[HarfBuzz] Thai shaping and dotted circle

[Jonathan Kew]

On 30/9/13 19:08, Behdad Esfahbod wrote:
> On 13-09-30 09:05 AM, Toresson, Alexander (EXT) wrote:
>> Hello all,
>>
>>
>> For for example Bengali, a dotted circle (U+25CC) is inserted before
>> standalone combining marks. The same is not done for Thai, except for the
>> first character in a paragraph/text (--bot for hb-shape/hb-view). Why?
>> According to http://www.microsoft.com/typography/otfntdev/thaiot/other.htm,
>> “invalid combinations” should cause a dotted circle to be inserted.
>
> That's something we want to fix, but we have not got to yet.
>

....although it raises the difficult and potentially controversial 
question of what exactly is an "invalid combination".

Historically, there have been numerous problems when shaping engines 
such as Uniscribe enforce a particular idea of what is "valid", 
typically based on majority-language spelling conventions for a certain 
script. This may render the engine/fonts unusable for users of minority 
languages, if they want to use marks (or other letters) in contexts or 
combinations that were not considered by the majority-language-biased 
implementers.

JK

>
>> Speaking of invalid combinations, it seems like HarfBuzz allows for example
>> U+0E48 to be combined with for example latin U+0041, which seems rather
>> permissive.
>>
>>
>>
>> I have been testing HarfBuzz 0.9.21.
>>
>>
>>
>> BR, Alexander
>>
>>
>>
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>