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Re: RTL characters in Ahem

From: John Daggett <jdaggett@mozilla.com>
Date: Thu, 5 Mar 2015 13:42:08 +0900
Message-ID: <CALYZoVO01SVpDKOLdhW982MU6kRVnp1Fp9guoU=rQJ=zkmuDug@mail.gmail.com>
To: Richard Ishida <ishida@w3.org>
Cc: Koji Ishii <kojiishi@gmail.com>, "www-style@w3.org" <www-style@w3.org>
Richard Ishida wrote:

> I may find a use for it, but I'd still prefer to update Ahem.  Reasons
> include, but are not limited to, it's often useful to have blanks
> where the spaces are, as Ahem does, and it's particularly useful to
> have the wall-to-wall painting of the space that Ahem offers, so that
> you can compare shapes simply.  I also found that it doesn't support
> script such as arabic or complex scripts, where the glyphs change
> according to context - in Ken's font you just see the arabic text in a
> different font.

I don't think simply adding single glyphs within certain scripts to Ahem is
such a great idea. Displaying Arabic or Thai requires more than just single
glyphs, it requires fonts with shaping information, in the form of AAT,
OpenType or Graphite tables. Similarly, vertical writing mode support
requires fonts with vertical metrics and support for vertical alternates.

For complex layout features, tests should use fonts that at least mimic the
core set of required features that an actual font used for content would
require. There might be clever type designers out there who could design a
pan-Arabic-CJK-Thai Ahem testing font with the full set of all the proper
features actual fonts would contain but it's not a simple task I think.
Using the full set of Noto fonts from Google [1] would be a more sensible
approach I think. Yes, those fonts are not a trivial size but I don't
really think the size of these fonts is such a big problem.

Yes, you can fudge things and add glyphs to Ahem. That will allow you to
test some features but not others. However, those tests won't be testing
the same codepath used by browsers when they actually display real content
with real fonts with these different features enabled. Real fonts are
readily available. It would be better to use them instead for tests.

Cheers,

John Daggett
Mozilla Japan

[1] https://code.google.com/p/noto/
Received on Thursday, 5 March 2015 04:42:37 UTC

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