Draft: xfce4-screenshooter cannot capture open popup menus, dropdowns, or combo boxes

Problem

When attempting to screenshot an open popup menu, dropdown, or combo box, the screenshot fails to capture the menu — it either closes before the screenshot is taken, or the screenshot captures the desktop behind it.

This happens because xfce4-screenshooter uses XGrabKeyboard / XGrabKey to listen for the Print key. When a popup menu is open, the menu owns an active X11 keyboard grab. The screenshooter's grab request is rejected, so the shortcut never fires — or the menu dismisses itself when focus changes.

This is a long-standing issue. A related report exists from 2019.

Steps to reproduce

  1. Open any popup menu (Whisker Menu, right-click context menu, dropdown in a dialog)
  2. Press Print
  3. The menu closes and/or the screenshot does not capture the menu

Expected behavior

Pressing Print with a popup menu open should capture the screen including the open menu, without dismissing it.

Proposed solution

XInput2 raw key events (XI_RawKeyPress) bypass all active X11 keyboard grabs. A persistent daemon listening via XI2 receives the Print keypress regardless of what currently owns the keyboard grab.

I have implemented this as --listen mode:

xfce4-screenshooter --listen

The daemon:

  • Listens for raw key events via XI2 on a private X display connection
  • Reads configurable keybindings from the xfce4-screenshooter xfconf channel under /listen/bindings/N/{key,region}
  • Falls back to built-in defaults (Print → fullscreen, Shift+Print → select, Alt+Print → window) on fresh install — zero configuration needed
  • Seeds defaults to xfconf on first run so users can customize via xfconf-query
  • Registers a DBus service (org.xfce.Screenshooter) so normal shortcut invocations (xfce4-screenshooter -f) hand off to the daemon instead of double-firing
  • Reloads bindings live when xfconf changes — no restart needed
  • Installs an autostart .desktop file to /etc/xdg/autostart/ so the daemon starts automatically on login
  • Handles SIGTERM/SIGHUP cleanly for session manager shutdown

Files changed

File Change
lib/screenshooter-capture-x11.c XI2 listener thread, DBus service, xfconf bindings
lib/screenshooter-capture-x11.h Expose screenshooter_xi2_listen() and screenshooter_xi2_reset_capture()
lib/screenshooter-global.h Add listen_mode field to ScreenshotData
lib/screenshooter-actions.c NULL-guard g_object_unref(sd->screenshot), handle Back button in listen mode
src/main.c Add --listen/-l CLI option, DBus handoff, cb_finalize_listen
meson.build Enable HAVE_XI2 when X11 backend is built
data/ System autostart .desktop file

Testing

Tested on Linux Mint 22.3 XFCE with xfwm4 compositor:

  • Print → fullscreen screenshot ✓
  • Shift+Print → region selector ✓
  • Alt+Print → active window ✓
  • Whisker menu open → Print → captures menu ✓
  • Daemon dead → Print → fallback to normal capture ✓
  • Live binding reload via xfconf ✓
  • Clean exit on SIGTERM ✓

Branch

feature/xi2-listen-mode on my fork: https://gitlab.xfce.org/newman2x/xfce4-screenshooter

Questions for maintainers

  1. Is --listen mode the right approach, or would you prefer a different mechanism?
  2. Should the DBus service name be org.xfce.Screenshooter or something else?
  3. Should bindings live in the xfce4-screenshooter xfconf channel or in xfce4-keyboard-shortcuts?
  4. Is /etc/xdg/autostart/ the right place for the daemon autostart entry?