[nautilus] nautilus-desktop: draw background when screen is not composited

[Alberts Muktupāvels <muktupavels src gnome org>]

commit e1649a30606d0c9906510f1e9b3fbf545979823b
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Mon Aug 15 21:30:36 2016 +0300

    nautilus-desktop: draw background when screen is not composited
    
    At least GNOME Flashback session with Metacity still can be used
    without compositing manager. Since transparency is not available
    nautilus currently draw black background.
    
    Fix it by checking if compositing manager is running and if it is
    not then get background surface from root window and draw it on
    nautilus desktop window.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=769360

 nautilus-desktop/nautilus-desktop-window.c |  103 ++++++++++++++++++++++++++++
 1 files changed, 103 insertions(+), 0 deletions(-)
---
diff --git a/nautilus-desktop/nautilus-desktop-window.c b/nautilus-desktop/nautilus-desktop-window.c
index 7c3abec..c8909da 100644
--- a/nautilus-desktop/nautilus-desktop-window.c
+++ b/nautilus-desktop/nautilus-desktop-window.c
@@ -32,6 +32,9 @@
 #include <gio/gio.h>
 #include <glib/gi18n.h>
 
+#define GNOME_DESKTOP_USE_UNSTABLE_API
+#include <libgnome-desktop/gnome-bg.h>
+
 #include <eel/eel-vfs-extensions.h>
 #include <src/nautilus-file-utilities.h>
 #include <src/nautilus-icon-names.h>
@@ -45,12 +48,92 @@ struct NautilusDesktopWindowDetails {
        gboolean loaded;
 
        GtkWidget *desktop_selection;
+
+       gboolean composited;
+       cairo_surface_t *surface;
 };
 
 G_DEFINE_TYPE (NautilusDesktopWindow, nautilus_desktop_window, 
               NAUTILUS_TYPE_WINDOW);
 
 static void
+background_changed (NautilusDesktopWindow *window)
+{
+       GtkWidget *widget = GTK_WIDGET (window);
+       GdkScreen *screen = gtk_widget_get_screen (widget);
+
+       g_clear_pointer (&window->details->surface, cairo_surface_destroy);
+
+       window->details->surface = gnome_bg_get_surface_from_root (screen);
+       gtk_widget_queue_draw (widget);
+}
+
+static GdkFilterReturn
+filter_func (GdkXEvent             *xevent,
+             GdkEvent              *event,
+             NautilusDesktopWindow *window)
+{
+       XEvent *xev = (XEvent *) xevent;
+       GdkAtom gdkatom;
+
+       if (xev->type != PropertyNotify) {
+               return GDK_FILTER_CONTINUE;
+       }
+
+       gdkatom = gdk_atom_intern_static_string ("_XROOTPMAP_ID");
+       if (xev->xproperty.atom != gdk_x11_atom_to_xatom (gdkatom)) {
+               return GDK_FILTER_CONTINUE;
+       }
+
+       background_changed (window);
+
+       return GDK_FILTER_CONTINUE;
+}
+
+static void
+nautilus_desktop_window_composited_changed (GtkWidget *widget)
+{
+       NautilusDesktopWindow *window = NAUTILUS_DESKTOP_WINDOW (widget);
+       GdkScreen *screen = gtk_widget_get_screen (widget);
+       gboolean composited = gdk_screen_is_composited (screen);
+       GdkWindow *root;
+       gint events;
+
+       if (window->details->composited == composited) {
+               return;
+       }
+
+       window->details->composited = composited;
+       root = gdk_screen_get_root_window (screen);
+
+       if (composited) {
+               gdk_window_remove_filter (root, (GdkFilterFunc) filter_func, window);
+
+               g_clear_pointer (&window->details->surface, cairo_surface_destroy);
+       } else {
+               events = gdk_window_get_events (root);
+
+               gdk_window_set_events (root, events | GDK_PROPERTY_CHANGE_MASK);
+               gdk_window_add_filter (root, (GdkFilterFunc) filter_func, window);
+               background_changed (window);
+       }
+}
+
+static gboolean
+nautilus_desktop_window_draw (GtkWidget *widget,
+                              cairo_t   *cr)
+{
+       NautilusDesktopWindow *window = NAUTILUS_DESKTOP_WINDOW (widget);
+
+       if (window->details->surface) {
+               cairo_set_source_surface (cr, window->details->surface, 0, 0);
+               cairo_paint (cr);
+       }
+
+       return GTK_WIDGET_CLASS (nautilus_desktop_window_parent_class)->draw (widget, cr);
+}
+
+static void
 nautilus_desktop_window_update_directory (NautilusDesktopWindow *window)
 {
        GFile *location;
@@ -74,8 +157,21 @@ nautilus_desktop_window_update_directory (NautilusDesktopWindow *window)
 static void
 nautilus_desktop_window_finalize (GObject *obj)
 {
+       NautilusDesktopWindow *window = NAUTILUS_DESKTOP_WINDOW (obj);
+       GdkScreen *screen;
+       GdkWindow *root;
+
        nautilus_desktop_link_monitor_shutdown ();
 
+       if (window->details->composited == FALSE) {
+               screen = gtk_widget_get_screen (GTK_WIDGET (window));
+               root = gdk_screen_get_root_window (screen);
+
+               gdk_window_remove_filter (root, (GdkFilterFunc) filter_func, window);
+       }
+
+       g_clear_pointer (&window->details->surface, cairo_surface_destroy);
+
        G_OBJECT_CLASS (nautilus_desktop_window_parent_class)->finalize (obj);
 }
 
@@ -221,11 +317,16 @@ nautilus_desktop_window_constructed (GObject *obj)
 static void
 nautilus_desktop_window_init (NautilusDesktopWindow *window)
 {
+       GtkWidget *widget = GTK_WIDGET (window);
+       GdkScreen *screen = gtk_widget_get_screen (widget);
+
        window->details = G_TYPE_INSTANCE_GET_PRIVATE (window, NAUTILUS_TYPE_DESKTOP_WINDOW,
                                                       NautilusDesktopWindowDetails);
        gtk_style_context_add_class (gtk_widget_get_style_context (GTK_WIDGET (window)),
                                     "nautilus-desktop-window");
 
+       window->details->composited = gdk_screen_is_composited (screen);
+       nautilus_desktop_window_composited_changed (widget);
 }
 
 static void
@@ -401,6 +502,8 @@ nautilus_desktop_window_class_init (NautilusDesktopWindowClass *klass)
        wclass->unrealize = unrealize;
        wclass->map = map;
        wclass->delete_event = nautilus_desktop_window_delete_event;
+       wclass->composited_changed = nautilus_desktop_window_composited_changed;
+       wclass->draw = nautilus_desktop_window_draw;
 
        nclass->sync_title = real_sync_title;
        nclass->close = real_window_close;