Re: Cross-staff notes using only one music expression

[Leo Correia de Verdier]

As Knute writes the upper staff needs to be created and kept alive. In this 
case, the PianoStaff context contains a Keep_alive_together_engraver that can 
take care of the keeping alive, but the staff still needs to be initiated. I’m 
not sure if that can be done from inside the musical expression in the lower 
staff. At least I don’t know how it would be done or why it would be desirable. 
I’m also not sure when the Keep_alive_together_engraver actually works, but the 
following seems to compile as I’d expect:

\version "2.18.2"
\new PianoStaff <<
  \new Staff = "up"
  \new Staff = "down" \relative c'' {
    \key a \major
    %\context Staff = "up" { \key a \major }
    \time 3/8
    \voiceOne
    \repeat tremolo 6 {
      <a e'>32
      {
        \change Staff = "up"
        \voiceTwo
        <cis a' dis>32
      }
    }
  \change Staff = "down"
  } >>

As you can see from the result the key signature of the upper staff needs to be 
placed from the expression for the lower staff to appear at all (the commented 
away line under the key signature for the lower staff).


HTH

/Leo

> 13 nov. 2019 kl. 16:59 skrev Knute Snortum <address@hidden>:
> 
> 
> On Tue, Nov 12, 2019 at 6:58 AM Paolo Prete <address@hidden> wrote:
> Hello,
> 
> in the following snippet, I can obtain a cross-staff tremolo:
> 
> http://lilybin.com/y4csd8/1
> 
> However, in this way, I'm forced to fill the "up" staff with invisible rests 
> ( in this case:  s4. ) for the duration of the tremolo. Is there a way to 
> avoid this and use only one music expression for the cross-staff notes?
> 
> 
> Thanks
> 
> I am not a Lilypond expert, but I believe the answer is no.  The reason is 
> that in order to change staff to "up", Lilypond needs to have that staff 
> "alive."  If there is no "up" staff, then there is no way to change to it. 
> 
> ---
> Knute Snortum
> (via Gmail)