[luatex] Unicode math issue with LuaLaTeX

[Ulrik Vieth]

Hi all,

last week I reported some weird results while testing unicode-math with 
xelatex und lualatex.

While the xelatex issue has been confirmed by others and seems to be a 
specific problem of 64 bit systems, the luatex issues remained unclear.

I have now done some more testing to investigate what's going on.

My test essentially consists of $\sqrt{x}$ followed by \showlists within 
the wrapper of a minimal LuaLaTeX document.

What happens is that the radical rule thickness is caclulated based
on the height of the radical glyph instead (as for TFM fonts) instead of 
using the RadicalRuleThicknessParameter (as for OpenType fonts).

(I'm looking at note 2 in section 5.5 of the LuaTeX reference,
which is about the difference between TFM and OpenType fonts.)

Here is the relevant output of \showlist for $\sqrt{x}$:

\mathon
\hbox(15.03995+0.09)x14.78, direction TLT
.\hbox(9.73+2.59)x9.28, shifted -4.90997, direction TLT
..\EU2/XITSMath(0)/m/n/10 √
.\vbox(15.03995+0.09)x5.5, direction TLT
..\kern0.39998      <- should be \kern 0.49997 (RadicalExtraAscender 50)
..\rule(9.73+0.0)x* <- should be \rule 0.66667 (RadicalRuleThickness 66)
..\kern0.49997      <- seems  OK \kern 0.49997 (RadicalVerticalGap 50)
..\hbox(4.41+0.09)x5.5, direction TLT
...\EU2/XITSMath(0)/m/n/10 ��
\mathoff

Form the log file, it appears that XITSMath is loaded in \fam 4,
but I do not see any \Umathradical... assignments for this font.

Could it be that some of the TFM-based \Umathradical... parameters
from cmsy + cmex in \fam2 + \fam3 are retained instead of applying
the OpenType math parameters from XITSMath in \fam 4?

Traditional \TeX always used to treat \fam2 + \fam3 as the source
of global \fontdimen parameters applicable to all font families.
Does this still hold for LuaTeX?  Does it no longer apply for XeTeX?

Could it be that unicode-math.sty is taking an inappropriate approach
by loading the new OpenType math font into a new family, instead of 
replacing and overriding the default value in \fam2 + \fam3?

So much for my analysis of the LuaLaTeX problem with unicode-math.
Hopefully, it should be simple now to fix it, once it is understood.

Regards, Ulrik

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