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+;;; exwm-systemtray.el --- System Tray Module for  -*- lexical-binding: t -*-
+;;;                        EXWM
+
+;; Copyright (C) 2016-2022 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)
+
+(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."
+  :version "25.3"
+  :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 (elt exwm-workspace--workareas
+                         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 (- (aref workarea 2) 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."
+  (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."
+  (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."
+  (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."
+  (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."
+  (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."
+  (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 (- (elt (elt exwm-workspace--workareas
+                                       exwm-workspace-current-index)
+                                  3)
+                             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 (- (elt (elt exwm-workspace--workareas
+                                       exwm-workspace-current-index)
+                                  3)
+                             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 (- (elt (elt exwm-workspace--workareas
+                           exwm-workspace-current-index)
+                      3)
+                 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
+    ;; 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