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

[Chookij Vanatham <chookij vanatham eng sun com>]

K.Theppitak,

] 
] Dear K.Chookij,
] 
] IMO, the code point assignments of both Windows and Solaris extensions are
] not different in the shaper engine's point of view. The difference is only
] the U+F71B glyph shape, not the different code tables as in the case of
] tis620-0, tis620-1 and tis620-2.
] 
] So, I don't think tis620-3 is necessary here.
I think this is the good reason as well and I agree.

] 
] However, let me guess that you mean to choose to handle tis620-3 with
] Wtt2.0 cell clustering engine. (Please excuse me if I'm wrong.)  But I
] think Wtt2.0 can be applied to other tis620 encodings as well.
This is correct and that's why I have been trying to point out and hopefully,
there is the flexibility in Pango engine design to have different rules of
cell-clustering for the same font (charset-name) but seems to be that,
it's not important issues to anybody. Unless, someone can tell me that,
we can have this capability and they need to ship out their own Thai Pango
engine to satify their own need. If that's the case, we wouldn't need
to worry about this. Or, any other ideas are wellcome but making sure that
don't force users to use what we provide but, at least, give the options
to them.

] 
] It should be nice if there is a way for users to choose their preferred
] shaping engine. Otherwise, just choose the best one for them.
Again, providing open options as much as they should be, is the most
important things to users.

Chookij V.

] 
] -Theppitak.
] 
] On Wed, 1 Nov 2000, Chookij Vanatham wrote:
] 
] > 
] > 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.
] > ] 
] > 
] 
] ____________________________________________________________________
] Theppitak Karoonboonyanan
] Software and Language Engineering Laboratory, NECTEC
] http://www.links.nectec.or.th/~thep/  mailto:theppitak nectec or th
] 
]