Interpretation of FeatureVariationRecords is not according to spec

[tamirhassan]

Hi Lawrence and/or dev team,

When using Samsa (the version hosted on axis-praxis.org) to test OTVARs with several FeatureVariationRecords with intersecting conditions, Samsa's behaviour seems not to be according to spec.

The spec says: Feature variation records must be ordered in the order of precedence for the condition sets. During processing, the feature variation records will be read, and the corresponding condition sets tested, in the order in which they occur. If the condition set for a given record does not match the runtime context, then the next record is checked. The first feature variation record for which the condition set matches the runtime context will be considered as a candidate: if the version of the FeatureTableSubstitution table is supported, then this feature variation record will be used, and no additional feature variation records will be considered.
(https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2#featVarTbl)

This means that only one FeatureVariationRecord can ever be active for all glyphs in the font depending on slider placement. So, if you have two glyph substitutions, glyph A with condition X and glyph B with condition Y, if condition X is true, condition Y isn't checked when drawing glyph B by InDesign, Chrome and other software that (claims to) support OTVARs. But Samsa seems to carry on down the pecking order of FeatureVariationRecords until it finds one relevant for the current glyph.

[Lorp]

Thanks Tamir. Can you share the font you’re testing?

[tamirhassan]

Unfortunately I can't as it's an unpublished client project. But if you make changes, I am happy to test Samsa with this font to check that they work. Would this be OK for you? Have I explained the problem clearly enough?