.stdscr.nodelay = true

      ball = Ball.new
      separator = Separator.new
      player = Player.new
      computer = Computer.new

      loop do
        t = Time.now.to_f

        Curses.clear()
        separator.draw
        ball.draw
        player.draw
        computer.draw
        Curses.refresh()

        case Curses.getch
        when Curses::Key::UP
          player.up(1)
        when Curses::Key::DOWN
          player.down(1)
        when ESC
          break
        end

        ball.update

        if ball.coming_to_right? and computer.can_move?
          if ball.y < computer.cy
            computer.up(1)
          elsif ball.y > computer.cy
            computer.down(1)
          end
        end

        if ball.is_out_left?
          if computer.score.inc.won?
            break
          else
            ball.reset!
          end
        elsif ball.is_out_right?
          if player.score.inc.won?
            break
          else
            ball.reset!
          end
        end

        dt = (Time.now.to_f - t) * 1000.0
        sleep((FPS - dt) * 0.001) if dt < FPS
      end

      run # :D
    end
  end
end

Pong::Main.new.run if $0 == __FILE__