Fix Missing Glyphs When Generating TTF in FontForge

When exporting a font project to TrueType Font (TTF) format in FontForge, designers frequently find that specific glyphs present in the workspace vanish in the final generated file. This issue typically stems from missing Unicode values, improper contour direction, unmerged vector overlaps, or format incompatibility between cubic and quadratic Bézier curves. This guide explains the core technical reasons glyphs disappear during the TTF compilation process and provides direct solutions to restore them.

Missing or Incorrect Unicode Encodings

The most frequent cause of missing glyphs is an unassigned or invalid Unicode code point. FontForge allows you to draw in arbitrary slots, but operating systems and text engines identify glyphs using their mapped character codes. If a glyph has no Unicode value or is mapped to a slot outside standard encoding ranges, the TTF generation process may exclude it from the character mapping (cmap) table, making it invisible to typing applications.

To resolve this:

  1. Select the affected glyph.
  2. Go to Element > Glyph Info.
  3. Under the Unicode tab, verify that a valid code point is assigned.
  4. Ensure the font’s encoding layout is set properly via Encoding > Reencode > ISO 10646-1 (Unicode, BMP) or Unicode (Full).

Incorrect Path Direction (Contour Winding)

TrueType rasterizers rely on specific path directions—known as the non-zero winding rule—to determine which areas of a vector are filled and which are empty (like the counters in an "O" or "B"). In TrueType outlines, exterior paths must wind clockwise, and interior paths must wind counter-clockwise. If these directions are inverted or mixed, the rasterizer may treat the entire glyph as an empty space.

To fix contour winding:

  1. Select all glyphs using Edit > Select > Select All.
  2. Navigate to Element > Correct Direction.
  3. If necessary, manually inspect problem glyphs using Element > Clockwise.

Overlapping Paths and Intersecting Vectors

FontForge permits overlapping shapes during the drafting stage (such as crossing stem lines or accents placed over letters). However, the TrueType format struggles with complex self-intersections during conversion, causing renderers to drop the malformed contour entirely upon generation.

To resolve overlapping vectors:

  1. Select the problematic glyphs.
  2. Go to Element > Overlap > Remove Overlap (or press Ctrl+Shift+O / Cmd+Shift+O).
  3. Clean up the resulting geometry by selecting Element > Simplify > Simplify.

Cubic vs. Quadratic Spline Incompatibilities

FontForge often works in cubic Bézier curves (standard for PostScript and OpenType fonts), whereas TrueType format strictly requires quadratic Bézier curves. When generating a TTF file, FontForge automatically converts cubic splines to quadratic splines. If a glyph has intricate details, unusual point placements, or missing on-curve extrema, the conversion algorithm can fail and omit the outline.

To prevent conversion drops:

  1. Open Element > Font Info.
  2. Select the Layers panel.
  3. Switch the outline layer type from Cubic to Quadratic before generating the font.
  4. Add necessary on-curve extrema by selecting all glyphs and clicking Element > Add Extrema.
  5. Round coordinate positions to integers via Element > Round > To Int, as TrueType coordinates do not support fractional points.

Ignored Validation Errors on Generation

When clicking File > Generate Fonts, FontForge runs an automatic validation check. If an alert box appears warning that errors were detected, clicking through without reviewing the warnings often results in the compiler dropping corrupt glyphs.

To catch issues early:

  1. Run Element > Validation > Find Problems.
  2. Check for missing points, intersecting paths, and non-integral coordinates.
  3. Resolve any errors identified in the validation report prior to generating the TTF file.