[gnome-flashback] wm: set _GNOME_WM_KEYBINDINGS property

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 87a28b85a89a1af941546d399ce5848794a107f0
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon Mar 7 22:06:48 2022 +0200

    wm: set _GNOME_WM_KEYBINDINGS property
    
    This property is used by GNOME Control Center to show Keyboard
    Shortcuts for current WM.

 gnome-flashback/Makefile.am      |   2 +
 gnome-flashback/gf-application.c |   6 +
 gnome-flashback/gf-wm.c          | 299 +++++++++++++++++++++++++++++++++++++++
 gnome-flashback/gf-wm.h          |  32 +++++
 4 files changed, 339 insertions(+)
---
diff --git a/gnome-flashback/Makefile.am b/gnome-flashback/Makefile.am
index f026b89..3b8c87f 100644
--- a/gnome-flashback/Makefile.am
+++ b/gnome-flashback/Makefile.am
@@ -47,6 +47,8 @@ gnome_flashback_SOURCES = \
        gf-main.c \
        gf-session.c \
        gf-session.h \
+       gf-wm.c \
+       gf-wm.h \
        $(BUILT_SOURCES) \
        $(NULL)
 
diff --git a/gnome-flashback/gf-application.c b/gnome-flashback/gf-application.c
index 5769e50..c3981bd 100644
--- a/gnome-flashback/gf-application.c
+++ b/gnome-flashback/gf-application.c
@@ -22,6 +22,7 @@
 
 #include "gf-application.h"
 #include "gf-confirm-display-change-dialog.h"
+#include "gf-wm.h"
 #include "backends/gf-backend.h"
 #include "liba11y-keyboard/gf-a11y-keyboard.h"
 #include "libaudio-device-selection/gf-audio-device-selection.h"
@@ -44,6 +45,8 @@ struct _GfApplication
 {
   GObject                  parent;
 
+  GfWm                    *wm;
+
   GfBackend               *backend;
 
   gint                     bus_name;
@@ -285,6 +288,7 @@ gf_application_dispose (GObject *object)
   g_clear_pointer (&application->display_change_dialog, gtk_widget_destroy);
 
   g_clear_object (&application->backend);
+  g_clear_object (&application->wm);
 
   G_OBJECT_CLASS (gf_application_parent_class)->dispose (object);
 }
@@ -325,6 +329,8 @@ gf_application_init (GfApplication *application)
   GtkSettings *settings;
   GfMonitorManager *monitor_manager;
 
+  application->wm = gf_wm_new ();
+
   application->backend = gf_backend_new (GF_BACKEND_TYPE_X11_CM);
 
   monitor_manager = gf_backend_get_monitor_manager (application->backend);
diff --git a/gnome-flashback/gf-wm.c b/gnome-flashback/gf-wm.c
new file mode 100644
index 0000000..f96ec0a
--- /dev/null
+++ b/gnome-flashback/gf-wm.c
@@ -0,0 +1,299 @@
+/*
+ * Copyright (C) 2022 Alberts Muktupāvels
+ *
+ * This program 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.
+ *
+ * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+#include "gf-wm.h"
+
+#include <gdk/gdk.h>
+#include <gdk/gdkx.h>
+#include <X11/Xatom.h>
+
+struct _GfWm
+{
+  GObject parent;
+
+  Atom    wm_check_atom;
+  Atom    wm_name_atom;
+  Atom    utf8_string_atom;
+
+  Window  wm_check;
+};
+
+G_DEFINE_TYPE (GfWm, gf_wm, G_TYPE_OBJECT)
+
+static char *
+get_wm_name (GfWm *self)
+{
+  GdkDisplay *display;
+  Display *xdisplay;
+  int result;
+  Atom actual_type;
+  int actual_format;
+  unsigned long n_items;
+  unsigned long bytes_after;
+  unsigned char *prop;
+  char *wm_name;
+
+  display = gdk_display_get_default ();
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  gdk_x11_display_error_trap_push (display);
+
+  result = XGetWindowProperty (xdisplay,
+                               self->wm_check,
+                               self->wm_name_atom,
+                               0,
+                               G_MAXLONG,
+                               False,
+                               self->utf8_string_atom,
+                               &actual_type,
+                               &actual_format,
+                               &n_items,
+                               &bytes_after,
+                               &prop);
+
+  gdk_x11_display_error_trap_pop_ignored (display);
+
+  if (result != Success ||
+      actual_type != self->utf8_string_atom ||
+      actual_format != 8 ||
+      n_items == 0)
+    {
+      XFree (prop);
+      return NULL;
+    }
+
+  wm_name = g_strndup ((const char *) prop, n_items);
+  XFree (prop);
+
+  if (!g_utf8_validate (wm_name, -1, NULL))
+    {
+      g_free (wm_name);
+      return NULL;
+    }
+
+  return wm_name;
+}
+
+static void
+update_gnome_wm_keybindings (GfWm *self)
+{
+  GdkDisplay *display;
+  Display *xdisplay;
+  char *wm_name;
+  char *gnome_wm_keybindings;
+
+  display = gdk_display_get_default ();
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  wm_name = get_wm_name (self);
+  gnome_wm_keybindings = g_strdup_printf ("%s,GNOME Flashback",
+                                          wm_name ? wm_name : "Unknown");
+
+  gdk_x11_display_error_trap_push (display);
+
+  XChangeProperty (xdisplay,
+                   self->wm_check,
+                   XInternAtom (xdisplay, "_GNOME_WM_KEYBINDINGS", False),
+                   self->utf8_string_atom,
+                   8,
+                   PropModeReplace,
+                   (guchar *) gnome_wm_keybindings,
+                   strlen (gnome_wm_keybindings));
+
+  gdk_x11_display_error_trap_pop_ignored (display);
+
+  g_free (gnome_wm_keybindings);
+  g_free (wm_name);
+}
+
+static Window
+get_net_supporting_wm_check (GfWm       *self,
+                             GdkDisplay *display,
+                             Window      window)
+{
+  Display *xdisplay;
+  int result;
+  Atom actual_type;
+  int actual_format;
+  unsigned long n_items;
+  unsigned long bytes_after;
+  unsigned char *prop;
+  Window wm_check;
+
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  gdk_x11_display_error_trap_push (display);
+
+  result = XGetWindowProperty (xdisplay,
+                               window,
+                               self->wm_check_atom,
+                               0,
+                               G_MAXLONG,
+                               False,
+                               XA_WINDOW,
+                               &actual_type,
+                               &actual_format,
+                               &n_items,
+                               &bytes_after,
+                               &prop);
+
+  gdk_x11_display_error_trap_pop_ignored (display);
+
+  if (result != Success ||
+      actual_type != XA_WINDOW ||
+      n_items == 0)
+    {
+      XFree (prop);
+      return None;
+    }
+
+  wm_check = *(Window *) prop;
+  XFree (prop);
+
+  return wm_check;
+}
+
+static void
+update_wm_check (GfWm *self)
+{
+  GdkDisplay *display;
+  Display *xdisplay;
+  Window wm_check;
+
+  display = gdk_display_get_default ();
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  wm_check = get_net_supporting_wm_check (self,
+                                          display,
+                                          XDefaultRootWindow (xdisplay));
+
+  if (wm_check == None)
+    return;
+
+  if (wm_check != get_net_supporting_wm_check (self, display, wm_check))
+    return;
+
+  self->wm_check = wm_check;
+
+  gdk_x11_display_error_trap_push (display);
+  XSelectInput (xdisplay, self->wm_check, StructureNotifyMask);
+
+  if (gdk_x11_display_error_trap_pop (display) != 0)
+    {
+      self->wm_check = None;
+    }
+
+  update_gnome_wm_keybindings (self);
+}
+
+static GdkFilterReturn
+event_filter_cb (GdkXEvent *xevent,
+                 GdkEvent  *event,
+                 gpointer   data)
+{
+  GfWm *self;
+  XEvent *e;
+
+  self = GF_WM (data);
+  e = (XEvent *) xevent;
+
+  if (self->wm_check != None)
+    {
+      if (e->type == DestroyNotify &&
+          e->xdestroywindow.window == self->wm_check)
+        {
+          update_wm_check (self);
+        }
+      else if (e->type == PropertyNotify &&
+               e->xproperty.window == self->wm_check)
+        {
+          if (e->xproperty.atom == self->wm_check_atom)
+            update_wm_check (self);
+          else if (e->xproperty.atom == self->wm_name_atom)
+            update_gnome_wm_keybindings (self);
+        }
+    }
+  else
+    {
+      GdkDisplay *display;
+      Display *xdisplay;
+
+      display = gdk_display_get_default ();
+      xdisplay = gdk_x11_display_get_xdisplay (display);
+
+      if (e->type == PropertyNotify &&
+          e->xproperty.window == XDefaultRootWindow (xdisplay) &&
+          e->xproperty.atom == self->wm_check_atom)
+        {
+          update_wm_check (self);
+        }
+    }
+
+  return GDK_FILTER_CONTINUE;
+}
+
+static void
+gf_wm_finalize (GObject *object)
+{
+  GfWm *self;
+
+  self = GF_WM (object);
+
+  gdk_window_remove_filter (NULL, event_filter_cb, self);
+
+  G_OBJECT_CLASS (gf_wm_parent_class)->finalize (object);
+}
+
+static void
+gf_wm_class_init (GfWmClass *self_class)
+{
+  GObjectClass *object_class;
+
+  object_class = G_OBJECT_CLASS (self_class);
+
+  object_class->finalize = gf_wm_finalize;
+}
+
+static void
+gf_wm_init (GfWm *self)
+{
+  GdkDisplay *display;
+  Display *xdisplay;
+
+  display = gdk_display_get_default ();
+  xdisplay = gdk_x11_display_get_xdisplay (display);
+
+  self->wm_check_atom = XInternAtom (xdisplay,
+                                     "_NET_SUPPORTING_WM_CHECK",
+                                     False);
+
+  self->wm_name_atom = XInternAtom (xdisplay, "_NET_WM_NAME", False);
+  self->utf8_string_atom = XInternAtom (xdisplay, "UTF8_STRING", False);
+
+  gdk_window_add_filter (NULL, event_filter_cb, self);
+  XSelectInput (xdisplay, GDK_ROOT_WINDOW (), PropertyChangeMask);
+  XSync (xdisplay, False);
+
+  update_wm_check (self);
+}
+
+GfWm *
+gf_wm_new (void)
+{
+  return g_object_new (GF_TYPE_WM, NULL);
+}
diff --git a/gnome-flashback/gf-wm.h b/gnome-flashback/gf-wm.h
new file mode 100644
index 0000000..e40b7c3
--- /dev/null
+++ b/gnome-flashback/gf-wm.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2022 Alberts Muktupāvels
+ *
+ * This program 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.
+ *
+ * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GF_WM_H
+#define GF_WM_H
+
+#include <glib-object.h>
+
+G_BEGIN_DECLS
+
+#define GF_TYPE_WM (gf_wm_get_type ())
+G_DECLARE_FINAL_TYPE (GfWm, gf_wm, GF, WM, GObject)
+
+GfWm *gf_wm_new (void);
+
+G_END_DECLS
+
+#endif