Re: adjusting horizontal spacing - a function dedicated to Graham

[Janek Warchoł]

*Please* always reply to the whole list.

2013/9/21 Peter Gentry <address@hidden>:
> Thanks Janek
>
> Strangely as I said on the list the problem is not visible today. Errors that 
> are not repeatable are notoriously difficult to track
> down. I will continue playinf with a cut down example to see if I can get 
> repeatability.

For what it's worth, this minimal example is working for me (both 2.16
and 2.17.27):

stretchHorizontalSpacing =
#(define-music-function (parser location exponent) (number?)
   (_i "This function determines the default value of the property
@var{common-shortest-duration} and multiplies it by a moment
derived from the @var{exponent} passed as an argument.
Negative values of @var{exponent} make the spacing tighter,
while positive values make the spacing looser.
")
   #{
     \override Score.SpacingSpanner #'common-shortest-duration =
     #(lambda (grob)
        (let* ((func (assoc-get 'common-shortest-duration
                       (reverse (ly:grob-basic-properties grob))))
               (default-value (func grob))
               ;; When dealing with moments, we need to operate on an
               ;; exponential scale. We use 'inexact->exact' to make sure
               ;; that 'rationalize' will return an exact result as well.
               (factor (inexact->exact (expt 2 (- 0 exponent))))
               ;; The second argument to 'rationalize' has to be fairly
               ;; small to allow lots of stretching/squeezing.
               (multiplier (ly:make-moment (rationalize factor 1/2000))))
          (ly:moment-mul default-value multiplier)))
   #})

horizontalSpacingLoose = \stretchHorizontalSpacing #1
horizontalSpacingTight = \stretchHorizontalSpacing #-1

\layout {
  \horizontalSpacingLoose
}

\bookpart {
  \score {
    { c'4 d' e' f' }
  }
}

\bookpart {
  \score {
    { c'8 d' e' f' g' a' b' c'' }
  }
}

As well as this one:

% function definitions...

\bookpart {
  \score {
    { c'4 d' e' f' }
    \layout {
      \horizontalSpacingLoose
    }
  }
}

\bookpart {
  \score {
    { c'8 d' e' f' g' a' b' c'' }
    \layout {
      \horizontalSpacingLoose
    }
  }
}

Note that you *cannot* place \layout block like this:

\bookpart {
  \score {
    { c'4 d' e' f' }
  }
  \layout {
    \horizontalSpacingLoose
  }
}

hth, and please reply to the list,
Janek