[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: custom engraver in scheme: accessing nested Music object

From: Reinhold Kainhofer
Subject: Re: custom engraver in scheme: accessing nested Music object
Date: Wed, 10 Aug 2011 17:38:21 +0200
User-agent: KMail/1.13.6 (Linux/2.6.38-11-generic; KDE/4.7.0; i686; ; )

Am Mittwoch, 10. August 2011, 17:11:44 schrieb Ricardo Wurmus:
> On Aug 10, Neil Puttock wrote:
> > BTW, if you're prepared to wrap the notes in a chord (so you have
> > access to 'articulations), you won't even need a scheme engraver (all
> > the processing can take place in the NoteHead's stencil callback).
> It should be a generic engraver, so I cannot assume that notes will
> always be wrapped in a chord. I'll play around with defining a function
> for process-acknowledged and see where it leads me.

One detail that might be interesting for you is that you can define engraver-
wide variables by wrapping the whole engraver in a (let (..) ...) block.
See e.g. the scheme engraver instance regtest (input/regression/scheme- in the source code tree):

\header {

  texidoc = "Scheme engravers may be instantiated, with
  instance-scoped slots, by defining a 1 argument procedure which
  shall return the engraver definition as an alist, with the private
  slots defined in a closure.  The argument procedure argument is the
  context where the engraver is instantiated."


\version "2.14.0"

\layout {
  \context {
    #(let ((instance-counter 0))
       (lambda (context)
         (set! instance-counter (1+ instance-counter))
         (let ((instance-id instance-counter)
               (private-note-counter 0))
               . ,(lambda (engraver event)
                    (set! private-note-counter (1+ private-note-counter))
                    (let ((text (ly:engraver-make-grob engraver 'TextScript 
                      (ly:grob-set-property! text 'text
                                             (format #f "~a.~a" instance-id

  \relative c'' { c4 d e f }
  \\ \relative c' { c4 d e f }

In this example, instance-counter is a global variable, which is reused by 
every voice, while instance-id and private-note-counter are variables that are 
separate for each voice. In this example, instance-id stores the number of the 
voice, while private-note-counter counts the number of notes in each voice 
In particular, the engravers used in the first and in the second voice will 
have different private-note-counter variables.

You can use this to collect information from all encountered objects and thin 
in 'process-acknowledged or 'stop-translation-timestep procell all of them at 
once. For a list of all possible "functions" inside the engraver, see 

Reinhold Kainhofer, address@hidden,
 * Financial & Actuarial Math., Vienna Univ. of Technology, Austria
 *, DVR: 0005886
 * LilyPond, Music typesetting,

reply via email to

[Prev in Thread] Current Thread [Next in Thread]