Re: vertical spacing of footnotes

[Jean Abou Samra]

Le mardi 14 février 2023 à 13:02 +0100, Valentin Petzel a écrit :

As far as I see this is not the problem. Footnotes appear to be simply stacked
by extent, not by baseline. This already creates issues with footnotes
extending over multiple lines, as the spacing between different footnotes will
be less than the spacing between different lines of footnotes.

Meanwhile we could easily get an acceptable behaviour (I suppose) by changing
from a equal baseline distance model to a model that aligns baselines to some
grid, such as this:

fns = \markuplist {
  "Meter change."
  "Chord stem."
  "Bar line."
  \justify { Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut eget
ante venenatis mi consectetur ornare. Cras facilisis dictum venenatis. }
  "Key change."
}

\markup\column\fns

#(define (cumsum . x)
   (define (impl init a . b)
     (if (null? b)
         (list (+ init a))
         (cons (+ init a) (apply impl (cons (+ a init) b)))))
   (apply impl (cons 0 x)))

\markup\vspace #3

#(define-markup-command (column-to-grid layout props ml) (markup-list?)
   #:properties ((baseline-skip 3.5))
   (let* ((iml (interpret-markup-list layout props ml))
          (exts (map (lambda (s) (ly:stencil-extent s Y)) iml))
          (under-bl-exts (map car exts))
          (under-bl-grids (map (lambda (x) (* (1- (ceiling (/ x baseline-
skip))) baseline-skip)) under-bl-exts))
          (grid-points (cons 0 (apply cumsum under-bl-grids)))
          (moved-iml (map (lambda (stc amt) (ly:stencil-translate-axis stc amt
Y)) iml grid-points)))
     (display under-bl-exts)
     (apply ly:stencil-add moved-iml)))

\markup\column-to-grid\fns

\markup\vspace #3

\markup\override #'(baseline-skip . 2.5) \column-to-grid\fns

That is merely a heuristic. It will fail in a case like

\version "2.24.0"

#(define-markup-command (print-ext layout props arg) (markup?)
   (let ((stil (interpret-markup layout props arg)))
     (ly:message "~s" (ly:stencil-extent stil Y))
     stil))

fns = \markuplist {
  "Meter change."
  "Chord stem."
  "Bar line."
  \justify { #@(make-list 200 (list "IJKLM" "abcdefghij")) }
  "Key change."
}

#(define (cumsum . x)
   (define (impl init a . b)
     (if (null? b)
         (list (+ init a))
         (cons (+ init a)
               (apply impl
                      (+ a init)
                      b))))
   (apply impl 0 x))


#(define-markup-command (column-to-grid layout props ml) (markup-list?)
   #:properties ((baseline-skip 3.5))
   (let* ((iml (interpret-markup-list layout props ml))
          (exts (map (lambda (s) (ly:stencil-extent s Y)) iml))
          (under-bl-exts (map car exts))
          (under-bl-grids (map (lambda (x) (* (1- (ceiling (/ x baseline-skip))) baseline-skip)) under-bl-exts))
          (grid-points (cons 0 (apply cumsum under-bl-grids)))
          (moved-iml (map (lambda (stc amt) (ly:stencil-translate-axis stc amt Y)) iml grid-points)))
     (apply ly:stencil-add moved-iml)))


\markup\override #'(baseline-skip . 2.05) \column-to-grid\fns

because I sneakily inserted ascenders and descenders so that some of the lines need to be spaced apart by a tiny bit more than baseline-skip.

As an alternative to my "extra stencil data" idea, which was a bit hasty, one could conceivably let \footnote just accept a markup list and deal with it. Then it could use \column or whatever to achieve equal spacing of all lines.

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