[HarfBuzz] Change in HarfBuzz after version 0.90 ?

Jonathan Kew jfkthame at googlemail.com
Fri Dec 27 09:09:35 PST 2013

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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