[XeTeX] fontspec and scaling

[maxwell]

On 2015-01-20 04:55, Zdenek Wagner wrote:
> If I understand the scaling attribute correctly, let say, you have
> scaling=1.4 and you request \normalsize which id 10pt. Fontspec will
> multiply it and request 14pt font size instead. If there is an optical
> size available, it will be used.

This last was my question: will the scaling attribute in Fontspec 
automatically use an optical size (or since scaling will probably not 
result in an exact optical size, will Fontspec scale the closest optical 
size).

>> ...how do I know whether a font supports optical
>> sizes (and which specific sizes it has)?
> 
> fontinfo -z FILENAME

There isn't any 'fontinfo' program on our Linux system, and I couldn't 
find such a program in a websearch.  (There is a Firefox plugin by that 
name, written by Jonathan Kew, but that doesn't seem to be what you're 
referring to.  Also some libraries for Python etc.)  There is however a 
"font information" dialog box in FontForge.  One of its tabs is "Size".  
For the font I'm working with (MvElaafNormal.otf.ttf), the "design size" 
shows up as 0.0 pts.  I suspect that means there are no optical sizes in 
this font.

But none of the other fonts I looked at with FontForge (including Charis 
SIL and several free Adobe fonts) have anything but 0.0pts in the 
"design size".  Maybe it's only very high end fonts that have multiple 
optical sizes?  In which case I've been on a wild goose chase worrying 
about whether Fontspec's scaling function will choose the appropriate 
optical size...

    Mike Maxwell
    University of Maryland