background: simplify desktop detection to use EWMH standard

This replaces caja desktop detection with a generic check for
_NET_WM_WINDOW_TYPE_DESKTOP windows and makes the background plugin work
with any EWMH-compliant file manager.

It now treats the background plugin as a fallback: If there's no file
manager drawing the background, then m-s-d will draw it.

This also allows us to remove a bunch of unnecessary code:
- D-Bus session manager listener
- startup delays
- screen size tracking
- crossfade support (this is broken on msd anyway)
- checking show-desktop-icons gsettings (this is only used by caja)
- checking draw-background gsettings (this should be deprecated)

Fixes #335
Fixes mate-desktop/mate-session-manager#159

1 files changed, 79 insertions, 322 deletions

diff --git a/plugins/background/msd-background-manager.c b/plugins/background/msd-background-manager.c
index 78a38bf..5264bfa 100644
--- a/plugins/background/msd-background-manager.c
+++ b/plugins/background/msd-background-manager.c
@@ -47,107 +47,88 @@
 #include "mate-settings-profile.h"
 #include "msd-background-manager.h"
 
-#define MATE_SESSION_MANAGER_DBUS_NAME "org.gnome.SessionManager"
-#define MATE_SESSION_MANAGER_DBUS_PATH "/org/gnome/SessionManager"
-
 struct _MsdBackgroundManager {
 	GObject          parent;
 
 	GSettings       *settings;
 	MateBG          *bg;
 	cairo_surface_t *surface;
-	MateBGCrossfade *fade;
-	GList           *scr_sizes;
 
-	gboolean         msd_can_draw;
-	gboolean         caja_can_draw;
-	gboolean         do_fade;
 	gboolean         draw_in_progress;
-
-	guint            timeout_id;
-
-	GDBusProxy      *proxy;
-	gulong           proxy_signal_id;
 };
 
 G_DEFINE_TYPE (MsdBackgroundManager, msd_background_manager, G_TYPE_OBJECT)
 
 static gpointer manager_object = NULL;
 
-/* Whether MSD is allowed to draw background */
-static gboolean
-msd_can_draw_bg (MsdBackgroundManager *manager)
-{
-	return g_settings_get_boolean (manager->settings, MATE_BG_KEY_DRAW_BACKGROUND);
-}
-
-/* Whether to change background with a fade effect */
-static gboolean
-can_fade_bg (MsdBackgroundManager *manager)
-{
-	return g_settings_get_boolean (manager->settings, MATE_BG_KEY_BACKGROUND_FADE);
-}
-
-/* Whether Caja is configured to draw desktop (show-desktop-icons) */
+/* Check if any window with _NET_WM_WINDOW_TYPE_DESKTOP exists */
 static gboolean
-caja_can_draw_bg (MsdBackgroundManager *manager)
-{
-	return g_settings_get_boolean (manager->settings, MATE_BG_KEY_SHOW_DESKTOP);
-}
-
-static gboolean
-caja_is_drawing_bg (MsdBackgroundManager *manager)
+desktop_window_exists (void)
 {
 	Display       *display = gdk_x11_get_default_xdisplay ();
 	Window         window = gdk_x11_get_default_root_xwindow ();
-	Atom           caja_prop, wmclass_prop, type;
-	Window         caja_window;
+	Atom           client_list, desktop_type, window_type, type;
 	int            format;
 	unsigned long  nitems, after;
 	unsigned char *data;
 	GdkDisplay    *gdk_display;
 	gboolean       running = FALSE;
 
-	if (!manager->caja_can_draw)
+	/* This atom will be present if a window owns the desktop (e.g. caja) */
+	desktop_type = XInternAtom (display, "_NET_WM_WINDOW_TYPE_DESKTOP", True);
+	if (desktop_type == None)
 		return FALSE;
 
-	caja_prop = XInternAtom (display, "CAJA_DESKTOP_WINDOW_ID", True);
-	if (caja_prop == None)
+	/* This atom will contain the list of all windows managed by the window manager */
+	client_list = XInternAtom (display, "_NET_CLIENT_LIST", True);
+	if (client_list == None)
 		return FALSE;
 
-	XGetWindowProperty (display, window, caja_prop, 0, 1, False,
+	XGetWindowProperty (display, window, client_list, 0, 1024, False,
 			    XA_WINDOW, &type, &format, &nitems, &after, &data);
 
 	if (data == NULL)
 		return FALSE;
 
-	caja_window = *(Window *) data;
-	XFree (data);
-
-	if (type != XA_WINDOW || format != 32)
+	if (type != XA_WINDOW || format != 32) {
+		XFree (data);
 		return FALSE;
+	}
 
-	wmclass_prop = XInternAtom (display, "WM_CLASS", True);
-	if (wmclass_prop == None)
+	window_type = XInternAtom (display, "_NET_WM_WINDOW_TYPE", True);
+	if (window_type == None) {
+		XFree (data);
 		return FALSE;
+	}
 
 	gdk_display = gdk_display_get_default ();
-	gdk_x11_display_error_trap_push (gdk_display);
-
-	XGetWindowProperty (display, caja_window, wmclass_prop, 0, 20, False,
-			    XA_STRING, &type, &format, &nitems, &after, &data);
-
-	XSync (display, False);
-
-	if (gdk_x11_display_error_trap_pop (gdk_display) == BadWindow || data == NULL)
-		return FALSE;
-
-	/* See: caja_desktop_window_new(), in src/caja-desktop-window.c */
-	if (nitems == 20 && after == 0 && format == 8 &&
-	    !strcmp((char*) data, "desktop_window") &&
-	    !strcmp((char*) data + strlen((char*) data) + 1, "Caja"))
-	{
-		running = TRUE;
+	Window *windows = (Window *) data;
+
+	/* Read all the windows and determine if any of them own the desktop */
+	for (unsigned long i = 0; i < nitems && !running; i++) {
+		Atom           wm_type;
+		int            wm_format;
+		unsigned long  wm_nitems, wm_after;
+		unsigned char *wm_data;
+
+		gdk_x11_display_error_trap_push (gdk_display);
+
+		XGetWindowProperty (display, windows[i], window_type, 0, 32, False,
+				    XA_ATOM, &wm_type, &wm_format, &wm_nitems, &wm_after, &wm_data);
+
+		if (wm_data != NULL) {
+			Atom *types = (Atom *) wm_data;
+			for (unsigned long j = 0; j < wm_nitems; j++) {
+				/* Found a window managing the desktop. Bail out. */
+				if (types[j] == desktop_type) {
+					running = TRUE;
+					break;
+				}
+			}
+			XFree (wm_data);
+		}
+
+		gdk_x11_display_error_trap_pop_ignored (gdk_display);
 	}
 	XFree (data);
 
@@ -155,15 +136,6 @@ caja_is_drawing_bg (MsdBackgroundManager *manager)
 }
 
 static void
-free_fade (MsdBackgroundManager *manager)
-{
-	if (manager->fade != NULL) {
-		g_object_unref (manager->fade);
-		manager->fade = NULL;
-	}
-}
-
-static void
 free_bg_surface (MsdBackgroundManager *manager)
 {
 	if (manager->surface != NULL) {
@@ -173,100 +145,53 @@ free_bg_surface (MsdBackgroundManager *manager)
 }
 
 static void
-free_scr_sizes (MsdBackgroundManager *manager)
+draw_background (MsdBackgroundManager *manager)
 {
-	if (manager->scr_sizes != NULL) {
-		g_list_free_full (manager->scr_sizes, g_free);
-		manager->scr_sizes = NULL;
-	}
-}
+	if (manager->draw_in_progress || desktop_window_exists ())
+		return;
 
-static void
-real_draw_bg (MsdBackgroundManager *manager,
-	      GdkScreen		   *screen)
-{
+	GdkDisplay *display = gdk_display_get_default ();
+	GdkScreen *screen = gdk_display_get_default_screen (display);
 	GdkWindow *window = gdk_screen_get_root_window (screen);
 	gint scale   = gdk_window_get_scale_factor (window);
 	gint width   = WidthOfScreen (gdk_x11_screen_get_xscreen (screen)) / scale;
 	gint height  = HeightOfScreen (gdk_x11_screen_get_xscreen (screen)) / scale;
 
+	manager->draw_in_progress = TRUE;
+
 	free_bg_surface (manager);
 	manager->surface = mate_bg_create_surface_scale (manager->bg, window, width, height, scale, TRUE);
+	mate_bg_set_surface_as_root (screen, manager->surface);
 
-	if (manager->do_fade)
-	{
-		free_fade (manager);
-		manager->fade = mate_bg_set_surface_as_root_with_crossfade (screen, manager->surface);
-		g_signal_connect_swapped (manager->fade, "finished", G_CALLBACK (free_fade), manager);
-	}
-	else
-	{
-		mate_bg_set_surface_as_root (screen, manager->surface);
-	}
-	manager->scr_sizes = g_list_prepend (manager->scr_sizes, g_strdup_printf ("%dx%d", width, height));
+	manager->draw_in_progress = FALSE;
 }
 
-static void
-draw_background (MsdBackgroundManager *manager,
-		 gboolean              may_fade)
+static gboolean
+queue_draw_background (MsdBackgroundManager *manager)
 {
-	if (!manager->msd_can_draw || manager->draw_in_progress || caja_is_drawing_bg (manager))
-		return;
-
-	mate_settings_profile_start (NULL);
-
-	GdkDisplay *display = gdk_display_get_default ();
-
-	manager->draw_in_progress = TRUE;
-	manager->do_fade = may_fade && can_fade_bg (manager);
-	free_scr_sizes (manager);
-
-	g_debug ("Drawing background on Screen");
-	real_draw_bg (manager, gdk_display_get_default_screen (display));
-
-	manager->scr_sizes = g_list_reverse (manager->scr_sizes);
-
-	manager->draw_in_progress = FALSE;
-	mate_settings_profile_end (NULL);
+	draw_background (manager);
+	return FALSE;
 }
 
 static void
 on_bg_changed (MateBG               *bg G_GNUC_UNUSED,
 	       MsdBackgroundManager *manager)
 {
-	g_debug ("Background changed");
-	draw_background (manager, TRUE);
+	g_idle_add ((GSourceFunc) queue_draw_background, manager);
 }
 
 static void
 on_bg_transitioned (MateBG               *bg G_GNUC_UNUSED,
 		    MsdBackgroundManager *manager)
 {
-	g_debug ("Background transitioned");
-	draw_background (manager, FALSE);
+	g_idle_add ((GSourceFunc) queue_draw_background, manager);
 }
 
 static void
-on_screen_size_changed (GdkScreen            *screen,
+on_screen_size_changed (GdkScreen            *screen G_GNUC_UNUSED,
 			MsdBackgroundManager *manager)
 {
-	if (!manager->msd_can_draw || manager->draw_in_progress || caja_is_drawing_bg (manager))
-		return;
-
-	GdkWindow *window = gdk_screen_get_root_window (screen);
-	gint scale = gdk_window_get_scale_factor (window);
-	gint scr_num = gdk_x11_screen_get_screen_number (screen);
-	gchar *old_size = g_list_nth_data (manager->scr_sizes, (guint) scr_num);
-	gchar *new_size = g_strdup_printf ("%dx%d", WidthOfScreen (gdk_x11_screen_get_xscreen (screen)) / scale,
-						    HeightOfScreen (gdk_x11_screen_get_xscreen (screen)) / scale);
-	if (g_strcmp0 (old_size, new_size) != 0)
-	{
-		g_debug ("Screen%d size changed: %s -> %s", scr_num, old_size, new_size);
-		draw_background (manager, FALSE);
-	} else {
-		g_debug ("Screen%d size unchanged (%s). Ignoring.", scr_num, old_size);
-	}
-	g_free (new_size);
+	g_idle_add ((GSourceFunc) queue_draw_background, manager);
 }
 
 static void
@@ -295,13 +220,8 @@ connect_screen_signals (MsdBackgroundManager *manager)
 static gboolean
 settings_change_event_idle_cb (MsdBackgroundManager *manager)
 {
-	mate_settings_profile_start ("settings_change_event_idle_cb");
-
 	mate_bg_load_from_preferences (manager->bg);
-
-	mate_settings_profile_end ("settings_change_event_idle_cb");
-
-	return FALSE;   /* remove from the list of event sources */
+	return FALSE;
 }
 
 static gboolean
@@ -310,27 +230,20 @@ settings_change_event_cb (GSettings            *settings G_GNUC_UNUSED,
 			  gint                  n_keys G_GNUC_UNUSED,
 			  MsdBackgroundManager *manager)
 {
-	/* Complements on_bg_handling_changed() */
-	manager->msd_can_draw = msd_can_draw_bg (manager);
-	manager->caja_can_draw = caja_can_draw_bg (manager);
-
-	if (manager->msd_can_draw && manager->bg != NULL && !caja_is_drawing_bg (manager))
-	{
-		/* Defer signal processing to avoid making the dconf backend deadlock */
-		g_idle_add ((GSourceFunc) settings_change_event_idle_cb, manager);
-	}
-
-	return FALSE;   /* let the event propagate further */
+	g_idle_add ((GSourceFunc) settings_change_event_idle_cb, manager);
+	return FALSE;
 }
 
-static void
-setup_background (MsdBackgroundManager *manager)
+gboolean
+msd_background_manager_start (MsdBackgroundManager  *manager,
+			      GError               **error)
 {
-	g_return_if_fail (manager->bg == NULL);
+	g_debug ("Starting background manager");
+	mate_settings_profile_start (NULL);
 
-	manager->bg = mate_bg_new();
+	manager->settings = g_settings_new (MATE_BG_SCHEMA);
 
-	manager->draw_in_progress = FALSE;
+	manager->bg = mate_bg_new();
 
 	g_signal_connect(manager->bg, "changed", G_CALLBACK (on_bg_changed), manager);
 
@@ -342,16 +255,20 @@ setup_background (MsdBackgroundManager *manager)
 
 	g_signal_connect (manager->settings, "change-event",
 			  G_CALLBACK (settings_change_event_cb), manager);
+
+	mate_settings_profile_end (NULL);
+	return TRUE;
 }
 
-static void
-remove_background (MsdBackgroundManager *manager)
+void
+msd_background_manager_stop (MsdBackgroundManager *manager)
 {
-	disconnect_screen_signals (manager);
+	g_debug ("Stopping background manager");
 
-	g_signal_handlers_disconnect_by_func (manager->settings, settings_change_event_cb, manager);
+	disconnect_screen_signals (manager);
 
 	if (manager->settings != NULL) {
+		g_signal_handlers_disconnect_by_func (manager->settings, settings_change_event_cb, manager);
 		g_object_unref (manager->settings);
 		manager->settings = NULL;
 	}
@@ -361,167 +278,7 @@ remove_background (MsdBackgroundManager *manager)
 		manager->bg = NULL;
 	}
 
-	free_scr_sizes (manager);
 	free_bg_surface (manager);
-	free_fade (manager);
-}
-
-static void
-on_bg_handling_changed (GSettings            *settings G_GNUC_UNUSED,
-			const char           *key G_GNUC_UNUSED,
-			MsdBackgroundManager *manager)
-{
-	mate_settings_profile_start (NULL);
-
-	if (caja_is_drawing_bg (manager))
-	{
-		if (manager->bg != NULL)
-			remove_background (manager);
-	}
-	else if (manager->msd_can_draw && manager->bg == NULL)
-	{
-		setup_background (manager);
-	}
-
-	mate_settings_profile_end (NULL);
-}
-
-static gboolean
-queue_setup_background (MsdBackgroundManager *manager)
-{
-	manager->timeout_id = 0;
-
-	setup_background (manager);
-
-	return FALSE;
-}
-
-static void
-queue_timeout (MsdBackgroundManager *manager)
-{
-	if (manager->timeout_id > 0)
-		return;
-
-	/* SessionRunning: now check if Caja is drawing background, and if not, set it.
-	 *
-	 * FIXME: We wait a few seconds after the session is up because Caja tells the
-	 * session manager that its ready before it sets the background.
-	 * https://bugzilla.gnome.org/show_bug.cgi?id=568588
-	 */
-	manager->timeout_id =
-		g_timeout_add_seconds (8, (GSourceFunc) queue_setup_background, manager);
-}
-
-static void
-disconnect_session_manager_listener (MsdBackgroundManager* manager)
-{
-#if GLIB_CHECK_VERSION(2,62,0)
-	if (manager->proxy) {
-		g_clear_signal_handler (&manager->proxy_signal_id, manager->proxy);
-	}
-#else
-	if (manager->proxy && manager->proxy_signal_id) {
-		g_signal_handler_disconnect (manager->proxy, manager->proxy_signal_id);
-		manager->proxy_signal_id = 0;
-	}
-#endif
-}
-
-static void
-on_session_manager_signal (GDBusProxy   *proxy G_GNUC_UNUSED,
-			   const gchar  *sender_name G_GNUC_UNUSED,
-			   const gchar  *signal_name,
-			   GVariant     *parameters G_GNUC_UNUSED,
-			   gpointer      user_data)
-{
-	MsdBackgroundManager *manager = MSD_BACKGROUND_MANAGER (user_data);
-
-	if (g_strcmp0 (signal_name, "SessionRunning") == 0) {
-		queue_timeout (manager);
-		disconnect_session_manager_listener (manager);
-	}
-}
-
-static void
-draw_bg_after_session_loads (MsdBackgroundManager *manager)
-{
-	GError *error = NULL;
-	GDBusProxyFlags flags;
-
-	flags = G_DBUS_PROXY_FLAGS_DO_NOT_LOAD_PROPERTIES |
-		G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START;
-	manager->proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SESSION,
-	                                                flags,
-	                                                NULL, /* GDBusInterfaceInfo */
-	                                                MATE_SESSION_MANAGER_DBUS_NAME,
-	                                                MATE_SESSION_MANAGER_DBUS_PATH,
-	                                                MATE_SESSION_MANAGER_DBUS_NAME,
-	                                                NULL, /* GCancellable */
-	                                                &error);
-	if (manager->proxy == NULL) {
-		g_warning ("Could not listen to session manager: %s",
-			   error->message);
-		g_error_free (error);
-		return;
-	}
-
-	manager->proxy_signal_id = g_signal_connect (manager->proxy,
-							   "g-signal",
-							   G_CALLBACK (on_session_manager_signal),
-							   manager);
-}
-
-gboolean
-msd_background_manager_start (MsdBackgroundManager  *manager,
-			      GError               **error)
-{
-	g_debug ("Starting background manager");
-	mate_settings_profile_start (NULL);
-
-	manager->settings = g_settings_new (MATE_BG_SCHEMA);
-
-	manager->msd_can_draw = msd_can_draw_bg (manager);
-	manager->caja_can_draw = caja_can_draw_bg (manager);
-
-	g_signal_connect (manager->settings, "changed::" MATE_BG_KEY_DRAW_BACKGROUND,
-	                  G_CALLBACK (on_bg_handling_changed), manager);
-	g_signal_connect (manager->settings, "changed::" MATE_BG_KEY_SHOW_DESKTOP,
-	                  G_CALLBACK (on_bg_handling_changed), manager);
-
-	/* If Caja is set to draw the background, it is very likely in our session.
-	 * But it might not be started yet, so caja_is_drawing_bg() would fail.
-	 * In this case, we wait till the session is loaded, to avoid double-draws.
-	 */
-	if (manager->msd_can_draw)
-	{
-		if (manager->caja_can_draw)
-			draw_bg_after_session_loads (manager);
-		else
-			setup_background (manager);
-	}
-
-	mate_settings_profile_end (NULL);
-
-	return TRUE;
-}
-
-void
-msd_background_manager_stop (MsdBackgroundManager *manager)
-{
-	g_debug ("Stopping background manager");
-
-	if (manager->proxy)
-	{
-		disconnect_session_manager_listener (manager);
-		g_object_unref (manager->proxy);
-	}
-
-	if (manager->timeout_id != 0) {
-		g_source_remove (manager->timeout_id);
-		manager->timeout_id = 0;
-	}
-
-	remove_background (manager);
 }
 
 static GObject*