Variant mensual ligatures?

[Michael O'Donnell]

I'm trying to set the Bodleian MS. Canon. Misc. 213 (early renaissance
manuscript, perhaps the first in void mensural notation) in a form that
captures most of the peculiarities of the copyist's notation, but
uniformly readable. I've solved several of the problems, but ...

The copyist uses a variant of the descending semibreves mensural
ligature, with a slanting box instead of the two square noteheads (this
is shown in the Wikipedia page on Mensural Notation
http://en.wikipedia.org/wiki/Mensural_notation#Ligatures in the leftmost
entry on line 5 of the table). The notation looks just like the
descending breve ligature, except that the stem goes up instead of down.

I don't expect the Lilypond mensural notation to provide this variant
directly, so I'm trying to find the right tweak in the source. There
seems to be no hook for mensural ligatures in the Scheme source. I have
stared at mensural-ligature-engraver.cc and mensural-ligature.cc without
absorbing any clue as to where/how the choices involved in creating
ligatures are actually made. It appears that there should be some
invocation of spanners and maybe beams to generate the slanted forms,
but I can't find the right spot in the code.

So, pointers into the code will be highly appreciated. Of course, if
someone wants to provide selectable variant ligature forms, ... :-)

When I've accomplished enough to make  a useful example, I'll post some
of my techniques.

Cheers,

Mike O'Donnell
http://people.cs.uchicago.edu/~odonnell/