Non-compatible glyph (winding / components)

Definition

A glyph passes the contour-count and point-count checks but still cannot interpolate cleanly: either a contour's winding direction flips between masters (producing a self-intersecting blob mid-axis), or the glyph's component reference list differs across masters (the fvar table assumes the outline structure is fixed). Fix by reversing the flipped contour's direction in one master, or by aligning the component lists across all masters.

How Patens surfaces this

The Patens audit module checks for non-compatible-glyph across five teaching surfaces: the edit-panel inline issue list, the project-wide audit page, the release pre-flight check, the family hub, and the home-page project tile. Every surface shows the same plain-English explanation and links back to this page. This rule is detection-only — there's no automatic fix because the correction is design-dependent (it requires a judgment call about the glyph's intended shape or the font's intended behaviour). The audit message links to the specific glyph or field that needs attention.

Run this check yourself

Patens runs every audit rule live as you draw — including this one. The editor (in private alpha) shows non-compatible-glyph firing on real glyphs, or check your own work from the CLI:

npx patens audit your-project.font.json

Canonical references

Primary literature where this rule is established or explained. Drawn from the open-licensed corpus — browse the full 42-source canonical library or read the research artifact.

• OpenType Specification 1.9.1 ↗

  Microsoft Typography · 1997 · Microsoft Corporation· § gvar — Glyph Variations Table

  Beyond contour and point count, gvar interpolation requires every master to share the same outline structure: identical contour winding direction (so deltas don't flip orientation mid-axis) and identical component reference list (composite glyphs interpolate by referencing the same base glyphs at every master).

Related rules in Variable-font compatibility

• master-axis-missing Master missing axis value
• master-axis-out-of-range Master axis value out of range
• master-axis-unknown Master references unknown axis
• master-contour-count Master contour count mismatch
• master-point-count Master point count mismatch
• opsz-without-cap-x-divergence opsz axis vacuous (no distinct opsz masters)
• stat-format-mismatch STAT italic axis uses wrong format
• stat-instance-name-mismatch STAT composed name does not match fvar instance
• stat-missing STAT table missing (familyAxes unset)