Fix FontForge Export Format Conflicts

Exporting fonts from FontForge often triggers errors or warnings when internal metadata, outline types, or table structures clash with the requirements of your target output format. Resolving these conflicting format specifications requires identifying whether the mismatch stems from outline point types, conflicting vertical metric definitions, or overlapping OpenType naming tables, and then aligning FontForge’s internal settings to match your desired export target (typically TrueType or OpenType-CFF).

1. Resolve Outline Type Conflicts (Quadratic vs. Cubic)

Font formats strictly enforce specific mathematical representations for curves. TrueType fonts (.ttf) require quadratic Bézier curves, while OpenType fonts with CFF outlines (.otf) require cubic Bézier curves.

  • To export as TTF:
    1. Navigate to Element > Font Info > Layers.
    2. Set the outline type to Quadratic.
    3. Alternatively, select all glyphs (Ctrl+A) and choose Element > Simplify > Convert to Quadratic.
  • To export as OTF (CFF):
    1. Navigate to Element > Font Info > Layers.
    2. Set the outline type to Cubic.
    3. Select all glyphs and choose Element > Simplify > Convert to Cubic.

Attempting to export cubic curves into a TrueType container without conversion causes FontForge to generate an automatic, often imperfect, rasterization or export failure.

2. Standardize Conflicting Vertical Metrics

A frequent source of critical export errors is discrepancies among the three separate vertical metric systems stored in modern fonts: OS/2 (Typo), OS/2 (Win), and hhea. When these values contradict each other, cross-platform line-spacing anomalies occur.

  1. Go to Element > Font Info > OS/2 > Metrics.
  2. Synchronize your vertical values:
    • Ensure Win Ascent and Win Descent accurately enclose your maximum glyph boundaries to prevent clipping on Windows.
    • Check Typo Ascent and Typo Descent to define your base line spacing.
  3. Check the Use Typo Metrics checkbox (fsSelection bit 7) under the OS/2 > Misc tab. This instructs modern operating systems to prioritize consistent typographic metrics over legacy calculations, bypassing conflicts between OS/2 and hhea tables.

3. Clear OpenType and TrueType Name Table Clashes

Conflicting naming specifications arise when legacy 4-style family models (Regular, Italic, Bold, Bold Italic) collide with modern OpenType naming schemes:

  1. Open Element > Font Info > TTF Names.
  2. Ensure that Family (ID 1) contains only standard style-linked groups.
  3. If your family contains extended weights (e.g., Light, Medium, Black), set Preferred Family (ID 16) and Preferred Styles (ID 17) explicitly.
  4. Remove any manual, redundant table entries that duplicate default generated fields, as manual overrides often conflict with FontForge’s automated OpenType name generation.

4. Run the Validation Engine

Before generating the final font file, use the built-in validator to isolate non-compliant structures:

  1. Choose Element > Validation > Find Problems.
  2. Select checks for Non-Integral Coordinates, Self-Intersecting Paths, and Missing Points at Extrema.
  3. Fix the detected geometry errors, as corrupt paths prevent proper table compilation during the export process.

5. Configure Export Options

When saving the file via File > Generate Fonts:

  1. Choose your desired output format from the dropdown menu (e.g., OpenType (CFF) or TrueType).
  2. Click the Options button next to the format selection.
  3. Uncheck PS Names if generating a TrueType font to prevent PostScript metadata injection.
  4. If converting cubic outlines to TrueType on the fly, enable Apple or OpenType output depending on the targeted environment, but keep Validate Before Saving active to catch residual format violations before writing the final binary.