Re: Adding tis620.2533-0 into Thai Pango engine

[Chookij Vanatham <chookij vanatham eng sun com>]

K.Theppitak,

Regarding the issue of adding tis620.2533-0 in Thai pango engine,
I've been thinking if actually, I would say that even Solaris uses Thai
fonts used in WindowsThai extension but, actually, we modified the glyph
at U+F71B which is used for bad sequence indicator.

Then, may be, we should have tis620-3 for Thai Solaris extension.

Let me know what you think and if you agree, please let me know
how this convention on encoding field on XLFD will be maintained
and well-known to anybody as the standard.

Thanks,

Chookij V.


] 
] ] 
] ] According to our experience, there are three different practices of Thai
] ] fonts for rendering :
] ] 
] ] 1. Plain tis620 : combining characters are placed at the safe positions to
] ]    prevent collapsion. There are two practices of this kind :
] ]    - negative-offset-zero-width diacritics (this makes the fonts apply to
] ]      many applications, such as Netscape, which support Western fonts
] ]      without knowing they are rendering Thai fonts)
] ]    - real monospace fonts (used in mule/emacs; this requires the
] ]      applications to combine characters into cells)
] ] 
] ] 2. MacThai extension : an extended tis620 code set, by using codes in the
] ]    range 0x80-0x9f and in some free slots to keep the prepositioned
] ]    combining characters. This needs a shaping algorithm to produce 
] ]    elegant rendering.
] ] 
] ] 3. WindowsThai extension : similar to MacThai extension, but used in
] ]    Windows Thai Editions.
] ] 
] ] The last two code sets are mapped to their own private area of Unicode and
] ] cannot be used together.
] ] 
] ] So, we are now discussing about a convention on the encoding field on XLFD
] ] to distinguish the three code sets :-
] ] 
] ]   -tis620-0   for plain tis620
] ]   -tis620-1   for MacThai extension
] ]   -tis620-2   for WindowsThai extension
] ] 
] ] Note that the years in the registry field are omitted, because tis620.2529
] ] and tis620.2533 do not differ in content. Both can be referred to as
] ] tis620 without confusion.
] ] 
] ] However, Mr Chookij, could you please describe how Wtt2.0 is implemented
] ] in Solaris,
] In Solaris, we have Wtt2.0 rule for the display. Wtt2.0 provides the table
] to check whether the current Thai character can be combined with the previous
] character. If it can't be combined like those invalid Thai sequences such as,
] U+0E48 + U+0E34 --> this is invalid sequence, then U+0E34 will be displayed
] as its own cell.
]