[HarfBuzz] A problem in thai shaper

[datao zhang]

> Date: Wed, 18 Apr 2012 07:16:17 +0100
> From: jfkthame at googlemail.com
> To: harfbuzz at lists.freedesktop.org
> Subject: Re: [HarfBuzz] A problem in thai shaper
> 
> On 18/4/12 02:22, Behdad Esfahbod wrote:
> > On 04/17/2012 06:47 PM, Khaled Hosny wrote:
> >> On Tue, Apr 17, 2012 at 05:10:37AM +0200, Khaled Hosny wrote:
> >>> On Mon, Apr 16, 2012 at 09:08:49PM -0400, Behdad Esfahbod wrote:
> >>>>> Problem 2:
> >>>>>
> >>>>> When there is no consonant exist, the dotted circle should be inserted as base
> >>>>> character. The logic should be the first step for the shaping engine to find
> >>>>> the invalid combing marks. Refer to
> >>>>> http://www.microsoft.com/typography/otfntdev/thaiot/shaping.aspx#comb
> >>>>
> >>>> Right. We do not handle invalid combining marks yet. That's something I want
> >>>> to do at some point but it's not high priority.
> >>>
> >>> I don't know about Thai, but the handling of "invalid" Arabic combining
> >>> marks in Uniscribe is completely brain dead and a real PITA and I'd
> >>> really like not to see HarfBuzz going there, a shaping engine is not a
> >>> spell checker and should not enforce any input pattern.
> >>>
> >>> http://www.microsoft.com/typography/OpenType%20Dev/arabic/shaping.mspx#invalid
> >>
> >> Incidentally, I came across this Typophile post, which is one example of
> >> why this "invalid" mark handling is not really a good idea:
> >> http://typophile.com/node/92130
> >
> > Interesting. I'm undecided about this as of now.
> 
> Just adding my vote in favor of Khaled's position.
> 
> The shaping engine should not attempt to enforce rules such as "only one 
> vowel mark on each consonant" or "nukta cannot apply to vowels" (IIRC, 
> MS may have relented on that one) or "the vowel mark must precede the 
> tone mark", etc. That's the role of a (language-specific) spell-checker.
> 
> JK
 
If shaping engine not attempt to enforce rules as your comments, it is necessary to anaylze the syllable of indic, because this belong to (language-spefic), the shaping engine only need apply all the feature that set by user. The user need analyze the syllable and decide to apply which feature should be applied. I don't think that is a good idea. not each of user is doing for a editor
so we can't expect each of user is a language expert. The editor can be used to check the word or other someting, but not the atom element (example the syllable of indic or thai). 
 
Br,
Dean
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