triangle = \markup \super \stencil
#(make-path-stencil
  '(
     M 39.785 0 C 38.094 2.195 36.371 4.359 34.703 6.574 C 33.102 8.711 31.516
     10.863 29.914 13 C 19.465 27.895 10.035 43.543 2.32 60.035 C 1.535 61.746
     0.723 63.449 0 65.191 C 0.801 69.602 1.875 70.801 3.895 73.688 C 6.566
     73.574 9.234 73.438 11.906 73.324 C 30.047 71.973 48.133 69.355 65.777 64.875
     C 67.602 64.402 69.43 63.949 71.234 63.406 C 72.406 61.859 72.297 60.68
     72.41 59.129 C 72.52 57.578 71.02 54.824 70.359 53.391 C 55.18 22.57 45.98
     14.617 46.672 16.559 C 44.633 18.898 42.598 21.242 40.562 23.586 C 40.961
     24.035 41.359 24.48 41.758 24.926 C 43.074 26.418 44.426 27.879 45.719
     29.395 C 54.234 39.633 53.914 35.664 61.777 54.098 C 58.156 54.957 57.215
     55.277 53.102 56.02 C 42.434 57.898 24.094 64.602 13.281 65.07 C 11.961
     65.062 10.641 65.062 9.32 65.062 C 12.281 58.301 15.328 50.117 17.441 46.32
     C 22.746 36.871 28.938 27.957 35.426 19.293 C 37.207 17.148 38.953 14.98
     40.738 12.84 C 42.027 11.324 43.383 9.859 44.699 8.367 C 45.098 7.922 45.496
     7.477 45.895 7.031 C 43.859 4.688 41.82 2.344 39.785 0 Z
     ) 0 .02 -.02 #t)

percent = \markup \raise #2 \stencil
#(make-path-stencil
  '(
     M 45.133 46.078 C 40.949 48.348 26.625 51.18 30.766 44.602 C 36.566 35.387
     52.078 33.191 46.809 46.395 C 46.477 47.152 45.961 47.816 45.344 48.367
     C 44.676 49.004 43.949 49.605 43.414 50.367 C 42.059 52.379 40.699 54.391
     39.34 56.398 C 40.094 56.148 40.863 55.957 41.621 55.719 C 42.133 55.52
     42.535 55.133 42.98 54.824 C 43.289 54.586 43.621 54.379 43.91 54.117 C
     44.539 53.488 45.227 52.906 45.727 52.164 C 46.328 51.363 46.953 50.578
     47.484 49.727 C 48.031 48.906 48.605 48.105 49.059 47.23 C 50.18 45.121
     51.086 42.898 51.754 40.605 C 51.953 39.922 52.141 39.234 52.293 38.539
     C 52.438 37.477 52.691 36.414 52.625 35.336 C 52.57 33.902 52.23 32.438
     51.406 31.242 C 50.742 30.285 49.707 29.578 48.555 29.363 C 48.031 29.262
     47.496 29.211 46.969 29.125 C 46.008 29.172 45.031 29.125 44.086 29.332
     C 42.004 29.73 40 30.465 38.09 31.371 C 36.902 31.938 35.762 32.605 34.668
     33.328 C 33.828 33.867 32.98 34.426 32.352 35.211 C 30.16 37.777 28.34
     40.629 26.344 43.344 C 26.145 43.645 25.98 43.969 25.789 44.277 C 25.348
     45.023 24.918 45.781 24.617 46.598 C 23.988 48.207 23.594 49.953 23.789
     51.688 C 23.93 52.867 24.395 54.043 25.246 54.895 C 25.699 55.32 26.277
     55.562 26.781 55.914 C 27.688 55.98 28.594 56.133 29.504 56.027 C 31.684
     55.844 33.809 55.254 35.875 54.555 C 37.586 53.969 39.262 53.285 40.91
     52.543 C 42.316 50.391 43.727 48.234 45.133 46.082 Z
     M 3.457 27.496 C 4.676 35.602 12.906 36.191 15.035 32.555 C 17.246 28.777
     8.188 21.516 4.559 24.641 C 3.137 26.609 1.449 28.098 0 30.031 C 0.098
     29.617 0.184 29.199 0.355 28.789 C 0.48 28.453 0.668 28.148 0.855 27.855
     C 2.344 25.453 3.848 23.047 5.566 20.895 C 5.949 20.461 6.336 20.02 6.754
     19.652 C 8.043 18.48 9.449 17.742 10.789 17.387 C 11.191 17.273 11.586
     17.203 11.973 17.172 C 12.418 17.121 12.863 17.09 13.281 17.145 C 14.781
     17.293 16.156 17.848 17.305 18.781 C 17.781 19.168 18.203 19.641 18.555
     20.203 C 18.684 20.406 18.832 20.59 18.949 20.812 C 19.312 21.629 19.742
     22.398 19.914 23.395 C 20.055 24.141 20.082 24.965 20.035 25.816 C 19.969
     27.062 19.812 28.352 19.531 29.652 C 19.414 30.195 19.25 30.746 19.016
     31.281 C 18.902 31.547 18.797 31.82 18.684 32.09 C 18.031 33.18 17.41 34.297
     16.746 35.379 C 16 36.609 15.227 37.828 14.359 38.934 C 13.547 39.949 12.609
     40.734 11.664 41.344 C 10.902 41.84 10.129 42.242 9.359 42.621 C 8.609
     42.902 7.844 43.262 7.121 43.309 C 2.969 43.078 0.758 37.094 0.223 32.145
     C 1.301 30.594 2.379 29.047 3.457 27.496 Z
     M 21.875 46.32 C 27.18 36.871 33.371 27.957 39.859 19.293 C 41.641 17.148
     43.387 14.98 45.172 12.84 C 46.461 11.324 47.816 9.863 49.133 8.371 C 49.531
     7.922 49.93 7.477 50.328 7.031 C 48.293 4.688 46.254 2.344 44.219 0 C 42.527
     2.195 40.805 4.363 39.137 6.574 C 37.535 8.711 35.949 10.863 34.348 13
     C 23.895 27.895 14.465 43.543 6.754 60.035 C 5.965 61.746 5.156 63.449 4.434
     65.191 C 5.621 68.223 10.188 71.027 11.469 69.984 C 15.059 62.918 19.211
     51.109 21.875 46.32 Z
     ) 0 .03 -.03 #t)

#(define percent-repeated-chords
  (lambda (context)
   (let ((chord '()))
     `((acknowledgers
         (chord-name-interface .
           ,(lambda (engraver grob source-engraver)
             (if (equal? (ly:grob-property grob 'text) chord)
                 (ly:grob-set-property! grob 'text percent))
             (set! chord (ly:grob-property grob 'text)))))
        (finalize . ,(lambda (translator) (set! chord '())))))))


\layout {
  \context {
    \ChordNames
    \consists #percent-repeated-chords
    majorSevenSymbol = \triangle
  }
}

\chords { c1:maj7 q }