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

[Chookij Vanatham <chookij vanatham eng sun com>]

Hi Owen,

Thanks for this info and I need to do some more homework for this
to make sure that Pango's Devanagari support will be workable well with
Hindi font we have on Solaris.

Chookij V.

] > 
] > ] 
] > ]  - Store the appropriate clustering rules as an additional 
] > ]    property on the font.
] > ] 
] > ]    This could either be an atom representing one of a set 
] > ]    of standard clustering rules or a more complex rule set.
] > 
] > This is an interesting idea as well and, for me, I would like to know
] > more. For now, I can't say anything more because I don't have experience
] > much on the font, unless any other related information, let me know,
] > just in case.
] 
] X provides a mechanism where extra properties can be attached to
] an X font and accessed by a client using the font. 
] 
] The data is basically, a string, though it is transferred to the
] client in a rather inefficient form for representing arbitrary string
] data: an atom interned on the X server.
] 
] 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.
]  - 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.
] 
] 
] Regards,
]                                         Owen