Lock Advance Widths to a Grid in FontForge

FontForge does not include a real-time constraint toggle that actively forces advance widths to stay locked to arbitrary increments while manually editing, but you can enforce strict width increments using grid settings, batch transformations, or Python automation. This guide explains the native mechanisms available to snap advance widths during design and how to quantize advance widths to specific increments across an entire font.

Enable Grid Snapping During Manual Editing

FontForge allows you to snap points and metrics lines to your font coordinate grid, which helps maintain consistent metric increments while dragging glyph boundaries.

  1. Open FontForge and navigate to File > Preferences.
  2. Select Editing under the Generic section.
  3. Ensure Snap Distance is set to your preferred pixel threshold (typically between 8 and 12).
  4. In the main font view, open the View menu and verify that Snap to Grid is checked.

When working in the Glyph window with Snap to Grid enabled, dragging the right side bearing (advance width line) will automatically align to whole coordinate units.

Quantize Advance Widths Using Python

The most precise and reliable way to lock advance widths to a custom increment (such as multiples of 8, 10, or 16 font units) is through FontForge's built-in Python scripting engine. This automatically rounds the advance width of every selected glyph to your chosen step size.

  1. Select the glyphs you want to constrain in the Font View.
  2. Go to File > Execute Script.
  3. Choose the Python radio button.
  4. Enter the following script, replacing GRID_STEP with your desired increment:
import fontforge

GRID_STEP = 10  # Set your desired increment in font units

font = fontforge.activeFont()
for glyph in font.selection.byGlyphs:
    current_width = glyph.width
    # Round to the nearest increment
    new_width = int(round(float(current_width) / GRID_STEP) * GRID_STEP)
    glyph.width = new_width
  1. Click OK. FontForge will immediately update the advance widths of all selected glyphs to conform to the specified increment.

Set Fixed Widths for Monospace Fonts

If your goal is to lock all advance widths to a single uniform value rather than variable increments:

  1. Select all glyphs in the font window (Edit > Select > Select All).
  2. Go to Metrics > Set Width....
  3. Enter your target width (for example, 600) and select Set width to.
  4. Click OK.

To ensure the font is recognized correctly by operating systems as a fixed-pitch font, navigate to Element > Font Info > OS/2 > Panose and set Proportion to Monospaced.