On 26.10.2015 11:30, Simon Cozens wrote:
On 09/10/2015 15:09, Khaled Hosny wrote:
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.
OK; I've implemented support in Harfbuzz for getting these metrics out
of the OS/2 table.
I don't think it's that simple, according to specs you need to check
with fsSelection (bit 7), and use sTypo* metrics only when this bit is
set. But of course there's no guarantee that font was generated properly
and sTypo* values are meaningful when this bit is set or garbage if it's
not. Also this bit selector is supposed to be consistent with os/2
version being >= 4; otherwise an option is to use usWin* metrics. And
usWin* metrics are broken too sometimes, just recently I had to fix and
issue when signed value was written to unsigned usWinDescent, which
won't play nice as you can imagine. Also there is an 'hhea' table that
could provide 'similar' functionality, but not always...
But probably more important is that this functionality doesn't seem to
belong to harfbuzz in a first place, as it never needs global metrics
internally (or does it?). If you only need a couple of fields it's easy
to get them manually from font blob.
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