[HarfBuzz] Streamlining hb_font_t some more

[Jonathan Kew]

On 9/10/15 14:32, Simon Cozens wrote:
> On 09/10/2015 15:09, Khaled Hosny wrote:
>> On Thu, Oct 08, 2015 at 11:54:09AM -0400, Behdad Esfahbod wrote:
>>>                                                                So, from my
>>> point of view, you should NOT use this for line height calculation.  You
>>> should just use the typographical ascender/descender of the font and hence not
>>> need glyph bounding boxes in Sile at all.
>>
>> Yes please, an approach similar to what browsers do would be much
>> appreciated. TeX way of handling interline spacing has always been
>> cumbersome and confusing (not that I know exactly what SILE do now, but
>> the further from TeX way here the better).
>
> OK. SILE currently does the same as TeX, and I agree that it's confusing.
>
> I have just released SILE 0.9.3, so now I have a clean slate to play
> with. I have merged the new shaping pipeline (sending whole paragraphs
> to Harfbuzz) and moved over to HB OT functions, dropping the Freetype
> dependency. This makes a *lot* of things happier. Bidi support is much
> better, and it's now *much* faster too: my 28 page test document which
> used to take 15 seconds in 0.9.3 now takes 5 seconds.
>
> I'm happy to look at using the font ascender/descender metrics for line
> heights - is there a good way to get those values out of Harfbuzz yet?
> Grepping the repository doesn't turn up much. (There's also typographic
> line gap information in the _hea table - should I be using that?)

You probably want to be using the "typographic" metrics from the OS/2 
table, if present, with the hhea metrics as a fallback for fonts that 
don't have OS/2. (They're rare, but can exist at least on OS X.)

JK