# [NTG-context] reencode fonts with fonts.trigger

Hans Hagen pragma at wxs.nl
Tue Feb 22 18:05:58 CET 2011

```On 22-2-2011 4:22, Ulrike Fischer wrote:
> Hello,
>
> Khaled had another idea to manipulate (reencode) fonts: He suggested
> to put a function in fonts.trigger. (Example below). I have some
> questions regarding this example:
>
> 1. Is there a basic flaw in the idea?

When triggers are done, there are only empty entries in the characters
table so swapping them has no effect. You can add info to them but some
entries in them will be added when scaling takes place.

> 2. Is the interface more or less stable or will it probably change
> in the future?

the triggers interface will stay

> If not
> 3. which tables/values in tfmdata must be copied/reassigned beside
> the indices information? (There seem to be quite a lot informations
> more than once in tfmdata. E.g. I find the boundingbox in two places
> (descriptions and shared.otfdata.glyphs)).

they are the same (descriptions is the unicode ordering of glyphs but
the subtables are shared, and best don't mess with those subtables as
they can be shared as well)

you probably don't have to change anything else as tex only works with
the tfm data (in node mode otf data is used but chess is unlikely to be
influenced by node mode)

> 4. Which tables/values must be created if I try to move a char to a
> place which is currently empty (like the "z" in the example)?

see above, for tex only the tfmdata counts so no other data has to be
created (unless you have kerns in which case you need to adapt all
character entries that kern with that glyph)

> 5. What is the recommanded lua-code to copy/reassign/remap the
> tables?  Does a library or some helper functions exist which would
> make it easier to move the tables around?

For basemode reencoding you can use the changed subtable:

\starttext

\directlua{
local function chess(tfmdata,value)
if value then
tfmdata.changed[75] = 81
tfmdata.changed[81] = 75
end
end
table.insert(fonts.triggers,"chess")
fonts.initializers.base.otf.chess = chess
}

\start
\font\TestA="file:SkakNew-Figurine.otf:chess=yes"  \TestA\char75
\char81 \par
\font\TestB="file:SkakNew-Figurine.otf:chess=no"   \TestB\char75
\char81 \par
\stop

\stoptext

-----------------------------------------------------------------