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Re: [ft-devel] A CFF in an SFNT can have only a single font

From: Werner LEMBERG
Subject: Re: [ft-devel] A CFF in an SFNT can have only a single font
Date: Thu, 18 Sep 2008 08:36:42 +0200 (CEST)

> When I read CFF driver (to synchronize the support of sfnt-wrapped
> Type1 and CID-keyed font), I found a comment in cffobjs.c.
>       /* UNDOCUMENTED!  A CFF in an SFNT can have only a single font. */
> It makes me reminds a note in OpenType specification:
>       "The CFF rasterizer does not currently support TTC files."
>       (
> Is this note sufficient reason to restrict face_index = 0?  If so, I
> want to revise the comment.

These two comments don't mean the same.  It is possible to have more
than a single font in a CFF which is not allowed if wrapped in an SFNT
-- this has been confirmed on the OpenType list but is missing in the
OpenType specification.  On the other hand, it is possible to
construct a TTC which consists of CFFs, each of them wrapped in an
SFNT; however, this isn't allowed either (and already documented --
see your above quote).

To state it differently:

  (1) A CFF wrapped in an SFNT must not contain subfonts.

  (2) A TTC must not contain CFFs wrapped in SFNTs.

Both limitations are due to lack of implementation in font engines.
Given that font editors like FontForge can circumvent this rather
easily, I can live with it :-)

It would be a good idea if (1) gets added to the OpenType


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