Re: How to get DISPLAY of emacsclient?

[Stefan Monnier <monnier@iro.umontreal.ca>]

chad [2022-11-29 19:41:11] wrote:
> On Tue, Nov 29, 2022 at 1:11 PM Max Nikulin <manikulin@gmail.com> wrote:
>> [...]
>> Add to user notes content of X selection when emacs is started as
>> daemong with no frames and the user prefers to avoid distraction due to
>> creation of a new frame.
> In general, you seem to assume that there's no way for emacs to create a
> new X11 frame object without it being immediately visible to the user. In
> my experience, that's only true in the limited subset of cases where the
> user has chosen a window manager that enforces that choice. Further, that
> wasn't the default when I last looked -- but that was quite some time ago,
> and I don't know about the current options/defaults for common X11-based
> display systems of today. Can anyone shed some light on this?

`xclip.el` (from GNU ELPA) uses:

    (defun xclip--hidden-frame ()
      (or xclip--hidden-frame
          (setq xclip--hidden-frame
                (make-frame-on-display (getenv "DISPLAY")
                                       '((visibility . nil)
                                         (user-position . t)
                                         (left . 0)
                                         (top . 0)
                                         (no-other-frame . t))))))

I haven't heard of a problem with that yet, but it probably hasn't been
widely tested (and it is specific to X11).

> This is a fundamentally different case from "the user wants to use a
> non-graphical X11-based mechanism that emacs normally doesn't enable until
> emacs actually connects to a working X11 display", and I think it should be
> possible to get emacs to make that connection without necessarily popping
> up a window that the user doesn't want.

server.el also does something similar to xclip-mode, tho with simpler
code:

    (defun server-select-display (display)
      ;; If the current frame is on `display' we're all set.
      ;; Similarly if we are unable to open frames on other displays, there's
      ;; nothing more we can do.
      (unless (or (not (fboundp 'make-frame-on-display))
                  (server--on-display-p (selected-frame) display))
        ;; Otherwise, look for an existing frame there and select it.
        (dolist (frame (frame-list))
          (when (server--on-display-p frame display)
    	(select-frame frame)))
        ;; If there's no frame on that display yet, create and select one.
        (unless (server--on-display-p (selected-frame) display)
          (let* ((buffer (generate-new-buffer " *server-dummy*"))
                 (frame (make-frame-on-display
                         display
                         ;; Make it display (and remember) some dummy buffer, so
                         ;; we can detect later if the frame is in use or not.
                         `((server-dummy-buffer . ,buffer)
                           ;; This frame may be deleted later (see
                           ;; server-unselect-display) so we want it to be as
                           ;; unobtrusive as possible.
                           (visibility . nil)))))
            (select-frame frame)
            (set-window-buffer (selected-window) buffer)
            frame))))

This code has been used a lot more widely, but in many/most cases we end
up making that frame visible soon after, so there might be cases where
it is not 100% unobtrusive but users don't notice it.


        Stefan