[HarfBuzz] Fwd: Change in HarfBuzz after version 0.90 ?

[Ed Trager]

Happy New Year, Behdad!

Hey just wondering what do you think about Jonathan's patch (attached
below)?

Best - Ed


---------- Forwarded message ----------
From: Jonathan Kew <jfkthame at googlemail.com>
Date: Fri, Dec 27, 2013 at 12:09 PM
Subject: Re: [HarfBuzz] Change in HarfBuzz after version 0.90 ?
To: Ed Trager <ed.trager at gmail.com>, Danh Hong <danhhong at gmail.com>, Behdad
Esfahbod <behdad at behdad.org>
Cc: Martin Hosken <mhosken at gmail.com>, Richard Wordingham <
richard.wordingham at ntlworld.com>, Theppitak Karoonboonyanan <
theppitak at gmail.com>, Harfbuzz <harfbuzz at lists.freedesktop.org>


On 27/12/13 16:21, Ed Trager wrote:

>
> Hi, Martin, Richard, and Danh Hong,
>
> With regard to forcing the re-ordering of the
> UCD-enforced-but-totally-broken normalisation of TAI THAM TONE MARK plus
> U+1A60, does the following approach in the OpenType feature file make
> sense as the quickest and cleanest way to do it or not?:
>
> Basically the idea is to compose the out-of-order pair of characters
> into a ligature; and then take that ligature and decompose it back to a
> pair of characters that are in the correct order:
>
> If there is a better way to do this in OpenType, please enlighten me!
> :-)  I was trying to get this to work last night, so far without success:
>
>
The trouble with this idea (or at least one trouble with it!) is that by
the time your lookups have a chance to do anything, harfbuzz has already
inserted dotted-circle glyphs because it treated the (normalized) sequence
as being a "broken" cluster. The pattern for a "consonant syllable" in the
SEAsian shaper allows for a <sakot, consonant> pair (i.e. a subjoined
consonant) among the various possible syllable-tail items, but it does not
allow for the <sakot> and <cons> to be separated by other marks, which is
what the normalization does.

You -might- be able to work around this by explicitly including the dotted
circles in your ligature-composition rules, though that will make them all
more cumbersome. The better way forward is for us to fix harfbuzz, as
previously suggested.

Possible patch attached; Behdad, wdyt?
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