Re: Changing Header Mid-Score

[Jean Abou Samra]

Le 09/12/2022 à 23:04, Kieren MacMillan a écrit :
> As far as I know:
> 1. a separate bookpart is required to change the properties that the titling 
> mechanism can read; and
> 2. a bookpart will always force a page break.
>
> Cue Jean providing code to contradict my claim in 3… 2… 1…  ;)


[Although 2.23 is the unstable release series, the stable
release 2.24 is going to come out of it very soon, so I
will stick with it.]


For a start, you can use \if \on-page #2 to print some
text only on page 2, so you could get along manually with

  \if \on-page #1 ...
  \if \on-page #2 ...
  ...


Doing that automatically is ... not exactly straightforward,
but possible too.


\version "2.23.82"

sceneMark = \tweak details.is-scene-mark ##t \textMark \etc

\layout {
  \context {
    \Score
    \consists
      #(lambda (context)
         (let ((scene-text ""))
           (make-engraver
            (acknowledgers
             ((text-mark-interface engraver grob source-engraver)
              (when (assq-ref (ly:grob-property grob 'details)
                              'is-scene-mark)
                (set! scene-text (ly:grob-property grob 'text)))))
            ((stop-translation-timestep engraver)
             (let ((col (ly:context-property context 
'currentCommandColumn)))
               (ly:grob-set-nested-property!
                col
                '(details scene-text)
                scene-text))))))
  }
}

#(define-markup-command (scene-text layout props gauge) (markup?)
   (let ((page-number (chain-assoc-get 'page:page-number props))
         (gauge-stil (interpret-markup layout props gauge)))
     (ly:make-stencil
      `(delay-stencil-evaluation
        ,(delay
          (ly:stencil-expr
           (interpret-markup
            layout
            props
            (hashv-ref (ly:output-def-lookup layout 
'page-number-scene-text-table)
                       page-number)))))
      (ly:stencil-extent gauge-stil X)
      (ly:stencil-extent gauge-stil Y))))

\paper {
  oddHeaderMarkup = \markup
  \fill-line {
    ""
    \unless \on-first-page-of-part \fontsize #2 \concat {
      \fromproperty #'header:title
      ": "
      %% The argument to \scene-text is used to approximate the dimensions
      %% of the final text.
      \scene-text "Act X, Scene X"
    }
    \if \should-print-page-number \fromproperty #'page:page-number-string
  }
  evenHeaderMarkup = \markup
  \fill-line {
    \if \should-print-page-number \fromproperty #'page:page-number-string
    \unless \on-first-page-of-part \fontsize #2 \concat {
      \fromproperty #'header:title
      ": "
      \scene-text "Act X, Scene X"
    }
    ""
  }
  #(use-modules (srfi srfi-1))
  page-post-process =
    #(lambda (paper pages)
       (for-each
        (lambda (page)
          (let* ((page-number (ly:prob-property page 'page-number))
                 (lines (ly:prob-property page 'lines))
                 (table (or (ly:output-def-lookup paper 
'page-number-scene-text-table #f)
                            (let ((table (make-hash-table)))
                              (ly:output-def-set-variable! paper 
'page-number-scene-text-table table)
                              table)))
                 (first-system
                  (any (lambda (line)
                         (ly:prob-property line 'system-grob #f))
                       lines))
                 (scene-text
                  (if first-system
                      (let ((first-column (ly:spanner-bound 
first-system LEFT)))
                        (assq-ref (ly:grob-property first-column 'details)
                                  'scene-text))
                      "")))
            (hashv-set! table page-number scene-text)))
        pages))
}


%%%%%%% EXAMPLE

\header {
  title = "Silly Opera"
}

{
  \sceneMark "Act I, Scene i"
  c'1 1 1
  \pageBreak
  c'1 1 1
  \pageBreak
  c'1 1 \sceneMark "Act I, Scene ii" 1
  \pageBreak
  c'1 1 1
}




Cheers,
Jean

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