[MPEG-OTSPEC] 回复: 回复: [EXTERNAL] Re: Shaping behavior standardization: multi-engine or "Super USE"?

[John Hudson]

On 21082020 8:21 pm, Dave Crossland wrote:
> On Fri, Aug 21, 2020, 4:55 PM Andrew Glass <Andrew.Glass at microsoft.com 
> <mailto:Andrew.Glass at microsoft.com>> wrote:
>
>     I agree with John, existing engines need to be maintained so long
>     as existing fonts would not be 100% compatible if shaped via USE.
>     That is certainly the case for Indic 1 & 2 tags, hence the goal of
>     supporting Indic 3 via USE.
>
>
> I'm confused - it seems from a discussion on another thread (below) 
> that "indic 3" was an idea floated a a few years ago, but it's been at 
> a dead stop for a while... Is that right?
>
> I'm guessing because of the regression risk to existing working fonts?

No. The whole point of defining new script tags would be to avoid 
compatibility issues for existing fonts, in the same way that assigning 
the Indic 2 tags avoided breaking existing fonts using Indic 1 shaping.

At the first OTWG meeting in April 2014—a whole day of which ended up 
being mostly about USE, which at that stage wasn't implemented in any 
shipping products—Andrew suggested the future possibility of passing 
already supported scripts like Devanagari, Bengali, etc. to USE. At the 
time, I recall some questions about what benefit there would be to this, 
given that working solutions for those scripts already existed, but I 
don't remember who asked that. Andrew suggested some reasons, but I 
can't recall what they were. Andrew?

It was some time later, when Ned implemented USE in Core Text, that he 
included the option to use unofficial Indic 3 tags to pass scripts to 
USE. I did some experiments with this, notably with Kannada fonts, which 
turned out to need radically different OTL in order to work in USE. So 
I'm not in any rush to commit to spending time doing Indic 3 
implementations for fonts that already work fine with Indic 2. [Note 
that in addition to registering the tags, USE data for the characters 
would need to be agreed; as I recall, there was a HarfBuzz issue related 
to that with proposed values.]

I think there are two reasons why registering the Indic 3 tags has 
stalled: the general reason that everything else has stalled, and the 
specific reason that there isn't a very compelling case to inspire font 
makers to do something radically different when what they're doing 
already works.

JH

-- 

John Hudson
Tiro Typeworks Ltd    www.tiro.com
Salish Sea, BC        tiro at tiro.com

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