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

[Owen Taylor <otaylor redhat com>]

Chookij Vanatham <chookij vanatham eng sun com> writes:

> Hi Owen, Robert,
> 
> In Solaris, we bought Thai TrueType fonts from Monotype and we are using the
> exact Thai font layout which has been using in Thai MS window. Even we use
> the exact layout but we don't do the same clustering (display cell). We use
> the rule of clustering (display cell) from Wtt2.0 standard (from NECTEC).
> I'm figuring out where I should add the code in Thai pango engine so that
> it can be run on Solaris and having Wtt2.0 rule clustering (cell).
> 
> I run into one question that might be related to the design of Pango but
> not specific to Thai.
> 
> If different platforms use the same "charset" name, ie, tis620.2529-1, and
> idividual platform wants to have its own clustering rule, would that be
> possible ?
> 
> or another word,
> 
> if Solaris wants to have its own clustering rule which is different than what
> it has in other platform for tis620.2529-1, would that be possible to do
> that ?

I think it is highly problematical if different fonts are available with
the same charset name but they don't work the same way.

Trying to base this on the "platform" is not going to work, considering
the fact that you can run on a remote X display, and that users
are perfectly free to install the Linux fonts on their Solaris
box (etc.) if they are so inspired.

In fact, if I understand the problem you are running to be
the problem that Thai fonts vary in their conventions for:

 - The advance widths
 - Where the glyph falls with respect to the drawing origin

Then I've seen at least three different sets of conventions for
freely available Thai fonts on Linux; I tried to make the Thai
shaper a little bit robust against this. If I recall correctly,
it worked with two out of the three sets of fonts.

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.

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. 

Regards,
                                        Owen