Re: Help with custom noteheads

[Jean Abou Samra]

Le 11/08/2022 à 13:40, Andrew Bernard a écrit :
> So here is an MWE showing the start of what I want to do - make 
> circular unfilled noteheads, and fitting in the staff size. This is 
> only a start, as the set of note styles I need have many extra 
> doodads, so this is just to get going.
>
> It's been a long time since I have done any Lilypond Scheme. I'm 
> wanting help on how to size and position the noteheads properly. This 
> initial code is only my first sketch. I'm aware I need to flip the 
> side when the stem points down - that's not the main focus. I am also 
> foggy on the last arguments specfying the x and y extents. I can't 
> recall what extents are and how they affect this context (having 
> trouble searching for extent in the NR).



Extents are also called 'dimensions'. The extents of a grob
don't affect it itself, but they affect how other grobs react
to it, for example how a stem will attach to a note head, or
what space is reserved between two staves.

Stencils also have extents. They are used whenever stacking
stencils, aligning them, etc.

If the X-extent and Y-extent are not set to something particular,
the default to compute a grob's extents is to get them from
the stencil.

I don't think you'll find much about this topic in the
official documentation, but there is a bit of info here:

https://extending-lilypond.readthedocs.io/en/latest/backend.html#coordinates-extents-and-reference-points



> The code is my own using the Bezier approximation for a circle. The 
> variable k is kappa - as referenced in a previous post on 'Circles' 
> and r is radius.


LilyPond supports exact circles, as you have found out in the
PostScript code in the other thread. Use make-circle-stencil to
create a circle. By the way, if you don't want to learn about
stencil functions, you could also use a markup:

  (grob-interpret-markup grob #{ \markup \draw-circle ... #})


Here's a commented snippet that should help you get started:


\version "2.23.11"

\layout {
  \context {
    \Score
    % custom circular noteheads
    \override NoteHead.stencil =
      #(lambda (grob)
         (let* (;; The thickness of lines in the staff symbol; depends
                ;; on font size.
                (staff-thickness (ly:staff-symbol-line-thickness grob))
                ;; Our own thickness -- scale it by the staff symbol's
                ;; thickness.
                (thickness (* staff-thickness (ly:grob-property grob 
'thickness)))
                ;; Our radius, measured to the center of the line.
                (radius (- (* 1/2 (ly:staff-symbol-staff-space grob)) ; 
half space
                           (* 1/2 thickness) ; account for our thickness
                           (* 1/2 staff-thickness) ; account for staff 
line thickness
                           ))
                ;; Draw the circle.
                (circle (make-circle-stencil radius thickness #f)))
           ;; LilyPond expects a note head to tell how it should mesh with
           ;; other with its X extent.  The part of the X extent before 0
           ;; is the “breapth” value.  In our case, use 1/2*thickness 
for the
           ;; breapth so that a reversed note head (not on the normal 
size of
           ;; the stem due to seconds in chords) has the center of its
           ;; circle line on the stem.
           (ly:stencil-translate-axis
            (ly:stencil-aligned-to circle X LEFT)
            (* -1/2 thickness)
            X)))%}
     \override NoteHead.thickness = 1.15
     \override Stem.thickness = 1.15 % match stem to note head
     %% Attach stem exactly on the left or right of the note head, and at
     %% the vertical center.  In coordinates relative to the note head 
dimensions,
     %% that means '(1 . 0) or '(-1 . 0)
     \override NoteHead.stem-attachment =
       #(lambda (grob)
          (let* ((stem (ly:grob-object grob 'stem))
                 (direction (ly:grob-property stem 'direction)))
            (cons direction 0)))
  }
}


test =
#(define-music-function (size) (number?)
   #{
     \new Staff \with { \magnifyStaff #size } \relative {
       c'4 d e f |
       g a b c |
       c2 b | a g | f e | d c |
       c1 | d | e | f | e | d | c |
       <c d>1 | <c d>2 <c d>4 <c d>8 <c d>16 16
     }
   #})

\test 0.5
\test 0.7
\test 0.9
\test 1.1
\test 1.3
\test 1.6



Regards,
Jean