\tagsOn, \tagsOff

[Kieren MacMillan]

[ v2.9.14 ]

Hello, all --

No, this isn't Karate Kid 5!  ;-)

This is a continuation of the thread "setting up a very complex  
choral layout", with a possible feature request...

I think we could solve all my multi-output issues -- and add a really  
powerful tool to the Lilypond kit -- if we had a \tagsOn (and maybe  
\tagsOff?) trigger, which would tell Score to listen (or not) to a  
given tag.

For instance, let's say I want the following systems on my page:
        4 measures, 2 staves (SA + TB)
        3 measures, 4 staves (S+A+T+B)
        5 measures, 1 staff (SATB/unison)

I'd be able to use

global =
{
        \time 4/4
        \tagsOn { #'sa #'tb } s1*4 \break
        \tagsOn { #'s #'a #'t #'b } s1*3 \break
        \tagsOn { #'satb } s1*5
}

or [with \tagsOn not automatically turning off any tag not listed, we  
need a \tagsOff, e.g.,]

global =
{
        \time 4/4
        \tagsOn { #'sa #'tb } s1*4 \break
        \tagsOff { #'sa #'tb } \tagsOn { #'s #'a #'t #'b } s1*4 \break
        \tagsOn { #'s #'a #'t #'b } \tagsOn { #'satb }
}

Then in the score, I'd simply include all seven staves (S, A, T, B,  
SA, TB, SATB), and let \tag-ging and \RemoveEmptyStaffContext take  
care of the individual adjustments. In a perfect world -- v4.x? --  
Lily would automatically (or under some fairly hands-off guidance) be  
able to switch between given possibilities to maintain optimal page  
formatting.

I don't think there's a way to really do this kind of thing right now  
in Lily (someone please correct me if I'm wrong!), and I think it  
would be wicked helpful. Of course, if there's an even better way of  
handling this than taking advantage of \tag, I'm open to suggestions/ 
discussions.

If enough people think this is worthwhile -- in any form -- then I'm  
happy to consider adding it to my current sponsorship bill, depending  
on the cost.

Thanks,
Kieren.