Re: Staff switch line (documentation?) bug

[Yuval Harel]

On Tue, 15 Feb 2005 02:43:26 -0800, Graham Percival <address@hidden>  
wrote:
> On 15-Feb-05, at 1:25 AM, Erik Sandberg wrote:
> > PianoStaff.followVoice=##t changes the property for the entire piano  
> > staff,
> > this is why the other voices are affected as well. Instead you should  
> > set
> > Voice.followVoice=##t, or just followVoice=##t. This produces the  
> > correct
> > behaviour.
>
> OK, got it.  Fixed in CVS.
>
> - Graham

Sorry, this still seems wrong to me.

First, PianoStaff.followVoice=##t usually does not produce voice followers  
where the staff is not switched. When it behaves well it is still a useful  
feature, and should be documented. Also, I think the behavior I've shown  
should still be considered a bug.

Second, the new example given in the documentation  
(http://lilypond.org/doc/v2.5/Documentation/user/out-www/lilypond/Staff-switch-lines.html)  
is misleading, and IMO bad style. The property is set before the context  
in which it belongs is instantiated. If I understand correctly, this only  
works because the staff and voice context are unnamed. Someone not yet  
familiar with \set commands will expect this example to always work  
throughout the piano staff. But it won't have effect outside the main  
voice, and will produce an unexpected extra Staff if the first staff is  
named (it probably is going to be named eventually, if the piece has any  
staff switches in the opposite direction).
Also, I don't understand why the example code shows a {c} but the output  
shows a {c'}.

I suggest that \showStaffSwitch be changed to mean {\set  
PianoStaff.followVoice=##t}, and the documentation to say:

"""
Whenever a voice switches to another staff, a line connecting the notes  
can be printed automatically. This is switched on using \showStaffSwitch,  
and turned off using \hideStaffSwitch.

     \context PianoStaff <<
       \context Staff=one \context Voice {
         \showStaffSwitch
         c'1
         \change Staff=two
         b2 a
         \change Staff=one
         \hideStaffSwitch
         c'1
         \change Staff=two
         b2 a
       }
      \context Staff=two { \clef bass s1*4 }
     >>

\showStaffSwitch will show staff-switch lines for all voice in the current  
PianoStaff. It is equivalent to {\set PianoStaff.followVoice = ##t}. To  
produce lines for the current voice only, use {\set followVoice = ##t}.
"""

Thanks,
        Yuval