So it'll go:
\version "2.19"
%% Path drawings:
my-clef-C =
#(make-path-stencil
'(M 0.000 -1.500
L 0.000 -1.850
C 0.000 -1.890 0.032 -1.920 0.075 -1.920
C 0.122 -1.920 0.150 -1.890 0.150 -1.850
L 0.150 1.850
C 0.150 1.890 0.122 1.920 0.075 1.920
C 0.032 1.920 0.000 1.890 0.000 1.850
Z
M 0.350 -1.500
L 0.350 -1.850
C 0.350 -1.890 0.382 -1.920 0.425 -1.920
C 0.472 -1.920 0.500 -1.890 0.500 -1.850
L 0.500 1.850
C 0.500 1.890 0.472 1.920 0.425 1.920
C 0.382 1.920 0.350 1.890 0.350 1.850
Z
M 1.800 -1.500
L 1.800 -1.850
C 1.800 -1.890 1.832 -1.920 1.875 -1.920
C 1.922 -1.920 1.950 -1.890 1.950 -1.850
L 1.950 1.850
C 1.950 1.890 1.922 1.920 1.875 1.920
C 1.832 1.920 1.800 1.890 1.800 1.850
Z
M 2.150 -1.500
L 2.150 -1.850
C 2.150 -1.890 2.182 -1.920 2.225 -1.920
C 2.272 -1.920 2.300 -1.890 2.300 -1.850
L 2.300 1.850
C 2.300 1.890 2.272 1.920 2.225 1.920
C 2.182 1.920 2.150 1.890 2.150 1.850
Z
M 0.500 -1.100
C 0.500 -1.030 0.520 -0.970 0.620 -0.950
L 1.600 -0.670
C 1.690 -0.650 1.800 -0.620 1.800 -0.700
L 1.800 0.070
C 1.800 -0.020 1.700 -0.020 1.630 -0.050
L 0.750 -0.300
C 0.550 -0.370 0.500 -0.330 0.500 -0.200
Z
M 0.500 -0.100
C 0.500 -0.030 0.520 0.030 0.620 0.050
L 1.600 0.330
C 1.690 0.350 1.800 0.380 1.800 0.300
L 1.800 1.170
C 1.800 0.980 1.700 0.980 1.630 0.950
L 0.750 0.700
C 0.550 0.630 0.500 0.670 0.500 0.800
Z)
0 1 -1 #t)
my-clef-F =
#(make-path-stencil
'(M -0.10 -0.35
C -0.10 -1.11 0.48 -1.80 1.25 -1.80
C 1.75 -1.80 2.20 -1.60 2.50 -1.05
C 2.55 -0.95 2.50 -0.90 2.43 -0.95
C 2.20 -1.17 1.90 -1.48 1.45 -1.48
C 0.70 -1.48 0.15 -0.85 0.15 -0.15
C 0.15 0.45 0.62 0.83 1.05 0.83
C 1.55 0.83 1.90 0.50 1.90 0.05
C 1.90 -0.35 1.55 -0.71 1.20 -0.71
C 0.80 -0.71 0.60 -0.40 0.63 -0.17
C 0.75 -0.30 0.90 -0.31 1.00 -0.31
C 1.20 -0.31 1.38 -0.10 1.38 0.15
C 1.38 0.35 1.20 0.55 0.95 0.55
C 0.60 0.52 0.39 0.25 0.39 -0.05
C 0.39 -0.52 0.62 -0.89 1.20 -0.89
C 1.65 -0.89 2.07 -0.50 2.07 0.10
C 2.07 0.66 1.56 1.01 1.05 1.01
C 0.28 1.01 -0.10 0.35 -0.10 -0.35
M 2.42 0.20
C 2.54 0.20 2.64 0.30 2.64 0.42
C 2.64 0.54 2.54 0.64 2.42 0.64
C 2.30 0.64 2.20 0.54 2.20 0.42
C 2.20 0.30 2.30 0.20 2.42 0.20
M 2.42 -0.20
C 2.54 -0.20 2.64 -0.30 2.64 -0.42
C 2.64 -0.54 2.54 -0.64 2.42 -0.64
C 2.30 -0.64 2.20 -0.54 2.20 -0.42
C 2.20 -0.30 2.30 -0.20 2.42 -0.20
Z)
0 1 1 #t)
\layout {
\context {
\Score
\override Clef.stencil =
#(lambda (grob)
(let* ((sz (ly:grob-property grob 'font-size 0))
(mlt (magstep sz))
(glyph (ly:grob-property grob 'glyph-name)))
(cond
((equal? glyph "clefs.C")
(ly:stencil-scale my-clef-C (* 1 mlt) (* 1 mlt)))
((equal? glyph "clefs.C_change")
(ly:stencil-scale my-clef-C (* .8 mlt) (* .8 mlt)))
((equal? glyph "clefs.F")
(ly:stencil-scale my-clef-F (* 1 mlt) (* 1 mlt)))
((equal? glyph "clefs.F_change")
(ly:stencil-scale my-clef-F (* .8 mlt) (* .8 mlt)))
(else (ly:clef::print grob)))))
}
}
%% Test:
#(set-global-staff-size 30)
{
\clef C
\set Staff.clefPosition = #1
\set Staff.middleCPosition = #1
\key aes \major
\time 3/4
c'2.
\clef F c
}