Arbitrary accidental glyphs

[Graham Breed]

I'm trying to get accidentals using glyphs that don't come 
from the standard font.  This is in order to get arbitrary 
microtonal accidentals, particularly using Sagittal. 
Torsten Anders has looked at this before and I'm picking up 
on his work.

The idea is that you install the Sagittal font from here:

http://users.bigpond.net.au/d.keenan/sagittal/

stick

      \override Accidental #'font-name = #"Sagittal"

in a script, and characters from Accidental's 
glyph-name-alist can come from Sagittal.  The problem is 
that LilyPond can't retrieve named glyphs from a 
non-standard font.  I've tried hacking the code to use 
numbered glyphs instead, but that didn't work.  Neither did 
loading the Sagittal font using the same method as the music 
font.

Now I'm trying to get it to work in the obvious way.  I've 
copied these methods from Open_type_font to Pango_font:

Box get_indexed_char (size_t) const;
size_t name_to_index (string) const;

And my test script fails like this:

Backtrace:
In unknown file:
   ?:  9* [#<procedure {#f} ()>]
In /home/graham/usr/share/lilypond/2.11.52/scm/lily.scm:
 734: 10* [ly:parse-file "ET22-sagittal.ly"]
In /home/graham/usr/share/lilypond/2.11.52/ly/init.ly:
  38: 11* (if (or # output-empty-score-list) (# parser #))
  39: 12  [print-book-with-defaults # #]
In /home/graham/usr/share/lilypond/2.11.52/scm/lily-library.scm:
    ...
 135: 13  [ly:book-process #<Book> #< Output_def> #< 
Output_def> "ET22-sagittal"]
In unknown file:
   ?: 14* [output-framework "ET22-sagittal" #<Paper_book> 
(#<module b6cb5cd0>) ()]
In /home/graham/usr/share/lilypond/2.11.52/scm/framework-ps.scm:
 460: 15* (let* (# # # # ...) (if # #) (if # #) ...)
 491: 16* [for-each #<procedure {#f} (page)> (#<Stencil  >)]
In unknown file:
   ?: 17* [#<procedure {#f} (page)> #<Stencil  >]
In /home/graham/usr/share/lilypond/2.11.52/scm/framework-ps.scm:
 494: 18* [dump-page #<Paper_outputter> #<Stencil  > 1 1 {#f}]
 120: 19* [ly:outputter-dump-stencil #<Paper_outputter> 
#<Stencil  >]
In unknown file:
   ?: 20* [placebox 91.5904809657505 -20.5881212598425 ...
   ?: 21* [named-glyph #<Font_metric (#f . 1.0)> "flat"]
In /home/graham/usr/share/lilypond/2.11.52/scm/output-ps.scm:
 185: 22  [ly:format "~a /~a glyphshow " ...
 186: 23* [ps-font-command #<Font_metric (#f . 1.0)>]
In /home/graham/usr/share/lilypond/2.11.52/scm/framework-ps.scm:
  28: 24  (let* (# #) (string-append "magfont" # "m" ...))
  31: 25  [string-append "magfont" ...
  33: 26* [ly:string-substitute " " "_" ...
  35: 27* [ly:string-substitute "/" "_" ...
  37: 28* [ly:string-substitute "%" "_" {#f}]

So it looks like the Scheme isn't getting something it wants 
from the Font_metric object.  I haven't worked out what yet.

Any help on this would be welcome!  I don't want to replace 
the Stencil in Scheme unless there's no other way.  I'd 
obviously prefer a solution that can be merged into the 
official distribution so that I don't have to maintain a 
patched version.  Allowing the music font to be overridden 
is the best way because it might be useful for other things 
as well.


                   Graham