Optionally keep empty lookups for interpolatability #3073
Conversation
| lookup = ot.Lookup() | ||
| lookup.LookupType = 2 | ||
| lookup.LookupFlag = 0 | ||
| lookup.SubTable = [] |
There was a problem hiding this comment.
Are we sure that we don't actually want tp have lookup.SubTable = None here instead of the empty list?
We need to check what varLib makes of these, whether it disinguishes one with SubTable=[] vs one with SubTable=None. In general what we want in these cases is that this particular lookup "does not participate" in variations basically.
There was a problem hiding this comment.
This would be really interesting indeed, to allow sparse models at the lookup level.
There was a problem hiding this comment.
but it's impossible with FEA because truly empty lookups have no type, it's their rules that give them their type. Unless you want to hack this by adding dummy pos .notdef .notdef 0 ...
There was a problem hiding this comment.
It's okay to give the lookup type 0. Except that both fonttools compiler and varLib would choke on it then. :(
| @@ -1069,6 +1089,8 @@ def add_lookup_call(self, lookup_name): | |||
| assert lookup_name in self.named_lookups_, lookup_name | |||
| self.cur_lookup_ = None | |||
| lookup = self.named_lookups_[lookup_name] | |||
| if lookup is None and self.cur_feature_name_ in ("kern", "dist"): | |||
There was a problem hiding this comment.
why just kern/dist? I'd leave that out unspecified.
Maybe we can have a global setting in the Builder that controls whether to emit empty lookups or not, and activate that selectively from ufo2ft when building VFs
There was a problem hiding this comment.
I think you need to specify the subtype of the lookup and I'm not sure how to make them universal.
WIP.
For dealing with googlefonts/fontmake#894 (comment), we may want to inject empty lookups into fonts, to give varLib something to grab onto. We could do this at the feature level in ufo2ft, before passing the font to varLib to merge. This is some hacking to make feaLib not drop empty lookups.