Re: [Devel] Kerning problem with capitals

[Antoine Leca]

On Friday, December 10th, 2004 10:50 PM, George Williams va escriure:
>
> The LookupType 2 sub-tables (pair adjustment -- ie kerning) of GPOS
> allow for a "device table" which can contain a correction for each
> letter pair in pixels for any given ppem.
>
> They don't seem to have a connection to tt points (nothing the grid
> fitting instructions could control)... probably a good thing given the
> combinatorial number of points that would be needed for kerning.

That's too much a simplification.

GPOS LookupType 2, like any other, links to a ValueTable (see
http://www.microsoft.com/typography/otspec/gpos.htm, about 60%) which in
turn links to Anchor Table, which can be of 3 formats. Format 3 is indeed a
"device table", which is really another name for delta (the same idea as
TrueType DELTA[CP] instructions, but obviously in another format); format 1
is just a (x;y) position; but format 2 links a displacement to... a contour
point. So here you are back to the TT points.

By the way, it was historically the only one features (device table and
repositionning wrt contour points) that Apple acknowledged as superior in
TrueType Open with respect to GX  ;-).


Antoine