(track this down:
dginn% ./oble -c ~/Downloads/haarcascade_frontalface_alt.xml
Corrupt JPEG data: 160038 extraneous bytes before marker 0x69
ERROR: frame is null...)
FOR SCREENSAVER:
* gnome-screensaver-command --poke
	* find irc channel to ask if my understanding is correct
	* file bug
	* track down bug
		* compile gnome-screensaver

http://coderrr.wordpress.com/2008/04/20/getting-idle-time-in-unix/#comment-1927
in c:
#include <X11/extensions/scrnsaver.h>

main() {
  XScreenSaverInfo *info = XScreenSaverAllocInfo();
  Display *display = XOpenDisplay(0);

  XScreenSaverQueryInfo(display, DefaultRootWindow(display), info);
  printf("%u ms\n", info->idle);
}
in ruby inline:
require 'inline'

class XScreenSaver
  class << self
    inline do |builder|
      builder.add_link_flags '-lXss'
      builder.include '<X11/extensions/scrnsaver.h>'
      builder.c %{
        double idle_time() {
          static Display *display;
          XScreenSaverInfo *info = XScreenSaverAllocInfo();

          if (!display)  display = XOpenDisplay(0);
          if (!display)  return -1;

          XScreenSaverQueryInfo(display, DefaultRootWindow(display), info);

          return info->idle / 1000.0;
        }
      }
    end
  end
end

if __FILE__ == $0
  loop { puts XScreenSaver.idle_time; sleep 0.2 }
end