FontForge Simplify Command Explained

The Simplify command in FontForge is an optimization tool designed to reduce the total number of points on a glyph's contour while preserving its original shape as closely as possible. This article explains how the command functions, why point reduction is critical in digital typography, and how FontForge determines which points to eliminate.

How the Simplify Command Operates

When you run the Simplify command (accessible via Element > Simplify > Simplify or the shortcut Ctrl+Shift+M), FontForge analyzes the selected Bézier curves and contours. It evaluates sequences of connected curve segments to see if they can be mathematically replaced by fewer, longer Bézier curves without exceeding an internal error threshold.

If the new, simplified curve deviates from the original path by less than the defined margin of error, FontForge removes the intermediate on-curve points and adjusts the off-curve directional handles accordingly.

Key Actions Performed by Simplify

  • Removes Redundant Points: Autotraced artwork or digitized scans often contain hundreds of unnecessary nodes. Simplify eliminates clustered or collinear points along straight lines and gentle curves.
  • Preserves Corners and Extremities: The algorithm detects sharp directional changes (corners) and retains the points that define them, preventing corners from turning into unintended rounded arcs.
  • Straightens Near-Lines: If a series of points forms a curve that is nearly flat, the command straightens the segment and discards the unnecessary curve handles.
  • Recalculates Control Handles: When points are removed between curves, FontForge recalculates the remaining off-curve handles to maintain the contour’s original curvature and smoothness (continuity).

Why Simplify is Important in Font Creation

  1. Smaller File Sizes: Every node and control point in a glyph requires data. Fewer points reduce the final compiled font file size (such as TTF or OTF).
  2. Better Rendering and Rasterization: Modern font engines render outlines faster and with fewer rendering artifacts when curves are defined cleanly with minimal, well-placed points.
  3. Easier Manual Editing: Reducing a path to its essential extrema makes adjusting, scaling, and interpolating glyphs far more manageable for the designer.
  4. Optimized Hinting: Font hinting works best when contours are clean and devoid of stray points, especially on straight stems and baseline curves.

Standard Simplify vs. Simplify More

In addition to the standard command, FontForge includes Simplify More. While standard Simplify uses fixed default values, Simplify More opens a dialog box allowing you to adjust specific parameters:

  • Error Threshold: Defines how far (in font units) the new path is allowed to stray from the original contour before FontForge refuses to remove a point.
  • Angle Limits: Specifies the threshold angle at which a point is recognized as a sharp corner and protected from smoothing.
  • Handle Length Limits: Prevents FontForge from generating disproportionately long Bézier handles that can cause rendering glitches or self-intersecting loops.