Re: the custos: understanding how it works

[Jacques Menu]

Hello Leszek,

Here is an example from this list.

JM

\version "2.18.1"

\layout {

  indent = 0

  ragged-right = ##t

  \context {

    \Staff

    \consists "Custos_engraver"

    %      \override Staff.Custos.stencil = ##f

    %      \override Staff.Custos.style = ##f

  }

}

\relative c' {

  d1

  \once\override Staff.Custos.style = #ly:custos::print

  \break

  a'1

  \once\override Staff.Custos.stencil = ##f

  %\revert Staff.Custos.stencil

  %\revert Staff.Custos.style

  \break

  a'1

  \break

  g1

  \once\override Staff.Custos.style = #ly:custos::print

  \break

  f1

  \break

  e1

}

\relative c' {

  d1

  b1

  % \revert Staff.Custos.stencil

%  \revert Staff.Custos.style

  \once\override Staff.Custos.style = #ly:custos::print

%  \override Staff.Custos.style = #ly:custos::print

  \break

  a'1

%  \override Staff.Custos.stencil = ##f

  \once\override Staff.Custos.stencil = ##f

  \break

  f'1

  \break

  d1

  \once\override Staff.Custos.style = #ly:custos::print

  \break

  c1

  \break

  b1

}

Le 22 nov. 2015 à 16:41, Leszek Wroński <address@hidden> a écrit :

I was delighted to learn that Lilypond allows one to use custodes. I was wondering how they really work, namely, how one can, upon a linebreak, check what the next pitch is. I have limited Scheme experience. I first tried the code for the first example from here: http://www.lilypond.org/doc/v2.19/Documentation/notation/typesetting-mensural-music and enclosed it (that is, the part inside "\score { } ") in "\displayMusic{ }" . But this, while enlightening in some respects, didn't really tell me what's going on when the custos is to be displayed. So I downloaded the source code, and after grepping found two files of interest: custos.cc and custos-engraver.cc . In the latter I found an _expression_ headed by 

"void

 Custos_engraver::acknowledge_note_head (Grob_info info)"

(line 83). Could anyone tell me if I'm on the right track? My problem is that, while I'm willing to learn, I have a very limited experience with C++ and with any object programming whatsoever (having spent much time decades ago with Turbo Pascal 5 :-)). I'd be very grateful for any pointers regarding what happens during a linebreak (and, in general, how one should learn such things).

Best regards,

Leszek Wronski.

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