Re: intercepting implicit/explicit page breaks

[Thomas Morley]

2016-09-04 16:31 GMT+02:00 Knut Petersen <address@hidden>:
> Hi everybody!
>
> I use
>
> #(define (display-breaks grob)
>    (if (and (grob::has-interface grob 'paper-column-interface)
>             (eq? #t (ly:grob-property grob 'non-musical)))
>        (if (eq? 1 (ly:item-break-dir grob))
>            (let* ((moment (ly:grob-property grob 'when))(m moment)
>                   (bar (ly:grob-property grob 'rhythmic-location))(b (car
> bar)))
>                  (format out "~a new system at bar ~a~%" (format-moment m)
> b)
>              ))
>        (ly:message "Need NonMusicalPaperColumn grob to determine line
> breaks.")))
>
> activated by
>
>      \override NonMusicalPaperColumn #'after-line-breaking = #display-breaks
>
> That reliably gives the moment and bar number of an implicit or explicit
> break,
> but I also need to know if this break is a PAGE break.
>
> I assume the information is not available at the time of the callback used
> above, but
> that isn't a problem as it would be used by a script after lilypond has
> finished.
>
> Any idea where/when to get that information from lilypond?
>
> thx,
>  Knut
>



I once made:

#(define* (print-pages-first-bar-numbers layout pages #:optional print-to-file)
;; If `print-to-file' is set #t the output is written to a file
;; otherwise usually displayed in Terminal
  (let* ((lines (map (lambda (page) (ly:prob-property page 'lines)) pages))
         ;; list of systems of each pages
         (sys
           (map
             (lambda (line)
               (append-map
                 (lambda (l)
                   (let ((system-grob (ly:prob-property l 'system-grob)))
                     (if (not (null? system-grob))
                         (list system-grob)
                         system-grob))
                   )
                 line))
             lines))
         ;; list of rhythmic-locations of first sys
         ;; returning a BarNumber and a moment, the moment is usually zero
         (sys-rhythmic-location
           (map
             (lambda (s)
               (if (and (not (null? s)) (ly:grob? (car s)))
                   (grob::rhythmic-location (car s))
                   #f))
             sys))
         (start-bar-numbers
           (map
             (lambda (r-l)
               (if (pair? r-l)
                   (car r-l)
                   #f))
               sys-rhythmic-location))
         (formatted-output
           (map
             (lambda (page b-nr)
               (if b-nr
                   (format #f "page ~a starts with BarNumber ~a\n" page b-nr)
                   (format #f "page ~a contains no music\n" page))
                   )
             (iota (length pages) 1 1)
             start-bar-numbers)))
    (if (not (null? start-bar-numbers))
        (if print-to-file
            (let* ((output-name (ly:parser-output-name))
                   (outfilename (format "~a-page-first-bars.log" output-name))
                   (outfile (open-output-file outfilename)))
              (if (output-port? outfile)
                  (begin
                    (format #t "\n\tprinting to ~a" outfilename)
                    (for-each
                      (lambda (i) (display i outfile))
                      formatted-output))
                  (ly:warning
                    (_ "Unable to open output file ~a to print the information")
                    outfilename))
              (close-output-port outfile))
            (for-each display formatted-output)))))

\paper {
  #(define (page-post-process layout pages)
    (print-pages-first-bar-numbers layout pages #f))
}


{ c''1 \break d'' \pageBreak e'' }


Intended was to get the first BarNumber of every page, you may extend
it to get BarNumbers at line-break.
If you don't need to rely on the info of your initial code in order to
base some other action on it, post-processing sounds preferable to me.

Cheers,
  Harm