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


I happenned to find this topic discussed in two lists: here in gtk list
and in a local list of Thai developers. So, please let me say something.

On Tue, 24 Oct 2000, Chookij Vanatham wrote:

> ] One possibility is to add a capability to the X/Pango interface
> ] to find out the exact name of the font that is being used, and
> ] then modify the shaping rules based on some list of foundry/family
> ] names.
> I think this way is better than just checking charset-name.

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, and which category the Thai fonts in Solaris could fall in?
Or do we need a new category?

Please let me know your opinion on this categorization as well.
Thank you.

> ] Another possibilty, if we can identify some particular way of
> ] doing it (perhaps the Solaris way), as definitely the _right_
> ] way to do it, is just to standardize on that, and require the
> ] fonts work in that fashion. This would have to be done in
> ] coordination with the Thai Linux/open source community, of
> ] course. 
> Well!!! I think this choice is a bit harder and don't know how long
> it will take.

It shouldn't be long if it is accepted here. :-)
Another developer contributing to Qt is also in our local discussion list.
So, the convention could be applied at both places consistently.

Theppitak Karoonboonyanan
Software and Language Engineering Laboratory, NECTEC  mailto:theppitak nectec or th

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