X のウィンドウのクラスとタイトルを取得する(Fiddle バージョン)

win_class_title.rb

require 'fiddle/import'

module X11
  extend Fiddle::Importer
  dlload 'libX11.so'
  typealias 'XID', 'unsigned long'
  typealias 'Window', 'XID'
  typealias 'Status', 'int'
  typealias 'Atom', 'unsigned long'
  XClassHint = struct(['char *name', 'char *class_name'])
  XTextProperty = struct(['unsigned char *value', 'Atom encoding', 'int format', 'unsigned long nitems'])

  extern 'Display* XOpenDisplay(char*)'
  extern 'int XGetInputFocus(Display*, Window*, int*)'
  extern 'int XGetClassHint(Display*, Window, XClassHint*)'
  extern 'Status XQueryTree(Display*, Window, Window*, Window*, Window**, unsigned int*)'
  extern 'int XFree(void*)'
  extern 'Status XGetWMName(Display*, Window, XTextProperty*)'
  extern 'int Xutf8TextPropertyToTextList(Display*, XTextProperty*, char***, int*)'
  extern 'void XFreeStringList(char**)'
end

display = X11.XOpenDisplay(nil)
raise "Cannot open display: #{ENV['DISPLAY']}" if display.null?
win_buf = ' '*X11.sizeof('Window')
revert_to = ' '*X11.sizeof('unsigned long')
root = ' '*X11.sizeof('Window')
parent = ' '*X11.sizeof('Window')
children = ' '*X11.sizeof('void*')
nchildren = ' '*X11.sizeof('unsigned int')
loop do
  X11.XGetInputFocus(display, win_buf, revert_to)
  window = win_buf.unpack1('L')
  class_hint = X11::XClassHint.malloc
  while window > 0
    X11.XGetClassHint(display, window, class_hint)
    X11.XQueryTree(display, window, root, parent, children, nchildren)
    children_ptr = Fiddle::Pointer[children].ptr
    X11.XFree(children_ptr) unless children_ptr.null?
    break unless class_hint.name.null? && class_hint.class_name.null?
    window = parent.unpack1('L')
  end
  win_class = class_hint.class_name.to_s
  prop = X11::XTextProperty.malloc
  prop.encoding = 1
  X11.XGetWMName(display, window, prop)
  text_list = ' '*X11.sizeof('void*')
  count = ' '*X11.sizeof('int*')
  X11.Xutf8TextPropertyToTextList(display, prop, text_list, count)
  title = Fiddle::Pointer[text_list].ptr.ptr.to_s.force_encoding('utf-8')
  p [win_class, title]
  X11.XFree(class_hint.name) unless class_hint.name.null?
  X11.XFree(class_hint.class_name) unless class_hint.class_name.null?
  X11.XFreeStringList(Fiddle::Pointer[text_list].ptr)
  sleep 0.1
end

ffi バージョンはこちら https://gist.github.com/tmtm/f9642c3ea740edf87f04940cc57f9b0f