core: Preserve focus across decoration changes

Changes in window decoration result in the window being reparented
in and out its frame. This in turn causes unmap/map events, and
XI_FocusOut if the window happened to be focused.

In order to preserve the focused window across the decoration change,
add a flag so that the focus may be restored on MapNotify.

Closes: #273

src/core/frame.c

@@ -109,6 +109,12 @@ meta_window_ensure_frame (MetaWindow *window)
   /* FIXME handle this error */
   meta_x11_error_trap_pop (x11_display);
 
+  /* Ensure focus is restored after the unmap/map events triggered
+   * by XReparentWindow().
+   */
+  if (meta_window_has_focus (window))
+    window->restore_focus_on_map = TRUE;
+
   /* stick frame to the window */
   window->frame = frame;
 
@@ -201,6 +207,12 @@ meta_window_destroy_frame (MetaWindow *window)
 
   meta_ui_frame_unmanage (frame->ui_frame);
 
+  /* Ensure focus is restored after the unmap/map events triggered
+   * by XReparentWindow().
+   */
+  if (meta_window_has_focus (window))
+    window->restore_focus_on_map = TRUE;
+
   meta_x11_display_unregister_x_window (x11_display, frame->xwindow);
 
   window->frame = NULL;

src/core/window-private.h

@@ -415,6 +415,9 @@ struct _MetaWindow
   /* whether or not the window is from a program running on another machine */
   guint is_remote : 1;
 
+  /* whether focus should be restored on map */
+  guint restore_focus_on_map : 1;
+
   /* if non-NULL, the bounds of the window frame */
   cairo_region_t *frame_bounds;
 

src/core/window.c

@@ -4653,6 +4653,9 @@ meta_window_focus (MetaWindow  *window,
 
   g_return_if_fail (!window->override_redirect);
 
+  /* This is a oneshot flag */
+  window->restore_focus_on_map = FALSE;
+
   meta_topic (META_DEBUG_FOCUS,
               "Setting input focus to window %s, input: %d take_focus: %d\n",
               window->desc, window->input, window->take_focus);

src/x11/events.c

@@ -1374,6 +1374,12 @@ handle_other_xevent (MetaX11Display *x11_display,
           window = meta_window_x11_new (display, event->xmap.window,
                                         FALSE, META_COMP_EFFECT_CREATE);
         }
+      else if (window && window->restore_focus_on_map)
+        {
+          meta_window_focus (window,
+                             meta_display_get_current_time_roundtrip (display));
+        }
+
       break;
     case MapRequest:
       if (window == NULL)