[XeTeX] Problems with thickness of \frac rule and width of accents (\hat) with XeLaTeX

Ulrik Vieth ulrik.vieth at arcor.de
Mon Aug 16 00:15:35 CEST 2010

Hi,

I tested it with both XeLaTeX and LuaLaTeX (both from TL2010 pretest).
In short, the problem only occurs in XeLaTeX, but not in LuaLaTeX,
despite using the same macro packages and fonts for both engines.

I do not really understand the problem with the fraction rule thickness.
It probably should be the same on both engines (despite conceptual
differences), as it should be based on the same OpenType parameter
RadicalRuleThickness, but it seems to be different nonetheless:

XeLaTeX:
.......\kern4.7461
.......\rule(0.47998+0.0)x*
.......\kern2.97542

LuaLaTeX:
.......\kern3.43199
.......\rule(0.79199+0.0)x*
.......\kern2.98799

The LuaTeX value of 0.792pt at 12pt matches the scaled value of 0.66pt
at 10pt of the OpenType font parameter for XITS Math.

The XeTeX value of 0.48pt at 12pt matches the scaled value of 0.4pt
at 10pt, which is suspiciously similar to the default rule thickness
of CM fonts. I don't know how this comes about. I'm not sure if this
is an engine bug or if it could be caused by a macro problem.

As for the overly wide hat, this is obviously an engine bug in XeTeX.
The behavior is clearly wrong and the problem does not occur in LuaTeX.

I believe I have seen a similar problem before in XeTeX, which had
been fixed by Jonathan during a lunch break at EuroTeX 2009 last year.
I wonder if an old bug has resurfaced now or if anything went wrong
merging the bug fixes (or if it was a different bug that was fixed).

Regards, Ulrik

P.S: On second thought, I'm not sure any more if this was really
the same bug that was fixed or just a similar one. It could have been
about the positioning of math accents (e.g. centering \dot and \ddot)
rather than the width of wide math accents, but it also had to do
with an incorrect calculation of the size based on the subscripts.

On 08/15/2010 09:37 PM, drgz drgz wrote:
> Anyhow, I'm playing around with XeLaTeX (the newest version coming with
> MikTeX) trying to compile some documents. And almost everything is as it
> should be, except the thickness of the rule in \frac (does not get any
> thicker) and the width of the \hat accent (which gets wider than it should).
> I've attached a link to a compiled PDF which illustrates what I
> experience - see http://folk.ntnu.no/mitrevsk/temp/xelatex/ex.pdf
>
> No matter which OTF font with unicode-math support I select I experience
> this problem when I compile with XeLaTeX. Is there any way to fix this ?