Re: Getting spanner length

[Aaron Hill]

On 2019-01-17 6:43 am, Leo Correia de Verdier wrote:
> Dear list!
>
> I’m all new to lily pond and trying to create a custom spanner (a 
> couple of
> parallel lines connecting some of the holes of two fingering charts). 
> To
> hack this together I would need the length of the spanner I’m modifying 
> or
> replacing. I’ve put this piece of code together to extract it and can’t
> understand what mistake I’ve made:
>
> \version "2.18.2"
> \relative c'' {
>   \once \override TextSpanner.stencil =
>   #(lambda (grob)
>      (let (grob-X (interval-length (ly:stencil-extent (ly:grob-property
> grob 'stencil) X)))
>        (make-line-stencil .2 1 1 grob-X 4)
>        )
>      )
>   d \startTextSpan
>   c b
>   a \stopTextSpan
> }
>
>
> I attempted to abstract it from this piece of code
> https://www.mail-archive.com/address@hidden/msg81685.html
>
> Do you have any other sources or better suggestions for custom 
> spanners?
> This doesn’t have to be very complex or be able to cover line breaks.

Two issues:

- You are missing a set of parentheses for the let statement.
- You are attempting to query a grob property from within the property.

Try this:

%%%%
\version "2.18.2"
\relative c'' {
  \once \override TextSpanner.stencil =
  #(lambda (grob)
     (let ((grob-X (interval-length
        (ly:stencil-extent (ly:line-spanner::print grob) X))))
       (make-line-stencil .2 1 1 grob-X 4)))
  d \startTextSpan
  c b
  a \stopTextSpan
}
%%%%


-- Aaron Hill