Re: Lilypond to Braille

[Keith OHara]

Maurits Lamers <maurits <at> weidestraat.nl> writes:

> I might be wrong, but I don't think creating a separate Braille context 
will work, as it would require the
> same music to be defined twice, one as normal music and one as Braille. 

I do not know what you mean by 'defining' the music, but I suspect you
can get two types of output with only 'defining' the music once.
music = \chordmode {c2:dim ges2:m}

<<\new ChordNames \music
   \new Staff \music >>

\new Staff \with { \consists Chord_name_engraver } 
  \transpose c aes,  \music

In any case, I suggested the second output only for the use by
sighted programmers to help debug the output.  You only really
need the text output.

> My main question here still is how this would work if both Braille and 
normal notation would be generated. If
> the Braille engravers "override" the normal engravers, how would this 
work exactly?
> 

In LilyPond added engravers do not replace the existing engravers,
but act in parallel to them.  Most engravers (and the midi performers)
are written in C++, but it is easier to make a quick example with
a Scheme engraver. 
I do not program in Scheme, but was able to copy from the
"scheme-engraver" regression test  
<http://lilypond.org/doc/v2.17/input/regression/0b/lily-86b85ffb.ly>
and the example "Defining an engraver in Scheme: ambitus engraver" 
<http://www.lilypond.org/doc/v2.17/Documentation/snippets/>
to make demonstration tha prints nubmers on stdout based on the
pitches that go to the Staff

\version "2.16.2"
\new Staff \with {
  \consists
  #(make-engraver
    (listeners
     ((note-event engraver event)
      (let* ((pitch (ly:event-property event 'pitch))
             (octave (ly:pitch-octave pitch))
             (notename (ly:pitch-notename pitch))
             (alteration (ly:pitch-alteration pitch))
             (a (ly:engraver-make-grob engraver 'TextScript event))
             (b (ly:engraver-make-grob engraver 'TextScript event)))
       (format #t "~a: ~a (~a)" octave notename alteration) (newline)
       (ly:grob-set-property! a 'font-size -4)
       (ly:grob-set-property! b 'direction UP)
       (ly:grob-set-property! b 'font-size -4)
       (ly:grob-set-property! a 'text (format #f "~a" pitch))
       (ly:grob-set-property! b 'text (format #f "~a:~a(~a)" 
                                       octave notename alteration))))))
} \transpose c ees \relative c' { c2 d( e f) g a( b c) }