Re: Supporting stylistic sets

["समीर सिंह Sameer Singh" <lumarzeli30@gmail.com>]

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Forgot to attach, here it is.

On Sat, Sep 24, 2022 at 10:39 PM समीर सिंह Sameer Singh <
lumarzeli30@gmail.com> wrote:

> On Sat, Sep 24, 2022 at 9:44 PM Eli Zaretskii <eliz@gnu.org> wrote:
>
>> > From: समीर सिंह Sameer Singh <lumarzeli30@gmail.com>
>> > Date: Sat, 24 Sep 2022 21:20:03 +0530
>> > Cc: emacs-devel@gnu.org
>> >
>> > On Sat, Sep 24, 2022 at 8:52 PM Eli Zaretskii <eliz@gnu.org> wrote:
>> >
>> >  > From: समीर सिंह Sameer Singh <lumarzeli30@gmail.com>
>> >  > Date: Sat, 24 Sep 2022 20:32:26 +0530
>> >  > Cc: emacs-devel@gnu.org
>> >  >
>> >  > no, the same would work
>> >
>> >  Then I don't understand how will HarfBuzz know to apply the first tag
>> >  to 'i', but the second one to 'l'.
>> >
>> > The font file has a GSUB table for this purpose
>>
>> I'm sorry, I still don't understand.  (I'm not an expert on fonts, so
>> I'd appreciate a slightly more detailed explanations.)  Are you saying
>> that each tag can be used by a single character in a font?  IOW, no
>> feature tag can ever be shared by two or more characters in a font?
>>
>
> IIUC, then yes.
>
>
>> The HarfBuzz docs says:
>>
>>   The hb_feature_t is the structure that holds information about
>>   requested feature application. The feature will be applied with the
>>   given value to all glyphs which are in clusters between start
>>   (inclusive) and end (exclusive).
>>
>> This seems to say that we need to set START and END of each feature to
>> buffer positions of the characters to which we want the feature to be
>> applied.  That is why I said that START and END should be set
>> separately for each feature, according to the positions of the
>> corresponding characters in the buffer submitted to hb_shape_full.
>>
>
> I don't think that is the case, I have attached a slightly modified
> harfbuzz-tutorial[1],
> where I have defined four features for a,g,i and l respectively with the
> same start and end variables.
> It works as expected.
>
> You can provide it with the path to a firacode font file and the text
> which it has to display and it will produce a png.
>
> [1] https://github.com/harfbuzz/harfbuzz-tutorial
>

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