[luatex] font expansion

Robert w.m.l at gmx.net
Fri Jul 7 18:20:54 CEST 2017

On 06.07.17 23:46, Hans Hagen wrote:
> Indeed the expansion is not reported. The kern value is unchanged but
> there is an additional kern (factor) traveling with the kern node which
> will be dealt with in the backend.
> If you see no difference in the pdf file, then there is an issue inm the
> macros or font related code.
> Anyway, I can only speak for context, so what I observe is not what you
> observe (others have to check that).

Here's another plain tex example:

\pdfvariable compresslevel0
\input luaotfload.sty
\font\x="Latin Modern Roman:+kern" at 10pt \x
\expandglyphsinfont\font 1000 1000 5
\adjustspacing=2 vabe\par
\adjustspacing=3 vabe\par

In the uncompressed pdf, both lines are exactly the same. However, if I 
remove lines 3 and 4 from the example, then there is indeed a 
difference, so the problem seems to be with luaotfload (which I thought 
uses context code)?

> Level 1 is rather useless .. (it was part of experiments when pdftex
> evolved) and by not mentioning it we hope that it will not be used

Level 1 makes sense for users who need to reproduce a document with 
unchanged line (and page) breaks. But anyway, I'll keep in mind that the 
luatex manual can't be trusted.

>> With luatex, however, there is no difference between
>> | \expandglyphsinfont 20 20 5 autoexpand
>> and
>> | \expandglyphsinfont 20 20 5
> Because we don't have pre-generated (copies of) fonts at all,

OK, so I take it that autoexpand is always true. But then I wonder why 
\expandglyphsinfont still accepts the autoexpand keywords at all, and 
also the font table still has the key "auto_expand", if its value makes 
no difference?

>> Existing expanded font instances are ignored, and only the base font
>> is embedded in the pdf. Expansion seems to be calculated mechanically
>> and linearly instead of taking into account the width axis of a
>> Multiple Master font.
> There is no support for multiple masters which is obsolete technology
> and (recently) has been cq. is being replaced by variable fonts.

Obsolete or not, MM fonts (and MetaFont) with their parametrised width 
axis still allow typographically superior quality over expansion by 
linear distortion. Variable fonts may well be the future, and I would be 
excited to see them supported by luatex one day (I reckon this is not 
yet the case?), but at present production-ready fonts don't even seem to 
be available.


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