arbitrary repeat counter

[Simon Bailey]

Hi,

There's a handy snippet for counting repeated bars in the manual. But
I'm running into limitations when for instance I'd like to have 2- or
4-bar sections that I'd like to count. Usage example: a bass guitar
has a 4-bar riff that's repeated 8 times, but I can't use a volta
repeat in the part because the rest of the ensemble doesn't have
repeatable music; I'd like to print a counting number over the centre
of the first bar of each phrase.

For 2-bar phrases, using the example from the manual, I get the
following, but the Counter is centred over the middle bar-line. Does
anyone have a suggestion for some scheme magic I can investigate to
calculate the X-offset to the centre of the first bar?

\new Staff \relative c' {
  <<
    {
      \set countPercentRepeats = ##t
      \hide DoublePercentRepeat
      \repeat percent 4 { s1*2}
    }
    \repeat unfold 4 { c4. 8 r4 8 r | d4. 4. 4 }
  >>
}

For 4-bar phrases, the best thing I've managed to come up with is this:

\new Staff \relative c {
  \clef bass
  <<
    \context Voice = "foo" {
      \repeat unfold 4 { r4 d8 r r f r4 | a8 r r g r a f r8 | r4 d'8 r
r f, r4 | a8 r r g8 ~ g4 r | }
    }
    \context Voice = "foo" {
      \hide MultiMeasureRest
      \override Voice.MultiMeasureRestText.font-encoding = #'fetaText
      \override Voice.MultiMeasureRestText.font-size = #-2
      s1*4 | R1^"(2)" s1*3  | R1^"(3)" s1*3  | R1-"(4)" s1*3  |
    }
  >>
}

but that's all a bit "manual" ;)

I was thinking it may be possible to override the stencil for the
PercentRepeatCounter and do some math on the current percent repeat
count, but I have no idea how to:

a) get the current repeat number
b) replace a text-interface::print stencil

I've just spent 2 hours digging through LSR and the exending lilypond
manual, but that was a bit fruitless.

I'm also wondering if there's any form of convention to show these
repeated phrases – as a player, if I was given a part with these
repeated phrases and no counting, I'd add the numbers in pencil and
probably a flare to the final barline of each phrase. I'm open to
suggestions ;)

Thanks, kind regards,
sb

-- 
Do not meddle in the affairs of trombonists, for they are subtle and
quick to anger.