replace-stencil and overlay-stencil (was: Re: time signature 4 / \breve ?)

[Aaron Hill]

On 2019-10-16 7:00 pm, Graham King wrote:
> \version "2.19.82"
> {
>   \once \override Staff.TimeSignature #'stencil =
>     #(lambda (grob)
>       (grob-interpret-markup
>        grob
>        #{ \markup
>           \override #'(baseline-skip . 1)
>           \center-column {
>             \musicglyph "four"
>             \musicglyph "noteheads.sM1" } #}))
>   \time 8/1
>   c'\breve c' c' c'
> }

If you find yourself doing this type of stencil \override on a regular 
basis, you could wrap it up in a more general-purpose helper similar to 
the following:

%%%%
\version "2.19.83"

replace-stencil = #(define-music-function (grob text) (grob-list? 
markup?)
  (define (stencil grob) (grob-interpret-markup grob text))
  #{ \override $grob . stencil = $stencil #})

{
  \once \replace-stencil Staff.TimeSignature
    \markup \override #'(baseline-skip . 1)
      \center-column { \musicglyph "four" \musicglyph "noteheads.sM1" }
  \time 8/1 c'\breve c' c' c'
}
%%%%

Putting together the function above got me thinking about and working on 
a version that overlays \markup on an existing stencil instead of 
replacing it:

%%%%
\version "2.19.83"

overlay-stencil = #(define-music-function (grob align text)
  (grob-list? (number-pair? '(0 . 0)) markup?)
  (define stencil (grob-transformer 'stencil (lambda (grob orig)
    (let ((x (interval-index (ly:stencil-extent orig X) (car align)))
          (y (interval-index (ly:stencil-extent orig Y) (cdr align)))
          (new (grob-interpret-markup grob text)))
      (ly:stencil-add orig (ly:stencil-translate new (cons x y)))))))
  #{ \override $grob . stencil = $stencil #})

red-x = \markup \with-dimensions-from \null
  \vcenter \center-align \with-color #red "X"

{
  \overlay-stencil Staff.Clef #'(-1 . 1) "Clef"
  b'8 c''
  \temporary \overlay-stencil NoteHead \red-x
  g' a'
  \revert NoteHead.stencil
  b'2
}
%%%%

Not sure how useful these would be in practice, but the resulting syntax 
might be preferable for some folks.


-- Aaron Hill

overlay-stencil.cropped.png
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