[HarfBuzz] application of hangul *jmo features to broken syllables

[Jonathan Kew]

Maybe we should try something along the lines of the attached patch. The 
idea here is to ONLY apply the *jmo features to jamo that are 
specifically identified by the shaper, rather than applying them globally.

The extra work being done here should be offset by the fact that we 
won't generally be trying as many non-matching lookups on every glyph; 
we'll only apply the lookups for (at most) one of the *jmo features, 
instead of all of them.

WDYT?

On 6/1/14 14:44, Jonathan Kew wrote:
> The Hangul shaper should NOT apply the *jmo features to glyphs that are
> not part of a properly-structured Korean syllable.
>
> Some examples of current behavior:
>
> [GOOD: complete LVT sequence, proper features applied]
> hb-unicode-encode 1101,1161,11f0 | hb-shape UnBatang_0613.ttf
> [uni1101.ljmo01=0+1024|uni1161.vjmo01=1+0|uni11F0.tjmo01=2+0]
>
> [GOOD: lone L does not have features applied]
> hb-unicode-encode 1101 | hb-shape UnBatang_0613.ttf
> [uni1101=0+1024]
>
> [GOOD: LT without V is not valid, don't apply features]
> hb-unicode-encode 1101,11f0 | hb-shape UnBatang_0613.ttf
> [uni1101=0+1024|uni11F0=1+0]
>
> [GOOD: lone T, don't apply features]
> hb-unicode-encode 11f0 | hb-shape UnBatang_0613.ttf
> [uni11F0=0+0]
>
> [BAD: lone V, shouldn't apply vjmo]
> hb-unicode-encode 1161 | hb-shape UnBatang_0613.ttf
> [uni1161.vjmo02=0+0]
>
> [BAD: VT pair without L is not valid, shouldn't apply *jmo]
> hb-unicode-encode 1161,11f0 | hb-shape UnBatang_0613.ttf
> [uni1161.vjmo01=0+0|uni11F0.tjmo01=1+0]
>
> Note the last two examples; these are incorrect, IMO. In both these
> cases, Uniscribe does not apply the *jmo features.
>
> JK

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