Architecture for Fret Diagrams

[Han-Wen Nienhuys]

address@hidden writes:
> I've been studying and thinking about architectures for Fret Diagrams in
> lilypond.
> 
> It seems to me that there should be a FretDiagrams context which would
> process exactly the same music expression as the ChordNames context. 
> Then, a lead sheet with fret diagrams could look like:
> 
> \score {
>        <<
>          \new ChordNames \chords { chords }
>          \new FretDiagrams \chords { chords }
>          \notes the melody
>          \lyricsto "" \new Lyrics \lyrics { the text }
>        >>
>      }
> 
> 
> As far as the Fret_diagrams_engraver goes, I'm thinking that it could
> work as follows:  If there are no string events, then it could just do
> an alist lookup for the fret diagram, based on the chord name, which is
> available using the code from the Chord_name_engraver.  If there are
> string events, then it could create the fret diagram using the string
> (and possibly finger) events.
> 
> First, does this architecture seem reasonable?

I think that it is a good idea to make sure that you can feed
everything accepted by ChordNames to FretDiagrams as well.

I would not base anything on the chord name itself (ie. the output
string). Systems for chord names are highly non-standard, so they're
not a good basis to interpret.  I suppose that you would have to
devise some kind of lookup structure, and given a chord in standard
format, it looks up the standard fingerings for guitar.

It would even be cooler if there could be an automated system that
generates a suitable fingering for a chord, given the pitches of the
chord and the tuning of the strings. I suspect that that might not be
easy to keep track of limitations of the human hand, though.

> Second, where do I look to find out how a context is created?

See ly/engraver-init.ly

> Third, can I just call make-item, setting the "text" property to be a
> fret-diagram markup, much like the Chord_name_engraver does now?  If

Yes. You could copy Chord_name_engraver, but plug-in a different
Scheme function to go from chords to frets.

In any case, it would probably be a good idea if you would send the
first tries to the mailing list as patches.

-- 

 Han-Wen Nienhuys   |   address@hidden   |   http://www.xs4all.nl/~hanwen