Re: [Lilypond-auto] Issue 3518 in lilypond: Support temporary divisi staves

[lilypond]

Comment #6 on issue 3518 by address@hidden: Support temporary divisi staves
http://code.google.com/p/lilypond/issues/detail?id=3518

User interface issues aside, this can't work perfectly due to the rigid  
structure of our backend.

Here is why: basically we want to arrive at a decision when to switch to  
divisi staves and when to switch back to a single staff.  We basically  
typeset everything in both ways.  However, in order to be actually able to  
switch, the line breaks have to be chosen synchronously, which means that  
the material that ends up dead still influences the line breaks.

Now the non-divisi staff, being the recessive one, can afford to be empty  
during the divisi times which helps.  That still leaves us with two kinds  
of material that don't end up on the page but influence line breaking:

a) material in the non-divisi staff during non-divisi times that gets  
replaced by divisi staves because _elsewhere_ in the line there are divisi  
passages.  Since the non-divisi staff tends to be more crowded, this causes  
the ultimately used divisi staves to reserve space that is not needed.

b) material in the divisi staves during non-divisi times that does _not_  
get used because there just is no divisi material on the entire line.  This  
is somewhat less likely to cause problems than case a) since in general the  
divisi staves will be less crowded horizontally.

A good solution would again require softening the strict sequentiality of  
before/after line-breaking decision-making.

It might help to work with quoted voices here and make it easy to specify  
the ranges outside of divisi passages that should be typeset in the divisi  
staves.  In that manner, a user can specify something like 10 measures or  
so of range around the divisi passages outside of which no material will  
flow into the divisi staves, thus not affecting the spacing in the  
non-divisi staff.  Also saving typesetting time.  Of course, if those  
passages _do_ end up on the page after all, we are in trouble.

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