compositor: rework how backgrounds are managed

Background handling in GNOME is very roundabout at the moment.

gnome-settings-daemon uses gnome-desktop to read the background from
disk into a screen-sized pixmap. It then sets the XID of that pixmap
on the _XROOTPMAP_ID root window property.

mutter puts that pixmap into a texture/actor which gnome-shell then
uses.

Having the gnome-settings-daemon detour from disk to screen means we
can't easily let the compositor handle transition effects when
switching backgrounds. Also, having the background actor be
per-screen instead of per-monitor means we may have oversized
textures in certain multihead setups.

This commit changes mutter to read backgrounds from disk itself, and
it changes backgrounds to be per-monitor.

This way background handling/compositing is left to the compositor.

https://bugzilla.gnome.org/show_bug.cgi?id=682427

src/Makefile.am

@@ -8,6 +8,7 @@ SUBDIRS=wm-tester tools compositor/plugins
 INCLUDES=								\
 	-DCLUTTER_ENABLE_EXPERIMENTAL_API				\
 	-DCOGL_ENABLE_EXPERIMENTAL_API					\
+	-DCOGL_ENABLE_EXPERIMENTAL_2_0_API                              \
 	$(MUTTER_CFLAGS)						\
 	-I$(srcdir)							\
 	-I$(srcdir)/core						\
@@ -48,8 +49,11 @@ libmutter_la_SOURCES =				\
 	compositor/cogl-utils.h			\
 	compositor/compositor.c			\
 	compositor/compositor-private.h		\
+	compositor/meta-background.c		\
 	compositor/meta-background-actor.c	\
 	compositor/meta-background-actor-private.h	\
+	compositor/meta-background-group.c	\
+	compositor/meta-background-group-private.h	\
 	compositor/meta-module.c		\
 	compositor/meta-module.h		\
 	compositor/meta-plugin.c		\
@@ -71,7 +75,9 @@ libmutter_la_SOURCES =				\
 	compositor/region-utils.c		\
 	compositor/region-utils.h		\
 	meta/compositor.h			\
+	meta/meta-background.h			\
 	meta/meta-background-actor.h		\
+	meta/meta-background-group.h		\
 	meta/meta-plugin.h			\
 	meta/meta-shadow-factory.h		\
 	meta/meta-window-actor.h		\
@@ -175,6 +181,8 @@ libmutterinclude_base_headers =		\
 	meta/keybindings.h			\
 	meta/main.h				\
 	meta/meta-background-actor.h		\
+	meta/meta-background-group.h		\
+	meta/meta-background.h			\
 	meta/meta-plugin.h			\
 	meta/meta-shaped-texture.h		\
 	meta/meta-shadow-factory.h		\

src/compositor/compositor.c

@@ -13,10 +13,11 @@
 #include "xprops.h"
 #include <meta/prefs.h>
 #include <meta/main.h>
+#include <meta/meta-background-actor.h>
+#include <meta/meta-background-group.h>
 #include <meta/meta-shadow-factory.h>
 #include "meta-window-actor-private.h"
 #include "meta-window-group.h"
-#include "meta-background-actor-private.h"
 #include "window-private.h" /* to check window->hidden */
 #include "display-private.h" /* for meta_display_lookup_x_window() */
 #include <X11/extensions/shape.h>
@@ -117,21 +118,6 @@ process_property_notify (MetaCompositor	*compositor,
 {
   MetaWindowActor *window_actor;
 
-  if (event->atom == compositor->atom_x_root_pixmap)
-    {
-      GSList *l;
-
-      for (l = meta_display_get_screens (compositor->display); l; l = l->next)
-        {
-	  MetaScreen  *screen = l->data;
-          if (event->window == meta_screen_get_xroot (screen))
-            {
-              meta_background_actor_update (screen);
-              return;
-            }
-        }
-    }
-
   if (window == NULL)
     return;
 
@@ -254,27 +240,6 @@ meta_get_top_window_group_for_screen (MetaScreen *screen)
   return info->top_window_group;
 }
 
-/**
- * meta_get_background_actor_for_screen:
- * @screen: a #MetaScreen
- *
- * Gets the actor that draws the root window background under the windows.
- * The root window background automatically tracks the image or color set
- * by the environment.
- *
- * Returns: (transfer none): The background actor corresponding to @screen
- */
-ClutterActor *
-meta_get_background_actor_for_screen (MetaScreen *screen)
-{
-  MetaCompScreen *info = meta_screen_get_compositor_data (screen);
-
-  if (!info)
-    return NULL;
-
-  return info->background_actor;
-}
-
 /**
  * meta_get_window_actors:
  * @screen: a #MetaScreen
@@ -606,14 +571,8 @@ meta_compositor_manage_screen (MetaCompositor *compositor,
 
   info->window_group = meta_window_group_new (screen);
   info->top_window_group = meta_window_group_new (screen);
-  info->background_actor = meta_background_actor_new_for_screen (screen);
-  clutter_actor_set_reactive (info->background_actor, TRUE);
   info->overlay_group = clutter_group_new ();
 
-  clutter_container_add (CLUTTER_CONTAINER (info->window_group),
-                         info->background_actor,
-                         NULL);
-
   clutter_container_add (CLUTTER_CONTAINER (info->stage),
                          info->window_group,
                          info->top_window_group,
@@ -1066,6 +1025,7 @@ sync_actor_stacking (MetaCompScreen *info)
   GList *expected_window_node;
   GList *tmp;
   GList *old;
+  GList *backgrounds;
   gboolean has_windows;
   gboolean reordered;
 
@@ -1083,15 +1043,19 @@ sync_actor_stacking (MetaCompScreen *info)
    * (we really need extra API to make that reliable.)
    */
 
-  /* First we check if the background is at the bottom. Then
+  /* First we collect a list of all backgrounds, and check if they're at the
-   * we check if the window actors are in the correct sequence */
+   * bottom. Then we check if the window actors are in the correct sequence */
+  backgrounds = NULL;
   expected_window_node = info->windows;
   for (old = children; old != NULL; old = old->next)
     {
       ClutterActor *actor = old->data;
 
-      if (actor == info->background_actor)
+      if (META_IS_BACKGROUND_GROUP (actor) ||
+          META_IS_BACKGROUND_ACTOR (actor))
         {
+          backgrounds = g_list_prepend (backgrounds, actor);
+
           if (has_windows)
             reordered = TRUE;
         }
@@ -1109,7 +1073,10 @@ sync_actor_stacking (MetaCompScreen *info)
   g_list_free (children);
 
   if (!reordered)
-    return;
+    {
+      g_list_free (backgrounds);
+      return;
+    }
 
   /* reorder the actors by lowering them in turn to the bottom of the stack.
    * windows first, then background */
@@ -1120,7 +1087,16 @@ sync_actor_stacking (MetaCompScreen *info)
       clutter_actor_lower_bottom (CLUTTER_ACTOR (window_actor));
     }
 
-  clutter_actor_lower_bottom (info->background_actor);
+  /* we prepended the backgrounds above so the last actor in the list
+   * should get lowered to the bottom last.
+   */
+  for (tmp = backgrounds; tmp != NULL; tmp = tmp->next)
+    {
+      ClutterActor *actor = tmp->data;
+
+      clutter_actor_lower_bottom (CLUTTER_ACTOR (actor));
+    }
+  g_list_free (backgrounds);
 }
 
 void
@@ -1276,8 +1252,6 @@ meta_compositor_sync_screen_size (MetaCompositor  *compositor,
 
   XResizeWindow (xdisplay, xwin, width, height);
 
-  meta_background_actor_screen_size_changed (screen);
-
   meta_verbose ("Changed size for stage on screen %d to %dx%d\n",
 		meta_screen_get_screen_number (screen),
 		width, height);

src/compositor/meta-background-actor-private.h

@@ -9,7 +9,6 @@
 void meta_background_actor_set_visible_region  (MetaBackgroundActor *self,
                                                 cairo_region_t      *visible_region);
 
-void meta_background_actor_update              (MetaScreen *screen);
+cairo_region_t *meta_background_actor_get_visible_region (MetaBackgroundActor *self);
-void meta_background_actor_screen_size_changed (MetaScreen *screen);
 
 #endif /* META_BACKGROUND_ACTOR_PRIVATE_H */

src/compositor/meta-background-actor.c

@@ -34,223 +34,23 @@
 #include "cogl-utils.h"
 #include "compositor-private.h"
 #include <meta/errors.h>
+#include <meta/meta-background.h>
 #include "meta-background-actor-private.h"
 
-/* We allow creating multiple MetaBackgroundActors for the same MetaScreen to
- * allow different rendering options to be set for different copies.
- * But we want to share the same underlying CoglTexture for efficiency and
- * to avoid driver bugs that might occur if we created multiple CoglTexturePixmaps
- * for the same pixmap.
- *
- * This structure holds common information.
- */
-typedef struct _MetaScreenBackground MetaScreenBackground;
-
-struct _MetaScreenBackground
-{
-  MetaScreen *screen;
-  GSList *actors;
-
-  float texture_width;
-  float texture_height;
-  CoglTexture *texture;
-  CoglMaterialWrapMode wrap_mode;
-  guint have_pixmap : 1;
-};
-
 struct _MetaBackgroundActorPrivate
 {
-  MetaScreenBackground *background;
-  CoglPipeline *pipeline;
-
   cairo_region_t *visible_region;
-  float dim_factor;
 };
 
-enum
-{
-  PROP_0,
-
-  PROP_DIM_FACTOR,
-
-  PROP_LAST
-};
-
-static GParamSpec *obj_props[PROP_LAST];
-
 G_DEFINE_TYPE (MetaBackgroundActor, meta_background_actor, CLUTTER_TYPE_ACTOR);
 
-static void set_texture                (MetaScreenBackground *background,
-                                        CoglHandle            texture);
-static void set_texture_to_stage_color (MetaScreenBackground *background);
-
-static void
-on_notify_stage_color (GObject              *stage,
-                       GParamSpec           *pspec,
-                       MetaScreenBackground *background)
-{
-  if (!background->have_pixmap)
-    set_texture_to_stage_color (background);
-}
-
-static void
-free_screen_background (MetaScreenBackground *background)
-{
-  set_texture (background, COGL_INVALID_HANDLE);
-
-  if (background->screen != NULL)
-    {
-      ClutterActor *stage = meta_get_stage_for_screen (background->screen);
-      g_signal_handlers_disconnect_by_func (stage,
-                                            (gpointer) on_notify_stage_color,
-                                            background);
-      background->screen = NULL;
-    }
-}
-
-static MetaScreenBackground *
-meta_screen_background_get (MetaScreen *screen)
-{
-  MetaScreenBackground *background;
-
-  background = g_object_get_data (G_OBJECT (screen), "meta-screen-background");
-  if (background == NULL)
-    {
-      ClutterActor *stage;
-
-      background = g_new0 (MetaScreenBackground, 1);
-
-      background->screen = screen;
-      g_object_set_data_full (G_OBJECT (screen), "meta-screen-background",
-                              background, (GDestroyNotify) free_screen_background);
-
-      stage = meta_get_stage_for_screen (screen);
-      g_signal_connect (stage, "notify::color",
-                        G_CALLBACK (on_notify_stage_color), background);
-
-      meta_background_actor_update (screen);
-    }
-
-  return background;
-}
-
-static void
-update_wrap_mode_of_actor (MetaBackgroundActor *self)
-{
-  MetaBackgroundActorPrivate *priv = self->priv;
-
-  cogl_pipeline_set_layer_wrap_mode (priv->pipeline, 0, priv->background->wrap_mode);
-}
-
-static void
-update_wrap_mode (MetaScreenBackground *background)
-{
-  GSList *l;
-  int width, height;
-
-  meta_screen_get_size (background->screen, &width, &height);
-
-  /* We turn off repeating when we have a full-screen pixmap to keep from
-   * getting artifacts from one side of the image sneaking into the other
-   * side of the image via bilinear filtering.
-   */
-  if (width == background->texture_width && height == background->texture_height)
-    background->wrap_mode = COGL_MATERIAL_WRAP_MODE_CLAMP_TO_EDGE;
-  else
-    background->wrap_mode = COGL_MATERIAL_WRAP_MODE_REPEAT;
-
-  for (l = background->actors; l; l = l->next)
-    update_wrap_mode_of_actor (l->data);
-}
-
-static void
-set_texture_on_actor (MetaBackgroundActor *self)
-{
-  MetaBackgroundActorPrivate *priv = self->priv;
-  MetaDisplay *display = meta_screen_get_display (priv->background->screen);
-
-  /* This may trigger destruction of an old texture pixmap, which, if
-   * the underlying X pixmap is already gone has the tendency to trigger
-   * X errors inside DRI. For safety, trap errors */
-  meta_error_trap_push (display);
-  cogl_pipeline_set_layer_texture (priv->pipeline, 0, priv->background->texture);
-  meta_error_trap_pop (display);
-
-  clutter_actor_queue_redraw (CLUTTER_ACTOR (self));
-}
-
-static void
-set_texture (MetaScreenBackground *background,
-             CoglHandle            texture)
-{
-  MetaDisplay *display = meta_screen_get_display (background->screen);
-  GSList *l;
-
-  /* This may trigger destruction of an old texture pixmap, which, if
-   * the underlying X pixmap is already gone has the tendency to trigger
-   * X errors inside DRI. For safety, trap errors */
-  meta_error_trap_push (display);
-  if (background->texture != COGL_INVALID_HANDLE)
-    {
-      cogl_handle_unref (background->texture);
-      background->texture = COGL_INVALID_HANDLE;
-    }
-  meta_error_trap_pop (display);
-
-  if (texture != COGL_INVALID_HANDLE)
-    background->texture = cogl_handle_ref (texture);
-
-  background->texture_width = cogl_texture_get_width (background->texture);
-  background->texture_height = cogl_texture_get_height (background->texture);
-
-  for (l = background->actors; l; l = l->next)
-    set_texture_on_actor (l->data);
-
-  update_wrap_mode (background);
-}
-
-/* Sets our pipeline to paint with a 1x1 texture of the stage's background
- * color; doing this when we have no pixmap allows the application to turn
- * off painting the stage. There might be a performance benefit to
- * painting in this case with a solid color, but the normal solid color
- * case is a 1x1 root pixmap, so we'd have to reverse-engineer that to
- * actually pick up the (small?) performance win. This is just a fallback.
- */
-static void
-set_texture_to_stage_color (MetaScreenBackground *background)
-{
-  ClutterActor *stage = meta_get_stage_for_screen (background->screen);
-  ClutterColor color;
-  CoglHandle texture;
-
-  clutter_stage_get_color (CLUTTER_STAGE (stage), &color);
-
-  /* Slicing will prevent COGL from using hardware texturing for
-   * the tiled 1x1 pixmap, and will cause it to draw the window
-   * background in millions of separate 1x1 rectangles */
-  texture = meta_create_color_texture_4ub (color.red, color.green,
-                                           color.blue, 0xff,
-                                           COGL_TEXTURE_NO_SLICING);
-  set_texture (background, texture);
-  cogl_handle_unref (texture);
-}
-
 static void
 meta_background_actor_dispose (GObject *object)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (object);
-  MetaBackgroundActorPrivate *priv = self->priv;
 
   meta_background_actor_set_visible_region (self, NULL);
 
-  if (priv->background != NULL)
-    {
-      priv->background->actors = g_slist_remove (priv->background->actors, self);
-      priv->background = NULL;
-    }
-
-  g_clear_pointer(&priv->pipeline, cogl_object_unref);
-
   G_OBJECT_CLASS (meta_background_actor_parent_class)->dispose (object);
 }
 
@@ -260,11 +60,15 @@ meta_background_actor_get_preferred_width (ClutterActor *actor,
                                            gfloat       *min_width_p,
                                            gfloat       *natural_width_p)
 {
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (actor);
+  ClutterContent *content;
-  MetaBackgroundActorPrivate *priv = self->priv;
+  gfloat width;
-  int width, height;
 
-  meta_screen_get_size (priv->background->screen, &width, &height);
+  content = clutter_actor_get_content (actor);
+
+  if (content)
+    clutter_content_get_preferred_size (content, &width, NULL);
+  else
+    width = 0;
 
   if (min_width_p)
     *min_width_p = width;
@@ -279,11 +83,15 @@ meta_background_actor_get_preferred_height (ClutterActor *actor,
                                             gfloat       *natural_height_p)
 
 {
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (actor);
+  ClutterContent *content;
-  MetaBackgroundActorPrivate *priv = self->priv;
+  gfloat height;
-  int width, height;
 
-  meta_screen_get_size (priv->background->screen, &width, &height);
+  content = clutter_actor_get_content (actor);
+
+  if (content)
+    clutter_content_get_preferred_size (content, NULL, &height);
+  else
+    height = 0;
 
   if (min_height_p)
     *min_height_p = height;
@@ -291,64 +99,19 @@ meta_background_actor_get_preferred_height (ClutterActor *actor,
     *natural_height_p = height;
 }
 
-static void
-meta_background_actor_paint (ClutterActor *actor)
-{
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (actor);
-  MetaBackgroundActorPrivate *priv = self->priv;
-  guint8 opacity = clutter_actor_get_paint_opacity (actor);
-  guint8 color_component;
-  int width, height;
-
-  meta_screen_get_size (priv->background->screen, &width, &height);
-
-  color_component = (int)(0.5 + opacity * priv->dim_factor);
-
-  cogl_pipeline_set_color4ub (priv->pipeline,
-                              color_component,
-                              color_component,
-                              color_component,
-                              opacity);
-
-  cogl_set_source (priv->pipeline);
-
-  if (priv->visible_region)
-    {
-      int n_rectangles = cairo_region_num_rectangles (priv->visible_region);
-      int i;
-
-      for (i = 0; i < n_rectangles; i++)
-        {
-          cairo_rectangle_int_t rect;
-          cairo_region_get_rectangle (priv->visible_region, i, &rect);
-
-          cogl_rectangle_with_texture_coords (rect.x, rect.y,
-                                              rect.x + rect.width, rect.y + rect.height,
-                                              rect.x / priv->background->texture_width,
-                                              rect.y / priv->background->texture_height,
-                                              (rect.x + rect.width) / priv->background->texture_width,
-                                              (rect.y + rect.height) / priv->background->texture_height);
-        }
-    }
-  else
-    {
-      cogl_rectangle_with_texture_coords (0.0f, 0.0f,
-                                          width, height,
-                                          0.0f, 0.0f,
-                                          width / priv->background->texture_width,
-                                          height / priv->background->texture_height);
-    }
-}
-
 static gboolean
 meta_background_actor_get_paint_volume (ClutterActor       *actor,
                                         ClutterPaintVolume *volume)
 {
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (actor);
+  ClutterContent *content;
-  MetaBackgroundActorPrivate *priv = self->priv;
+  gfloat width, height;
-  int width, height;
 
-  meta_screen_get_size (priv->background->screen, &width, &height);
+  content = clutter_actor_get_content (actor);
+
+  if (!content)
+    return FALSE;
+
+  clutter_content_get_preferred_size (content, &width, &height);
 
   clutter_paint_volume_set_width (volume, width);
   clutter_paint_volume_set_height (volume, height);
@@ -356,215 +119,48 @@ meta_background_actor_get_paint_volume (ClutterActor       *actor,
   return TRUE;
 }
 
-static void
-meta_background_actor_set_dim_factor (MetaBackgroundActor *self,
-                                      gfloat               dim_factor)
-{
-  MetaBackgroundActorPrivate *priv = self->priv;
-
-  if (priv->dim_factor == dim_factor)
-    return;
-
-  priv->dim_factor = dim_factor;
-
-  clutter_actor_queue_redraw (CLUTTER_ACTOR (self));
-
-  g_object_notify_by_pspec (G_OBJECT (self), obj_props[PROP_DIM_FACTOR]);
-}
-
-static void
-meta_background_actor_get_property(GObject         *object,
-                                   guint            prop_id,
-                                   GValue          *value,
-                                   GParamSpec      *pspec)
-{
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (object);
-  MetaBackgroundActorPrivate *priv = self->priv;
-
-  switch (prop_id)
-    {
-    case PROP_DIM_FACTOR:
-      g_value_set_float (value, priv->dim_factor);
-      break;
-    default:
-      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
-      break;
-    }
-}
-
-static void
-meta_background_actor_set_property(GObject         *object,
-                                   guint            prop_id,
-                                   const GValue    *value,
-                                   GParamSpec      *pspec)
-{
-  MetaBackgroundActor *self = META_BACKGROUND_ACTOR (object);
-
-  switch (prop_id)
-    {
-    case PROP_DIM_FACTOR:
-      meta_background_actor_set_dim_factor (self, g_value_get_float (value));
-      break;
-    default:
-      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
-      break;
-    }
-}
-
 static void
 meta_background_actor_class_init (MetaBackgroundActorClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
   ClutterActorClass *actor_class = CLUTTER_ACTOR_CLASS (klass);
-  GParamSpec *pspec;
 
   g_type_class_add_private (klass, sizeof (MetaBackgroundActorPrivate));
 
   object_class->dispose = meta_background_actor_dispose;
-  object_class->get_property = meta_background_actor_get_property;
-  object_class->set_property = meta_background_actor_set_property;
 
   actor_class->get_preferred_width = meta_background_actor_get_preferred_width;
   actor_class->get_preferred_height = meta_background_actor_get_preferred_height;
-  actor_class->paint = meta_background_actor_paint;
   actor_class->get_paint_volume = meta_background_actor_get_paint_volume;
-
-  /**
-   * MetaBackgroundActor:dim-factor:
-   *
-   * Factor to dim the background by, between 0.0 (black) and 1.0 (original
-   * colors)
-   */
-  pspec = g_param_spec_float ("dim-factor",
-                              "Dim factor",
-                              "Factor to dim the background by",
-                              0.0, 1.0,
-                              1.0,
-                              G_PARAM_READWRITE);
-  obj_props[PROP_DIM_FACTOR] = pspec;
-  g_object_class_install_property (object_class, PROP_DIM_FACTOR, pspec);
 }
 
 static void
 meta_background_actor_init (MetaBackgroundActor *self)
 {
-  MetaBackgroundActorPrivate *priv;
+  self->priv = G_TYPE_INSTANCE_GET_PRIVATE (self,
-
+                                            META_TYPE_BACKGROUND_ACTOR,
-  priv = self->priv = G_TYPE_INSTANCE_GET_PRIVATE (self,
+                                            MetaBackgroundActorPrivate);
-                                                   META_TYPE_BACKGROUND_ACTOR,
-                                                   MetaBackgroundActorPrivate);
-  priv->dim_factor = 1.0;
 }
 
 /**
  * meta_background_actor_new:
- * @screen: the #MetaScreen
  *
- * Creates a new actor to draw the background for the given screen.
+ * Creates a new actor to draw the background for the given monitor.
+ * This actor should be associated with a #MetaBackground using
+ * clutter_actor_set_content()
  *
  * Return value: the newly created background actor
  */
 ClutterActor *
-meta_background_actor_new_for_screen (MetaScreen *screen)
+meta_background_actor_new (void)
 {
   MetaBackgroundActor *self;
-  MetaBackgroundActorPrivate *priv;
-
-  g_return_val_if_fail (META_IS_SCREEN (screen), NULL);
 
   self = g_object_new (META_TYPE_BACKGROUND_ACTOR, NULL);
-  priv = self->priv;
-
-  priv->background = meta_screen_background_get (screen);
-  priv->background->actors = g_slist_prepend (priv->background->actors, self);
-
-  /* A CoglMaterial and a CoglPipeline are the same thing */
-  priv->pipeline = (CoglPipeline*) meta_create_texture_material (NULL);
-
-  set_texture_on_actor (self);
-  update_wrap_mode_of_actor (self);
 
   return CLUTTER_ACTOR (self);
 }
 
-/**
- * meta_background_actor_update:
- * @screen: a #MetaScreen
- *
- * Refetches the _XROOTPMAP_ID property for the root window and updates
- * the contents of the background actor based on that. There's no attempt
- * to optimize out pixmap values that don't change (since a root pixmap
- * could be replaced by with another pixmap with the same ID under some
- * circumstances), so this should only be called when we actually receive
- * a PropertyNotify event for the property.
- */
-void
-meta_background_actor_update (MetaScreen *screen)
-{
-  MetaScreenBackground *background;
-  MetaDisplay *display;
-  MetaCompositor *compositor;
-  Atom type;
-  int format;
-  gulong nitems;
-  gulong bytes_after;
-  guchar *data;
-  Pixmap root_pixmap_id;
-
-  background = meta_screen_background_get (screen);
-  display = meta_screen_get_display (screen);
-  compositor = meta_display_get_compositor (display);
-
-  root_pixmap_id = None;
-  if (!XGetWindowProperty (meta_display_get_xdisplay (display),
-                           meta_screen_get_xroot (screen),
-                           compositor->atom_x_root_pixmap,
-                           0, LONG_MAX,
-                           False,
-                           AnyPropertyType,
-                           &type, &format, &nitems, &bytes_after, &data) &&
-      type != None)
-  {
-     /* Got a property. */
-     if (type == XA_PIXMAP && format == 32 && nitems == 1)
-       {
-         /* Was what we expected. */
-         root_pixmap_id = *(Pixmap *)data;
-       }
-
-     XFree(data);
-  }
-
-  if (root_pixmap_id != None)
-    {
-      CoglHandle texture;
-      CoglContext *ctx = clutter_backend_get_cogl_context (clutter_get_default_backend ());
-      GError *error = NULL;
-
-      meta_error_trap_push (display);
-      texture = cogl_texture_pixmap_x11_new (ctx, root_pixmap_id, FALSE, &error);
-      meta_error_trap_pop (display);
-
-      if (texture != COGL_INVALID_HANDLE)
-        {
-          set_texture (background, texture);
-          cogl_handle_unref (texture);
-
-          background->have_pixmap = True;
-          return;
-        }
-      else
-        {
-          g_warning ("Failed to create background texture from pixmap: %s",
-                     error->message);
-          g_error_free (error);
-        }
-    }
-
-  background->have_pixmap = False;
-  set_texture_to_stage_color (background);
-}
-
 /**
  * meta_background_actor_set_visible_region:
  * @self: a #MetaBackgroundActor
@@ -584,120 +180,44 @@ meta_background_actor_set_visible_region (MetaBackgroundActor *self,
 
   priv = self->priv;
 
-  if (priv->visible_region)
+  g_clear_pointer (&priv->visible_region,
-    {
+                   (GDestroyNotify)
-      cairo_region_destroy (priv->visible_region);
+                   cairo_region_destroy);
-      priv->visible_region = NULL;
-    }
 
   if (visible_region)
-    {
+    priv->visible_region = cairo_region_copy (visible_region);
-      cairo_rectangle_int_t screen_rect = { 0 };
-      meta_screen_get_size (priv->background->screen, &screen_rect.width, &screen_rect.height);
-
-      /* Doing the intersection here is probably unnecessary - MetaWindowGroup
-       * should never compute a visible area that's larger than the root screen!
-       * but it's not that expensive and adds some extra robustness.
-       */
-      priv->visible_region = cairo_region_create_rectangle (&screen_rect);
-      cairo_region_intersect (priv->visible_region, visible_region);
-    }
 }
 
 /**
- * meta_background_actor_screen_size_changed:
+ * meta_background_actor_get_visible_region:
- * @screen: a #MetaScreen
+ * @self: a #MetaBackgroundActor
  *
- * Called by the compositor when the size of the #MetaScreen changes
+ * Return value (transfer full): a #cairo_region_t that represents the part of
+ * the background not obscured by other #MetaBackgroundActor or
+ * #MetaWindowActor objects.
  */
-void
+cairo_region_t *
-meta_background_actor_screen_size_changed (MetaScreen *screen)
+meta_background_actor_get_visible_region (MetaBackgroundActor *self)
 {
-  MetaScreenBackground *background = meta_screen_background_get (screen);
+  MetaBackgroundActorPrivate *priv = self->priv;
-  GSList *l;
+  ClutterActorBox content_box;
+  cairo_rectangle_int_t content_area = { 0 };
+  cairo_region_t *visible_region;
 
-  update_wrap_mode (background);
+  g_return_val_if_fail (META_IS_BACKGROUND_ACTOR (self), NULL);
 
-  for (l = background->actors; l; l = l->next)
+  if (!priv->visible_region)
-    clutter_actor_queue_relayout (l->data);
+      return NULL;
+
+  clutter_actor_get_content_box (CLUTTER_ACTOR (self), &content_box);
+
+  content_area.x = content_box.x1;
+  content_area.y = content_box.y1;
+  content_area.width = content_box.x2 - content_box.x1;
+  content_area.height = content_box.y2 - content_box.y1;
+
+  visible_region = cairo_region_create_rectangle (&content_area);
+  cairo_region_intersect (visible_region, priv->visible_region);
+
+  return visible_region;
 }
-
-/**
- * meta_background_actor_add_glsl_snippet:
- * @actor: a #MetaBackgroundActor
- * @hook: where to insert the code
- * @declarations: GLSL declarations
- * @code: GLSL code
- * @is_replace: wheter Cogl code should be replaced by the custom shader
- *
- * Adds a GLSL snippet to the pipeline used for drawing the background.
- * See #CoglSnippet for details.
- */
-void
-meta_background_actor_add_glsl_snippet (MetaBackgroundActor *actor,
-                                        MetaSnippetHook      hook,
-                                        const char          *declarations,
-                                        const char          *code,
-                                        gboolean             is_replace)
-{
-  MetaBackgroundActorPrivate *priv;
-  CoglSnippet *snippet;
-
-  g_return_if_fail (META_IS_BACKGROUND_ACTOR (actor));
-
-  priv = actor->priv;
-
-  if (is_replace)
-    {
-      snippet = cogl_snippet_new (hook, declarations, NULL);
-      cogl_snippet_set_replace (snippet, code);
-    }
-  else
-    {
-      snippet = cogl_snippet_new (hook, declarations, code);
-    }
-
-  if (hook == META_SNIPPET_HOOK_VERTEX ||
-      hook == META_SNIPPET_HOOK_FRAGMENT)
-    cogl_pipeline_add_snippet (priv->pipeline, snippet);
-  else
-    cogl_pipeline_add_layer_snippet (priv->pipeline, 0, snippet);
-
-  cogl_object_unref (snippet);
-}
-
-/**
- * meta_background_actor_set_uniform_float:
- * @actor: a #MetaBackgroundActor
- * @uniform_name:
- * @n_components: number of components (for vector uniforms)
- * @count: number of uniforms (for array uniforms)
- * @uniform: (array length=uniform_length): the float values to set
- * @uniform_length: the length of @uniform. Must be exactly @n_components x @count,
- *                  and is provided mainly for language bindings.
- *
- * Sets a new GLSL uniform to the provided value. This is mostly
- * useful in congiunction with meta_background_actor_add_glsl_snippet().
- */
-
-void
-meta_background_actor_set_uniform_float (MetaBackgroundActor *actor,
-                                         const char          *uniform_name,
-                                         int                  n_components,
-                                         int                  count,
-                                         const float         *uniform,
-                                         int                  uniform_length)
-{
-  MetaBackgroundActorPrivate *priv;
-
-  g_return_if_fail (META_IS_BACKGROUND_ACTOR (actor));
-  g_return_if_fail (uniform_length == n_components * count);
-
-  priv = actor->priv;
-
-  cogl_pipeline_set_uniform_float (priv->pipeline,
-                                   cogl_pipeline_get_uniform_location (priv->pipeline,
-                                                                       uniform_name),
-                                   n_components, count, uniform);
-}
-

src/compositor/meta-background-group-private.h

@@ -0,0 +1,11 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+#ifndef META_BACKGROUND_GROUP_PRIVATE_H
+#define META_BACKGROUND_GROUP_PRIVATE_H
+
+#include <meta/screen.h>
+#include <meta/meta-background-group.h>
+
+void meta_background_group_set_visible_region  (MetaBackgroundGroup *self,
+                                                cairo_region_t      *visible_region);
+#endif /* META_BACKGROUND_GROUP_PRIVATE_H */

src/compositor/meta-background-group.c

@@ -0,0 +1,92 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+#include <config.h>
+
+#include "compositor-private.h"
+#include "clutter-utils.h"
+#include "meta-background-actor-private.h"
+#include "meta-background-group-private.h"
+
+G_DEFINE_TYPE (MetaBackgroundGroup, meta_background_group, CLUTTER_TYPE_GROUP);
+
+struct _MetaBackgroundGroupPrivate
+{
+  ClutterLayoutManager *layout_manager;
+};
+
+static void
+meta_background_group_dispose (GObject *object)
+{
+  G_OBJECT_CLASS (meta_background_group_parent_class)->dispose (object);
+}
+
+static void
+meta_background_group_class_init (MetaBackgroundGroupClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->dispose = meta_background_group_dispose;
+
+  g_type_class_add_private (klass, sizeof (MetaBackgroundGroupPrivate));
+}
+
+static void
+meta_background_group_init (MetaBackgroundGroup *self)
+{
+  self->priv = G_TYPE_INSTANCE_GET_PRIVATE (self,
+                                            META_TYPE_BACKGROUND_GROUP,
+                                            MetaBackgroundGroupPrivate);
+
+  self->priv->layout_manager = clutter_bin_layout_new (CLUTTER_BIN_ALIGNMENT_FIXED,
+                                                       CLUTTER_BIN_ALIGNMENT_FIXED);
+
+  clutter_actor_set_layout_manager (CLUTTER_ACTOR (self), self->priv->layout_manager);
+}
+
+/**
+ * meta_background_group_set_visible_region:
+ * @self: a #MetaBackgroundGroup
+ * @visible_region: (allow-none): the parts of the background to paint
+ *
+ * Sets the area of the backgrounds that is unobscured by overlapping windows.
+ * This is used to optimize and only paint the visible portions.
+ */
+void
+meta_background_group_set_visible_region (MetaBackgroundGroup *self,
+                                          cairo_region_t      *region)
+{
+  GList *children, *l;
+
+  children = clutter_actor_get_children (CLUTTER_ACTOR (self));
+  for (l = children; l; l = l->next)
+    {
+      ClutterActor *actor = l->data;
+
+      if (META_IS_BACKGROUND_ACTOR (actor))
+        {
+          meta_background_actor_set_visible_region (META_BACKGROUND_ACTOR (actor), region);
+        }
+      else if (META_IS_BACKGROUND_GROUP (actor))
+        {
+          int x, y;
+
+          if (!meta_actor_is_untransformed (actor, &x, &y))
+            continue;
+
+          cairo_region_translate (region, -x, -y);
+          meta_background_group_set_visible_region (META_BACKGROUND_GROUP (actor), region);
+          cairo_region_translate (region, x, y);
+        }
+    }
+  g_list_free (children);
+}
+
+ClutterActor *
+meta_background_group_new (void)
+{
+  MetaBackgroundGroup *background_group;
+
+  background_group = g_object_new (META_TYPE_BACKGROUND_GROUP, NULL);
+
+  return CLUTTER_ACTOR (background_group);
+}

src/compositor/meta-window-group.c

@@ -7,11 +7,12 @@
 
 #include <gdk/gdk.h> /* for gdk_rectangle_intersect() */
 
+#include "clutter-utils.h"
 #include "compositor-private.h"
 #include "meta-window-actor-private.h"
 #include "meta-window-group.h"
 #include "meta-background-actor-private.h"
-#include "clutter-utils.h"
+#include "meta-background-group-private.h"
 
 struct _MetaWindowGroupClass
 {
@@ -203,9 +204,10 @@ meta_window_group_paint (ClutterActor *actor)
           meta_window_actor_set_visible_region_beneath (window_actor, visible_region);
           cairo_region_translate (visible_region, x, y);
         }
-      else if (META_IS_BACKGROUND_ACTOR (l->data))
+      else if (META_IS_BACKGROUND_ACTOR (l->data) ||
+               META_IS_BACKGROUND_GROUP (l->data))
         {
-          MetaBackgroundActor *background_actor = l->data;
+          ClutterActor *background_actor = l->data;
           int x, y;
 
           if (!meta_actor_is_untransformed (CLUTTER_ACTOR (background_actor), &x, &y))
@@ -215,7 +217,11 @@ meta_window_group_paint (ClutterActor *actor)
           y += paint_y_offset;
 
           cairo_region_translate (visible_region, - x, - y);
-          meta_background_actor_set_visible_region (background_actor, visible_region);
+
+          if (META_IS_BACKGROUND_GROUP (background_actor))
+            meta_background_group_set_visible_region (META_BACKGROUND_GROUP (background_actor), visible_region);
+          else
+            meta_background_actor_set_visible_region (META_BACKGROUND_ACTOR (background_actor), visible_region);
           cairo_region_translate (visible_region, x, y);
         }
     }

src/meta/compositor-mutter.h

@@ -44,7 +44,6 @@ ClutterActor *meta_get_top_window_group_for_screen (MetaScreen *screen);
 void        meta_disable_unredirect_for_screen  (MetaScreen *screen);
 void        meta_enable_unredirect_for_screen   (MetaScreen *screen);
 
-ClutterActor *meta_get_background_actor_for_screen (MetaScreen *screen);
 void meta_set_stage_input_region     (MetaScreen    *screen,
                                       XserverRegion  region);
 void meta_empty_stage_input_region   (MetaScreen    *screen);

src/meta/meta-background-actor.h

@@ -24,9 +24,13 @@
 #define META_BACKGROUND_ACTOR_H
 
 #include <clutter/clutter.h>
+#include <cogl/cogl.h>
 
+#include <meta/gradient.h>
 #include <meta/screen.h>
 
+#include <gsettings-desktop-schemas/gdesktop-enums.h>
+
 /**
  * MetaBackgroundActor:
  *
@@ -60,41 +64,6 @@ struct _MetaBackgroundActor
 
 GType meta_background_actor_get_type (void);
 
-ClutterActor *meta_background_actor_new_for_screen (MetaScreen *screen);
+ClutterActor *meta_background_actor_new (void);
-
-/**
- * MetaSnippetHook:
- * Temporary hack to work around Cogl not exporting CoglSnippetHook in
- * the 1.0 API. Don't use.
- */
-typedef enum {
-  /* Per pipeline vertex hooks */
-  META_SNIPPET_HOOK_VERTEX = 0,
-  META_SNIPPET_HOOK_VERTEX_TRANSFORM,
-
-  /* Per pipeline fragment hooks */
-  META_SNIPPET_HOOK_FRAGMENT = 2048,
-
-  /* Per layer vertex hooks */
-  META_SNIPPET_HOOK_TEXTURE_COORD_TRANSFORM = 4096,
-
-  /* Per layer fragment hooks */
-  META_SNIPPET_HOOK_LAYER_FRAGMENT = 6144,
-  META_SNIPPET_HOOK_TEXTURE_LOOKUP
-} MetaSnippetHook;
-
-
-void meta_background_actor_add_glsl_snippet (MetaBackgroundActor *actor,
-                                             MetaSnippetHook      hook,
-                                             const char          *declarations,
-                                             const char          *code,
-                                             gboolean             is_replace);
-
-void meta_background_actor_set_uniform_float (MetaBackgroundActor *actor,
-                                              const char          *uniform_name,
-                                              int                  n_components,
-                                              int                  count,
-                                              const float         *uniform,
-                                              int                  uniform_length);
 
 #endif /* META_BACKGROUND_ACTOR_H */

src/meta/meta-background-group.h

@@ -0,0 +1,46 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+#ifndef META_BACKGROUND_GROUP_H
+#define META_BACKGROUND_GROUP_H
+
+#include <clutter/clutter.h>
+
+/**
+ * MetaBackgroundGroup:
+ *
+ * This class is a subclass of ClutterGroup with special handling for
+ * MetaBackgroundActor when painting the group. It makes sure to only
+ * draw the parts of the backgrounds not occluded by opaque windows.
+ *
+ * See #MetaWindowGroup for more information behind the motivation,
+ * and details on implementation.
+ */
+
+#define META_TYPE_BACKGROUND_GROUP            (meta_background_group_get_type ())
+#define META_BACKGROUND_GROUP(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), META_TYPE_BACKGROUND_GROUP, MetaBackgroundGroup))
+#define META_BACKGROUND_GROUP_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), META_TYPE_BACKGROUND_GROUP, MetaBackgroundGroupClass))
+#define META_IS_BACKGROUND_GROUP(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), META_TYPE_BACKGROUND_GROUP))
+#define META_IS_BACKGROUND_GROUP_CLASS(klass)  (G_TYPE_CHECK_CLASS_TYPE ((klass), META_TYPE_BACKGROUND_GROUP))
+#define META_BACKGROUND_GROUP_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), META_TYPE_BACKGROUND_GROUP, MetaBackgroundGroupClass))
+
+typedef struct _MetaBackgroundGroup        MetaBackgroundGroup;
+typedef struct _MetaBackgroundGroupClass   MetaBackgroundGroupClass;
+typedef struct _MetaBackgroundGroupPrivate MetaBackgroundGroupPrivate;
+
+struct _MetaBackgroundGroupClass
+{
+  ClutterGroupClass parent_class;
+};
+
+struct _MetaBackgroundGroup
+{
+  ClutterGroup parent;
+
+  MetaBackgroundGroupPrivate *priv;
+};
+
+GType meta_background_group_get_type (void);
+
+ClutterActor *meta_background_group_new (void);
+
+#endif /* META_BACKGROUND_GROUP_H */

src/meta/meta-background.h

@@ -0,0 +1,110 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+/*
+ * meta-background.h: CoglTexture for paintnig the system background
+ *
+ * Copyright 2013 Red Hat, Inc.
+ *
+ * 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 2 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#ifndef META_BACKGROUND_H
+#define META_BACKGROUND_H
+
+#include <cogl/cogl.h>
+#include <clutter/clutter.h>
+
+#include <meta/gradient.h>
+#include <meta/screen.h>
+
+#include <gsettings-desktop-schemas/gdesktop-enums.h>
+
+/**
+ * MetaBackground:
+ *
+ * This class handles loading a background from file, screenshot, or
+ * color scheme. The resulting object can be associated with one or
+ * more #MetaBackgroundActor objects to handle loading the background.
+ */
+
+#define META_TYPE_BACKGROUND            (meta_background_get_type ())
+#define META_BACKGROUND(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), META_TYPE_BACKGROUND, MetaBackground))
+#define META_BACKGROUND_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), META_TYPE_BACKGROUND, MetaBackgroundClass))
+#define META_IS_BACKGROUND(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), META_TYPE_BACKGROUND))
+#define META_IS_BACKGROUND_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), META_TYPE_BACKGROUND))
+#define META_BACKGROUND_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), META_TYPE_BACKGROUND, MetaBackgroundClass))
+
+typedef struct _MetaBackground        MetaBackground;
+typedef struct _MetaBackgroundClass   MetaBackgroundClass;
+typedef struct _MetaBackgroundPrivate MetaBackgroundPrivate;
+
+/**
+ * MetaBackgroundEffects:
+ * Which effects to enable on the background
+ */
+
+typedef enum
+{
+  META_BACKGROUND_EFFECTS_NONE       = 0,
+  META_BACKGROUND_EFFECTS_DESATURATE = 1 << 0,
+  META_BACKGROUND_EFFECTS_BLUR       = 1 << 1,
+  META_BACKGROUND_EFFECTS_VIGNETTE   = 1 << 2,
+} MetaBackgroundEffects;
+
+struct _MetaBackgroundClass
+{
+  GObjectClass parent_class;
+};
+
+struct _MetaBackground
+{
+  GObject parent;
+
+  MetaBackgroundPrivate *priv;
+};
+
+GType meta_background_get_type (void);
+
+MetaBackground *meta_background_new (MetaScreen           *screen,
+                                     int                   monitor,
+				     MetaBackgroundEffects effects);
+MetaBackground *meta_background_copy (MetaBackground        *self,
+                                      int                    monitor,
+				      MetaBackgroundEffects  effects);
+
+void meta_background_load_gradient (MetaBackground            *self,
+                                    GDesktopBackgroundShading  shading_direction,
+                                    ClutterColor              *color,
+                                    ClutterColor              *second_color);
+void meta_background_load_color (MetaBackground *self,
+                                 ClutterColor   *color);
+void meta_background_load_still_frame (MetaBackground *self);
+void meta_background_load_file_async (MetaBackground          *self,
+                                      const char              *filename,
+                                      GDesktopBackgroundStyle  style,
+                                      GCancellable            *cancellable,
+                                      GAsyncReadyCallback      callback,
+                                      gpointer                 user_data);
+gboolean meta_background_load_file_finish (MetaBackground       *self,
+                                           GAsyncResult         *result,
+                                           GError              **error);
+
+const char *meta_background_get_filename (MetaBackground *self);
+GDesktopBackgroundStyle meta_background_get_style (MetaBackground *self);
+GDesktopBackgroundShading meta_background_get_shading (MetaBackground *self);
+const ClutterColor *meta_background_get_color (MetaBackground *self);
+const ClutterColor *meta_background_get_second_color (MetaBackground *self);
+
+#endif /* META_BACKGROUND_H */