+/* Merge a face into a realized face.
+
+ F is frame where faces are (to be) realized.
+
+ FACE_NAME is named face to merge.
+
+ If FACE_NAME is nil, FACE_ID is face_id of realized face to merge.
+
+ If FACE_NAME is t, FACE_ID is lface_id of face to merge.
+
+ BASE_FACE_ID is realized face to merge into.
+
+ Return new face id.
+*/
+
+int
+merge_faces (f, face_name, face_id, base_face_id)
+ struct frame *f;
+ Lisp_Object face_name;
+ int face_id, base_face_id;
+{
+ Lisp_Object attrs[LFACE_VECTOR_SIZE];
+ struct face *base_face;
+
+ base_face = FACE_FROM_ID (f, base_face_id);
+ if (!base_face)
+ return base_face_id;
+
+ if (EQ (face_name, Qt))
+ {
+ if (face_id < 0 || face_id >= lface_id_to_name_size)
+ return base_face_id;
+ face_name = lface_id_to_name[face_id];
+ face_id = lookup_derived_face (f, face_name, 0, base_face_id, 1);
+ if (face_id >= 0)
+ return face_id;
+ return base_face_id;
+ }
+
+ /* Begin with attributes from the base face. */
+ bcopy (base_face->lface, attrs, sizeof attrs);
+
+ if (!NILP (face_name))
+ {
+ if (!merge_named_face (f, face_name, attrs, 0))
+ return base_face_id;
+ }
+ else
+ {
+ struct face *face;
+ if (face_id < 0)
+ return base_face_id;
+ face = FACE_FROM_ID (f, face_id);
+ if (!face)
+ return base_face_id;
+ merge_face_vectors (f, face->lface, attrs, 0);
+ }
+
+ /* Look up a realized face with the given face attributes,
+ or realize a new one for ASCII characters. */
+ return lookup_face (f, attrs, 0, NULL);
+}
+