[lltx] $n\choose k$-issue with OpenType math fonts

[Philipp Stephani]

Am 05.03.2011 09:23, schrieb Taco Hoekwater:
> On 03/05/2011 03:04 AM, Philipp Stephani wrote:
>>
>> No, the parameters are fine and I think the only difference is the size
>> of the delimiters, which is caused by LuaOTFLoad setting the
>> FractionDelimiterSize parameters which don't really exist in the fonts
>> (they are LuaTeX-only additions); changing line 116 of luaotfload.lua to
>>              mc.FractionDelimiterDisplayStyleSize = 1.7 * size
>> yields much better results. However, that is a font-specific design
>> issue, and I wonder whether LuaTeX should really use those parameters if
>> the font doesn't have them.
> 
> The problem is that nothing in the existing MATH parameters seems to
> apply. But perhaps the results could be better if the FractionDelimiter
> parameters were initialized based on some MATH parameter that does
> exist.

There surely exists a reason why Microsoft chose to leave out the three
parameters delim1, delim2, and sub2. Perhaps they thought that
distinguishing between \left(1 \atop 2\right) and 1 \atopwithdelims() 2
would be too surprising and seldom relevant. (On the LaTeX side, I have
encountered very few instances of \genfrac which wraps all the stacking
primitives.) I think better than guessing correct parameter values would
be to do the equivalent of \left(1 \atop 2\right) if the user requested
1 \atopwithdelims() 2 and the parameters are undefined.