tvl-depot/third_party/exwm/exwm-systemtray.el

;;; exwm-systemtray.el --- System Tray Module for  -*- lexical-binding: t -*-
;;;                        EXWM

;; Copyright (C) 2016-2024 Free Software Foundation, Inc.

;; Author: Chris Feng <chris.w.feng@gmail.com>

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This module adds system tray support for EXWM.

;; To use this module, load and enable it as follows:
;;   (require 'exwm-systemtray)
;;   (exwm-systemtray-enable)

;;; Code:

(require 'xcb-ewmh)
(require 'xcb-icccm)
(require 'xcb-xembed)
(require 'xcb-systemtray)

(require 'exwm-core)
(require 'exwm-workspace)

(declare-function exwm-workspace--workarea "exwm-workspace.el" (frame))

(defclass exwm-systemtray--icon ()
  ((width :initarg :width)
   (height :initarg :height)
   (visible :initarg :visible))
  :documentation "Attributes of a system tray icon.")

(defclass xcb:systemtray:-ClientMessage
  (xcb:icccm:--ClientMessage xcb:ClientMessage)
  ((format :initform 32)
   (type :initform 'xcb:Atom:MANAGER)
   (time :initarg :time :type xcb:TIMESTAMP)      ;new slot
   (selection :initarg :selection :type xcb:ATOM) ;new slot
   (owner :initarg :owner :type xcb:WINDOW))      ;new slot
  :documentation "A systemtray client message.")

(defgroup exwm-systemtray nil
  "System tray."
  :group 'exwm)

(defcustom exwm-systemtray-height nil
  "System tray height.

You shall use the default value if using auto-hide minibuffer."
  :type 'integer)

(defcustom exwm-systemtray-icon-gap 2
  "Gap between icons."
  :type 'integer)

(defvar exwm-systemtray--connection nil "The X connection.")

(defvar exwm-systemtray--embedder-window nil "The embedder window.")
(defvar exwm-systemtray--embedder-window-depth nil
  "The embedder window's depth.")

(defcustom exwm-systemtray-background-color 'workspace-background
  "Background color of systemtray.
This should be a color, the symbol `workspace-background' for the background
color of current workspace frame, or the symbol `transparent' for transparent
background.

Transparent background is not yet supported when Emacs uses 32-bit depth
visual, as reported by `x-display-planes'.  The X resource \"Emacs.visualClass:
TrueColor-24\" can be used to force Emacs to use 24-bit depth."
  :type '(choice (const :tag "Transparent" transparent)
                 (const :tag "Frame background" workspace-background)
                 (color :tag "Color"))
  :initialize #'custom-initialize-default
  :set (lambda (symbol value)
         (when (and (eq value 'transparent)
                    (not (exwm-systemtray--transparency-supported-p)))
           (display-warning 'exwm-systemtray
                            "Transparent background is not supported yet when \
using 32-bit depth.  Using `workspace-background' instead.")
           (setq value 'workspace-background))
         (set-default symbol value)
         (when (and exwm-systemtray--connection
                    exwm-systemtray--embedder-window)
           ;; Change the background color for embedder.
           (exwm-systemtray--set-background-color)
           ;; Unmap & map to take effect immediately.
           (xcb:+request exwm-systemtray--connection
                         (make-instance 'xcb:UnmapWindow
                                        :window exwm-systemtray--embedder-window))
           (xcb:+request exwm-systemtray--connection
                         (make-instance 'xcb:MapWindow
                                        :window exwm-systemtray--embedder-window))
           (xcb:flush exwm-systemtray--connection))))

;; GTK icons require at least 16 pixels to show normally.
(defconst exwm-systemtray--icon-min-size 16 "Minimum icon size.")

(defvar exwm-systemtray--list nil "The icon list.")

(defvar exwm-systemtray--selection-owner-window nil
  "The selection owner window.")

(defvar xcb:Atom:_NET_SYSTEM_TRAY_S0)

(defun exwm-systemtray--embed (icon)
  "Embed an ICON."
  (exwm--log "Try to embed #x%x" icon)
  (let ((info (xcb:+request-unchecked+reply exwm-systemtray--connection
                  (make-instance 'xcb:xembed:get-_XEMBED_INFO
                                 :window icon)))
        width* height* visible)
    (when info
      (exwm--log "Embed #x%x" icon)
      (with-slots (width height)
          (xcb:+request-unchecked+reply exwm-systemtray--connection
              (make-instance 'xcb:GetGeometry :drawable icon))
        (setq height* exwm-systemtray-height
              width* (round (* width (/ (float height*) height))))
        (when (< width* exwm-systemtray--icon-min-size)
          (setq width* exwm-systemtray--icon-min-size
                height* (round (* height (/ (float width*) width)))))
        (exwm--log "Resize from %dx%d to %dx%d"
                   width height width* height*))
      ;; Add this icon to save-set.
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ChangeSaveSet
                         :mode xcb:SetMode:Insert
                         :window icon))
      ;; Reparent to the embedder.
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ReparentWindow
                         :window icon
                         :parent exwm-systemtray--embedder-window
                         :x 0
                         ;; Vertically centered.
                         :y (/ (- exwm-systemtray-height height*) 2)))
      ;; Resize the icon.
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ConfigureWindow
                         :window icon
                         :value-mask (logior xcb:ConfigWindow:Width
                                             xcb:ConfigWindow:Height
                                             xcb:ConfigWindow:BorderWidth)
                         :width width*
                         :height height*
                         :border-width 0))
      ;; Set event mask.
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ChangeWindowAttributes
                         :window icon
                         :value-mask xcb:CW:EventMask
                         :event-mask (logior xcb:EventMask:ResizeRedirect
                                             xcb:EventMask:KeyPress
                                             xcb:EventMask:PropertyChange)))
      ;; Grab all keys and forward them to Emacs frame.
      (unless (exwm-workspace--minibuffer-own-frame-p)
        (xcb:+request exwm-systemtray--connection
            (make-instance 'xcb:GrabKey
                           :owner-events 0
                           :grab-window icon
                           :modifiers xcb:ModMask:Any
                           :key xcb:Grab:Any
                           :pointer-mode xcb:GrabMode:Async
                           :keyboard-mode xcb:GrabMode:Async)))
      (setq visible (slot-value info 'flags))
      (if visible
          (setq visible
                (/= 0 (logand (slot-value info 'flags) xcb:xembed:MAPPED)))
        ;; Default to visible.
        (setq visible t))
      (when visible
        (exwm--log "Map the window")
        (xcb:+request exwm-systemtray--connection
            (make-instance 'xcb:MapWindow :window icon)))
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:xembed:SendEvent
                         :destination icon
                         :event
                         (xcb:marshal
                          (make-instance 'xcb:xembed:EMBEDDED-NOTIFY
                                         :window icon
                                         :time xcb:Time:CurrentTime
                                         :embedder
                                         exwm-systemtray--embedder-window
                                         :version 0)
                          exwm-systemtray--connection)))
      (push `(,icon . ,(make-instance 'exwm-systemtray--icon
                                      :width width*
                                      :height height*
                                      :visible visible))
            exwm-systemtray--list)
      (exwm-systemtray--refresh))))

(defun exwm-systemtray--unembed (icon)
  "Unembed an ICON."
  (exwm--log "Unembed #x%x" icon)
  (xcb:+request exwm-systemtray--connection
      (make-instance 'xcb:UnmapWindow :window icon))
  (xcb:+request exwm-systemtray--connection
      (make-instance 'xcb:ReparentWindow
                     :window icon
                     :parent exwm--root
                     :x 0 :y 0))
  (setq exwm-systemtray--list
        (assq-delete-all icon exwm-systemtray--list))
  (exwm-systemtray--refresh))

(defun exwm-systemtray--refresh ()
  "Refresh the system tray."
  (exwm--log)
  ;; Make sure to redraw the embedder.
  (xcb:+request exwm-systemtray--connection
      (make-instance 'xcb:UnmapWindow
                     :window exwm-systemtray--embedder-window))
  (let ((x exwm-systemtray-icon-gap)
        map)
    (dolist (pair exwm-systemtray--list)
      (when (slot-value (cdr pair) 'visible)
        (xcb:+request exwm-systemtray--connection
            (make-instance 'xcb:ConfigureWindow
                           :window (car pair)
                           :value-mask xcb:ConfigWindow:X
                           :x x))
        (setq x (+ x (slot-value (cdr pair) 'width)
                   exwm-systemtray-icon-gap))
        (setq map t)))
    (let ((workarea (exwm-workspace--workarea exwm-workspace-current-index)))
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ConfigureWindow
                         :window exwm-systemtray--embedder-window
                         :value-mask (logior xcb:ConfigWindow:X
                                             xcb:ConfigWindow:Width)
                         :x (- (slot-value workarea 'width) x)
                         :width x)))
    (when map
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:MapWindow
                         :window exwm-systemtray--embedder-window))))
  (xcb:flush exwm-systemtray--connection))

(defun exwm-systemtray--refresh-background-color (&optional remap)
  "Refresh background color after theme change or workspace switch.
If REMAP is not nil, map and unmap the embedder window so that the background is
redrawn."
  ;; Only `workspace-background' is dependent on current theme and workspace.
  (when (eq 'workspace-background exwm-systemtray-background-color)
    (exwm-systemtray--set-background-color)
    (when remap
      (xcb:+request exwm-systemtray--connection
                    (make-instance 'xcb:UnmapWindow
                                   :window exwm-systemtray--embedder-window))
      (xcb:+request exwm-systemtray--connection
                    (make-instance 'xcb:MapWindow
                                   :window exwm-systemtray--embedder-window))
      (xcb:flush exwm-systemtray--connection))))

(defun exwm-systemtray--set-background-color ()
  "Change the background color of the embedder.
The color is set according to `exwm-systemtray-background-color'.

Note that this function does not change the current contents of the embedder
window; unmap & map are necessary for the background color to take effect."
  (when (and exwm-systemtray--connection
             exwm-systemtray--embedder-window)
    (let* ((color (cl-case exwm-systemtray-background-color
                    ((transparent nil) ; nil means transparent as well
                     (if (exwm-systemtray--transparency-supported-p)
                         nil
                       (message "%s" "[EXWM] system tray does not support \
`transparent' background; using `workspace-background' instead")
                       (face-background 'default exwm-workspace--current)))
                    (workspace-background
                     (face-background 'default exwm-workspace--current))
                    (t exwm-systemtray-background-color)))
           (background-pixel (exwm--color->pixel color)))
      (xcb:+request exwm-systemtray--connection
                    (make-instance 'xcb:ChangeWindowAttributes
                                   :window exwm-systemtray--embedder-window
                                   ;; Either-or.  A `background-pixel' of nil
                                   ;; means simulate transparency.  We use
                                   ;; `xcb:CW:BackPixmap' together with
                                   ;; `xcb:BackPixmap:ParentRelative' do that,
                                   ;; but this only works when the parent
                                   ;; window's visual (Emacs') has the same
                                   ;; visual depth.
                                   :value-mask (if background-pixel
                                                   xcb:CW:BackPixel
                                                 xcb:CW:BackPixmap)
                                   ;; Due to the :value-mask above,
                                   ;; :background-pixmap only takes effect when
                                   ;; `transparent' is requested and supported
                                   ;; (visual depth of Emacs and of system tray
                                   ;; are equal).  Setting
                                   ;; `xcb:BackPixmap:ParentRelative' when
                                   ;; that's not the case would produce an
                                   ;; `xcb:Match' error.
                                   :background-pixmap xcb:BackPixmap:ParentRelative
                                   :background-pixel background-pixel)))))

(defun exwm-systemtray--transparency-supported-p ()
  "Check whether transparent background is supported.
EXWM system tray supports transparency when the visual depth of the system tray
window matches that of Emacs.  The visual depth of the system tray window is the
default visual depth of the display.

Sections \"Visual and background pixmap handling\" and
\"_NET_SYSTEM_TRAY_VISUAL\" of the System Tray Protocol Specification
\(https://specifications.freedesktop.org/systemtray-spec/systemtray-spec-latest.html#visuals)
indicate how to support actual transparency."
  (let ((planes (x-display-planes)))
    (if exwm-systemtray--embedder-window-depth
        (= planes exwm-systemtray--embedder-window-depth)
      (<= planes 24))))

(defun exwm-systemtray--on-DestroyNotify (data _synthetic)
  "Unembed icons on DestroyNotify.
Argument DATA contains the raw event data."
  (exwm--log)
  (let ((obj (make-instance 'xcb:DestroyNotify)))
    (xcb:unmarshal obj data)
    (with-slots (window) obj
      (when (assoc window exwm-systemtray--list)
        (exwm-systemtray--unembed window)))))

(defun exwm-systemtray--on-ReparentNotify (data _synthetic)
  "Unembed icons on ReparentNotify.
Argument DATA contains the raw event data."
  (exwm--log)
  (let ((obj (make-instance 'xcb:ReparentNotify)))
    (xcb:unmarshal obj data)
    (with-slots (window parent) obj
      (when (and (/= parent exwm-systemtray--embedder-window)
                 (assoc window exwm-systemtray--list))
        (exwm-systemtray--unembed window)))))

(defun exwm-systemtray--on-ResizeRequest (data _synthetic)
  "Resize the tray icon on ResizeRequest.
Argument DATA contains the raw event data."
  (exwm--log)
  (let ((obj (make-instance 'xcb:ResizeRequest))
        attr)
    (xcb:unmarshal obj data)
    (with-slots (window width height) obj
      (when (setq attr (cdr (assoc window exwm-systemtray--list)))
        (with-slots ((width* width)
                     (height* height))
            attr
          (setq height* exwm-systemtray-height
                width* (round (* width (/ (float height*) height))))
          (when (< width* exwm-systemtray--icon-min-size)
            (setq width* exwm-systemtray--icon-min-size
                  height* (round (* height (/ (float width*) width)))))
          (xcb:+request exwm-systemtray--connection
              (make-instance 'xcb:ConfigureWindow
                             :window window
                             :value-mask (logior xcb:ConfigWindow:Y
                                                 xcb:ConfigWindow:Width
                                                 xcb:ConfigWindow:Height)
                             ;; Vertically centered.
                             :y (/ (- exwm-systemtray-height height*) 2)
                             :width width*
                             :height height*)))
        (exwm-systemtray--refresh)))))

(defun exwm-systemtray--on-PropertyNotify (data _synthetic)
  "Map/Unmap the tray icon on PropertyNotify.
Argument DATA contains the raw event data."
  (exwm--log)
  (let ((obj (make-instance 'xcb:PropertyNotify))
        attr info visible)
    (xcb:unmarshal obj data)
    (with-slots (window atom state) obj
      (when (and (eq state xcb:Property:NewValue)
                 (eq atom xcb:Atom:_XEMBED_INFO)
                 (setq attr (cdr (assoc window exwm-systemtray--list))))
        (setq info (xcb:+request-unchecked+reply exwm-systemtray--connection
                       (make-instance 'xcb:xembed:get-_XEMBED_INFO
                                      :window window)))
        (when info
          (setq visible (/= 0 (logand (slot-value info 'flags)
                                      xcb:xembed:MAPPED)))
          (exwm--log "#x%x visible? %s" window visible)
          (if visible
              (xcb:+request exwm-systemtray--connection
                  (make-instance 'xcb:MapWindow :window window))
            (xcb:+request exwm-systemtray--connection
                (make-instance 'xcb:UnmapWindow :window window)))
          (setf (slot-value attr 'visible) visible)
          (exwm-systemtray--refresh))))))

(defun exwm-systemtray--on-ClientMessage (data _synthetic)
  "Handle client messages.
Argument DATA contains the raw event data."
  (let ((obj (make-instance 'xcb:ClientMessage))
        opcode data32)
    (xcb:unmarshal obj data)
    (with-slots (window type data) obj
      (when (eq type xcb:Atom:_NET_SYSTEM_TRAY_OPCODE)
        (setq data32 (slot-value data 'data32)
              opcode (elt data32 1))
        (exwm--log "opcode: %s" opcode)
        (cond ((= opcode xcb:systemtray:opcode:REQUEST-DOCK)
               (unless (assoc (elt data32 2) exwm-systemtray--list)
                 (exwm-systemtray--embed (elt data32 2))))
              ;; Not implemented (rarely used nowadays).
              ((or (= opcode xcb:systemtray:opcode:BEGIN-MESSAGE)
                   (= opcode xcb:systemtray:opcode:CANCEL-MESSAGE)))
              (t
               (exwm--log "Unknown opcode message: %s" obj)))))))

(defun exwm-systemtray--on-KeyPress (data _synthetic)
  "Forward all KeyPress events to Emacs frame.
Argument DATA contains the raw event data."
  (exwm--log)
  ;; This function is only executed when there's no autohide minibuffer,
  ;; a workspace frame has the input focus and the pointer is over a
  ;; tray icon.
  (let ((dest (frame-parameter (selected-frame) 'exwm-outer-id))
        (obj (make-instance 'xcb:KeyPress)))
    (xcb:unmarshal obj data)
    (setf (slot-value obj 'event) dest)
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:SendEvent
                       :propagate 0
                       :destination dest
                       :event-mask xcb:EventMask:NoEvent
                       :event (xcb:marshal obj exwm-systemtray--connection))))
  (xcb:flush exwm-systemtray--connection))

(defun exwm-systemtray--on-workspace-switch ()
  "Reparent/Refresh the system tray in `exwm-workspace-switch-hook'."
  (exwm--log)
  (unless (exwm-workspace--minibuffer-own-frame-p)
    (exwm-workspace--update-offsets)
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:ReparentWindow
                       :window exwm-systemtray--embedder-window
                       :parent (string-to-number
                                (frame-parameter exwm-workspace--current
                                                 'window-id))
                       :x 0
                       :y (- (slot-value (exwm-workspace--workarea
                                           exwm-workspace-current-index)
                                         'height)
                             exwm-workspace--frame-y-offset
                             exwm-systemtray-height))))
  (exwm-systemtray--refresh-background-color)
  (exwm-systemtray--refresh))

(defun exwm-systemtray--on-theme-change (_theme)
  "Refresh system tray upon theme change."
  (exwm-systemtray--refresh-background-color 'remap))

(defun exwm-systemtray--refresh-all ()
  "Reposition/Refresh the system tray."
  (exwm--log)
  (unless (exwm-workspace--minibuffer-own-frame-p)
    (exwm-workspace--update-offsets)
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:ConfigureWindow
                       :window exwm-systemtray--embedder-window
                       :value-mask xcb:ConfigWindow:Y
                       :y (- (slot-value (exwm-workspace--workarea
                                           exwm-workspace-current-index)
                                         'height)
                             exwm-workspace--frame-y-offset
                             exwm-systemtray-height))))
  (exwm-systemtray--refresh))

(cl-defun exwm-systemtray--init ()
  "Initialize system tray module."
  (exwm--log)
  (cl-assert (not exwm-systemtray--connection))
  (cl-assert (not exwm-systemtray--list))
  (cl-assert (not exwm-systemtray--selection-owner-window))
  (cl-assert (not exwm-systemtray--embedder-window))
  (unless exwm-systemtray-height
    (setq exwm-systemtray-height (max exwm-systemtray--icon-min-size
                                      (with-selected-window (minibuffer-window)
                                        (line-pixel-height)))))
  ;; Create a new connection.
  (setq exwm-systemtray--connection (xcb:connect))
  (set-process-query-on-exit-flag (slot-value exwm-systemtray--connection
                                              'process)
                                  nil)
  ;; Initialize XELB modules.
  (xcb:xembed:init exwm-systemtray--connection t)
  (xcb:systemtray:init exwm-systemtray--connection t)
  ;; Acquire the manager selection _NET_SYSTEM_TRAY_S0.
  (with-slots (owner)
      (xcb:+request-unchecked+reply exwm-systemtray--connection
          (make-instance 'xcb:GetSelectionOwner
                         :selection xcb:Atom:_NET_SYSTEM_TRAY_S0))
    (when (/= owner xcb:Window:None)
      (xcb:disconnect exwm-systemtray--connection)
      (setq exwm-systemtray--connection nil)
      (warn "[EXWM] Other system tray detected")
      (cl-return-from exwm-systemtray--init)))
  (let ((id (xcb:generate-id exwm-systemtray--connection)))
    (setq exwm-systemtray--selection-owner-window id)
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:CreateWindow
                       :depth 0
                       :wid id
                       :parent exwm--root
                       :x 0
                       :y 0
                       :width 1
                       :height 1
                       :border-width 0
                       :class xcb:WindowClass:InputOnly
                       :visual 0
                       :value-mask xcb:CW:OverrideRedirect
                       :override-redirect 1))
    ;; Get the selection ownership.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:SetSelectionOwner
                       :owner id
                       :selection xcb:Atom:_NET_SYSTEM_TRAY_S0
                       :time xcb:Time:CurrentTime))
    ;; Send a client message to announce the selection.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:SendEvent
                       :propagate 0
                       :destination exwm--root
                       :event-mask xcb:EventMask:StructureNotify
                       :event (xcb:marshal
                               (make-instance 'xcb:systemtray:-ClientMessage
                                              :window exwm--root
                                              :time xcb:Time:CurrentTime
                                              :selection
                                              xcb:Atom:_NET_SYSTEM_TRAY_S0
                                              :owner id)
                               exwm-systemtray--connection)))
    ;; Set _NET_WM_NAME.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:ewmh:set-_NET_WM_NAME
                       :window id
                       :data "EXWM: exwm-systemtray--selection-owner-window"))
    ;; Set the _NET_SYSTEM_TRAY_ORIENTATION property.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:xembed:set-_NET_SYSTEM_TRAY_ORIENTATION
                       :window id
                       :data xcb:systemtray:ORIENTATION:HORZ)))
  ;; Create the embedder.
  (let ((id (xcb:generate-id exwm-systemtray--connection))
        frame parent embedder-depth embedder-visual embedder-colormap y)
    (setq exwm-systemtray--embedder-window id)
    (if (exwm-workspace--minibuffer-own-frame-p)
        (setq frame exwm-workspace--minibuffer
              y (if (>= (line-pixel-height) exwm-systemtray-height)
                    ;; Bottom aligned.
                    (- (line-pixel-height) exwm-systemtray-height)
                  ;; Vertically centered.
                  (/ (- (line-pixel-height) exwm-systemtray-height) 2)))
      (exwm-workspace--update-offsets)
      (setq frame exwm-workspace--current
            ;; Bottom aligned.
            y (- (slot-value (exwm-workspace--workarea
                               exwm-workspace-current-index)
                             'height)
                 exwm-workspace--frame-y-offset
                 exwm-systemtray-height)))
    (setq parent (string-to-number (frame-parameter frame 'window-id)))
    ;; Use default depth, visual and colormap (from root window), instead of
    ;; Emacs frame's.  See Section "Visual and background pixmap handling" in
    ;; "System Tray Protocol Specification 0.3".
    (let* ((vdc (exwm--get-visual-depth-colormap exwm-systemtray--connection
                                                 exwm--root)))
      (setq embedder-visual (car vdc))
      (setq embedder-depth (cadr vdc))
      (setq embedder-colormap (caddr vdc)))
    ;; Note down the embedder window's depth.  It will be used to check whether
    ;; we can use xcb:BackPixmap:ParentRelative to emulate transparency.
    (setq exwm-systemtray--embedder-window-depth embedder-depth)
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:CreateWindow
                       :depth embedder-depth
                       :wid id
                       :parent parent
                       :x 0
                       :y y
                       :width 1
                       :height exwm-systemtray-height
                       :border-width 0
                       :class xcb:WindowClass:InputOutput
                       :visual embedder-visual
                       :colormap embedder-colormap
                       :value-mask (logior xcb:CW:BorderPixel
                                           xcb:CW:Colormap
                                           xcb:CW:EventMask)
                       :border-pixel 0
                       :event-mask xcb:EventMask:SubstructureNotify))
    (exwm-systemtray--set-background-color)
    ;; Set _NET_WM_NAME.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:ewmh:set-_NET_WM_NAME
                       :window id
                       :data "EXWM: exwm-systemtray--embedder-window"))
    ;; Set _NET_WM_WINDOW_TYPE.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:ewmh:set-_NET_WM_WINDOW_TYPE
                       :window id
                       :data (vector xcb:Atom:_NET_WM_WINDOW_TYPE_DOCK)))
    ;; Set _NET_SYSTEM_TRAY_VISUAL.
    (xcb:+request exwm-systemtray--connection
        (make-instance 'xcb:xembed:set-_NET_SYSTEM_TRAY_VISUAL
                       :window exwm-systemtray--selection-owner-window
                       :data embedder-visual)))
  (xcb:flush exwm-systemtray--connection)
  ;; Attach event listeners.
  (xcb:+event exwm-systemtray--connection 'xcb:DestroyNotify
              #'exwm-systemtray--on-DestroyNotify)
  (xcb:+event exwm-systemtray--connection 'xcb:ReparentNotify
              #'exwm-systemtray--on-ReparentNotify)
  (xcb:+event exwm-systemtray--connection 'xcb:ResizeRequest
              #'exwm-systemtray--on-ResizeRequest)
  (xcb:+event exwm-systemtray--connection 'xcb:PropertyNotify
              #'exwm-systemtray--on-PropertyNotify)
  (xcb:+event exwm-systemtray--connection 'xcb:ClientMessage
              #'exwm-systemtray--on-ClientMessage)
  (unless (exwm-workspace--minibuffer-own-frame-p)
    (xcb:+event exwm-systemtray--connection 'xcb:KeyPress
                #'exwm-systemtray--on-KeyPress))
  ;; Add hook to move/reparent the embedder.
  (add-hook 'exwm-workspace-switch-hook #'exwm-systemtray--on-workspace-switch)
  (add-hook 'exwm-workspace--update-workareas-hook
            #'exwm-systemtray--refresh-all)
  ;; Add hook to update background colors.
  (add-hook 'enable-theme-functions #'exwm-systemtray--on-theme-change)
  (add-hook 'disable-theme-functions #'exwm-systemtray--on-theme-change)
  (add-hook 'menu-bar-mode-hook #'exwm-systemtray--refresh-all)
  (add-hook 'tool-bar-mode-hook #'exwm-systemtray--refresh-all)
  (when (boundp 'exwm-randr-refresh-hook)
    (add-hook 'exwm-randr-refresh-hook #'exwm-systemtray--refresh-all))
  ;; The struts can be updated already.
  (when exwm-workspace--workareas
    (exwm-systemtray--refresh-all)))

(defun exwm-systemtray--exit ()
  "Exit the systemtray module."
  (exwm--log)
  (when exwm-systemtray--connection
    (when (slot-value exwm-systemtray--connection 'connected)
      ;; Hide & reparent out the embedder before disconnection to prevent
      ;; embedded icons from being reparented to an Emacs frame (which is the
      ;; parent of the embedder).
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:UnmapWindow
                         :window exwm-systemtray--embedder-window))
      (xcb:+request exwm-systemtray--connection
          (make-instance 'xcb:ReparentWindow
                         :window exwm-systemtray--embedder-window
                         :parent exwm--root
                         :x 0
                         :y 0))
      (xcb:disconnect exwm-systemtray--connection))
    (setq exwm-systemtray--connection nil
          exwm-systemtray--list nil
          exwm-systemtray--selection-owner-window nil
          exwm-systemtray--embedder-window nil
          exwm-systemtray--embedder-window-depth nil)
    (remove-hook 'exwm-workspace-switch-hook
                 #'exwm-systemtray--on-workspace-switch)
    (remove-hook 'exwm-workspace--update-workareas-hook
                 #'exwm-systemtray--refresh-all)
    (remove-hook 'enable-theme-functions #'exwm-systemtray--on-theme-change)
    (remove-hook 'disable-theme-functions #'exwm-systemtray--on-theme-change)
    (remove-hook 'menu-bar-mode-hook #'exwm-systemtray--refresh-all)
    (remove-hook 'tool-bar-mode-hook #'exwm-systemtray--refresh-all)
    (when (boundp 'exwm-randr-refresh-hook)
      (remove-hook 'exwm-randr-refresh-hook #'exwm-systemtray--refresh-all))))

(defun exwm-systemtray-enable ()
  "Enable system tray support for EXWM."
  (exwm--log)
  (add-hook 'exwm-init-hook #'exwm-systemtray--init)
  (add-hook 'exwm-exit-hook #'exwm-systemtray--exit))



(provide 'exwm-systemtray)

;;; exwm-systemtray.el ends here