Editing Separating footers with a horizontal line

Separating footers from the main content of the page using a horizontal line can be done by altering the <code>oddFooterMarkup</code> paper variable (and <code>evenFooterMarkup</code>, if they should be different). However, this requires printing the horizontal line only if any footer is shown on that page; this snippet demonstrates how to program such a condition.

<lilypond version="2.24" full>
#(define (separator-condition layout props arg)
   ;; only print `arg' if copyright and/or tagline is printed on that page
   (if (or (and (chain-assoc-get 'header:copyright props)
                ;; on-first-page-of-part copied from ly/titling-init.ly
                (= (chain-assoc-get 'page:page-number props -1)
                   (ly:output-def-lookup layout 'first-page-number)))
           (and (chain-assoc-get 'header:tagline props)
                ;; on-last-page (two following conditions)
                (chain-assoc-get 'page:is-bookpart-last-page props #f)
                (chain-assoc-get 'page:is-last-bookpart props #f)))
       (interpret-markup layout props arg)
       empty-stencil))

\header {
  tagline = "Special tagline"
}

\paper {
  #(set-paper-size "a9landscape")
  oddFooterMarkup = \markup \center-column {
    \on-the-fly \separator-condition \with-color #grey \override #'(span-factor . 1/3) \draw-hline
    %% Copyright header field only on first page in each bookpart.
    \if \on-first-page-of-part \fill-line {
      \fromproperty #'header:copyright
    }
    %% Tagline only on last page in each book.
    \if \on-last-page \fill-line {
      \fromproperty #'header:tagline
    }
  }
}

\bookpart {
  \markup "(Public Domain content)"
}
\bookpart {
  \header { copyright = "©" }
  \markup "(Copyright content)"
  \pageBreak
  \markup \column { "(no Copyright statement""on subsequent page)" }
}
\bookpart {
  \markup "(final page with tagline)"
}
</lilypond>

[[Category:Non-music]]
[[Category:Paper and layout]]
[[Category:Stylesheet]]
[[Category:Titles]]