Re: Fallback fails for Linux Libertine O to Junicode over private area, debugging?

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 1/7/2022 4:18 PM, J. P. Ascher via ntg-context wrote:
> Hi, all,
> 
> I'm a long time lurker (on gmane), first time poster. First, thank you
> all, very much, for your excellent work and superb community.
> ConTeXt has become a critical part of my academic writing and integral
> to my research.  I'm not exaggerating when I say it changed how
> I thought about texts and became a major source for my dissertation
> work.  Thank you!
> 
> I'm trying to get a typescript for setting a text in Libertine with
> Junicode fallbacks for characters in MUFI, in the private use area.
> For some reason Libertine roman will not fallback no matter what
> I do. However Libertine italic will.  I can also work around it by using
> Junicode as a base and forcing fallback to Libertine.
> 
> My question is: why?  What's wrong with Libertine roman?  Or my approach?
> 
> My hypothesis is that there's something about `LinLibertine_R.otf`
> that's not quite right.  I looked in FontForge, but couldn't
> spot anything.
> 
> Does anyone have a suggestion as to another place to look?  Or something
> I'm overlooking?
> 
> Minimal example (attached too, if it comes through):
> 
> ```
> \definefontfeature[default][default][script=latn]
> 
> 
> % Libertine with a Junicode fallback, lib-fb-jun
> 
> \definefontfallback[junicodefallback][name:Junicode][privateusearea][check=yes,force=no]
> 
> \starttypescript [serif] [lib-fb-jun]
>    \definefontsynonym [Libertine-Roman]     [file:linlibertiner]
>    \definefontsynonym [Libertine-Slanted]  [file:linlibertineri]  % works fine
> \stoptypescript
>   
> \starttypescript [serif] [lib-fb-jun] [name]
>    \definefontsynonym [Serif]            [Libertine-Roman]   [features=default,fallbacks=junicodefallback]
>    \definefontsynonym [SerifSlanted]     [Libertine-Slanted] [features=default,fallbacks=junicodefallback]
> \stoptypescript
>   
> \starttypescript [lib-fb-jun]
>    \definetypeface [lib-fb-jun] [rm] [serif] [lib-fb-jun] [default]
> \stoptypescript
> 
> 
> % Junicode with Libertine as a fallback, preferring Libertine, jun-pr-lib
> % this hack does what I want the above to do
> 
> \definefontfallback[preferlibertine][name:linlibertineo][0-FFFFF][check=yes,force=yes]
> 
> \starttypescript[serif] [jun-pr-lib]
>     \definefontsynonym [JunicodeRoman] [name:Junicode]
> \stoptypescript
> 
> \starttypescript[serif] [jun-pr-lib] [name]
>     \definefontsynonym [Serif] [JunicodeRoman] [fallbacks=preferlibertine]
> \stoptypescript
> 
> \starttypescript [jun-pr-lib]
>    \definetypeface [jun-pr-lib] [rm] [serif] [jun-pr-lib] [default]
> \stoptypescript
> 
> 
> % some tracking stuff
> 
> \enabletrackers[fonts.missing=replace]
> \enabledirectives[logs.errors]
> 
> 
> % text, we use lib-fb-jun first, then jun-pr-lib
> 
> \starttext
> \setupbodyfont[lib-fb-jun]
> 
> {\em emph. lib-fb-jun: \Uchar61125 \char64259 \utfchar{"eec5} (three glyphs)}
> 
> lib-fb-jun: \Uchar61125 \char64259 \utfchar{"eec5} (three glyphs)  % <- fallback fails here
> 
> \switchtobodyfont[jun-pr-lib]
> 
> jun-pr-lib: \Uchar61125 \char64259 \utfchar{"eec5} (three glyphs) % <- works
> 
> \stoptext
> ```
> 
> Any ideas?
when you use a complex font (in this case with lots of ligatures) doing 
a fallback can interfere with these features especially when they have 
been put in the private areas which are basically 'undefined'

you're accessing an st ligature directly but normally you will do that 
by enabling a font feature

Hans

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                                           Hans Hagen | PRAGMA ADE
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