Variable vertical metrics

In a variable font with optical sizes can the vertical metrics be interpolatable ? I have been reading the spec and could not find something.

Technically yes, but not very recommendable. Which one do you want to variate and why?

All hhea, typo and win. Let’s say you want to tighten lines in display sizes.

I tried it in a file and Glyphs just exports the ones from the default master (my guess). There seems to be no variation exported.

Why would you want to solve this in a font? For which environment?

You would have to do this with ttx postprocessing. Definitely do not variate win values, it will cause clipping where you do not want it; and if you variate the others, make sure you Use Typo Metrics.

It’s not a specific case study. Just a generic question. I am just trying to figure out the possibilities.

So you could variate hhea and typo but you would not variate win.
I have a test file with different metrics for the text and display sizes and still Glyphs does not export an MVAR table. Is that intentional?

This would be handled by the MVAR table. It is on my list.