Re: Intervalic Chord Names

[Aaron Hill]

On 2018-08-29 10:25, Tom Swan wrote:
> continued reply... Re: accidentals, yes that will be necessary. Do you
> have an idea about how to go about that?

Hi Tom,

Building upon the code from scm/chord-name.scm (and related files) as 
well as (LSR #750)[1], here is a more complete version of the 
interval-based chord root namer:

[1]:http://lsr.di.unimi.it/LSR/Item?id=750

```lilypond
    \version "2.18.2"

    #(define (intervalic-namer pitch lowercase?)
      (let ((handle-case (if lowercase? string-downcase (lambda (x) x)))
            (alt (ly:pitch-alteration pitch)))
        (make-line-markup (list
          (make-simple-markup (handle-case
            (vector-ref #("I" "II" "III" "IV" "V" "VI" "VII")
              (ly:pitch-notename pitch))))
          (if (= 0 alt) empty-markup
            (alteration->text-accidental-markup alt))))))

    #(define (intervalic-namer-custom-alts pitch lowercase?)
      (let ((handle-case (if lowercase? string-downcase (lambda (x) x)))
            (alt (ly:pitch-alteration pitch))
            (custom-alts `((,FLAT . "b") (,SHARP . "#"))))
        (make-line-markup (list
          (make-simple-markup (handle-case
            (vector-ref #("I" "II" "III" "IV" "V" "VI" "VII")
              (ly:pitch-notename pitch))))
          (if (= 0 alt) empty-markup
            (make-small-markup (make-raise-markup 0.7 (make-text-markup
              (ly:assoc-get alt custom-alts "?")))))))))

    theChords = \chordmode { c8 d/fis e:m7 f:maj7 g:7 a:m bes:sus4 b:dim 
}
    \score { << \new ChordNames \chordmode {
      \omit Score.BarNumber
      \override Score.RehearsalMark.self-alignment-X = #-1
      \mark "Default naming"
      \theChords \break
      \mark "Interval-based naming"
      \set chordRootNamer = #intervalic-namer
      \theChords \break
      \mark "Lowercase minor"
      \set chordNameLowercaseMinor = ##t
      \theChords \break
      \mark "Custom alterations"
      \set chordRootNamer = #intervalic-namer-custom-alts
      \theChords
    } >> \layout { indent = 0 } }
```

The above namer comes in two flavors, depending on whether you prefer 
the normal glyphs for alterations or if you want to customize the 
symbols.

The one thing this does not handle is ensuring the tonic of the current 
key signature appears as "I".  To do that appears to require more work 
as `chordRootNamer` does not provide access to the context in order to 
query for the current key.  I believe you might need to go down the 
route of a custom engraver.  If you search on this mailing list, there 
has been prior discussion about supporting the Nashville numbering 
system (which admittedly is much more than just interval-based naming).  
But in that thread, there is a lot of potentially relevant material to 
this topic, such as getting the key signature information into the 
ChordNames context.

-- Aaron Hill