Re: A little polish of Thai shaper

[Owen Taylor <otaylor redhat com>]

Theppitak Karoonboonyanan <thep links nectec or th> writes:

> May I Cc: to Mark Leisher so that he could answer some question.
> 
> On Thu, Jun 14, 2001 at 09:40:43AM -0400, Owen Taylor wrote:
> > I think the problem is that there is no standard for where vowels
> > are placed within the character cell, so you can have different
> > types of iso10646 fonts with different placements of vowels. :-(
> > 
> >  1) Vowel is to left of origin, and will align properly with previous
> >     character after advancing the previous characters advance.
> > 
> >  2) Vowel is to the right of the origin; it should be drawn at the
> >     same x location as the previous character.
> > 
> > I believe the current shaping rules used for iso10646-1 are 2) and
> > give the right results for Mark Leisher's ClearlyU fonts. These are,
> > on XFree86 at least, the fonts that non-Thai speakers are likely to
> > have with Thai glyphs. However, the fonts that Thai speakers are using
> > are probably more important...
> 
> I think this should be answered by Mark Leisher himself whether he
> would accept my last patch to ClealyU.
> 
> To my understanding: In the Unicode book, most combining characters
> referred to are put after base character. So, I think it would be
> natural for choice 1), as the normal advancing method will simply yield
> the desired result.

I'm basically fairly skeptical of assuming that you can get things
right by simply rendering Unicode code points in order as if they were
roman characters.

But since it _does_ almost work for Thai, I can see where using
metrics that accomodate this can be considered more natrual.

If the ClearlyU font is the only exception out there to this rule,
then it's probably just best to ignore the way it currently does
metrics and let things break with it.

It bothers me a little that people running XFree86 will see the Thai
parts of the Pango examples rendered wrong until a fixed version is
widespread.

Perhaps it might make sense to submit a patch directly to the XFree86
people to speed up the process of getting a version with correct Thai
glyphs.

Regards,
                                        Owen