Why FontForge Shows Missing Glyph Errors

FontForge displays missing glyph errors when a font project lacks required character definitions, contains broken composite references, or suffers from encoding mismatches between its internal mapping and target platforms. These errors commonly arise during font validation or export, pointing to issues such as a missing .notdef character, incomplete platform character maps (cmap tables), or unassigned Unicode slots. Understanding these core triggers allows you to quickly locate empty glyph slots, repair component dependencies, and successfully generate valid font files.

1. The Missing .notdef Glyph

The most frequent cause of missing glyph warnings is the absence of the .notdef (not defined) glyph at character code 0. Both OpenType and TrueType specifications strictly require this glyph, as it serves as the fallback symbol (often drawn as an empty box or a box with a question mark) rendered by operating systems when a requested character is not supported by the font. If .notdef is empty, unassigned, or completely absent, FontForge will generate an error during font compilation and validation.

2. Broken Composite Glyph References

Composite glyphs—such as accented characters like é or ñ—frequently depend on base characters (such as e or n) and separate accent components. If you create a composite glyph that points to a component you later deleted, renamed, or left empty, FontForge registers a missing glyph error. The software cannot construct the final compound outline without every required child component present in the project.

3. Encoding Table and Character Map (cmap) Mismatches

Fonts often contain multiple character map (cmap) subtables to ensure compatibility across different operating systems, such as Windows (Unicode BMP) and macOS (Mac Roman). If a glyph is mapped in one platform table but omitted in another, FontForge warns that the glyph is missing from the respective target encoding. Switching the font's active encoding scheme under the Encoding menu to a standard that includes slots you have not yet drawn will also trigger visual and technical missing-glyph indicators.

4. Omission of Essential Standard Characters

Font validation checks expect a minimum standard set of characters for basic typographic rendering. Missing characters often include:

  • Standard space (uni0020)
  • Non-breaking space (uni00A0)
  • Basic punctuation marks (period, comma, hyphen)

When you run Element > Validation > Find Problems or export to formats like TTF or OTF, FontForge scans for these essential typographical metrics. If standard space widths or basic glyphs are undefined, a warning is raised.

5. Corrupted or Incomplete File Imports

Importing glyphs from external vectors (such as individual SVG files or fragmented UFO directories) can leave character slots partially declared in the font's internal database without outline data attached. FontForge recognizes the slot assignment in the database, but because the outline or glyph reference data is null, it flags the entry as missing during generation.

How to Fix Missing Glyph Errors

  • Create the .notdef glyph: Go to the first slot in the font view, open it, and draw a simple rectangle outline to serve as the default fallback shape.
  • Re-encode the font: Navigate to Encoding > Reencode and select Unicode (BMP) or ISO 10646-1 (Unicode, Full) to eliminate legacy platform encoding discrepancies.
  • Unlink composite references: If accented characters cause issues, select them and navigate to Edit > Unlink Reference to convert components into standalone bezier outlines.
  • Run Validation: Open Element > Validation > Find Problems, check the specific missing glyph categories, and let FontForge pinpoint the exact slots requiring attention before final export.