[HarfBuzz] Thai shaping and dotted circle

[Theppitak Karoonboonyanan]

On Tue, Oct 1, 2013 at 3:10 PM, Richard Wordingham
<richard.wordingham at ntlworld.com> wrote:
> On Tue, 1 Oct 2013 08:26:29 +0700
> Theppitak Karoonboonyanan <thep at linux.thai.net> wrote:
>
>> On Tue, Oct 1, 2013 at 5:49 AM, Richard Wordingham
>> <richard.wordingham at ntlworld.com> wrote:
>
>> Relying on 'mkmk' is a little bit costly, as it would need two sets
>> of glyphs under different GDEF's for each combining vowel. And
>> currently, most fonts are not prepared for this. However, it looks
>> more feasible to cover minority languages.
>
> I don't understand the need for 'two sets of glyphs under different
> GDEF's for each combining vowel'.

For two practical reasons:

- Most OpenType engines cannot properly handle a glyph with both
  Base Mark and Mark anchors in the same glyph. Either one works
  and the other doesn't. And the safest solution is to make another
  copy of the glyph with different anchors. (I may be wrong with this.
  But it works well so far.)

- A best practice for Thai typography is to provide smaller glyph for
  Mark than Base Mark of the same character. You can see such
  common practice for tone marks, for example, in most Thai fonts
  in the market.

>  On the other hand, a mkmk lookup
> might become about 7 times as large when one includes all pairs of
> marks above.  Combinations of marks below with one another further
> increase the amount of mkmk lookup.

Yes, that's right.

Regards,
-- 
Theppitak Karoonboonyanan
http://linux.thai.net/~thep/