[Silgraphite-fonts] Converting OpenType Layout to Graphite

[Richard W. <ric...@nt...>]

Is there a tool around that will convert the GSUB, GPOS and GDEF
tables of an OpenType font to Graphite?  I am hesitant to try
writing one to convert GPOS tables; I have never understood why some
of my attached marks jump backwards as I type using a Graphite font.
(I suppose it might be an effect of the complex-first rule - is there a
compiler option to warn that it has taken effect?)

My motivation is that I have an OpenType Lanna script font that I want
the user (probably mostly me) to be able to customise using
typographical features.  It works with HarfBuzz (and with m17n when
some of its bugs are fixed - not sure if the fixes are in a released
version yet), but it will be some time before Uniscribe/DirectWrite
will work with it. Unfortunately, readily available feature support for
OpenType seems only to be available in browsers. However, LibreOffice
(via an extension, I believe) does seem to have support for Graphite
features!

This conversion would be part of the font build process.  I intend to
continue developing the OpenType font, and I want to automate the
process of converting it to Graphite.

An alternative that currently works, at least in LibreOffice, is to
associate different combination of features with languages.  However,
as Martin Hosken has pointed out, this approach soon runs out of
languages, and requires a map from feature combinations to 'language'.

Richard.