%% http://lsr.di.unimi.it/LSR/Item?id=856

\paper { tagline = ##f }

%% see also lists.gnu.org/archive/html/lilypond-user/2013-12/msg00828.html
% by Paul Morris

% tonic-num: number of the tonic note 0-6, C=0, B=6
% acc-type: the accidental sign type, 1/2=sharp, -1/2=flat
% acc-count: the number and type of accidentals in the key signature
%                  values are: -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
%                  (negative = flats, positive = sharps)
% tonic-acc: #f if the tonic note is not sharp or flat, otherwise a pair
% maj-num: number of the tonic note 0-6, if the key sig were major
% mode-num: number of the mode 0-6
% txt-size: size of key name text
% padd: padding between key signature and key name
% mult: for correct resizing when the staff is resized

#(define Custom_key_engraver
   (make-engraver
    (acknowledgers
     ((key-signature-interface engraver grob source-engraver)
      ;; if key cancellation then do nothing,
      ;; else modify the key signature stencil
      (if (not (eq? 'KeyCancellation
                    (grob::name grob)))
          (let* ((context (ly:translator-context engraver))
                 (tonic-pitch (ly:context-property context 'tonic))
                 (tonic-num (ly:pitch-notename tonic-pitch))
                 (acc-list (ly:grob-property grob 'alteration-alist))

                 (acc-type (if (null? acc-list)
                               0 (cdr (list-ref acc-list 0))))

                 (acc-count (* (length acc-list)
                              (if (< acc-type 0) -1 1)))

                 (maj-num (case acc-count
                            ((0) 0)
                            ((1) 4) ((2) 1) ((3) 5) ((4) 2) ((5) 6) ((6) 3) ((7) 0)
                            ((-1) 3) ((-2) 6) ((-3) 2) ((-4) 5) ((-5) 1) ((-6) 4) ((-7) 0)))

                 (mode-num (modulo (- tonic-num maj-num) 7))
                 (key-letter (case tonic-num
                               ((0) "C" ) ((1) "D" ) ((2) "E" ) ((3) "F" )
                               ((4) "G" ) ((5) "A" ) ((6) "B" )))

                 (mult (magstep (ly:grob-property grob 'font-size 0.0)))

                 (txt-sharp #{ \markup {
                   \translate #(cons (* mult -0.3) (* mult 0.8))
                   \magnify #(* mult 0.9) \sharp
                   } #})

                 (txt-flat #{ \markup {
                   \translate #(cons (* mult -0.2) (* mult 0.4))
                   \magnify #(* mult 0.9) \flat
                   } #})

                 (tonic-acc (if (pair? (assq tonic-num acc-list))
                                (if (= acc-type 0.5) txt-sharp txt-flat)
                                ""))

                 (key-mode (case mode-num
                             ((0) "Major") ((1) "Dorian") ((2) "Phrygian") ((3) "Lydian")
                             ((4) "Mixolydian") ((5) "Minor") ((6) "Locrian")))

                 ;; F Major and D Minor each get extra padding
                 ;; so the name appears above the staff
                 (padd (if (= acc-count -1)
                           (+ 0.5 (* mult 1.2))
                           0.5))

                 (txt-size 0.7)
                 (key-name #{ \markup { #key-letter #tonic-acc #key-mode } #})
                 (key-name-scaled (ly:stencil-scale
                                   (grob-interpret-markup grob key-name)
                                   txt-size txt-size))

                 (key-sig-stencil (ly:key-signature-interface::print grob))
                 (grob-y-ext (ly:grob-property grob 'Y-extent)))

            ;; Names for C Major, A Minor, etc. have to be moved up above the staff
            ;; padd has no effect if there are no sharps or flats in the key signature
            (if (equal? grob-y-ext (cons +inf.0 -inf.0))
                (set! key-name-scaled
                      (ly:stencil-translate-axis key-name-scaled 3 Y)))

            (ly:grob-set-property! grob 'stencil
              (ly:stencil-combine-at-edge key-sig-stencil 1 1
                key-name-scaled padd))))))))

\layout {
  \context {
    \Staff
    \consists \Custom_key_engraver
  }
}

\markup \null % avoid clipped text

\new Staff \relative f'' {
  \key c \major
  c1
  \key a \minor
  a1
  \key a \major
  a1
  \key fis \minor
  fis1
  \key ees \major
  ees1
  \key c \minor
  c'1
  \key c \dorian
  c1
  \key c \phrygian
  c1
  \key c \lydian
  c1
  \key c \mixolydian
  c1
  \key c \locrian
  c1
}