[luatex] Picking defaults for axes on variable fonts

[Sergio Callegari]

On Fri, 23 Apr 2021 09:57:13 +0200 luigi.scarso at gmail.com (luigi 
scarso) wrote:

> On Fri, Apr 23, 2021 at 9:48 AM Sergio Callegari <sergio.callegari at 
> unibo.it>
> wrote:
>
> > Hi,
> >
> > I have noticed that luatex now supports variable fonts and I've started
> > experimenting. I am asking a question here but I am unsure if it is
> > actually tied to luatex or luaotfload or maybe fontspec. In case, please
> > be so kind to address me to the correct forum.
> >
> >
> hm, luatex and luahbtex don't support variable fonts directly,
> it's a matter of the format (latex,  context, optex... ) .
Thanks for providing this info. Can you be so kind to expand a little, 
as there are still a couple of things that are not 100% clear to me?

- Common widom found on the net is that variable fonts work only with 
the LuaTeX engine, no others and that this become possible only with 
LuaTex 1.13. As a matter of fact, xeTeX works without an hiccup on the 
file, but after it it is impossible to make a PDF because dvipdfmx 
reports "invalid font" . This suggests that the engine and specific the 
part of it responsible for the PDF generation plays a role. The only 
item that comes to my mind given the situation is lua. If so, would it 
be luaotfload the upstream to ask the question to?

- The errors reported when attempting to use variable fonts appear to 
happen /after/ the format and the tex machinery has completed its work, 
that is after the:

  406 words of node memory still in use:
    3 hlist, 1 vlist, 1 rule, 2 glue, 3 kern, 1 glyph, 4 attribute, 48 
glue_spec
, 4 attribute_list, 1 write nodes
    avail lists: 2:17,3:4,4:1,5:28,6:2,7:116,9:14

What appears to fail is the step following this one, that is the PDF 
generation. This looks consistent with what happens in xetex. But if I 
am correct, in both pdftex and luatex the pdf generation is unseparable 
from the engine, apart from the role of luaotfload...

Any suggestion?

Sergio