Appendix — Microsoft VOLT Integration

Microsoft VOLT offers an external authoring route for specialized OpenType layout work. FontLab’s Lookups panel can help inspect the layout involved in that exchange, while also providing its own visual editor and debugger.

The Lookups Panel

Use Window > Panels > Lookups to inspect features, their lookups, and the rules within a lookup. The panel initializes from available binary layout tables and keeps its visual document separate from Features-panel code. The visual editing and tracing workflow is taught in The Lookups Panel; contextual calls and their surrounding glyphs are developed in Contextual Substitution.

Transfer Features code into that document with the Lookups menu’s all-feature or selected-feature import commands. Transfer visual work back as FEA with Copy feature / Copy features or Copy lookup / Copy lookups, then paste and review it in Features. See The Features Panel for replacement scope and compilation. These transfers are useful independently of a VOLT round trip.

A successful Compile in Lookups makes its document supply normal previews and export. A successful Compile features in Features selects that code instead. The debugger tests its own document without changing this choice. Some imported constructions can be inspected in retained binary form but cannot yet be changed and recompiled visually without loss; heed the reported limitation before replacing working layout data.

VOLT Import and Export

Microsoft VOLT is a free Windows tool for authoring OpenType layout in fonts with TrueType outlines. It offers an external route when complex-script positioning or other specialized layout exceeds the intended FontLab workflow. Treat FontLab–VOLT interchange as experimental, particularly for contextual lookups. This is a static-font exchange workflow; keep variable and multi-master source work in FontLab.

FontLab can exchange a .vtp VOLT project and can read supported VOLT data from a font carrying its project tables. On the FontLab side, Import Features… accepts a VOLT project, and Export Features… offers a VOLT project format.

Keep the project with the corresponding exported font. The glyph identities and ordering used by the project must match that font. Exporting the project from one revision and pairing it with another revision's glyph set can invalidate the correspondence even when the family names agree.

After external editing, import into a copy of the source and compare the resulting features, classes, lookup order, flags, and text behavior. Name conversion can occur during exchange, including adaptations of class names or hyphenated names. Inspect the converted references rather than assuming that every identifier is reproduced literally.

Check complex contextual and attachment behavior after exchange. Review import/export diagnostics, then test the converted font with the same strings, script and language settings, and features as the original. Retain the original layout if a construction cannot be represented faithfully.

For an advanced standalone conversion, fontTools includes voltLib.voltToFea, which converts supported VOLT project data to FEA. This is an additional tool, not a claim about the implementation used by FontLab's own import command. Keep both the original project and the converted source, and compare behavior before replacing a working font's layout.

Neither a successful .vtp export nor a closed import dialog proves that a complex-script font is ready to ship. Test the complete intended text behavior after the final compilation and retain the native FontLab source for future changes.