1 files changed, 8 insertions, 0 deletions
diff --git a/src/font.h b/src/font.h
index 1a09df2558c..798676d546e 100644
--- a/src/font.h
+++ b/src/font.h
@@ -689,6 +689,14 @@ struct font_driver
 				   int c, unsigned variations[256]));
 
   void (*filter_properties) P_ ((Lisp_Object font, Lisp_Object properties));
+
+  /* Optional.
+
+     Return non-zero if FONT_OBJECT can be used as a (cached) font
+     for ENTITY on frame F.  */
+  int (*cached_font_ok) P_ ((struct frame *f,
+                             Lisp_Object font_object,
+                             Lisp_Object entity));
 };