[HarfBuzz] Streamlining hb_font_t some more

[Behdad Esfahbod]

On 15-10-09 12:33 PM, Jonathan Kew wrote:
> 
> 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.)

Jonathan,

Can you please point me out to the exact logic you use?  I want to implement
the same.

Thanks,

behdad