Clarify comment

diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 211d672434ac0e9ed20f90e063ea79bb3a78a268..eaca78100ff1a1ba63e13b49dbb0e88a216326fe 100644 (file)
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -2981,8 +2981,8 @@ append_move_region (GdkWindowObject *impl_window,
     }
 }
 
-/* Moves bits and update area by dx/dy in impl window,
-   takes ownership of region */
+/* Moves bits and update area by dx/dy in impl window.
+   Takes ownership of region to avoid copy (because we may change it) */
 static void
 move_region_on_impl (GdkWindowObject *private,
                     GdkRegion *region, /* In impl window coords */