Setup dual-screen and create a multi-monitor wallpaper using xrandr en RMagick

xrandr-setup.rb

#!/usr/bin/ruby

# This script reads your monitor settings using the `xrandr` tool. It selects a
# random wallpaper for each monitor from a specified directory. A large image is
# created to fit all monitors, which can then be set using any tool.

require 'RMagick'

class Screen
  attr_reader :name, :width, :height, :offset_x, :offset_y

  def initialize(name, width, height, offset_x, offset_y)
    @name     = name
    @width    = width
    @height   = height
    @offset_x = offset_x
    @offset_y = offset_y
  end
end

class Plane
  attr_reader :width, :height, :screens

  def initialize()
    @width   = 0
    @height  = 0
    @screens = []
  end

  def add_screen(screen)
    @width  = [@width, screen.offset_x + screen.width].max
    @height = [@height, screen.offset_y+ screen.height].max
    screens << screen
  end

  def print()
    puts "Plane #{width}x#{height}"
    screens.each do |s|
      puts "  Screen #{s.name}: " +
        "#{s.width}x#{s.height} at #{s.offset_x},#{s.offset_y}"
    end
  end
end

def plane_from_xrandr()
  plane = Plane.new()

  `xrandr`.lines.each do |line|
    if line =~ /^(.+) connected (\d+)x(\d+)\+(\d+)\+(\d+)/ then
      screen = Screen.new($1, $2.to_i, $3.to_i, $4.to_i, $5.to_i)
      plane.add_screen(screen)
    end
  end

  return plane
end

def random_files(dir, n)
  files = Dir.entries(dir).collect { |f| File.join(dir, f) }.select do |f|
    File.file? f
  end

  files.shuffle.take(n)
end

def dual_screen()
  plane = plane_from_xrandr()
  plane.print()

  if plane.screens.size == 2 then
    primary   = plane.screens.find { |s| s.name =~ /LVDS/ }.name
    secondary = plane.screens.find { |s| s.name =~ /VGA/ }.name

    `xrandr --output #{primary}   --auto --primary`
    `xrandr --output #{secondary} --auto --right-of #{primary}`
  end
end

def make_wallpaper(wallpaper_dir, output_file)
  plane = plane_from_xrandr()
  plane.print()

  wallpapers = random_files(wallpaper_dir, plane.screens.size)

  image = Magick::Image.new(plane.width, plane.height)

  plane.screens.each_with_index do |screen, i|
    puts "Selected wallpaper #{wallpapers[i]} for screen #{i}"
    wallpaper = Magick::Image.read(wallpapers[i]).first
    wallpaper = wallpaper.resize_to_fill(screen.width, screen.height)
    image = image.composite(wallpaper, screen.offset_x, screen.offset_y,
      Magick::CopyCompositeOp)
  end

  puts "Writing to #{output_file}..."
  image.write(output_file)
end

if ARGV.size >= 2 then
  make_wallpaper(ARGV[0], ARGV[1])
elsif ARGV.size == 0 then
  dual_screen()
else
  puts "Usage:"
  puts "#{$0} <wallpaper dir> <output image>   Generate a wallpaper"
  puts "#{$0}                                  Default dual-screen setup"
end