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Re: [css3-writing-modes] Yet another approach to discuss Tr fallback issue for UTR#50 and text-orientation

From: Eric Muller <emuller@adobe.com>
Date: Thu, 31 Oct 2013 15:36:09 -0700
Message-ID: <5272DB59.7030407@adobe.com>
To: <public-i18n-cjk@w3.org>
I believe option A (mandate a behavior) is overwhelmingly preferable, 
for the reasons listed in Koji's message.

Some of the arguments for option B do not seem very convincing:

1. It is very likely that fallback is more costly  than no fallback, for 
all architectures.
2. sounds like an argument that works both ways. In fact, in combination 
with my observation on argument 1, it says that fallback is pretty much 
undesirable (why would do something that is not useful and costs?), at 
which point one has to conclude that "A without fallback" is the best 
choice.

I believe that fallback cannot be implemented in the context of 
OpenType. Fallback implies a way to discover that the fallback should be 
triggered. The only conceivable way is to detect whether the application 
of an OT feature (namely 'vert') did change the glyph. However, OpenType 
features are not about doing things, they are about ensuring some 
property after their application. What 'vert' guarantees is that after 
it is applied, the glyph is appropriate for upright presentation. It 
could very well be that the font is built to handle only vertical 
writing and that the glyphs are already appropriate for upright 
presentation, before 'vert' is applied, in which case 'vert' does 
nothing. (If it helps, you can replace 'vert'/vertical presentation by 
'lnum'/lining digits, 'tnum'/tabular digits, etc.) While it is true that 
a foundry would rarely build a font such that it is usable only for 
vertical writing, remember that rendering systems often have to deal 
with fonts which have been generated by machine, e.g. fonts subsetted 
for use in a particular document/style.

For me, the choice is rather straightforward: "mandate no fallback" is 
by far the best resolution.

Eric.
Received on Thursday, 31 October 2013 22:36:34 UTC

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