Wait while xprintidle increases predictably thereby waiting until activity has been observed in the xorg

wait-while-idle.rb

#!/usr/bin/env ruby

if %x{type xprintidle &> /dev/null; echo $?}.strip == '1'
  raise 'xprintidle not found'
end

def idle
  %x{xprintidle}.to_i
end

t = Time.now
i = idle - 100

wait = (ENV['IDLE_POLL'] || 100).to_i / 1000.0

loop do
  sleep wait
  prediction = (Time.now - t) * 1000.0 + i
  break if prediction > idle
end