[HarfBuzz] disabling Arabic shaping when direction is vertical

[Behdad Esfahbod]

On 14-09-15 05:40 PM, Jonathan Kew wrote:
> Hi Behdad,
> 
> If the harfbuzz buffer direction is vertical (TTB or BTT), I think we should
> refrain from doing Arabic shaping.[1]
> 
> We could do this, for example, by adding an early return such as
>   if (unlikely (HB_DIRECTION_IS_VERTICAL (buffer->props.direction)))
>     return;
> in setup_masks_arabic(), so that the shaping analysis and setting of per-glyph
> features doesn't happen. WDYT?

I can agree to that.  In that case, lets also not collect the features.

b

> (It's less clear to me what should be done in Indic and similar shapers, so
> I'm ignoring that for now...)
> 
> JK
> 
> 
> [1] See CSS Writing Modes, section 5.1.1 Vertical Typesetting and Font
> Features: "...characters from horizontal cursive scripts (such as Arabic) are
> shaped in their isolated forms when typeset upright".
> 

-- 
behdad
http://behdad.org/