Yet another post on rendering prime symbols
Frédéric Wang
what it is about [1]. We want to write MathML formulas with prime
symbols such as "x'". The markup recommended by the Math WG is
<msup><mi>x</mi><mo>'</mo></msup>
However, because the glyphs for these symbols are already shrunk and
raised from the baseline in most fonts, authors have rather used
<mrow><mi>x</mi><mo>'</mo></mrow>
The markup <mi>x'</mi> has even been proposed in some cases. Bugzilla
contains bugs to improve the rendering of the recommended markup [2] as
well as the other cases which also have inconsistencies [3]. William F.
Hammond has a page with several testcases [4].
In the case of the recommended markup, Karl suggested to reverse the
scale and fix the translation [5]. Recently, someone mentioned on the
MathML mailing list the "ssty" feature of OpenType which could help to
do this work when rendering the glyph. As you know, we are currently
relying on STIX fonts whose official version does not have OpenType
features (however, the "XITS fonts" [6] do). Other OpenType Math fonts
we plan to support in the future (Asana Math, Cambria Math and Neo
Euler) seems to support this ssty feature as well.
I've seen that some work has be made in Mozilla to use Harfbuzz as a
text rendering engine. I don't know what is the current status, but I'm
wondering whether this library would help to enable the ssty feature
when drawing primes? I've tried some experiments with
-moz-font-feature-settings but it does not seem to have any effect...
Frédéric Wang
[1] See also http://www.w3.org/TR/MathML3/chapter7.html#chars.pseudo-scripts
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=442637
[3] https://bugzilla.mozilla.org/show_bug.cgi?id=140439
[4] http://www.albany.edu/~hammond/gellmu/primeaccents2.xhtml
[5]
http://groups.google.com/group/mozilla.dev.tech.mathml/browse_thread/thread/066a97ae5456d41a#
[6] https://github.com/khaledhosny/xits-math