[XeTeX] support for variation & multiple master fonts

[Jonathan Kew]

An informal poll of user opinion:

How many of you care about support for AAT variation fonts (like  
Skia), and/or Multiple Master fonts (MinionMM, MyriadMM, etc.), and  
at the same time are *not* running Tiger (10.4.x)?

Bear in mind that (as far as I can tell) Adobe has dropped support  
for MM fonts, and so there are not likely to be many more of them  
appearing (and those that exist won't be maintained and updated). And  
Apple has shown no sign of interest in continuing to develop the AAT  
variation technology. So although XeTeX currently supports these,  
they're looking rather like dead-end paths in the font world.

What I'm likely to do (as a consequence of other internal changes) is  
to drop support for variations on pre-10.4 systems in the next update  
of XeTeX. This is because I am changing the way XeTeX interacts with  
the xdv->pdf driver, to make it more feasible to create a portable  
back end. This may also, incidentally, help performance somewhat  
(though I don't know yet if it will be a substantial improvement).

Unfortunately, the APIs that the new PDF back-end will use for  
variation support are only available on Tiger, not on earlier  
systems. So this means that, assuming I go ahead with this change,  
variations (and MM axes) will no longer work on Jaguar and Panther  
systems.

I note, in any case, that these APIs (despite being new on 10.4!) are  
also already flagged by Apple as being "deprecated". While I don't  
know anything about Apple's future plans, this does make me wonder  
whether support for the whole variation/MM idea will eventually be  
dropped from the system.

Sure, it's fun to be able to play with different settings of Skia --  
I've used it myself in a few documents, and it's been neat to use the  
width axis to fit titles neatly to the available space, for example.  
And those of us who have the multimaster Minion and Myriad fonts no  
doubt have our favorite settings. But as far as I understand it,  
newer OpenType versions like Minion Pro are no longer MM; instead,  
you get a range of separate instances. (Right? I don't have a current  
Adobe collection to check this stuff!)

Anyhow, at this time I'd be interested to know whether people care  
much about var/MM support, in particular on older OS versions -- how  
many people will be impacted, and how badly, if it becomes a 10.4- 
only feature in XeTeX? I know that's a fairly vague question, but I'd  
appreciate any comments, either here on the list or privately.

Thanks,

JK