scaled lyrics

[Jan-Peter Voigt]

Hello list,

when I am typesetting christian/latin or german music, there are often 
passages with short notes and a lot of long syllables. The character 'M' 
is a quite long one and if you have the german word "schlem -- men", it 
also takes a lot of space.
If I use proportional duration scaling for the notes, it only works - 
for texts like these - with a very wide spreading of the notes. So I 
tried to scale the lyrics proportionally:

--snip--
\version "2.14.2"

#(define-public (create-damp-stencil axis mx gamma proc)
  (lambda (grob)
          (let* ((stil (proc grob)) ; produce stencil
                 (extent (ly:stencil-extent stil axis)) ; get stencil 
extent
                 (size (- (cdr extent) (car extent))) ; there's a 
ly:function for this, I think
                 (fac (* (/ mx size) (- 1 (expt gamma (- size)))))) ; 
calculate scale-factor: maximum/size * (1 - (gamma ^ (-size)))
                (if (< fac 1.0) ; if we make it smaller, return scales 
else original stencil
                    (ly:stencil-scale stil (if (eq? axis X) fac 1) (if 
(eq? axis Y) fac 1))
                    stil)
)))

% some text with different syllable lengths ... many characters and a 
lot of 'm's
credo = \lyricmode {
  Cre -- do in u -- num De -- um Je -- sum Chri -- stum
}

\relative c'' {
  \repeat unfold 2 { \repeat unfold 11 { c8 } r }
} \addlyrics {
  \credo
  \override LyricText #'stencil = #(create-damp-stencil X 4 1.6 
lyric-text::print)
  \credo
}
--snip--

The scaling formula maximum/size * (1 - (gamma ^ (-size))) is a first 
shot, wich scales all syllables to not be greater than maximum. So in 
this example the 8ths are not spread in the second part by 'sum' or 'Chris'.
But I don't like the look of the uneven scaled text. Has anyone an idea 
of a "softer" scaling function? Or has anyone another idea on this topic?

Right now I simply try a scaled stencil:
--snip--
\version "2.14.2"

#(define-public (create-scale-stencil fac proc)
  (lambda (grob)
          (let ((stil (proc grob)))
               (if (pair? fac)(ly:stencil-scale stil (car fac) (cdr fac))
                   (begin (ly:message "not a pair of numbers: ~A!" fac) 
stil)))))

% some text with different syllable lengths ... many characters and a 
lot of 'm's
credo = \lyricmode {
  Cre -- do in u -- num De -- um Je -- sum Chri -- stum
}

\relative c'' {
  \repeat unfold 2 { \repeat unfold 11 { c8 } r }
} \addlyrics {
  \credo
  \override LyricText #'stencil = #(create-scale-stencil '(.7 . 1) 
lyric-text::print)
  \credo
}
--snip--

What do you think of this?

Cheers,
Jan-Peter