Comment #16 on issue 2492 by [email protected]: Kievan notation - improper
beaming functionality
http://code.google.com/p/lilypond/issues/detail?id=2492
There are a couple issues at play.
First, if the NoteHead glyphs change based on direction, then you need a
pure height function for NoteHead Y-extent. You can put this in an
unpure-pure-container. Checkout define-grobs.scm to see how they work and
read the part of CG on pure grobs.
Second, you've made a check against Kievan stems in is_normal_stem. This
makes it impossible to determine beam direction which calculates directions
based on normal stems. Why are Kievan stems not allowed to be normal?
