Re: Guidance on the repeated slur in \volta 2

[Jean Abou Samra]

Le 27/10/2022 à 23:06, Volodymyr Prokopyuk a écrit :
> Hello,
>
> When working with the manually shaped slurs using the \tweak 
> control-points approach, I've got the right output, but with the 
> following programming error: bounds of this piece aren't breakable 
> that always happens when the shaped slur is attached to the last note 
> in a measure.
>
> *Minimal failing example*
>
> \version "2.23.14"
>
> \relative {
>   \repeat volta 2 {
>     g'1( |
>     \alternative {
>       \volta 1 { g2 g) | }
>       \volta 2 {
>         g2 g
>         \tweak control-points
>           #'((-5.5 . -3.0) (-3.5 . -3.0) (-1.5 . -3.0) (-0.3 . -2.0)) 
> ( <>)
>         \bar "|."
>       }
>     }
>   }
> }
>
>
> The output is rendered, but with the below programming error
>
> GNU LilyPond 2.23.14 (running Guile 2.2)
> Processing `shaped-slur.ly <http://shaped-slur.ly>'
> Parsing...
> Interpreting music...
> Preprocessing graphical objects...
> Finding the ideal number of pages..
> Fitting music on 1 page...
> Drawing systems...
> shaped-slur.ly:10:9: programming error: bounds of this piece aren't 
> breakable.
>
>         \tweak control-points
> shaped-slur.ly:10:9: continuing, cross fingers
> Converting to `shaped-slur.pdf'...
> Success: compilation successfully completed
>
> *Minimal working example*
> *
> *
> However,/if there is a rest/ after the note with the attached shaped 
> slur, there is no programming error
>
> \version "2.23.14"
>
> \relative {
>   \repeat volta 2 {
>     g'1( |
>     \alternative {
>       \volta 1 { g2 g) | }
>       \volta 2 {
>         g2 g4
>         \tweak control-points
>           #'((-5.5 . -3.0) (-3.5 . -3.0) (-1.5 . -3.0) (-0.3 . -2.0)) 
> ( <>) r
>         \bar "|."
>       }
>     }
>   }
> }
>
> What is the reason for the programming error in the failing example? 
> Is there a way to get the output from the failing example, but without 
> the programming error?




This sounds like this issue in the LilyPond bug tracker:

https://gitlab.com/lilypond/lilypond/-/issues/6232

When you do

\version "2.23.80"

{ c'( <>) c' }

this is equivalent to

\version "2.23.80"

{ c'( c') }


In other words, using the empty chord <> attaches the event at
the same moment as the notes that follow this empty chord. Now,
in

{ c'( <>) }

you are conceptually attaching the end of the slur to some
non-existent note after the end of the piece. I understand
the request that it should work, but I think it's not very
surprising that it doesn't work.

If I were you, I would just use \repeatTie and \shape.
You are already using \shape, so the default layout
of \repeatTie that looks like a tie and not like a slur
is not so problematic.

Best,
Jean