Implement wave-style variant of underlining.

  * doc/lispref/display.texi: Document new face attribute.
  * lisp/cus-face.el (custom-face-attributes): Add wave-style underline
  attribute.
  * lisp/faces.el (set-face-attribute): Update docstring.
  * src/dispextern.h (face_underline_type): New enum.
  (face): Add field for underline type.
  * src/nsterm.m (ns_draw_underwave): New function.
  (ns_draw_text_decoration): Use it.
  * src/w32term.c (w32_restore_glyph_string_clip, w32_draw_underwave):
  New functions.
  (x_draw_glyph_string): Use them.
  * src/xfaces.c (Qline, Qwave): New Lisp objects.
  (check_lface_attrs, merge_face_ref)
  (Finternal_set_lisp_face_attribute, realize_x_face): Handle
  wave-style underline face attributes.
  * src/xterm.c (x_draw_underwave): New function.
  (x_draw_glyph_string): Use it.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 6e070f3dbe..fc7bec97f7 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -1510,6 +1510,13 @@ enum face_box_type
   FACE_SUNKEN_BOX
 };
 
+/* Underline type. */
+
+enum face_underline_type
+{
+  FACE_UNDER_LINE,
+  FACE_UNDER_WAVE
+};
 
 /* Structure describing a realized face.
 
@@ -1585,6 +1592,9 @@ struct face
      drawing shadows.  */
   unsigned use_box_color_for_shadows_p : 1;
 
+  /* Style of underlining. */
+  enum face_underline_type underline_type;
+
   /* Non-zero if text in this face should be underlined, overlined,
      strike-through or have a box drawn around it.  */
   unsigned underline_p : 1;