Re: reinstating hidden stave

[Lukas-Fabian Moser]

Hi Andrew,

> This came up as one of my queries a short while ago. It appears to be 
> a surprisingly tricky topic. Have a look back through the archives for 
> the full discussion. Here's the code I came up with. Hope this helps.
>
> Andrew
>
> %======
> \version "2.19.82"
>
> % manual staff hiding and showing .
> % must be used with \RemoveEmptyStaves on.
>
> hideStaffWithOnlyRests =
> \set Staff.keepAliveInterfaces = #'()

This would tend to kill a staff no matter what its contents are. (Try

\layout {
  \context {
    \Staff
    \RemoveAllEmptyStaves
  }
}

\new Staff {
  \repeat unfold 200 a4
  \hideStaffWithOnlyRests
  \repeat unfold 200 a4
}

to see the effect.)

That is actually useful in some situations... but not what the original 
question asked for, I think.

Also, the logical is actually not that tricky: the keepAliveInterfaces 
list determines what elements in a staff will force the staff to be 
displayed. So if you want to see a staff where it contains only rests, 
it suffices to add rest-interface to that list. This leads to your 
definition of showStaffWithOnlyRests, but hideStaffWithOnlyRests should 
restore the default list (as defined in ly/engraver-init.ly):

hideStaffWithOnlyRests =
\set Staff.keepAliveInterfaces = #'(
                                     bass-figure-interface
                                     chord-name-interface
                                     cluster-beacon-interface
                                     fret-diagram-interface
                                     lyric-syllable-interface
                                     note-head-interface
                                     tab-note-head-interface
                                     lyric-interface
                                     percent-repeat-item-interface
                                     percent-repeat-interface

                                     ;; need this, as stanza numbers 
are items, and appear only once.
                                     stanza-number-interface
                                     )

(It would probably be better to turn these into functions that really 
only add the rest-interface to the list resp. remove it, using some seme 
construct.)

Lukas