daemon: save root window to pixmap at _XROOTPMAP_ID

This combined with starting the X server with
-background none will give distros using plymouth
(or potentially other boot splashes) a a nice fade
transition when g-s-d starts.

https://bugzilla.gnome.org/show_bug.cgi?id=572173

3 files changed, 81 insertions, 0 deletions

diff --git a/daemon/gdm-simple-slave.c b/daemon/gdm-simple-slave.c
index 9d1347ad..fc8649c5 100644
--- a/daemon/gdm-simple-slave.c
+++ b/daemon/gdm-simple-slave.c
@@ -1215,6 +1215,14 @@ setup_server (GdmSimpleSlave *slave)
 
         /* Set the initial keyboard layout to something reasonable */
         gdm_slave_set_initial_keyboard_layout (GDM_SLAVE (slave));
+        /* The root window has a background that may be useful
+         * to cross fade or transition from when setting the
+         * login screen background.  We read it here, and stuff
+         * it into the standard _XROOTPMAP_ID root window property,
+         * so gnome-settings-daemon can get at it.
+         */
+        gdm_slave_save_root_windows (GDM_SLAVE (slave));
+
 }
 
 static void
diff --git a/daemon/gdm-slave.c b/daemon/gdm-slave.c
index a5ce62f4..53633c0d 100644
--- a/daemon/gdm-slave.c
+++ b/daemon/gdm-slave.c
@@ -43,6 +43,7 @@
 #include <dbus/dbus-glib-lowlevel.h>
 
 #include <X11/Xlib.h> /* for Display */
+#include <X11/Xatom.h> /* for XA_PIXMAP */
 #include <X11/cursorfont.h> /* for watch cursor */
 #include <X11/extensions/Xrandr.h>
 #include <X11/Xatom.h>
@@ -364,6 +365,77 @@ gdm_slave_run_script (GdmSlave   *slave,
         return ret;
 }
 
+static void
+gdm_slave_save_root_window_of_screen (GdmSlave *slave,
+                                      Atom      id_atom,
+                                      int       screen_number)
+{
+        Window root_window;
+        GC gc;
+        XGCValues values;
+        Pixmap pixmap;
+        int width, height, depth;
+
+        root_window = RootWindow (slave->priv->server_display,
+                                  screen_number);
+
+        width = DisplayWidth (slave->priv->server_display, screen_number);
+        height = DisplayHeight (slave->priv->server_display, screen_number);
+        depth = DefaultDepth (slave->priv->server_display, screen_number);
+        pixmap = XCreatePixmap (slave->priv->server_display,
+                                root_window,
+                                width, height, depth);
+
+        values.function = GXcopy;
+        values.plane_mask = AllPlanes;
+        values.fill_style = FillSolid;
+        values.subwindow_mode = IncludeInferiors;
+
+        gc = XCreateGC (slave->priv->server_display,
+                        root_window,
+                        GCFunction | GCPlaneMask | GCFillStyle | GCSubwindowMode,
+                        &values);
+
+        if (XCopyArea (slave->priv->server_display,
+                       root_window, pixmap, gc, 0, 0,
+                       width, height, 0, 0)) {
+
+                long pixmap_as_long;
+
+                pixmap_as_long = (long) pixmap;
+
+                XChangeProperty (slave->priv->server_display,
+                                 root_window, id_atom, XA_PIXMAP,
+                                 32, PropModeReplace, (guchar *) &pixmap_as_long,
+                                 1);
+
+        }
+
+        XFreeGC (slave->priv->server_display, gc);
+}
+
+void
+gdm_slave_save_root_windows (GdmSlave *slave)
+{
+        int i, number_of_screens;
+        Atom atom;
+
+        number_of_screens = ScreenCount (slave->priv->server_display);
+
+        atom = XInternAtom (slave->priv->server_display,
+                            "_XROOTPMAP_ID", False);
+
+        if (atom == 0) {
+                return;
+        }
+
+        for (i = 0; i < number_of_screens; i++) {
+                gdm_slave_save_root_window_of_screen (slave, atom, i);
+        }
+
+        XSync (slave->priv->server_display, False);
+}
+
 void
 gdm_slave_set_initial_keyboard_layout (GdmSlave *slave)
 {
diff --git a/daemon/gdm-slave.h b/daemon/gdm-slave.h
index 7af20edf..aaaa8f23 100644
--- a/daemon/gdm-slave.h
+++ b/daemon/gdm-slave.h
@@ -78,6 +78,7 @@ void                gdm_slave_set_initial_keyboard_layout (GdmSlave *slave);
 void                gdm_slave_set_initial_cursor_position (GdmSlave *slave);
 
 void                gdm_slave_set_busy_cursor        (GdmSlave   *slave);
+void                gdm_slave_save_root_windows      (GdmSlave   *slave);
 gboolean            gdm_slave_run_script             (GdmSlave   *slave,
                                                       const char *dir,
                                                       const char *username);