Thanks for the reply, Will.
On 2/10/2016 4:52 PM, Will Robertson wrote:
My understanding here is that Variant Selector acts like a character
to produce a difference glyph (analogous to a ligature), so doesn’t
need shaping/positioning information.
That's true, but the fonts that I am familiar with have a substitution
lookup (similar indeed to a ligature) that says "replace character X
followed by VS1 with character Y." I saw nothing like that in XITS.
For maths typesetting, this is activated with “script=math”, and there
are a bunch of (~50, too tired to look up the number now) font
parameters stored directly within the font to handle most spacing needs.
Yes, I saw a bunch of OT features in the font but nothing that looked
familiar in terms of accent positioning and the like. Which may be my
own ignorance, of course.
However, I am not sure about the technical side of applying maths
accents like \ddots. These are placed not as combining marks but with
the XeTeX primitive \Umathaccent (which can also place the accent
below the letter, etc.). I can only assume that a font designer can
provide additional details to fine-tune the spacing for certain cases;
to me it would seem necessary.
I wonder how this is done (and I agree it seems needed). It doesn't
seem to be with the usual OT mechanisms.
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