Fix underline-markup to make multiple calls have nice output (issue 559150043 by address@hidden)

[thomasmorley65]

Reviewers: ,

Message:
Does this one need a convert-rule?

If so, I'd need some help. My python-skill is more or less zero.


Description:
Fix underline-markup to make multiple calls have nice output

Amend regtest markup-commands.ly with an example for it.

Please review this at https://codereview.appspot.com/559150043/

Affected files (+47, -9 lines):
  M input/regression/markup-commands.ly
  M scm/define-markup-commands.scm


Index: input/regression/markup-commands.ly
diff --git a/input/regression/markup-commands.ly  
b/input/regression/markup-commands.ly
index  
60d1f2f843f54a7077b24a05dd68e0cb6caffa3e..047a902759862abdfeabb1958bb3daf90eb87440  
100644
--- a/input/regression/markup-commands.ly
+++ b/input/regression/markup-commands.ly
@@ -32,6 +32,7 @@

         draw-line: \draw-line #'(5 . 3)
         \underline "underlined"
+        \underline \underline \underline "multiple underlines"
       }
     }
   }
Index: scm/define-markup-commands.scm
diff --git a/scm/define-markup-commands.scm b/scm/define-markup-commands.scm
index  
a4be8d9d82db190bb51c410075243cac47342d0e..0684c27c7e178e96faf833d597df4e67786a97af  
100644
--- a/scm/define-markup-commands.scm
+++ b/scm/define-markup-commands.scm
@@ -667,29 +667,66 @@ Create a beam with the specified parameters.
 (define-markup-command (underline layout props arg)
   (markup?)
   #:category font
-  #:properties ((thickness 1) (offset 2))
+  #:properties ((thickness 1) (underline-offset 2) (underline-distance 2))
   "
 @cindex underlining text

 Underline @var{arg}.  Looks at @code{thickness} to determine line
-thickness, and @code{offset} to determine line y-offset.
+thickness, @code{underline-offset} to determine line y-offset from  
@var{arg} and
+@code{underline-distance} to determine the distance of additional lines  
from the
+others.

 @lilypond[verbatim,quote]
 \\markup \\fill-line {
   \\underline \"underlined\"
-  \\override #'((offset . 5) (thickness . 1))
+  \\override #'(underline-offset . 5)
+  \\override #'(thickness . 1)
   \\underline \"underlined\"
-  \\override #'((offset . 1) (thickness . 5))
+  \\override #'(underline-offset . 1)
+  \\override #'(thickness . 5)
   \\underline \"underlined\"
+  \\override #'(underline-offset . 5)
+  \\override #'(underline-distance . 4)
+  \\underline \\underline \\underline \"multiple underlined\"
 }
 @end lilypond"
   (let* ((thick (ly:output-def-lookup layout 'line-thickness))
          (underline-thick (* thickness thick))
-         (m (interpret-markup layout props arg))
-         (x1 (car (ly:stencil-extent m X)))
-         (x2 (cdr (ly:stencil-extent m X)))
-         (y (* thick (- offset)))
-         (line (make-line-stencil underline-thick x1 y x2 y)))
+         (m (interpret-markup
+              layout
+              ;; For multiple calls of underline-markup, this will result  
in
+              ;; the innermost underline ending up lowest.
+              (prepend-alist-chain
+                'underline-offset
+                (+ underline-offset underline-distance)
+                props)
+              arg))
+         (arg-x-ext (ly:stencil-extent m X))
+         (x1 (car arg-x-ext))
+         (x2 (cdr arg-x-ext))
+         (y (* thick (- underline-offset)))
+         (raw-line-stil (make-line-stencil underline-thick x1 y x2 y))
+         (line
+           (ly:make-stencil
+             (ly:stencil-expr raw-line-stil)
+             ;; We use x-extent of the arg-stencil instead of the  
line-stencil
+             ;; to avoid increasing lines with multiple calls of underline.
+             ;; As a consequence the line sticks out a bit into the space
+             ;; between elements of continuing text, without affecting it.
+             ;; For huge values of thickness this may cause undesired  
output,
+             ;; we regard this a very rare case, though.
+             ;; Alternatively we could have shortened the underline by its
+             ;; thickness, i.e. raw-line-stil would have been:
+             ;;    (make-line-stencil
+             ;;      underline-thick
+             ;;      (+ x1 (/ underline-thick 2))
+             ;;      y
+             ;;      (- x2 (/ underline-thick 2))
+             ;;      y))
+             ;; without need to reset x-extent, this causes a different  
ugliness
+             ;; for huge thickness, though.
+             arg-x-ext
+             (ly:stencil-extent raw-line-stil Y))))
     (ly:stencil-add m line)))

 (define-markup-command (tie layout props arg)