Re: [Silgraphite-fonts] Converting OpenType Layout to Graphite

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

On Thu, 18 Jun 2015 08:52:43 +0700, Martin Hosken wrote:

>> Is there a tool around that will convert the GSUB, GPOS and GDEF
>> tables of an OpenType font to Graphite?  

> No there isn't. The main reason is that Graphite fonts tend to do
> multiple things per pass, while OT fonts do lots of passes, at least
> conceptually. That and integrating the shaper into the generated
> Graphite means it's all a little tricky. Graphite fonts tend to take a
> very different approach to describing the problem. OTOH you could well
> be one of the people who could work it out!

I've got to fit work round these activities!

There's also the slight subtlety that GSUB isn't actually defined.  The
undocumented principle that marks on different components of a ligature
don't interact seems to be implemented differently in HarfBuzz and
Unicode/DirectWrite - my attempts to circumvent the rule have had
varying degrees of success.  A principled rendering of the Tai word for
'water' in Tai Tham has no end of problems.  (For those not familiar
with the word, it has two base characters, each with a mark.  The base
characters ligate, and the two marks swap round, as though the word were
<ligature, mark on base 2, mark on base 1>.)

> There are a couple of things going on here. 

> Did you see my email of
> last week that suggested a different way of doing glyph attachment?

Saw, but didn't study.  

> You may be using an older version of
> make_gdl (if you are using it at all) that had a bug in this area.

Last time I compiled I just used grCompiler V2.4 on handwritten code.
(OK, I used a few macros.)  I'm not familiar with make_gdl.  I'm using
my ugly font when I can because it'd easier to read so I haven't noticed
the jumping about recently. Something seems to have gone wrong with the
hinting or whatever in the Lannaworld-based graphite font.  

>> However,
>> LibreOffice (via an extension, I believe) does seem to have support
>> for Graphite features!  

> LibreOffice needs no extension to support Graphite fonts. You may be
> thinking of an older extension that allows one to turn off the
> Graphite support.

I was thinking of the 'typography toolbar'.  It turns out that it isn't
necessary.

> An alternative would be to allow the same feature setting syntax we
> use in fonts, to work with the OT support in libreoffice. But that would
> take some coding from someone.

Yes, but I'm not keen on recommending that people compile LibreOffice
for themselves.  My last build took 4 hours, though of course adding a
patch on top of a compiled build should be less painful.

Richard.