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+;;; exwm-cm.el --- Compositing Manager for EXWM  -*- lexical-binding: t -*-
+
+;; Copyright (C) 2016 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 provides a compositing manager (CM) for EXWM, mainly to
+;; enable transparency support.
+
+;; Usage:
+;; Add following lines to .emacs and modify accordingly:
+;;
+;; (require 'exwm-cm)
+;; ;; Make all Emacs frames opaque.
+;; (setq window-system-default-frame-alist '((x . ((alpha . 100)))))
+;; ;; Assign everything else a 80% opacity.
+;; (setq exwm-cm-opacity 80)
+;; (exwm-cm-enable)
+;;
+;; With the last line this CM would be started with EXWM.  You can also
+;; start and stop this CM with `exwm-cm-start' and `exwm-cm-stop' at any
+;; time.
+
+;; Theory:
+;; Due to its unique way of managing X windows, EXWM can not work with
+;; any existing CMs.  And this CM, designed specifically for EXWM,
+;; probably won't work well with other WMs, too.  The theories behind
+;; all CMs are basically the same, some peculiarities of this CM are
+;; summarized as the following sections.
+
+;; + Data structures:
+;;   This CM organizes all X windows concerned with compositing in a
+;;   tree hierarchy.  Below is a stripped-down version of such tree with
+;;   each node representing an X window (except the root placeholder),
+;;
+;;   (nil
+;;    (root-xwin
+;;     (unmanaged-xwin)
+;;     (workspace-container
+;;      (unmanaged-xwin)
+;;      (xwin-container
+;;       (xwin)
+;;       (floating-frame-container
+;;        (floating-frame)))
+;;      (xwin-container
+;;       (xwin))
+;;      (workspace-frame-container
+;;       (workspace-frame)))
+;;     (minibuffer-frame-container
+;;      (minibuffer-frame))))
+;;
+;;   where
+;;   - nodes with non-nil CDRs are containers,
+;;   - siblings are arranged in stacking order (top to bottom),
+;;   - and "managed" and "unmanaged" are in WM's sense.
+;;
+;;   During a painting process, the tree is traversed starting from the
+;;   root node, with each leaf visited and painted.  The attributes of
+;;   each X window (position, size, etc) are recorded as an instance of
+;;   class `exwm-cm--attr'.  Such instance is associated with the
+;;   corresponding X window ID through a hash table.  The instance also
+;;   contains a slot pointing to a subtree of the aforementioned tree,
+;;   with the root node being the parent of the X window.  This makes it
+;;   convenient to carry out operations such as insertion, deletion,
+;;   restacking and reparenting.
+
+;; + Compositing strategies:
+;;   - Only leaves are painted, since branches (containers) are always
+;;     invisible.
+;;   - The root X window is painted separately.
+;;   - Siblings below a workspace frame container are not painted; they
+;;     are considered hidden.
+;;   - Only the top workspace in one (RandR) output is painted.
+;;   - Workspace frames and floating frames are always clipped by its
+;;     Emacs windows displaying `exwm-mode' buffers, therefore they
+;;     don't block X windows.
+
+;; Reference:
+;; + xcompmgr (http://cgit.freedesktop.org/xorg/app/xcompmgr/)
+
+;;; Code:
+
+(require 'xcb-composite)
+(require 'xcb-damage)
+(require 'xcb-ewmh)
+(require 'xcb-icccm)
+(require 'xcb-renderutil)
+(require 'xcb-shape)
+
+(require 'exwm-core)
+(require 'exwm-workspace)
+(require 'exwm-manage)
+
+(defconst exwm-cm--OPAQUE (float #xFFFFFFFF)
+  "The opacity value of the _NET_WM_WINDOW_OPACITY property.")
+(defvar exwm-cm--_NET_WM_WINDOW_OPACITY nil "The _NET_WM_WINDOW_OPACITY atom.")
+(defvar exwm-cm-opacity nil
+  "The default value of opacity when it's not explicitly specified.
+
+The value should be a floating number between 0 (transparent) and 100
+(opaque).  A value of nil also means opaque.")
+
+(defvar exwm-cm--hash nil
+  "The hash table associating X window IDs to their attributes.")
+
+(defvar exwm-cm--conn nil "The X connection used by the CM.")
+(defvar exwm-cm--buffer nil "The rendering buffer.")
+(defvar exwm-cm--depth nil "Default depth.")
+(defvar exwm-cm--clip-changed t "Whether clip has changed.")
+(defvar exwm-cm--damages nil "All damaged regions.")
+(defvar exwm-cm--expose-rectangles nil
+  "Used by Expose event handler to collect exposed regions.")
+
+(defvar exwm-cm--background nil "The background (render) picture.")
+(defvar exwm-cm--background-atom-names '("_XROOTPMAP_ID" "_XSETROOT_ID")
+  "Property names for background pixmap.")
+(defvar exwm-cm--background-atoms nil "Interned atoms of the property names.")
+
+(defun exwm-cm--get-opacity (xwin)
+  "Get the opacity of X window XWIN.
+
+The value is between 0 (fully transparent) to #xFFFFFFFF (opaque)."
+  (let ((reply (xcb:+request-unchecked+reply exwm-cm--conn
+                   (make-instance 'xcb:icccm:-GetProperty-single
+                                  :window xwin
+                                  :property exwm-cm--_NET_WM_WINDOW_OPACITY
+                                  :type xcb:Atom:CARDINAL))))
+    ;; The X window might have already been destroyed.
+    (when reply
+      (slot-value reply 'value))))
+
+(defun exwm-cm-set-opacity (xwin opacity)
+  "Set the opacity of X window XWIN to OPACITY.
+
+The value is between 0 (fully transparent) to 100 (opaque).
+
+If called interactively, XWIN would be the selected X window."
+  (interactive
+   (list (exwm--buffer->id (window-buffer))
+         (read-number "Opacity (0 ~ 100): " 100)))
+  (when (and xwin
+             (<= 0 opacity 100))
+    (setq opacity (round (* exwm-cm--OPAQUE (/ opacity 100.0))))
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:icccm:-ChangeProperty-single
+                       :window xwin
+                       :property exwm-cm--_NET_WM_WINDOW_OPACITY
+                       :type xcb:Atom:CARDINAL
+                       :data opacity))
+    (xcb:flush exwm-cm--conn)))
+
+(defclass exwm-cm--attr ()
+  (
+   ;; The entity associated with this X window; can be a frame, a buffer
+   ;; or nil.
+   (entity :initform nil)
+   ;; The subtree of which the root node is the parent of this X window.
+   (tree :initarg :tree)
+   ;; Geometry.
+   (x :initarg :x)
+   (y :initarg :y)
+   (width :initarg :width)
+   (height :initarg :height)
+   ;; X window attributes.
+   (visual :initarg :visual)
+   (class :initarg :class)
+   ;; The opacity of this X window; can be 0 ~ #xFFFE or nil.
+   (opacity :initform nil)
+   ;; Determine whether this X window should be treated as opaque or
+   ;; transparent; can be nil (opaque), 'argb or 'transparent (both
+   ;; should be treated as transparent).
+   (mode :initform nil)
+   ;; The (render) picture of this X window.
+   (picture :initform nil)
+   ;; The 1x1 (render) picture with only alpha channel.
+   (alpha-picture :initform nil)
+   ;; Whether this X window is ever damaged.
+   (damaged :initform nil)
+   ;; The damage object monitoring this X window.
+   (damage :initarg :damage)
+   ;; The bounding region of this X window (can be irregular).
+   (border-size :initform nil)
+   ;; The rectangular bounding region of this X window.
+   (extents :initform nil)
+   ;; The region require repainting (used for transparent X windows).
+   (border-clip :initform nil)
+   ;; Shape-related parameters.
+   (shaped :initform nil)
+   (shape-x :initarg :shape-x)
+   (shape-y :initarg :shape-y)
+   (shape-width :initarg :shape-width)
+   (shape-height :initarg :shape-height))
+  :documentation "Attributes of an X window.")
+
+(defsubst exwm-cm--xwin->attr (xwin)
+  "Get the attributes of X window XWIN."
+  (gethash xwin exwm-cm--hash))
+
+(defsubst exwm-cm--get-tree (xwin)
+  "Get the subtree of the parent of X window XWIN."
+  (slot-value (exwm-cm--xwin->attr xwin) 'tree))
+
+(defsubst exwm-cm--set-tree (xwin tree)
+  "Reparent X window XWIN to another tree TREE."
+  (setf (slot-value (exwm-cm--xwin->attr xwin) 'tree) tree))
+
+(defsubst exwm-cm--get-parent (xwin)
+  "Get the parent of X window XWIN."
+  (car (exwm-cm--get-tree xwin)))
+
+(defsubst exwm-cm--get-siblings (xwin)
+  "Get a list of subtrees of the siblings of X window XWIN"
+  (cdr (exwm-cm--get-tree xwin)))
+
+(defsubst exwm-cm--get-subtree (xwin)
+  "Get the subtree of which the X window XWIN is the root node."
+  (assq xwin (exwm-cm--get-siblings xwin)))
+
+(defun exwm-cm--create-attr (xwin tree x y width height)
+  "Create attributes for X window XWIN.
+
+TREE is the subtree and the parent of this X window is the tree's root.
+X and Y specify the position with regard to the root X window.  WIDTH
+and HEIGHT specify the size of the X window."
+  (let (visual class map-state damage attr)
+    (cond
+     ((= xwin exwm--root)
+      ;; Redirect all subwindows to off-screen storage.
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:composite:RedirectSubwindows
+                         :window exwm--root
+                         :update xcb:composite:Redirect:Manual))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:ChangeWindowAttributes
+                         :window xwin
+                         :value-mask xcb:CW:EventMask
+                         :event-mask (logior xcb:EventMask:StructureNotify
+                                             xcb:EventMask:PropertyChange
+                                             xcb:EventMask:SubstructureNotify
+                                             xcb:EventMask:Exposure)))
+      (setq visual (slot-value (car (slot-value (xcb:get-setup exwm-cm--conn)
+                                                'roots))
+                               'root-visual)
+            class xcb:WindowClass:InputOutput))
+     ((eq xwin exwm-manage--desktop)
+      ;; Ignore any desktop; paint the background ourselves.
+      (setq visual 0
+            class xcb:WindowClass:InputOnly
+            map-state xcb:MapState:Unmapped))
+     (t
+      ;; Redirect this window to off-screen storage, or the content
+      ;; would be mirrored to its parent.
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:composite:RedirectWindow
+                         :window xwin
+                         :update xcb:composite:Redirect:Manual))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:ChangeWindowAttributes
+                         :window xwin
+                         :value-mask xcb:CW:EventMask
+                         :event-mask (logior xcb:EventMask:StructureNotify
+                                             xcb:EventMask:PropertyChange)))
+      (let ((reply (xcb:+request-unchecked+reply exwm-cm--conn
+                       (make-instance 'xcb:GetWindowAttributes
+                                      :window xwin))))
+        (if reply
+            (with-slots ((visual* visual)
+                         (class* class)
+                         (map-state* map-state))
+                reply
+              (setq visual visual*
+                    class class*
+                    map-state map-state*))
+          ;; The X window has been destroyed actually.  It'll get
+          ;; removed by a DestroyNotify event.
+          (setq visual 0
+                class xcb:WindowClass:InputOnly
+                map-state xcb:MapState:Unmapped)))
+      (when (/= class xcb:WindowClass:InputOnly)
+        (setq damage (xcb:generate-id exwm-cm--conn))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:damage:Create
+                           :damage damage
+                           :drawable xwin
+                           :level xcb:damage:ReportLevel:NonEmpty))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:shape:SelectInput
+                           :destination-window xwin
+                           :enable 1)))))
+    (setq attr (make-instance 'exwm-cm--attr
+                              :tree tree
+                              :x x
+                              :y y
+                              :width width
+                              :height height
+                              :visual visual
+                              :class class
+                              :damage damage
+                              :shape-x x
+                              :shape-y y
+                              :shape-width width
+                              :shape-height height))
+    (puthash xwin attr exwm-cm--hash)
+    (unless (or (= xwin exwm--root)
+                (= class xcb:WindowClass:InputOnly))
+      (exwm-cm--update-opacity xwin)
+      (when (= map-state xcb:MapState:Viewable)
+        (exwm-cm--map-xwin xwin t)))))
+
+(defun exwm-cm--update-geometry (xwin x y width height &optional above-sibling)
+  "Update the geometry of X window XWIN.
+
+X, Y, WIDTH and HEIGHT have the same meaning with the arguments used in
+`exwm-cm--create-attr'.  If ABOVE-SIBLING is non-nil, restack XWIN with
+`exwm-cm--restack.'"
+  (with-slots ((x* x)
+               (y* y)
+               (width* width)
+               (height* height)
+               extents shaped shape-x shape-y shape-width shape-height)
+      (exwm-cm--xwin->attr xwin)
+    (let ((stack-changed (and above-sibling
+                              (exwm-cm--restack xwin above-sibling)))
+          (position-changed (or (and x (/= x x*))
+                                (and y (/= y y*))))
+          (size-changed (or (and width (/= width width*))
+                            (and height (/= height height*))))
+          subtree dx dy damage new-extents)
+      (when position-changed
+        (setq subtree (exwm-cm--get-subtree xwin)
+              dx (- x x*)
+              dy (- y y*))
+        (dolist (node (cdr subtree))
+          (with-slots (x y) (exwm-cm--xwin->attr (car node))
+            (exwm--log "(CM) #x%X(*): @%+d%+d => @%+d%+d"
+                       (car node) x y (+ x dx) (+ y dy))
+            (exwm-cm--update-geometry (car node) (+ x dx) (+ y dy) nil nil)))
+        (exwm--log "(CM) #x%X: @%+d%+d => @%+d%+d" xwin x* y* x y)
+        (setf x* x
+              y* y)
+        (cl-incf shape-x dx)
+        (cl-incf shape-y dy))
+      (when size-changed
+        (setf width* width
+              height* height)
+        (unless shaped
+          (setf shape-width width
+                shape-height height)))
+      (when (or stack-changed position-changed size-changed)
+        (setq damage (xcb:generate-id exwm-cm--conn)
+              new-extents (xcb:generate-id exwm-cm--conn))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region damage
+                           :rectangles nil))
+        (when extents
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:CopyRegion
+                             :source extents
+                             :destination damage)))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region new-extents
+                           :rectangles (list (make-instance 'xcb:RECTANGLE
+                                                            :x x*
+                                                            :y y*
+                                                            :width width*
+                                                            :height height*))))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:UnionRegion
+                           :source1 damage
+                           :source2 new-extents
+                           :destination damage))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:DestroyRegion
+                           :region new-extents))
+        (exwm-cm--add-damage damage)))))
+
+(defun exwm-cm--update-opacity (xwin)
+  "Update the opacity of X window XWIN."
+  (with-slots (visual opacity mode alpha-picture extents)
+      (exwm-cm--xwin->attr xwin)
+    (let (format forminfo)
+      ;; Get the opacity.
+      (setf opacity (exwm-cm--get-opacity xwin))
+      (if opacity
+          (setf opacity (round (* #xFFFF (/ opacity exwm-cm--OPAQUE))))
+        (when (numberp exwm-cm-opacity)
+          (setf opacity (round (* #xFFFF (/ exwm-cm-opacity 100.0))))))
+      (when (and opacity
+                 (>= opacity #xFFFF))
+        (setf opacity nil))
+      ;; Determine the mode of the X window.
+      (setq format (xcb:renderutil:find-visual-format
+                    (xcb:renderutil:query-formats exwm-cm--conn) visual))
+      (when format
+        (catch 'break
+          (dolist (f (slot-value (xcb:renderutil:query-formats exwm-cm--conn)
+                                 'formats))
+            (when (eq format (slot-value f 'id))
+              (setq forminfo f)
+              (throw 'break nil)))))
+      (if (and forminfo
+               (eq xcb:render:PictType:Direct (slot-value forminfo 'type))
+               (/= 0 (slot-value (slot-value forminfo 'direct) 'alpha-mask)))
+          (setf mode 'argb)
+        (if opacity
+            (setf mode 'transparent)
+          (setf mode nil)))
+      ;; Clear resources.
+      (when alpha-picture
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:render:FreePicture
+                           :picture alpha-picture))
+        (setf alpha-picture nil))
+      (when extents
+        (let ((damage (xcb:generate-id exwm-cm--conn)))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:CreateRegion
+                             :region damage
+                             :rectangles nil))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:CopyRegion
+                             :source extents
+                             :destination damage))
+          (exwm-cm--add-damage damage))))))
+
+(defsubst exwm-cm--push (newelt place)
+  "Similar to `push' but preserve the reference."
+  (let ((oldelt (car place)))
+    (setf (car place) newelt
+          (cdr place) (cons oldelt (cdr place)))))
+
+(defsubst exwm-cm--delq (elt list)
+  "Similar to `delq' but preserve the reference."
+  (if (eq elt (car list))
+      (setf (car list) (cadr list)
+            (cdr list) (cddr list))
+    (delq elt list)))
+
+(defsubst exwm-cm--assq-delete-all (key alist)
+  "Similar to `assq-delete-all' but preserve the reference."
+  (when (eq key (caar alist))
+    (setf (car alist) (cadr alist)
+          (cdr alist) (cddr alist)))
+  (assq-delete-all key alist))
+
+(defun exwm-cm--create-tree (&optional xwin)
+  "Create a tree with XWIN being the root node."
+  (let (tree0 x0 y0 children containers)
+    ;; Get the position of this branch.
+    (if xwin
+        (with-slots (tree x y) (exwm-cm--xwin->attr xwin)
+          (setq tree0 (assq xwin (cdr tree))
+                x0 x
+                y0 y))
+      (setq tree0 (list nil)
+            x0 0
+            y0 0))
+    ;; Get children nodes.
+    (if (null xwin)
+        (setq children (list exwm--root))
+      (setq children
+            (reverse (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                                     (make-instance 'xcb:QueryTree
+                                                    :window xwin))
+                                 'children))))
+    ;; Get container nodes.
+    ;; Floating frame containers are determined dynamically.
+    (cond
+     ((null xwin)
+      (setq containers `((,exwm--root))))
+     ((= xwin exwm--root)
+      ;; Workspace containers and the minibuffer frame container.
+      (setq containers (mapcar (lambda (f)
+                                 (cons (frame-parameter f 'exwm-workspace) f))
+                               exwm-workspace--list))
+      (when (exwm-workspace--minibuffer-own-frame-p)
+        (push (cons
+               (frame-parameter exwm-workspace--minibuffer 'exwm-container)
+               exwm-workspace--minibuffer)
+              containers)))
+     ;; No containers in the minibuffer container.
+     ((and (exwm-workspace--minibuffer-own-frame-p)
+           (= xwin
+              (frame-parameter exwm-workspace--minibuffer 'exwm-container))))
+     ((= exwm--root
+         (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                         (make-instance 'xcb:QueryTree
+                                        :window xwin))
+                     'parent))
+      ;; Managed X window containers and the workspace frame container.
+      (let (frame)
+        (catch 'break
+          (dolist (f exwm-workspace--list)
+            (when (= xwin (frame-parameter f 'exwm-workspace))
+              (setq frame f)
+              (throw 'break nil))))
+        (cl-assert frame)
+        (dolist (pair exwm--id-buffer-alist)
+          (with-current-buffer (cdr pair)
+            (when (eq frame exwm--frame)
+              (push (cons exwm--container (cdr pair)) containers))))
+        (push (cons (frame-parameter frame 'exwm-container) frame)
+              containers))))
+    ;; Create subnodes.
+    (dolist (xwin children)
+      ;; Create attributes.
+      (let ((reply (xcb:+request-unchecked+reply exwm-cm--conn
+                       (make-instance 'xcb:GetGeometry
+                                      :drawable xwin))))
+        ;; It's possible the X window has been destroyed.
+        (if (null reply)
+            (setq xwin nil)
+          (when reply
+            (with-slots (x y width height) reply
+              (exwm-cm--create-attr xwin tree0
+                                    (+ x x0) (+ y y0) width height))
+            ;; Insert the node.
+            (setcdr (or (last (cdr tree0)) tree0) `((,xwin))))))
+      (cond
+       ((null xwin))
+       ((assq xwin containers)
+        ;; A branch.  Repeat the process.
+        (exwm-cm--create-tree xwin)
+        (let ((entity (cdr (assq xwin containers)))
+              entity-xwin)
+          (when entity
+            (setq entity-xwin (if (framep entity)
+                                  (frame-parameter entity 'exwm-outer-id)
+                                (buffer-local-value 'exwm--id entity)))
+            (setf (slot-value (exwm-cm--xwin->attr entity-xwin) 'entity) entity
+                  (slot-value (exwm-cm--xwin->attr xwin) 'entity) entity)
+            (let ((tmp (exwm-cm--get-parent entity-xwin)))
+              (when (/= xwin tmp)
+                ;; Workspace frame container.
+                (setf (slot-value (exwm-cm--xwin->attr tmp) 'entity)
+                      entity))))))
+       ((and (null containers)
+             (exwm--id->buffer xwin))
+        ;; A leaf but a floating frame container might follow.
+        (with-current-buffer (exwm--id->buffer xwin)
+          (when exwm--floating-frame
+            (push (cons (frame-parameter exwm--floating-frame 'exwm-container)
+                        exwm--floating-frame)
+                  containers))))))))
+
+(defun exwm-cm--restack (xwin above-sibling)
+  "Restack X window XWIN so as to it's exactly on top of ABOVE-SIBLING."
+  (let ((siblings (exwm-cm--get-siblings xwin))
+        node tmp)
+    (unless (= 1 (length siblings))
+      (setq node (assq xwin siblings))
+      (if (= above-sibling xcb:Window:None)
+          ;; Put at bottom.
+          (unless (eq node (cdr (last siblings)))
+            (exwm-cm--delq node siblings)
+            (setcdr (last siblings) (list node))
+            ;; Set the return value.
+            t)
+        ;; Insert before the sibling.
+        (setq tmp siblings)
+        (while (and tmp
+                    (/= above-sibling (caar tmp)))
+          (setq tmp (cdr tmp)))
+        (cl-assert tmp)
+        ;; Check if it's already at the requested position.
+        (unless (eq tmp (cdr siblings))
+          (exwm-cm--delq node siblings)
+          (exwm-cm--push node tmp)
+          ;; Set the return value.
+          t)))))
+
+(declare-function exwm-layout--iconic-state-p "exwm-layout.el" (&optional id))
+
+(defun exwm-cm--paint-tree (tree region &optional force-opaque frame-clip)
+  "Paint the tree TREE, with REGION specifying the clipping region.
+
+If FORCE-OPAQUE is non-nil, all X windows painted in this tree is
+assumed opaque.  FRAME-CLIP specifies the region should be clipped when
+painting a frame."
+  (unless tree
+    (setq tree (exwm-cm--get-tree exwm--root)))
+  (let ((root (car tree))
+        xwin attr entity current output outputs queue rectangles)
+    ;; Paint subtrees.
+    (catch 'break
+      (dolist (subtree (cdr tree))
+        (setq xwin (car subtree)
+              attr (exwm-cm--xwin->attr xwin))
+        (cond
+         ;; Skip destroyed X windows.
+         ((null attr))
+         ;; Skip InputOnly X windows.
+         ((= xcb:WindowClass:InputOnly
+             (slot-value attr 'class)))
+         ((and (eq root exwm--root)
+               (frame-live-p (setq entity (slot-value attr 'entity)))
+               (if (eq entity exwm-workspace--minibuffer)
+                   ;; Skip the minibuffer if the current workspace is
+                   ;; already painted.
+                   (unless (exwm-workspace--minibuffer-attached-p)
+                     current)
+                 ;; Skip lower workspaces on visited RandR output.
+                 ;; If RandR is not enabled, it'll just paint the first.
+                 (memq (setq output (frame-parameter entity
+                                                     'exwm-randr-output))
+                       outputs))))
+         ((cdr subtree)
+          ;; Paint the subtree.
+          (setq entity (slot-value attr 'entity))
+          (let (fullscreen clip)
+            (cond
+             ((buffer-live-p entity)
+              (with-current-buffer entity
+                ;; Collect frame clip but exclude fullscreen and
+                ;; floating X windows.
+                (setq fullscreen (memq xcb:Atom:_NET_WM_STATE_FULLSCREEN
+                                       exwm--ewmh-state))
+                (when (and (null fullscreen)
+                           ;; In case it's hidden.
+                           (null (exwm-layout--iconic-state-p))
+                           ;; The buffer of a floating X windows is not
+                           ;; displayed on a workspace frame.
+                           (null exwm--floating-frame)
+                           ;; Opaque regions are always clipped.
+                           (slot-value (exwm-cm--xwin->attr xwin) 'mode))
+                  ;; Prepare rectangles to clip the workspace frame.
+                  (with-slots (x y width height) (exwm-cm--xwin->attr xwin)
+                    (push (make-instance 'xcb:RECTANGLE
+                                         :x x
+                                         :y y
+                                         :width width
+                                         :height height)
+                          rectangles)))))
+             ((and rectangles
+                   (frame-live-p entity))
+              ;; Prepare region to clip the frame.
+              (setq clip (xcb:generate-id exwm-cm--conn))
+              (xcb:+request exwm-cm--conn
+                  (make-instance 'xcb:xfixes:CreateRegion
+                                 :region clip
+                                 :rectangles rectangles))))
+            (setq queue
+                  (nconc (exwm-cm--paint-tree subtree region fullscreen clip)
+                         queue))
+            (when fullscreen
+              ;; Fullscreen X windows are always opaque thus occludes
+              ;; anything in this workspace.
+              (throw 'break 'fullscreen))
+            (when clip
+              (xcb:+request exwm-cm--conn
+                  (make-instance 'xcb:xfixes:DestroyRegion
+                                 :region clip))))
+          (if (not (eq root exwm--root))
+              ;; Avoid painting any siblings below the workspace frame
+              ;; container.
+              (when (exwm-workspace--workspace-p (slot-value attr 'entity))
+                (throw 'break nil))
+            ;; Save some status.
+            (when (and (frame-live-p entity)
+                       (not (eq entity exwm-workspace--minibuffer)))
+              (push output outputs)
+              (when (eq entity exwm-workspace--current)
+                (setq current t)))))
+         ((and force-opaque
+               (slot-value attr 'damaged))
+          (exwm-cm--paint-opaque xwin region t))
+         ((slot-value attr 'damaged)
+          ;; Paint damaged leaf.
+          (setq entity (slot-value attr 'entity))
+          (when (slot-value attr 'mode)
+            (push xwin queue))
+          (cond
+           ((buffer-live-p entity)
+            (with-current-buffer entity
+              (cl-assert (= xwin exwm--id))
+              (when (and exwm--floating-frame
+                         ;; Opaque regions are always clipped.
+                         (slot-value (exwm-cm--xwin->attr xwin) 'mode))
+                ;; Prepare rectangles to clip the floating frame.
+                (with-slots (x y width height) (exwm-cm--xwin->attr xwin)
+                  (push (make-instance 'xcb:RECTANGLE
+                                       :x x
+                                       :y y
+                                       :width width
+                                       :height height)
+                        rectangles)))))
+           ((and frame-clip
+                 (frame-live-p entity))
+            ;; Apply frame clip.
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:xfixes:IntersectRegion
+                               :source1 region
+                               :source2 frame-clip
+                               :destination frame-clip))
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:xfixes:SubtractRegion
+                               :source1 region
+                               :source2 frame-clip
+                               :destination region))))
+          (exwm-cm--paint-opaque xwin region)
+          (when (and frame-clip
+                     (frame-live-p entity))
+            ;; Restore frame clip.
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:xfixes:UnionRegion
+                               :source1 region
+                               :source2 frame-clip
+                               :destination region)))))))
+    ;; Return the queue.
+    queue))
+
+(defun exwm-cm--paint-opaque (xwin region &optional force-opaque)
+  "Paint an X window XWIN clipped by region REGION if XWIN is opaque.
+
+Also update the attributes of XWIN and clip the region."
+  (with-slots (x y width height visual mode picture
+                 border-size extents border-clip)
+      (exwm-cm--xwin->attr xwin)
+    ;; Prepare the X window picture.
+    (unless picture
+      (setf picture (xcb:generate-id exwm-cm--conn))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:CreatePicture
+                         :pid picture
+                         :drawable xwin
+                         :format (xcb:renderutil:find-visual-format
+                                  (xcb:renderutil:query-formats exwm-cm--conn)
+                                  visual)
+                         :value-mask 0)))
+    ;; Clear cached resources if clip changed.
+    (when exwm-cm--clip-changed
+      (when border-size
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:DestroyRegion
+                           :region border-size))
+        (setf border-size nil))
+      (when extents
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:DestroyRegion
+                           :region extents))
+        (setf extents nil))
+      (when border-clip
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:DestroyRegion
+                           :region border-clip))
+        (setf border-clip nil)))
+    ;; Retrieve the border.
+    (unless border-size
+      (setf border-size (xcb:generate-id exwm-cm--conn))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:CreateRegionFromWindow
+                         :region border-size
+                         :window xwin
+                         :kind xcb:shape:SK:Bounding))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:TranslateRegion
+                         :region border-size
+                         :dx x
+                         :dy y)))
+    ;; Retrieve the extents.
+    (unless extents
+      (setf extents (xcb:generate-id exwm-cm--conn))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:CreateRegion
+                         :region extents
+                         :rectangles (list (make-instance 'xcb:RECTANGLE
+                                                          :x x
+                                                          :y y
+                                                          :width width
+                                                          :height height)))))
+    (cond
+     ((and mode
+           (null force-opaque))
+      ;; Calculate clipped border for the transparent X window.
+      (unless border-clip
+        (setf border-clip (xcb:generate-id exwm-cm--conn))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region border-clip
+                           :rectangles nil))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CopyRegion
+                           :source region
+                           :destination border-clip))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:IntersectRegion
+                           :source1 border-clip
+                           :source2 border-size
+                           :destination border-clip))))
+     (t
+      ;; Clip & render for the opaque X window.
+      ;; Set the clip region for the rendering buffer.
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:SetPictureClipRegion
+                         :picture exwm-cm--buffer
+                         :region region
+                         :x-origin 0
+                         :y-origin 0))
+      ;; Clip the region with border.
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:SubtractRegion
+                         :source1 region
+                         :source2 border-size
+                         :destination region))
+      ;; Render the picture to the buffer.
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:Composite
+                         :op xcb:render:PictOp:Src
+                         :src picture
+                         :mask xcb:render:Picture:None
+                         :dst exwm-cm--buffer
+                         :src-x 0
+                         :src-y 0
+                         :mask-x 0
+                         :mask-y 0
+                         :dst-x x
+                         :dst-y y
+                         :width width
+                         :height height))))))
+
+(defun exwm-cm--paint-transparent (xwin)
+  "Paint a transparent X window XWIN."
+  (with-slots (x y width height opacity picture alpha-picture border-clip)
+      (exwm-cm--xwin->attr xwin)
+    ;; Prepare the alpha picture for transparent X windows.
+    (when (and opacity (null alpha-picture))
+      (setf alpha-picture (xcb:generate-id exwm-cm--conn))
+      (let ((pixmap (xcb:generate-id exwm-cm--conn)))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:CreatePixmap
+                           :depth 8
+                           :pid pixmap
+                           :drawable exwm--root
+                           :width 1
+                           :height 1))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:render:CreatePicture
+                           :pid alpha-picture
+                           :drawable pixmap
+                           :format (xcb:renderutil:find-standard
+                                    (xcb:renderutil:query-formats
+                                     exwm-cm--conn)
+                                    xcb:renderutil:PICT_STANDARD:A_8)
+                           :value-mask xcb:render:CP:Repeat
+                           :repeat 1))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:render:FillRectangles
+                           :op xcb:render:PictOp:Src
+                           :dst alpha-picture
+                           :color (make-instance 'xcb:render:COLOR
+                                                 :red 0
+                                                 :green 0
+                                                 :blue 0
+                                                 :alpha opacity)
+                           :rects (list (make-instance 'xcb:RECTANGLE
+                                                       :x 0
+                                                       :y 0
+                                                       :width 1
+                                                       :height 1))))))
+    ;; Set the clip region for the rendering buffer.
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:xfixes:SetPictureClipRegion
+                       :picture exwm-cm--buffer
+                       :region border-clip
+                       :x-origin 0
+                       :y-origin 0))
+    ;; Render the picture to the buffer.
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:render:Composite
+                       :op xcb:render:PictOp:Over
+                       :src picture
+                       :mask (or alpha-picture xcb:render:Picture:None)
+                       :dst exwm-cm--buffer
+                       :src-x 0
+                       :src-y 0
+                       :mask-x 0
+                       :mask-y 0
+                       :dst-x x
+                       :dst-y y
+                       :width width
+                       :height height))
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:xfixes:DestroyRegion
+                       :region border-clip))
+    (setf border-clip nil)))
+
+(defun exwm-cm--paint (&optional region)
+  "Paint the whole tree within clipping region REGION.
+
+If REGION is omitted, `exwm-cm--damages' is assumed.  If it's t, paint
+the whole screen."
+  ;; Prepare the clipping region.
+  (cond
+   ((null region)
+    (when exwm-cm--damages
+      (setq region exwm-cm--damages)))
+   ((eq region t)
+    (with-slots (width height) (exwm-cm--xwin->attr exwm--root)
+      (let ((rect (make-instance 'xcb:RECTANGLE
+                                 :x 0
+                                 :y 0
+                                 :width width
+                                 :height height)))
+        (setq region (xcb:generate-id exwm-cm--conn))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region region
+                           :rectangles (list rect)))))))
+  (when region
+    ;; Prepare the rendering buffer.
+    (unless exwm-cm--buffer
+      (let ((pixmap (xcb:generate-id exwm-cm--conn))
+            (picture (xcb:generate-id exwm-cm--conn)))
+        (setq exwm-cm--buffer picture)
+        (with-slots (width height visual) (exwm-cm--xwin->attr exwm--root)
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:CreatePixmap
+                             :depth exwm-cm--depth
+                             :pid pixmap
+                             :drawable exwm--root
+                             :width width
+                             :height height))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:render:CreatePicture
+                             :pid picture
+                             :drawable pixmap
+                             :format (xcb:renderutil:find-visual-format
+                                      (xcb:renderutil:query-formats
+                                       exwm-cm--conn)
+                                      visual)
+                             :value-mask 0)))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:FreePixmap
+                           :pixmap pixmap))))
+    (let (queue)
+      ;; Paint opaque X windows and update clipping region.
+      (setq queue (exwm-cm--paint-tree nil region))
+      ;; Paint the background.
+      (exwm-cm--paint-background region)
+      ;; Paint transparent X windows.
+      (while queue
+        (exwm-cm--paint-transparent (pop queue))))
+    ;; Submit changes.
+    (with-slots (width height picture) (exwm-cm--xwin->attr exwm--root)
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:SetPictureClipRegion
+                         :picture exwm-cm--buffer
+                         :region xcb:xfixes:Region:None
+                         :x-origin 0
+                         :y-origin 0))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:Composite
+                         :op xcb:render:PictOp:Src
+                         :src exwm-cm--buffer
+                         :mask xcb:render:Picture:None
+                         :dst picture
+                         :src-x 0
+                         :src-y 0
+                         :mask-x 0
+                         :mask-y 0
+                         :dst-x 0
+                         :dst-y 0
+                         :width width
+                         :height height)))
+    ;; Cleanup.
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:xfixes:DestroyRegion
+                       :region region))
+    (when (eq region exwm-cm--damages)
+      (setq exwm-cm--damages nil))
+    (setq exwm-cm--clip-changed nil)
+    (xcb:flush exwm-cm--conn)))
+
+(defun exwm-cm--paint-background (region)
+  "Paint the background."
+  (unless exwm-cm--background
+    (setq exwm-cm--background (xcb:generate-id exwm-cm--conn))
+    (let (pixmap exist)
+      (catch 'break
+        (dolist (atom exwm-cm--background-atoms)
+          (with-slots (~lsb format value-len value)
+              (xcb:+request-unchecked+reply exwm-cm--conn
+                  (make-instance 'xcb:GetProperty
+                                 :delete 0
+                                 :window exwm--root
+                                 :property atom
+                                 :type xcb:Atom:PIXMAP
+                                 :long-offset 0
+                                 :long-length 4))
+            (when (and (= format 32)
+                       (= 1 value-len))
+              (setq pixmap (if ~lsb
+                               (xcb:-unpack-u4-lsb value 0)
+                             (xcb:-unpack-u4 value 0)))
+              (setq exist t)
+              (throw 'break nil)))))
+      (unless pixmap
+        (setq pixmap (xcb:generate-id exwm-cm--conn))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:CreatePixmap
+                           :depth exwm-cm--depth
+                           :pid pixmap
+                           :drawable exwm--root
+                           :width 1
+                           :height 1)))
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:CreatePicture
+                         :pid exwm-cm--background
+                         :drawable pixmap
+                         :format (xcb:renderutil:find-visual-format
+                                  (xcb:renderutil:query-formats exwm-cm--conn)
+                                  (slot-value (exwm-cm--xwin->attr exwm--root)
+                                              'visual))
+                         :value-mask xcb:render:CP:Repeat
+                         :repeat 1))
+      (unless exist
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:render:FillRectangles
+                           :op xcb:render:PictOp:Src
+                           :dst exwm-cm--background
+                           :color (make-instance 'xcb:render:COLOR
+                                                 :red #x8080
+                                                 :green #x8080
+                                                 :blue #x8080
+                                                 :alpha #xFFFF)
+                           :rects (list (make-instance 'xcb:RECTANGLE
+                                                       :x 0
+                                                       :y 0
+                                                       :width 1
+                                                       :height 1)))))))
+  (xcb:+request exwm-cm--conn
+      (make-instance 'xcb:xfixes:SetPictureClipRegion
+                     :picture exwm-cm--buffer
+                     :region region
+                     :x-origin 0
+                     :y-origin 0))
+  (with-slots (width height) (exwm-cm--xwin->attr exwm--root)
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:render:Composite
+                       :op xcb:render:PictOp:Src
+                       :src exwm-cm--background
+                       :mask xcb:render:Picture:None
+                       :dst exwm-cm--buffer
+                       :src-x 0
+                       :src-y 0
+                       :mask-x 0
+                       :mask-y 0
+                       :dst-x 0
+                       :dst-y 0
+                       :width width
+                       :height height))))
+
+(defun exwm-cm--map-xwin (xwin &optional silent)
+  "Prepare to map X window XWIN."
+  (let ((attr (exwm-cm--xwin->attr xwin)))
+    (setf (slot-value attr 'damaged) nil)
+    ;; Add to damage.
+    (when (slot-value attr 'extents)
+      (let ((damage (xcb:generate-id exwm-cm--conn)))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region damage
+                           :rectangles nil))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CopyRegion
+                           :source (slot-value attr 'extents)
+                           :destination damage))
+        (exwm-cm--add-damage damage))
+      (unless silent
+        (exwm-cm--paint)))))
+
+(defun exwm-cm--on-MapNotify (data _synthetic)
+  "Handle MapNotify events."
+  (let ((obj (make-instance 'xcb:MapNotify))
+        attr)
+    (xcb:unmarshal obj data)
+    (with-slots (event window) obj
+      (exwm--log "(CM) MapNotify: Try to map #x%X" window)
+      (setq attr (exwm-cm--xwin->attr window))
+      (when (and attr
+                 (/= (slot-value attr 'class) xcb:WindowClass:InputOnly)
+                 (or (= event exwm--root)
+                     ;; Filter out duplicated events.
+                     (/= exwm--root (exwm-cm--get-parent window))))
+        (exwm--log "(CM) MapNotify: Map")
+        (exwm-cm--map-xwin window)))))
+
+(defun exwm-cm--on-UnmapNotify (data _synthetic)
+  "Handle UnmapNotify events."
+  (let ((obj (make-instance 'xcb:UnmapNotify))
+        attr)
+    (xcb:unmarshal obj data)
+    (with-slots (event window) obj
+      (exwm--log "(CM) UnmapNotify: Try to unmap #x%X" window)
+      (setq attr (exwm-cm--xwin->attr window))
+      (when (and attr
+                 (or (= event exwm--root)
+                     ;; Filter out duplicated events.
+                     (/= exwm--root (exwm-cm--get-parent window))))
+        (exwm--log "(CM) UnmapNotify: Unmap")
+        (with-slots (picture damaged border-size extents border-clip) attr
+          (setf damaged nil)
+          (when picture
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:render:FreePicture
+                               :picture picture))
+            (setf picture nil))
+          (when border-size
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:xfixes:DestroyRegion
+                               :region border-size))
+            (setf border-size nil))
+          (when extents
+            (exwm-cm--add-damage extents)
+            (setf extents nil))
+          (when border-clip
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:xfixes:DestroyRegion
+                               :region border-clip))
+            (setf border-clip nil)))
+        (setq exwm-cm--clip-changed t)
+        (exwm-cm--paint)))))
+
+(defun exwm-cm--on-CreateNotify (data _synthetic)
+  "Handle CreateNotify events."
+  (let ((obj (make-instance 'xcb:CreateNotify))
+        tree0)
+    (xcb:unmarshal obj data)
+    (with-slots (window parent x y width height) obj
+      (exwm--log "(CM) CreateNotify: Create #x%X on #x%X @%sx%s%+d%+d"
+                 window parent width height x y)
+      (cl-assert (= parent exwm--root))
+      (cl-assert (null (exwm-cm--xwin->attr window)))
+      (setq tree0 (exwm-cm--get-subtree parent))
+      (exwm-cm--create-attr window tree0 x y width height)
+      (if (cdr tree0)
+          (exwm-cm--push (list window) (cdr tree0))
+        (setcdr tree0 `((,window)))))))
+
+(defun exwm-cm--on-ConfigureNotify (data synthetic)
+  "Handle ConfigureNotify events."
+  ;; Ignore synthetic ConfigureNotify events sent by the WM.
+  (unless synthetic
+    (let ((obj (make-instance 'xcb:ConfigureNotify)))
+      (xcb:unmarshal obj data)
+      (with-slots (event window above-sibling x y width height) obj
+        (exwm--log
+         "(CM) ConfigureNotify: Try to configure #x%X @%sx%s%+d%+d, above #x%X"
+         window width height x y above-sibling)
+        (cond
+         ((= window exwm--root)
+          (exwm--log "(CM) ConfigureNotify: Configure the root X window")
+          (when exwm-cm--buffer
+            (xcb:+request exwm-cm--conn
+                (make-instance 'xcb:render:FreePicture
+                               :picture exwm-cm--buffer))
+            (setq exwm-cm--buffer nil))
+          (with-slots ((x* x)
+                       (y* y)
+                       (width* width)
+                       (height* height))
+              (exwm-cm--xwin->attr exwm--root)
+            (setf x* x
+                  y* y
+                  width* width
+                  height* height))
+          (exwm-cm--paint))
+         ((null (exwm-cm--xwin->attr window)))
+         ((or (= event exwm--root)
+              ;; Filter out duplicated events.
+              (/= exwm--root (exwm-cm--get-parent window)))
+          (exwm--log "(CM) ConfigureNotify: Configure")
+          (with-slots ((x0 x)
+                       (y0 y))
+              (exwm-cm--xwin->attr (exwm-cm--get-parent window))
+            (exwm-cm--update-geometry window (+ x x0) (+ y y0) width height
+                                      above-sibling))
+          (setq exwm-cm--clip-changed t)
+          (exwm-cm--paint))
+         (t
+          (exwm--log "(CM) ConfigureNotify: Skip event from #x%X" event)))))))
+
+(defun exwm-cm--destroy (xwin)
+  "Prepare to destroy X window XWIN."
+  (with-slots (tree picture alpha-picture damage
+                    border-size extents border-clip)
+      (exwm-cm--xwin->attr xwin)
+    (cl-assert (assq xwin (cdr tree)))
+    (if (= 1 (length (cdr tree)))
+        (setcdr tree nil)
+      (exwm-cm--assq-delete-all xwin (cdr tree)))
+    (remhash xwin exwm-cm--hash)
+    ;; Release resources.
+    (when picture
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:FreePicture
+                         :picture picture))
+      (setf picture nil))
+    (when alpha-picture
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:render:FreePicture
+                         :picture alpha-picture))
+      (setf alpha-picture nil))
+    (when damage
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:damage:Destroy
+                         :damage damage))
+      (setf damage nil))
+    (when border-size
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:DestroyRegion
+                         :region border-size))
+      (setf border-size nil))
+    (when extents
+      (exwm-cm--add-damage extents)
+      (setf extents nil))
+    (when border-clip
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:xfixes:DestroyRegion
+                         :region border-clip))
+      (setf border-clip nil))))
+
+(defun exwm-cm--on-DestroyNotify (data _synthetic)
+  "Handle DestroyNotify events."
+  (let ((obj (make-instance 'xcb:DestroyNotify))
+        xwin)
+    (xcb:unmarshal obj data)
+    (setq xwin (slot-value obj 'window))
+    (exwm--log "(CM) DestroyNotify: Try to destroy #x%X" xwin)
+    (when (exwm-cm--xwin->attr xwin)
+      (exwm--log "(CM) DestroyNotify: Destroy")
+      (exwm-cm--destroy xwin))))
+
+(defun exwm-cm--on-CirculateNotify (data _synthetic)
+  "Handle CirculateNotify events."
+  (let ((obj (make-instance 'xcb:CirculateNotify))
+        attr)
+    (xcb:unmarshal obj data)
+    (with-slots (event window place) obj
+      (setq attr (exwm-cm--xwin->attr window))
+      (exwm--log "(CM) CirculateNotify: Try to circulate #x%X to %s"
+                 window place)
+      (when (and attr
+                 (or (= event exwm--root)
+                     ;; Filter out duplicated events.
+                     (/= exwm--root (exwm-cm--get-parent window))))
+        (exwm--log "(CM) CirculateNotify: Circulate")
+        (exwm-cm--update-geometry window nil nil nil nil
+                                  (if (= place xcb:Circulate:LowerHighest)
+                                      xcb:Window:None
+                                    (caar (exwm-cm--get-siblings window))))
+        (setq exwm-cm--clip-changed t)
+        (exwm-cm--paint)))))
+
+(defun exwm-cm--on-Expose (data _synthetic)
+  "Handle Expose events."
+  (let ((obj (make-instance 'xcb:Expose)))
+    (xcb:unmarshal obj data)
+    (with-slots (window x y width height count) obj
+      (when (eq window exwm--root)
+        (push (make-instance 'xcb:RECTANGLE
+                             :x x
+                             :y y
+                             :width width
+                             :height height)
+              exwm-cm--expose-rectangles))
+      (when (= count 0)
+        (let ((region (xcb:generate-id exwm-cm--conn)))
+          (xcb:+request exwm-cm--conn
+              (xcb:xfixes:CreateRegion
+               :region region
+               :rectangles exwm-cm--expose-rectangles))
+          (exwm-cm--add-damage region))
+        (setq exwm-cm--expose-rectangles nil)
+        (exwm-cm--paint)))))
+
+(defun exwm-cm--on-PropertyNotify (data _synthetic)
+  "Handle PropertyNotify events."
+  (let ((obj (make-instance 'xcb:PropertyNotify)))
+    (xcb:unmarshal obj data)
+    (with-slots (window atom) obj
+      (cond
+       ((and (= window exwm--root)
+             (memq atom exwm-cm--background-atoms))
+        (exwm--log "(CM) PropertyNotify: Update background")
+        (when exwm-cm--background
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:render:FreePicture
+                             :picture exwm-cm--background))
+          (setq exwm-cm--background nil)
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:ClearArea
+                             :exposures 1
+                             :window exwm--root
+                             :x 0
+                             :y 0
+                             :width 0
+                             :height 0))
+          (xcb:flush exwm-cm--conn)))
+       ((and (= atom exwm-cm--_NET_WM_WINDOW_OPACITY)
+             ;; Some applications also set this property on their parents.
+             (null (cdr (exwm-cm--get-subtree window))))
+        (when (exwm-cm--xwin->attr window)
+          (exwm--log "(CM) PropertyNotify: Update opacity for #x%X" window)
+          (exwm-cm--update-opacity window)
+          (exwm-cm--paint)))))))
+
+(defun exwm-cm--prepare-container (xwin)
+  "Make X window XWIN a container by deselecting unnecessary events."
+  (with-slots (damage) (exwm-cm--xwin->attr xwin)
+    (when damage
+      (xcb:+request exwm-cm--conn
+          (make-instance 'xcb:damage:Destroy
+                         :damage damage)))
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:shape:SelectInput
+                       :destination-window xwin
+                       :enable 0))))
+
+(defun exwm-cm--on-ReparentNotify (data _synthetic)
+  "Handle ReparentNotify events."
+  (let ((obj (make-instance 'xcb:ReparentNotify))
+        tree tree0 grandparent great-grandparent entity)
+    (xcb:unmarshal obj data)
+    (with-slots (window parent x y) obj
+      (exwm--log "(CM) ReparentNotify: Try to reparent #x%X to #x%X @%+d%+d"
+                 window parent x y)
+      (cond
+       ((null (exwm-cm--xwin->attr window))
+        (when (eq parent exwm--root)
+          (exwm--log "(CM) ReparentNotify: Create on the root X window")
+          (let ((reply (xcb:+request-unchecked+reply exwm-cm--conn
+                           (make-instance 'xcb:GetGeometry
+                                          :drawable window))))
+            (when reply
+              (with-slots (width height) reply
+                (setq tree0 (exwm-cm--get-subtree exwm--root))
+                (exwm-cm--create-attr window tree0 x y width height)
+                (if (cdr tree0)
+                    (exwm-cm--push (list window) (cdr tree0))
+                  (setcdr tree0 `((,window)))))
+              (exwm-cm--paint)))))
+       ((= parent (exwm-cm--get-parent window)))
+       (t
+        (unless (exwm-cm--xwin->attr parent)
+          ;; Only allow workspace frame here.
+          (setq grandparent
+                (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                                (make-instance 'xcb:QueryTree
+                                               :window parent))
+                            'parent))
+          (cond
+           ((null (exwm-cm--xwin->attr grandparent))
+            (exwm--log "(CM) ReparentNotify: Destroy (too deep)"))
+           ((and (= exwm--root
+                    (setq great-grandparent (exwm-cm--get-parent grandparent)))
+                 (setq tree0 (exwm-cm--get-subtree grandparent))
+                 (or (setq entity (exwm--id->buffer window))
+                     (null (cdr tree0))))
+            ;; Reparent a workspace frame or an X window into its
+            ;; container.
+            (exwm--debug
+             (if entity
+                 (exwm--log "(CM) ReparentNotify: \
+Create implicit X window container")
+               (exwm--log "(CM) ReparentNotify: \
+Create implicit workspace frame container")))
+            (unless entity
+              (setq entity 'workspace-frame))
+            (with-slots ((x0 x)
+                         (y0 y))
+                (exwm-cm--xwin->attr grandparent)
+              (with-slots (x y width height)
+                  (xcb:+request-unchecked+reply exwm-cm--conn
+                      (make-instance 'xcb:GetGeometry
+                                     :drawable parent))
+                (exwm-cm--create-attr parent tree0
+                                      (+ x x0) (+ y y0) width height)))
+            (if (null (cdr tree0))
+                (setcdr tree0 `((,parent)))
+              ;; The stacking order of the parent is unknown.
+              (let* ((siblings
+                      (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                                      (make-instance 'xcb:QueryTree
+                                                     :window grandparent))
+                                  'children)))
+                (cl-assert (memq parent siblings))
+                (if (= parent (car siblings))
+                    ;; At the bottom.
+                    (setcdr (last (cdr tree0)) `((,parent)))
+                  ;; Insert it.
+                  (exwm-cm--push (list parent)
+                                 ;; The stacking order is reversed.
+                                 (nthcdr (- (length siblings) 1
+                                            (cl-position parent siblings))
+                                         (cdr tree0)))))))
+           ((and (= exwm--root
+                    (exwm-cm--get-parent great-grandparent))
+                 (setq tree0 (exwm-cm--get-subtree grandparent))
+                 (= 1 (length (cdr tree0)))
+                 (exwm--id->buffer (caar (cdr tree0))))
+            ;; Reparent a floating frame into its container.
+            (exwm--log "(CM) ReparentNotify: Create floating frame container")
+            (setq entity 'floating-frame)
+            (with-slots ((x0 x)
+                         (y0 y))
+                (exwm-cm--xwin->attr grandparent)
+              (with-slots (x y width height)
+                  (xcb:+request-unchecked+reply exwm-cm--conn
+                      (make-instance 'xcb:GetGeometry
+                                     :drawable parent))
+                (exwm-cm--create-attr parent tree0
+                                      (+ x x0) (+ y y0) width height)))
+            (nconc (cdr tree0) `((,parent))))
+           (t
+            (exwm--log "(CM) ReparentNotify: Destroy")
+            (exwm-cm--destroy window))))
+        ;; Ensure there's a valid parent.
+        (when (exwm-cm--xwin->attr parent)
+          (exwm--log "(CM) ReparentNotify: Reparent")
+          (when (null (cdr (exwm-cm--get-subtree parent)))
+            ;; The parent is a new container.
+            (exwm-cm--prepare-container parent))
+          (setq tree (exwm-cm--get-subtree window))
+          (let ((tree (exwm-cm--get-tree window)))
+            (if (= 1 (length (cdr tree)))
+                (setcdr tree nil)
+              (exwm-cm--assq-delete-all window (cdr tree))))
+          (setq tree0 (exwm-cm--get-subtree parent))
+          (exwm-cm--set-tree window tree0)
+          ;; The size might have already changed (e.g. when reparenting
+          ;; a workspace frame).
+          (let ((reply (xcb:+request-unchecked+reply exwm-cm--conn
+                           (make-instance 'xcb:GetGeometry
+                                          :drawable window))))
+            ;; The X window might have already been destroyed.
+            (when reply
+              (with-slots (width height) reply
+                (with-slots ((x0 x)
+                             (y0 y))
+                    (exwm-cm--xwin->attr parent)
+                  (exwm-cm--update-geometry window (+ x x0) (+ y y0)
+                                            width height)))))
+          (when entity
+            ;; Decide frame entity.
+            (when (symbolp entity)
+              (catch 'break
+                (dolist (f (if (eq entity 'workspace-frame)
+                               exwm-workspace--list
+                             (frame-list)))
+                  (when (eq window (frame-parameter f 'exwm-outer-id))
+                    (setq entity f)
+                    (throw 'break nil))))
+              (when (exwm-workspace--workspace-p entity)
+                ;; The grandparent is a new workspace container.
+                (exwm-cm--prepare-container grandparent)
+                (setf (slot-value (exwm-cm--xwin->attr grandparent) 'entity)
+                      entity)))
+            (setf (slot-value (exwm-cm--xwin->attr parent) 'entity) entity)
+            (setf (slot-value (exwm-cm--xwin->attr window) 'entity) entity))
+          (if (cdr tree0)
+              (exwm-cm--push tree (cdr tree0))
+            (setcdr tree0 `(,tree)))
+          (exwm-cm--paint)))))))
+
+(defun exwm-cm--add-damage (damage)
+  "Add region DAMAGE to `exwm-cm--damages'."
+  (if (not exwm-cm--damages)
+      (setq exwm-cm--damages damage)
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:xfixes:UnionRegion
+                       :source1 exwm-cm--damages
+                       :source2 damage
+                       :destination exwm-cm--damages))
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:xfixes:DestroyRegion
+                       :region damage))))
+
+(defun exwm-cm--on-DamageNotify (data _synthetic)
+  "Handle DamageNotify events."
+  (let ((obj (make-instance 'xcb:damage:Notify))
+        parts)
+    (xcb:unmarshal obj data)
+    (cl-assert (exwm-cm--xwin->attr (slot-value obj 'drawable)))
+    (with-slots (x y width height damaged damage)
+        (exwm-cm--xwin->attr (slot-value obj 'drawable))
+      (setq parts (xcb:generate-id exwm-cm--conn))
+      (cond
+       (damaged
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region parts
+                           :rectangles nil))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:damage:Subtract
+                           :damage damage
+                           :repair xcb:xfixes:Region:None
+                           :parts parts))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:TranslateRegion
+                           :region parts
+                           :dx x
+                           :dy y)))
+       (t
+        (setf damaged t)
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:xfixes:CreateRegion
+                           :region parts
+                           :rectangles (list (make-instance 'xcb:RECTANGLE
+                                                            :width width
+                                                            :height height
+                                                            :x x
+                                                            :y y))))
+        (xcb:+request exwm-cm--conn
+            (make-instance 'xcb:damage:Subtract
+                           :damage damage
+                           :repair xcb:xfixes:Region:None
+                           :parts xcb:xfixes:Region:None))))
+      (exwm-cm--add-damage parts))
+    ;; Check if there are more damages immediately followed.
+    (unless (/= 0 (logand #x80 (slot-value obj 'level)))
+      (exwm-cm--paint))))
+
+(defun exwm-cm--on-ShapeNotify (data _synthetic)
+  "Handle ShapeNotify events."
+  (let ((obj (make-instance 'xcb:shape:Notify))
+        attr region1 region2)
+    (xcb:unmarshal obj data)
+    (with-slots (shape-kind affected-window shaped
+                            extents-x extents-y extents-width extents-height)
+        obj
+      (exwm--log "(CM) ShapeNotify: #x%X" affected-window)
+      (when (and (or (eq shape-kind xcb:shape:SK:Clip)
+                     (eq shape-kind xcb:shape:SK:Bounding))
+                 (setq attr (exwm-cm--xwin->attr affected-window)))
+        (with-slots ((shaped* shaped)
+                     x y width height
+                     shape-x shape-y shape-width shape-height)
+            attr
+          (setq region1 (xcb:generate-id exwm-cm--conn)
+                region2 (xcb:generate-id exwm-cm--conn))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:CreateRegion
+                             :region region1
+                             :rectangles `(,(make-instance 'xcb:RECTANGLE
+                                                           :width shape-width
+                                                           :height shape-height
+                                                           :x shape-x
+                                                           :y shape-y))))
+          (if shaped
+              (setf shaped* t
+                    shape-x (+ x extents-x)
+                    shape-y (+ y extents-y)
+                    shape-width (+ width extents-width)
+                    shape-height (+ height extents-height))
+            (setf shaped* nil
+                  shape-x x
+                  shape-y y
+                  shape-width width
+                  shape-height height))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:CreateRegion
+                             :region region2
+                             :rectangles `(,(make-instance 'xcb:RECTANGLE
+                                                           :width shape-width
+                                                           :height shape-height
+                                                           :x shape-x
+                                                           :y shape-y))))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:UnionRegion
+                             :source1 region1
+                             :source2 region2
+                             :destination region1))
+          (xcb:+request exwm-cm--conn
+              (make-instance 'xcb:xfixes:DestroyRegion
+                             :region region2))
+          (setq exwm-cm--clip-changed t)
+          (exwm-cm--paint region1))))))
+
+(defun exwm-cm--init ()
+  "Initialize EXWM compositing manager."
+  ;; Create a new connection.
+  (setq exwm-cm--conn (xcb:connect))
+  (set-process-query-on-exit-flag (slot-value exwm-cm--conn 'process) nil)
+  ;; Initialize ICCCM/EWMH support.
+  (xcb:icccm:init exwm-cm--conn)
+  (xcb:ewmh:init exwm-cm--conn)
+  ;; Check for Render extension.
+  (let ((version (xcb:renderutil:query-version exwm-cm--conn)))
+    (unless (and version
+                 (= 0 (slot-value version 'major-version))
+                 (<= 2 (slot-value version 'minor-version)))
+      (error "[EXWM] The server does not support Render extension")))
+  ;; Check for Composite extension.
+  (when (or (= 0
+               (slot-value (xcb:get-extension-data exwm-cm--conn
+                                                   'xcb:composite)
+                           'present))
+            (with-slots (major-version minor-version)
+                (xcb:+request-unchecked+reply exwm-cm--conn
+                    (make-instance 'xcb:composite:QueryVersion
+                                   :client-major-version 0
+                                   :client-minor-version 1))
+              (or (/= major-version 0) (< minor-version 1))))
+    (error "[EXWM] The server does not support Composite extension"))
+  ;; Check for Damage extension.
+  (when (or (= 0 (slot-value (xcb:get-extension-data exwm-cm--conn 'xcb:damage)
+                             'present))
+            (with-slots (major-version minor-version)
+                (xcb:+request-unchecked+reply exwm-cm--conn
+                    (make-instance 'xcb:damage:QueryVersion
+                                   :client-major-version 1
+                                   :client-minor-version 1))
+              (or (/= major-version 1) (< minor-version 1))))
+    (error "[EXWM] The server does not support Damage extension"))
+  ;; Check for XFixes extension.
+  (when (or (= 0 (slot-value (xcb:get-extension-data exwm-cm--conn 'xcb:xfixes)
+                             'present))
+            (with-slots (major-version minor-version)
+                (xcb:+request-unchecked+reply exwm-cm--conn
+                    (make-instance 'xcb:xfixes:QueryVersion
+                                   :client-major-version 2
+                                   :client-minor-version 0))
+              (or (/= major-version 2) (/= minor-version 0))))
+    (error "[EXWM] The server does not support XFixes extension"))
+  ;; Check for Shape extension.
+  (when (or (= 0 (slot-value (xcb:get-extension-data exwm-cm--conn 'xcb:shape)
+                             'present))
+            (with-slots (major-version minor-version)
+                (xcb:+request-unchecked+reply exwm-cm--conn
+                    (make-instance 'xcb:shape:QueryVersion))
+              (or (/= major-version 1) (< minor-version 1))))
+    (error "[EXWM] The server does not support Shape extension"))
+  ;; Intern atoms.
+  (let ((atom-name "_NET_WM_WINDOW_OPACITY"))
+    (setq exwm-cm--_NET_WM_WINDOW_OPACITY
+          (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                          (make-instance 'xcb:InternAtom
+                                         :only-if-exists 0
+                                         :name-len (length atom-name)
+                                         :name atom-name))
+                      'atom)))
+  (setq exwm-cm--background-atoms
+        (mapcar (lambda (atom-name)
+                  (slot-value (xcb:+request-unchecked+reply exwm-cm--conn
+                                  (make-instance 'xcb:InternAtom
+                                                 :only-if-exists 0
+                                                 :name-len (length atom-name)
+                                                 :name atom-name))
+                              'atom))
+                exwm-cm--background-atom-names))
+  ;; Register CM.
+  (with-slots (owner)
+      (xcb:+request-unchecked+reply exwm-cm--conn
+          (make-instance 'xcb:GetSelectionOwner
+                         :selection xcb:Atom:_NET_WM_CM_S0))
+    (when (/= owner xcb:Window:None)
+      (error "[EXWM] Other compositing manager detected")))
+  (let ((id (xcb:generate-id exwm-cm--conn)))
+    (xcb:+request exwm-cm--conn
+        (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))
+    ;; Set _NET_WM_NAME.
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:ewmh:set-_NET_WM_NAME
+                       :window id
+                       :data "EXWM-CM"))
+    ;; Get the selection ownership.
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:SetSelectionOwner
+                       :owner id
+                       :selection xcb:Atom:_NET_WM_CM_S0
+                       :time xcb:Time:CurrentTime)))
+  ;; Attach event listeners.
+  (xcb:+event exwm-cm--conn 'xcb:MapNotify #'exwm-cm--on-MapNotify)
+  (xcb:+event exwm-cm--conn 'xcb:UnmapNotify #'exwm-cm--on-UnmapNotify)
+  (xcb:+event exwm-cm--conn 'xcb:CreateNotify #'exwm-cm--on-CreateNotify)
+  (xcb:+event exwm-cm--conn 'xcb:ConfigureNotify #'exwm-cm--on-ConfigureNotify)
+  (xcb:+event exwm-cm--conn 'xcb:DestroyNotify #'exwm-cm--on-DestroyNotify)
+  (xcb:+event exwm-cm--conn 'xcb:ReparentNotify #'exwm-cm--on-ReparentNotify)
+  (xcb:+event exwm-cm--conn 'xcb:CirculateNotify #'exwm-cm--on-CirculateNotify)
+  (xcb:+event exwm-cm--conn 'xcb:Expose #'exwm-cm--on-Expose)
+  (xcb:+event exwm-cm--conn 'xcb:PropertyNotify #'exwm-cm--on-PropertyNotify)
+  (xcb:+event exwm-cm--conn 'xcb:damage:Notify #'exwm-cm--on-DamageNotify)
+  (xcb:+event exwm-cm--conn 'xcb:shape:Notify #'exwm-cm--on-ShapeNotify)
+  ;; Scan the window tree.
+  (setq exwm-cm--hash (make-hash-table))
+  (exwm-cm--create-tree)
+  ;; Set up the root X window.
+  (setq exwm-cm--depth
+        (slot-value (car (slot-value (xcb:get-setup exwm-cm--conn) 'roots))
+                    'root-depth))
+  (with-slots (visual picture) (exwm-cm--xwin->attr exwm--root)
+    (setf picture (xcb:generate-id exwm-cm--conn))
+    (xcb:+request exwm-cm--conn
+        (make-instance 'xcb:render:CreatePicture
+                       :pid picture
+                       :drawable exwm--root
+                       :format (xcb:renderutil:find-visual-format
+                                (xcb:renderutil:query-formats exwm-cm--conn)
+                                visual)
+                       :value-mask xcb:render:CP:SubwindowMode
+                       :subwindowmode xcb:SubwindowMode:IncludeInferiors)))
+  (xcb:flush exwm-cm--conn)
+  ;; Paint once.
+  (exwm-cm--paint t))
+
+(defun exwm-cm--exit ()
+  "Exit EXWM compositing manager."
+  (when exwm-cm--conn
+    (xcb:disconnect exwm-cm--conn)
+    (clrhash exwm-cm--hash)
+    (setq exwm-cm--hash nil
+          exwm-cm--conn nil
+          exwm-cm--buffer nil
+          exwm-cm--clip-changed t
+          exwm-cm--damages nil
+          exwm-cm--expose-rectangles nil
+          exwm-cm--background nil)))
+
+(defun exwm-cm-enable ()
+  "Enable compositing support for EXWM."
+  (add-hook 'exwm-init-hook #'exwm-cm--init t)
+  (add-hook 'exwm-exit-hook #'exwm-cm--exit t))
+
+(defun exwm-cm-start ()
+  "Start EXWM composting manager."
+  (interactive)
+  (unless exwm-cm--conn
+    (exwm-cm--init)))
+
+(defun exwm-cm-stop ()
+  "Stop EXWM compositing manager."
+  (interactive)
+  (exwm-cm--exit))
+
+(defun exwm-cm-toggle ()
+  "Toggle the running state of EXWM compositing manager."
+  (interactive)
+  (if exwm-cm--conn
+      (exwm-cm-stop)
+    (exwm-cm-start)))
+
+
+
+(provide 'exwm-cm)
+
+;;; exwm-cm.el ends here