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Re: Native browser/CSS support for TTC (raw and/or within WOFF)?

From: Adam Twardoch (List) <list.adam@twardoch.com>
Date: Fri, 18 Oct 2013 21:57:17 +0200
Message-ID: <5261929D.8060300@twardoch.com>
To: public-webfonts-wg@w3.org
Hm... hm... Well...

So: Looking at the WOFF 1.0 spec (http://www.w3.org/TR/WOFF/ ) I just 
realized that the WOFF container currently can host a TTF and OTF but I 
don't think it can host a TTC or OTC.

Currently, we have a WOFF Header which is functionally equivalent to the 
first portion of the SFNT Offset Table. It holds, among others, the 
original SFNT version ("flavor", i.e. either \00\01\00\00 or OTTO), and 
numTables.

The WOFF Header is followed by a Table directory which defines offsets 
to each SFNT table, thus being functionally equivalent to Table 
directory portion of the SFNT Offset Table. That's good enough for TTF 
or OTF, which only have one Table directory.

But in Font Collections (TTC and OTC), there is a TTC Header which 
defines the "flavor" as "ttcf", defines the numFonts and then provides a 
list of offsets to each font's SFNT Offset Table.

So perhaps, in order to simplify things, WOFF 2 could be set up to 
ALWAYS be thought of as a "Font Collection"? I mean, one can easily 
imagine to have a TTC or OTC to just have one font -- it'd be a 
perfectly valid "Font Collection". Not really necessary, but would be fine.

The Font Collection really adds very very minimal overhead to the SFNT 
structure. So perhaps we could leave WOFF 1.0 as it is, and clearly say 
that WOFF 1.0 is "only good to host a single SFNT font", but when 
defining WOFF 2.0, we could by definition make it TTC/OTC-compatible, by 
redefining the WOFF Header so that it always includes a "numFonts" 
(which in most cases will be =1), followed by a *Font directory* (which 
defines offsets to each font's Table directory), followed by an array of 
the Table directories of all fonts.

The metadata and the private block could remain singular, i.e. one per 
WOFF.

I realize that this would constitute a major change in how WOFF 2 is 
constructed, though, so perhaps it's not the best idea to do it right now.

Best,
Adam


-- 

May success attend your efforts,
-- Adam Twardoch
(Remove "list." from e-mail address to contact me directly.)
Received on Friday, 18 October 2013 19:57:46 UTC

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