[NTG-context] Issue loading an otf variable font

[NTG-context] Issue loading an otf variable font

[Florent Michel]

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Hi,

I was experimenting with variable fonts in ConTeXt. While all seems to work
well when using a ttf font (like Recursive_VF_1.085.ttf), I am struggling
to use .otf ones, like the Source Code Pro (downloaded from
https://github.com/adobe-fonts/source-code-pro/releases/tag/2.042R-u%2F1.062R-i%2F1.026R-vf
).

Minimal example:

________________________________________
\definefontfeature[myaxis][axis={weight=500}]
\definefontfamily[mainface][rm][Source Code VF]
  [features={default, myaxis}]

% Works when replacing the two above lines with these
%\definefontfamily[mainface][rm][Recursive]
%  [features={default, myaxis}]

\setupbodyfont[mainface]
\starttext
\mainface Hallo
\stoptext
________________________________________

The (from what I understand) relevant part of the log is:

__________________________________________________________________________
fonts           > otf loading > loading
'/home/florent/.local/share/fonts/SourceCodeVF-Upright.otf', hash
'sourcecodevf-upright-weight-500'
otf reader      > user instance: weight=500, factors: 0.42857142857142855
otf reader      > cff >     unknown local call 2, bias 107, case 2 : [48 32
60 164 26 72] n=6
otf reader      > cff >     unknown local call 2, bias 107, case 2 : [-10
42 -33 -90 10 26] n=6
otf reader      > cff >     unknown local call 2, bias 107, case 2 : [176
292 -5 -14 -15 -40] n=6
otf reader      > cff >     unknown local call 90, bias 107, case 2 : [-94
-168 -54 -92 28 76 49 132 5 14 -2 -4] n=12
otf reader      > cff >     unknown local call 2, bias 107, case 2 : [26
-26 21 58 -21 -58] n=6
otf reader      > cff >     unknown local call 1, bias 107, case 2 : [152
270 -25 -70 -38 -102] n=6
otf reader      > cff >     unknown local call 1, bias 107, case 2 : [-152
266 25 70 -36 -98] n=6
otf reader      > cff >     unknown local call 17, bias 107, case 2 : [] n=0
otf reader      > cff >     unknown local call 464, bias 107, case 2 : []
n=0
otf reader      > cff >     unknown local call 776, bias 107, case 2 : [172
29 80] n=3
otf reader      > fatal error in file
'/home/florent/.local/share/fonts/SourceCodeVF-Upright.otf':
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:1956: attempt to
perform arithmetic on a nil value (field '?')
stack traceback:
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2350: in metamethod
'mul'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:1956: in local 'a'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:2508: in upvalue
'process'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:2685: in upvalue
'processshape'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:2834: in upvalue
'parsecharstrings'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:3067: in upvalue
'readnoselect'
/home/florent/lmtx/tex/context/base/mkxl/font-cff.lmt:3279: in local
'reader'
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2094: in upvalue
'readtable'
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2203: in upvalue
'readdata'
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2263: in function
</home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2246>
[C]: in function 'xpcall'
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2352: in upvalue
'loadfont'
/home/florent/lmtx/tex/context/base/mkiv/font-otr.lua:2407: in field
'loadfont'
/home/florent/lmtx/tex/context/base/mkxl/font-otl.lmt:160: in field 'load'
/home/florent/lmtx/tex/context/base/mkxl/font-otl.lmt:663: in upvalue
'otftotfm'
/home/florent/lmtx/tex/context/base/mkxl/font-otl.lmt:691: in function
</home/florent/lmtx/tex/context/base/mkxl/font-otl.lmt:690>
(...tail calls...)
/home/florent/lmtx/tex/context/base/mkxl/font-def.lmt:364: in function
</home/florent/lmtx/tex/context/base/mkxl/font-def.lmt:352>
(...tail calls...)
/home/florent/lmtx/tex/context/base/mkxl/font-def.lmt:467: in field 'read'
/home/florent/lmtx/tex/context/base/mkxl/font-ctx.lmt:1385: in function
</home/florent/lmtx/tex/context/base/mkxl/font-ctx.lmt:1240>
(...tail calls...)
fonts           > otf loading > loading failed due to read error
fonts           > defining > forced type 'otf' of 'SourceCodeVF-Upright'
not found
__________________________________________________________________________

Interestingly, all works well if I delete the file SourceCodeVF-Upright.otf
from my font directory to force the use of SourceCodeVF-Upright.ttf
instead.
Is there something wrong in my example which causes issues with the otf
variant?

Cheers,
Florent

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