I made an underscore using a stretched hyphen (180% horizontally) and exported a Variable Font, the result is an underscore with the sidebearings/spacing of the 100% hyphen so letters are being pushed closer to it.
Intention (decomposed underscore)
If I add the decompose parameter in Variable Fonts, the file size increases from 315k to 473k.
Maybe there’s a solution in order to keep the spacing in stretched components?
There is a bug in CoreText (Apple text rendering) with components. But this seems to be a bug in Glyphs. Can you send me the file?
There are two things going on. First, the problem with CoreText I mentioned already. Second, the scale of components can’t be variated. The first two masters have a scale of 180%, the rest around 140. The default scaling of 180% is keep for all masters so the component looks to big in most masters.
The second master (Cp Th It) has a slant transformation. That is again not possible to put in a variable font, so the position is not correct.
So no direct bug in Glyphs. Maybe it should have warned about this…
Thanks for the explanation Georg, a warning would be nice, for sure.