[XeTeX] fontspec and scaling

[Mike Maxwell]

On 1/17/2015 3:57 PM, Zdenek Wagner wrote:
> 2015-01-17 20:39 GMT+01:00 Mike Maxwell <maxwell at umiacs.umd.edu>:
>> ...I guess my question is: _If_ a font provides
>> optical sizes, then presumably telling Fontspec which point size to use
>> causes it to choose the optical size provided in the font (assuming one
>> exists for the requested point size).  If this is correct, then to re-phrase
>> my original question: If instead of specifying a point size for a particular
>> font/stretch of text, I tell Fontspec to use scaling, then does it choose
>> the closest optical point size provided in the font (and maybe
>> magnify/demagnify it slightly if the scaling doesn't result in an exact
>> optical point size)?  Or does Fontspec instead magnify/demagnify the glyphs
>> from the document's default point size?
>
> See section 7.6 (page 21) of the fontspec manual, it is explained there.

I read that, but it doesn't refer to the 'scaling' attribute (it does use 
\scalebox in example 16, but I presume that's different).  Maybe the fact that 
it doesn't mention scaling is my clue; scaling simply resizes whatever optical 
size is already chosen?

If that's correct, then I should be using the 'OpticalSize' attribute instead of 
'scaling'.  But how do I know whether a font supports optical sizes (and which 
specific sizes it has)?  Are such sizes embedded within a single font file, or 
do TTF fonts that support this have separate files for specific sizes?  There's 
nothing obvious in the output of fc-list -v.
-- 
	Mike Maxwell
	maxwell at umiacs.umd.edu
	"My definition of an interesting universe is
	one that has the capacity to study itself."
         --Stephen Eastmond