View Kerning Values in a Matrix Grid in FontForge

FontForge provides a built-in matrix view that allows type designers to inspect and edit class-based kerning pairs across an entire font project. This guide outlines the exact steps to locate and open the kerning matrix grid via the GPOS lookups menu, navigate the intersection of glyph classes, and interpret or adjust kerning offset values directly.

Step 1: Open the Font Info Window

Launch FontForge and open your font file (.sfd, .otf, or .ttf). From the top menu bar, click on Element and select Font Info (or press Ctrl + Shift + F on Windows/Linux, Cmd + Shift + F on macOS).

Step 2: Navigate to GPOS Lookups

  1. In the left-hand navigation pane of the Font Info dialog, click on Lookups.
  2. At the top of the Lookups panel, switch to the GPOS tab (Glyph Positioning). This section contains all positioning rules, including pair adjustments and kerning.

Step 3: Open the Kerning Subtable

  1. Scroll through the list of lookups until you find the feature labeled 'kern' Horizontal Kerning in Latin lookup (or your specific script's kerning feature).
  2. Click the small + icon next to the 'kern' feature to expand its subtable list.
  3. Select the class-based kerning subtable.
  4. Click the Edit Data button on the right side of the window (or double-click the subtable name).

Step 4: Access the Kerning Matrix

Once the class kerning dialog appears:

  1. Look at the display options or tabs inside the subtable editor. FontForge displays the defined glyph classes for the first glyph (left side) and the second glyph (right side).
  2. Click on the Kerning Matrix or Pairs tab/view.
  3. FontForge will generate a two-dimensional grid:
    • Rows (Vertical axis): Represent the first glyph or first glyph class (the left character).
    • Columns (Horizontal axis): Represent the second glyph or second glyph class (the right character).
    • Cells (Intersection points): Display the kerning offset value in font design units. A negative value brings glyphs closer together, while a positive value adds spacing.

Step 5: Viewing and Editing Values

  • Inspection: Empty cells represent pairs with no kerning override (defaulting to normal side-bearing metrics). Cells containing numbers indicate active kerning overrides.
  • Editing: Double-click on any cell within the matrix grid to modify the numeric offset value directly.
  • Applying Changes: Once you have reviewed or modified the values, click OK in the subtable window, then click OK in the Font Info dialog to commit your adjustments to the font database.