Help with custom noteheads

[Andrew Bernard]

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).

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.

====

\version "2.23.11"

circa =
#(let ((k 0.5522)
      (r 1))
      (ly:make-stencil `(path 0.1
    (moveto ,r 0
    curveto ,r ,k ,k ,r 0 ,r
    curveto ,(- k) ,r ,(- r) ,k ,(- r) 0
    curveto ,(- r) ,(- k) ,(- k) ,(- r) 0 ,(- r)
    curveto ,k -1 1 ,(- k) 1 0
    ))
    (cons 1 1) (cons 1 1)))

insta = {
  c'4 d' e' f' g' a' b' c''
}

\score {
  \new Staff \insta

  \layout {
    \context {
      \Score
      % custom circular noteheads
      \override NoteHead.stencil = #circa
    }
  }
}

====


Andrew