Add ability to override workspace layout

A plugin that does workspace management on its on may want to set the
workspace layout without having to deal with putting a property
on the root window to be read back and parsed.

Add meta_screen_override_window_layout() that allows the same types
of layouts as _NET_DESKTOP_LAYOUT but without setting a property.

https://bugzilla.gnome.org/show_bug.cgi?id=640552

src/core/screen-private.h

@@ -50,14 +50,6 @@ struct _MetaMonitorInfo
 typedef void (* MetaScreenWindowFunc) (MetaScreen *screen, MetaWindow *window,
                                        gpointer user_data);
 
-typedef enum
-{
-  META_SCREEN_TOPLEFT,
-  META_SCREEN_TOPRIGHT,
-  META_SCREEN_BOTTOMLEFT,
-  META_SCREEN_BOTTOMRIGHT
-} MetaScreenCorner;
-
 typedef enum
 {
   META_SCREEN_UP,
@@ -127,6 +119,7 @@ struct _MetaScreen
   int columns_of_workspaces;
   MetaScreenCorner starting_corner;
   guint vertical_workspaces : 1;
+  guint workspace_layout_overridden : 1;
   
   guint keys_grabbed : 1;
   guint all_keys_grabbed : 1;

src/core/screen.c

@@ -2164,6 +2164,9 @@ meta_screen_update_workspace_layout (MetaScreen *screen)
   gulong *list;
   int n_items;
 
+  if (screen->workspace_layout_overridden)
+    return;
+  
   list = NULL;
   n_items = 0;
 
@@ -2249,6 +2252,43 @@ meta_screen_update_workspace_layout (MetaScreen *screen)
                 screen->starting_corner);
 }
 
+/**
+ * meta_screen_override_workspace_layout:
+ * @screen: a #MetaScreen
+ * @starting_corner: the corner at which the first workspace is found
+ * @vertical_layout: if %TRUE the workspaces are laid out in columns rather than rows
+ * @n_rows: number of rows of workspaces, or -1 to determine the number of rows from
+ *   @n_columns and the total number of workspaces
+ * @n_columns: number of columns of workspaces, or -1 to determine the number of columns from
+ *   @n_rows and the total number of workspaces
+ *
+ * Explicitly set the layout of workspaces. Once this has been called, the contents of the
+ * _NET_DESKTOP_LAYOUT property on the root window are completely ignored.
+ */
+void
+meta_screen_override_workspace_layout (MetaScreen      *screen,
+                                       MetaScreenCorner starting_corner,
+                                       gboolean         vertical_layout,
+                                       int              n_rows,
+                                       int              n_columns)
+{
+  g_return_if_fail (META_IS_SCREEN (screen));
+  g_return_if_fail (n_rows > 0 || n_columns > 0);
+  g_return_if_fail (n_rows != 0 && n_columns != 0);
+
+  screen->workspace_layout_overridden = TRUE;
+  screen->vertical_workspaces = vertical_layout != FALSE;
+  screen->starting_corner = starting_corner;
+  screen->rows_of_workspaces = n_rows;
+  screen->columns_of_workspaces = n_columns;
+
+  /* In theory we should remove _NET_DESKTOP_LAYOUT from _NET_SUPPORTED at this
+   * point, but it's unlikely that anybody checks that, and it's unlikely that
+   * anybody who checks that handles changes, so we'd probably just create
+   * a race condition. And it's hard to implement with the code in set_supported_hint()
+   */
+}
+
 static void
 set_workspace_names (MetaScreen *screen)
 {

src/include/screen.h

@@ -80,4 +80,17 @@ void meta_screen_get_monitor_geometry (MetaScreen    *screen,
                                        int            monitor,
                                        MetaRectangle *geometry);
 
+typedef enum
+{
+  META_SCREEN_TOPLEFT,
+  META_SCREEN_TOPRIGHT,
+  META_SCREEN_BOTTOMLEFT,
+  META_SCREEN_BOTTOMRIGHT
+} MetaScreenCorner;
+
+void meta_screen_override_workspace_layout (MetaScreen      *screen,
+                                            MetaScreenCorner starting_corner,
+                                            gboolean         vertical_layout,
+                                            int              n_rows,
+                                            int              n_columns);
 #endif