Fix identification of CSD windows when checking whether to force fullscreen

We try to exempt CSD windows from being forced fullscreen if they are
undecorated and the size of the screen; however, we also catch almost
all windows that *do* need to be forced fullscreen in this check, since
they also have decorations turned off.

Identify actual CSD windows by checking whether _GTK_FRAME_EXTENTS is set -
GTK+ will always set this on CSD windows even if they have no invisible
borders or shadows at the current time.

https://bugzilla.gnome.org/show_bug.cgi?id=723029

3 files changed, 20 insertions, 1 deletions

diff --git a/src/core/constraints.c b/src/core/constraints.c
index 0dc93cb0..a937f053 100644
--- a/src/core/constraints.c
+++ b/src/core/constraints.c
@@ -438,7 +438,7 @@ setup_constraint_info (ConstraintInfo      *info,
    * workarea smaller than the monitor.
    */
   if (meta_prefs_get_force_fullscreen() &&
-      window->decorated &&
+      (window->decorated || !meta_window_is_client_decorated (window)) &&
       meta_rectangle_equal (new, &xinerama_info->rect) &&
       window->has_fullscreen_func &&
       !window->fullscreen)
diff --git a/src/core/window-private.h b/src/core/window-private.h
index a98cee36..2eb8ae62 100644
--- a/src/core/window-private.h
+++ b/src/core/window-private.h
@@ -660,5 +660,6 @@ void meta_window_unset_demands_attention (MetaWindow *window);
 void meta_window_update_icon_now (MetaWindow *window);
 
 gboolean meta_window_can_tile_side_by_side (MetaWindow *window);
+gboolean meta_window_is_client_decorated (MetaWindow *window);
 
 #endif
diff --git a/src/core/window.c b/src/core/window.c
index 74994bd9..8e4345d2 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -8474,3 +8474,21 @@ meta_window_is_maximized (MetaWindow *window)
 {
   return META_WINDOW_MAXIMIZED (window);
 }
+
+/**
+ * meta_window_is_client_decorated:
+ *
+ * Check if if the window has decorations drawn by the client.
+ * (window->decorated refers only to whether we should add decorations)
+ */
+gboolean
+meta_window_is_client_decorated (MetaWindow *window)
+{
+  /* Currently the implementation here is hackish -
+   * has_custom_frame_extents() is set if _GTK_FRAME_EXTENTS is set
+   * to any value even 0. GTK+ always sets _GTK_FRAME_EXTENTS for
+   * client-side-decorated window, even if the value is 0 because
+   * the window is maxized and has no invisible borders or shadows.
+   */
+  return window->has_custom_frame_extents;
+}