Measure-centered bar numbers

For film scores, a common convention is to center bar numbers within their measure. This is achieved through setting the centerBarNumbers context property to true. When this is used, the type of the bar number grobs is CenteredBarNumber rather than BarNumber.

This example demonstrates a number of settings: the centered bar numbers are boxed and placed below the staves.

\version "2.24"

\layout {
  \context {
    \Score
    centerBarNumbers = ##t
    barNumberVisibility = #all-bar-numbers-visible
    \override CenteredBarNumber.stencil
      = #(make-stencil-boxer 0.1 0.25 ly:text-interface::print)
    \override CenteredBarNumberLineSpanner.direction = #DOWN
  }
}

\new StaffGroup <<
  \new Staff \relative c' {
    d4-. f8( e d4) bes'-> |
    d,-. f8( e d4) cis'-> |
    g-. f8( d e4) g-> |
    a,1-> |
  }
  \new Staff \relative c {
    \clef bass
    d4 f8 e d2~ |
    4 f8 e d2~ |
    4 4 2 |
    a1 |
  }
>>