Re: Changing decimals points to Persian ones via font features

[Hans Hagen <pragma@wxs.nl>]

On 8/2/2016 9:54 PM, Mohammad Hossein Bateni wrote:
> Could the problem be because math fonts use mode=base instead of
> mode=node?  Or is it because in math fonts, the digits and/or full-stop
> have different codes?

math fonts are defined and then don't change i.e. they are quite static 
and all juggling with individual symbols of sequences is done using 
predictable methods

> —MHB
>
> On Mon, Aug 1, 2016 at 9:46 AM, Mohammad Hossein Bateni
> <bateni@gmail.com <mailto:bateni@gmail.com>> wrote:
>
>     Dear list,
>
>     I want to add a customized font feature to the math font, to
>     automatically change the decimal point (unicode 0x2E) to the
>     Arabic/Farsi version (unicode 0x66B).  This will go well with the
>     mapping from Latin digits to Farsi digits (done in a sample with
>     mathdigits fallback).
>
>     For instance, I want to code in $123.45$ and get a result like
>     ۱۲۳٫۴۵.  However, I do not want to simply map 0x2E to 0x66B, because
>     then "full stop" outside a number will also change.  In particular,
>     I'd like to have the mapping only when full-stop is preceded and
>     succeeded by a digit.  This will, among other things, leave the
>     end-of-equation periods unchanged.
>
>     Here is how I tried to achieve it.
>
>
>     \startluacode
>     digits = { 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39 }
>     -- 0x66B instead of 0x2F gives an error!
>     replacements = { [0x002E] = { 0x2F } }
>     fonts.handlers.otf.addfeature {
>       name = "mpf",
>       type = "chainsubstitution",
>       lookups = { {
>         type = "multiple",
>         data = replacements,
>       } },
>       data = {
>         rules = {
>           {
>             current = { { 0x002E } },
>             after   = { digits },
>             before  = { digits },
>             lookups = { 1 },
>           }
>         }
>       }
>     }
>     \stopluacode
>
>     \definefontfeature[mathperiod][mpf=yes]
>
>     \resetfontfallback [mathdigits]
>     %\definefontfallback[mathdigits][dejavusansmono][digitsextendedarabicindic][check=yes,force=yes,offset=digitsnormal]
>
>     \definefontsynonym
>     [MathRoman][name:modern][features={math\mathsizesuffix,mathperiod},goodies=lm-math,fallbacks=mathdigits]
>
>     \starttext
>     $123.45.$
>
>     123.45.
>
>     \addff{mathperiod}
>     123.45.
>     \stoptext
>
>
>     Though this font feature works outside math, it does not seem to
>     have any effect within the math font.  Why is that?  Can we add font
>     feature to the math font?  Are the character codes different?
>
>     Notice that I could not get it to work, so I commented out the
>     fallback for Persian digits, to make things simpler.  To get the
>     proof of concept, I am trying to change period to forward slash (see
>     below).
>
>     Is the syntax I use for having two features in \defontfontsynonym
>     correct?  Actually, I did try with only mathperiod and it does not
>     work, either.
>
>     When I change 0x2F (slash) to 0x066B in "replacements", I get an
>     error as follows.
>
>
>     fonts           > otf chain > feature 'mpf', type
>     'gsub_contextchain', chain lookup 'mpf': rule 1 matches at char
>     U+0002E (period) for (1,1,1) chars, lookuptype 'gsub_multiple'
>
>     error:
>     ...ext/tex/texmf-context/tex/context/base/mkiv/font-ots.lua:1232:
>     attempt to index field '?' (a nil value)
>
>     tex error       > tex error on line 1 in file
>     /Users/bateni/farsitex/context/bostan/examples/mathfa/1.tex: ?
>
>     \page ->\par
>                  \dosingleempty \page_breaks_process
>     \strc_pagenumbers_flush_final_page ...\else \page
>
>     [\p_strc_pagenumbers_page ...
>     \dostoptext ...\strc_pagenumbers_flush_final_page
>                                                       \page \the
>     \everystoptext ...
>     l.1 \dostoptext
>
>     \clf_stoptext ->\luafunction \16>>clf_stoptext
>
>     l.46 \stoptext
>
>
>
>     Best,
>     MHB
>
>
>
>
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