[HarfBuzz] Problem with shaping Serif fonts

[Khaled Hosny]

On Wed, Oct 09, 2013 at 01:39:17AM +0200, Oliver Meier wrote:
> Hello
> 
> I recently started playing with harfbuzz and encountered a strange problem.
> I don't know what I'm doing wrong, but somehow multiple f's shaped
> for serif fonts like DejaVuSerif or FreeSerif get grouped in pairs
> or so..
> 
>         hb_buffer_set_direction( hb_buffer, HB_DIRECTION_LTR );
>         hb_buffer_set_script( hb_buffer, HB_SCRIPT_LATIN );
>         hb_buffer_set_language( hb_buffer,
> hb_language_from_string("en", strlen("en")) );
> 
>         hb_buffer_add_utf8( hb_buffer, "ffff", strlen("ffff"), 0,
> strlen("ffff") );
>         hb_shape( hb_ft_font, hb_buffer, NULL, 0 );
> 
>         hb_glyph_info_t     *glyph_info =
>             hb_buffer_get_glyph_infos(hb_buffer, &glyph_count);
> 
> At this point glyph_count=2 instead of 4. In the kerning i see that
> f's are indeed "grouped".
> 
> Can someone point me in the right direction, or is this a bug?

https://en.wikipedia.org/wiki/Typographic_ligature#Latin_alphabet

BTW, if you have any code that assumes the number of output glyphs will
be equal to the number of input characters, it is wrong.

Regards,
Khaled