Re: Clustering rules (was Re: Adding tis620.2533-0...)

[Prabhat Hegde <Prabhat Hegde Eng Sun COM>]

hi,

>
>We will be using this for representing ligaturing rules for Indic
>fonts in Pango, where:
>
> - There is no standard for Indic glyph encodings in common use
>   currently.

	i believe there is a standard called ISFOC developed by
	CDAC which is the most commonly used glyph encoding
	from document publishers downward. I am trying to get
	in touch with the CDAC folks to have open access to 
	these standards.

	having said that, i still think we will need rules on
	a per-font basis.
	
	prabhat.

> - The set of ligatures can depend quite a bit on the font.
>
>In this case, since the set of ligature rules is not at all
>fixed, we actually store the rules in the property.
>
>
>I don't think that we really need that much flexibility for
>Thai, since there is no reason for every font to have a different
>clustering rule. So, if we wanted to use a font property, 
>it would be more efficient to use a single atom as an enumeration.
>
>
>However, there are problems with this approach.
>
> - It seems to be limited to BFD (bitmap) fonts, since I don't think
>   there is any way to attach font properties to TrueType or Type1
>   fonts in X.
>
> - Using it for existing fonts would require modifying the font 
>   data, unlike the approach of representing it in the encoding
>   field, which can be done with simple X font aliases.
>
>> ] I think it would be useful if someone could enumerate the clustering
>> ] rules currently in use for Thai on X, so we can see:
>> ] 
>> ]  - How many different rules are in use
>> ]  - Which ones we need to support
>> ]  - How bad the problem is with legacy fonts without identified
>> ]    clustering rules.
>> 
>> I'll be providing the cell-clustering rules for Wtt2.0 and I think,
>> Thai folks overthere, for sure, K.Theppitak and I should be able
>> to work all-together or any other Thai folks, so that, we can have, at least,
>> the standardize on one set of clustering rules per encoding for Thai,
>> (XLFD: tis620-3.wtt20)
>
>OK, good.
>
>Regards,
>                                        Owen
>
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