Class-based kerning and variable fonts

hi—I’m exporting a variable font with two axes, weight and opsz, and it looks like kerning pairs based on classes aren’t being honored in the exported file. is it possible to flatten or expand kerning classes upon VF export? (additionally, is doing so a terrible idea for any technical reason?)

the glyphs file itself is fine, and class-based pairs are fine if I export instances to OTFs, so just trying to verify it’s something going on with the Variable file.

There could be multiple things interfering. One of them is the exceptions you have in one master but not in the other.

Is it a multi-script typeface?

nope, Latin only. there’s 2 axes, weight and optical size, 8 instances of each. some characters have brace layers, all in the same place for each sequence. also .sc, .case, fractions, supers & subs, a couple of discretionary shapes in lowers, one in uppers, a discretionary ligature to make a specific character (this is for a city that uses a specific star shape as a logo, so had to include that as a discretionary), and I think that’s it.

the instances are all 300-900 for both text & display. for example Text Thin and Display Thin are both set at 300. could it be that?

Try to sync kerning exceptions with this mekkablue script:

What version of Glyphs do you have?

latest cutting edge, I think: Version 2.6.2 (1252)

the script gave a lot of results, thank you. is it that all masters need some value in kerning pairs across the entire series to properly interpolate? that would make sense, and is something I hadn’t considered.

(also, can that value be set to zero, rather than being a blank field? that could be useful.)

The Variable font export should add the missing kerning entries automatically, At least it is supposed to do that. I’ll have a look.

i’ll send you a copy of the file in its current state so you’ll have something to test against.

in the meantime @mekkablue’s script only returned about 50 items out of sync so that’s not a problem to fix. i’ll post a result once i’ve tried that. thanks, both of you.

The problem is that the kerning in some masters is not class bases but set as exception. Habe a look at the open locks in the LT pair in the Bold masters.

thanks for looking, Georg. the reason I didn’t see it is that I usually don’t set exceptions, so I simply wasn’t looking at that part of the kerning panel.

edit: removing exceptions was exactly the problem and fixed export issue I was seeing. thanks again.