Re: Scheme help? snippet for movement page headers

[Shevek]

Here is a cleaner, updated version of the snippet. It now gives the stencil
the extent of the longest table of contents entry. Not ideal, but close
enough for practical use. Also added comments and cleaned up variable names.

\version "2.18.2"

#(define-markup-command (current-toc-section layout props)
   ()
   (ly:stencil-add (let* ((titles (map cddr (toc-items)))
                          (sorted-titles (stable-sort titles (lambda (item1
item2)
                                                               (<= (length
item1) (length item2)))))
                          (biggest-title (interpret-markup layout props
(caar sorted-titles)))
                          (x-extent (ly:stencil-extent biggest-title X))
                          (y-extent (ly:stencil-extent biggest-title Y))
                          )
                     (ly:make-stencil
                      `(delay-stencil-evaluation
                        ,(delay (ly:stencil-expr
                                 (let* ((table (ly:output-def-lookup layout
'label-page-table))
                                        (curr-page (chain-assoc-get
'page:page-number props))
                                        ;; TOC entries should be at the
beginning of sections/movements.
                                        ;; If a section starts mid-page, the
page header will show the new section.
                                        ;; To make it show the title
belonging to the first system of the page,
                                        ;; Change >= to <= and put TOC
entries at the END of sections.
                                        ;; That breaks the actual TOC,
however.
                                        (labels-up-to-curr (filter (lambda
(item) (>= curr-page (cdr item))) table))
                                        (most-recent-toc-page (apply max
(map cdr labels-up-to-curr)))
                                        ;; If there are multiple toc items
on the same page, behavior may be undefined.
                                        (most-recent-label (filter (lambda
(item) (eq? (cdr item) most-recent-toc-page)) labels-up-to-curr))
                                        (title-of-curr-label (cadr
(assoc-get (caar most-recent-label) (toc-items))))
                                        (curr-markup (interpret-markup
layout props
                                                       title-of-curr-label))
                                        ;; How do we get the true extent
outside of the delayed evaluation?
                                        ;    (x-ext (ly:stencil-extent
curr-markup X))
                                        ;    (y-ext (ly:stencil-extent
curr-markup Y))
                                        )
                                   ;    (set! x-extent x-ext)
                                   ;    (set! y-extent y-ext)
                                   curr-markup
                                   ))))
                      ;; Currently, we just use the extent of the longest
toc entry for all of them
                      x-extent
                      y-extent
                      ))
     ))

%% Uncomment below to test
% \paper {
%   evenHeaderMarkup = \markup \current-toc-section
%   oddHeaderMarkup = \markup { "foo" \current-toc-section "bar" }
% }
% 
% \score {
%   \new Staff {
%     \tocItem "Title 1"
%     s1
%     \pageBreak
%     s1
%     
%   }
% }
% 
% \score {
%   \new Staff {
%     \tocItem "Title 2 is long"
%     s1
%     \pageBreak
%     s1
%     
%   }
% }



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