[mutter] window/x11: Add function to convert the surface to client area

[Jonas Ådahl <jadahl src gnome org>]

commit be11525b28da70ff60eb40925127d187a3f50672
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Wed Feb 26 11:03:48 2020 +0100

    window/x11: Add function to convert the surface to client area
    
    Add a convenient function to get the client area rectangle from a given
    surface rectangle.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/1091

 src/x11/window-x11.c | 16 ++++++++++++++++
 src/x11/window-x11.h |  4 +++-
 2 files changed, 19 insertions(+), 1 deletion(-)
---
diff --git a/src/x11/window-x11.c b/src/x11/window-x11.c
index 2c745f4aa..49f7f1526 100644
--- a/src/x11/window-x11.c
+++ b/src/x11/window-x11.c
@@ -4092,3 +4092,19 @@ meta_window_x11_buffer_rect_to_frame_rect (MetaWindow    *window,
   frame_rect->width -= borders.invisible.left + borders.invisible.right;
   frame_rect->height -= borders.invisible.top + borders.invisible.bottom;
 }
+
+void
+meta_window_x11_surface_rect_to_client_rect (MetaWindow    *window,
+                                             MetaRectangle *surface_rect,
+                                             MetaRectangle *client_rect)
+{
+  MetaFrameBorders borders;
+
+  meta_frame_calc_borders (window->frame, &borders);
+
+  *client_rect = *surface_rect;
+  client_rect->x += borders.total.left;
+  client_rect->y += borders.total.top;
+  client_rect->width -= borders.total.left + borders.total.right;
+  client_rect->height -= borders.total.top + borders.total.bottom;
+}
diff --git a/src/x11/window-x11.h b/src/x11/window-x11.h
index 03c52c5ab..7f4f96f6c 100644
--- a/src/x11/window-x11.h
+++ b/src/x11/window-x11.h
@@ -92,5 +92,7 @@ gboolean meta_window_x11_always_update_shape     (MetaWindow *window);
 void meta_window_x11_buffer_rect_to_frame_rect   (MetaWindow    *window,
                                                   MetaRectangle *buffer_rect,
                                                   MetaRectangle *frame_rect);
-
+void meta_window_x11_surface_rect_to_client_rect (MetaWindow    *window,
+                                                  MetaRectangle *surface_rect,
+                                                  MetaRectangle *client_rect);
 #endif