music font scaling with \sacredHarpHeads

[Steve Tarr]

Hi,
I'm preparing some music for our local Sacred Harp singers and finding 
that the "blackness" of the Lilypond defaults and the Emmentaler font 
don't work well for shape-note (\sacredHarpHeads) music in small sizes. 
 If I scale a staff down to 14 points to keep an entire song on one 
sheet of paper, the half-note "mi" when printed on top of a staff line 
gets filled in so that it's almost indistinguishable from the 
quarter-note "mi".

To see the effect, compare the two staves generated by:

\version "2.13.15"
music = { \time 6/4 \sacredHarpHeads b'4 b'2 b'4 b'2 }
<<
    \new Staff
        {
            \music
        }

    \new Staff
        \with {
            fontSize = #-5
            \override StaffSymbol #'staff-space = #(magstep -5)
        }
        {
            \music
        }
>>

Other note shapes in the Sacred Harp 4-shape system don't have this 
problem, or don't exhibit it to the same degree.  The "mi", being 
smaller than the other shapes, is the first to be filled in.

I can mitigate the problem by reducing the staff line thickness, but 
that affects too many other things - note stem and bar line thickness,
for example.  And the note heads, in comparison to the staff lines, then 
look too heavy.

The best workaround I've found so far is to disable the loading of the 
Emmentaler fonts in design sizes smaller than the default 20 points by 
modifying the file scm/fonts.scm:

--- font.scm.orig       2010-03-12 17:47:07.771003400 -0800
+++ font.scm    2010-03-13 21:31:55.175195200 -0800
@@ -161,15 +161,10 @@
                     (caddr x))))
    `((fetaDynamic ,(ly:pt 20.0) ,feta-alphabet-size-vector)
      (fetaNumber ,(ly:pt 20.0) ,feta-alphabet-size-vector)
      (fetaMusic ,(ly:pt 20.0)
                #(
-                 ,(delay (ly:system-font-load (string-append name "-11")))
-                 ,(delay (ly:system-font-load (string-append name "-13")))
-                 ,(delay (ly:system-font-load (string-append name "-14")))
-                 ,(delay (ly:system-font-load (string-append name "-16")))
-                 ,(delay (ly:system-font-load (string-append name "-18")))
                  ,(delay (ly:system-font-load (string-append name "-20")))
                  ,(delay (ly:system-font-load (string-append name "-23")))
                  ,(delay (ly:system-font-load (string-append name "-26")))
                  ))
      (fetaBraces ,(ly:pt 20.0)


But of course, I'd rather find a way to do the same thing within my 
score rather than modifying a Lilypond system file.  I've found bits and 
pieces of information that suggest this can be done, but that it's not 
simple, and the only examples I have deal with text fonts and not the 
music fonts.

So is there a better way to control which fonts are loaded, or perhaps 
which of the loaded fonts in this series is actually selected for 
rendering note heads?

-Steve Tarr