Write STAT entries independently from fvar instances

[kontur]

As far as I can tell there seems to have been an implicit restriction to making STAT entries a "copy" of sorts of designspace fvar instances. In my understanding of the STAT table, the STAT table is much more likely to be a superset of instances, however, but this is currently not possible.

For example a font might (for whatever reason) declare only key instances in the fvar table, yet a more gradual definition should be exposed via the STAT table.

In light of recent Google fonts variable font requirements cases where the fvar instances are a subset of STAT named entries is in fact to be expected to be the rule and not the exception. The reasoning behind this is quite sound, particular with multi-axis fonts where the number of possible fvar combinations flood application font menus.

1. From what I can tell there is some sanitizing in the library that will, in fact, drop these entries when not present as fvar instances. This should not happen.
2. Entries not present as fvar instances need their names written, if missing.

[kontur]

Find a simple test case for this here.

From a rudimentary glyphs file with 2 axes and 4 masters and a few instances I am creating a designspace and extending it with STAT definitions that are more gradual that the defined instances. When you run test.sh you'll see the generated STAT-dump.xml drops those definitions which are not also defined as fvar instances originally.

[madig]

It could be done, but would require someone to put the work in. I currently have no time or interest in Google's font requirements. You can wing it yourself by using fontTools' STAT builder API in a custom build script.