Smooth Points vs Corner Points in FontForge
In FontForge, vector outlines are defined by on-curve points and their associated control handles, with smooth points and corner points serving as the primary building blocks. Smooth points ensure continuous, seamless curvature across a contour by locking control handles in a straight line, whereas corner points allow for sharp turns by letting each control handle move independently. Understanding the mechanical and visual differences between these two point types is essential for drawing clean, predictable glyph outlines in digital typography.
Corner Points
A corner point marks a location where a path abruptly changes direction, such as the apex of an uppercase "A" or the vertices of an "E".
- Handle Independence: The primary mechanical characteristic of a corner point is that its incoming and outgoing Bézier control handles operate entirely independently of each other. Changing the angle or length of one handle has no effect on the other.
- Curvature: Because the tangent angles do not match across the point, corner points naturally produce sharp breaks or abrupt transitions between segments, whether those segments are straight lines, curves, or a combination of both.
- Visual Representation: In the FontForge glyph canvas, corner points are traditionally rendered as small square nodes.
Smooth Points
A smooth point is used along continuous curves where the transition from one segment to the next must occur without any visible break or sharp angle, such as the crest of an "O" or the curves of an "S".
- Collinear Handles: Unlike corner points, a smooth point forces its incoming and outgoing control handles to remain collinear (locked at a 180-degree angle relative to each other through the on-curve point).
- Handle Adjustment: When you rotate or adjust the angle of one handle, FontForge automatically adjusts the opposite handle to preserve the straight line through the node, ensuring a continuous mathematical tangent. However, the length (magnitude) of each handle can still be adjusted independently to control the curvature on either side.
- Visual Representation: In the FontForge interface, smooth points are typically displayed as small circles.
Key Functional Differences
| Feature | Corner Point | Smooth Point |
|---|---|---|
| Handle Relationship | Fully independent angle and distance | Angle locked collinearly (180°); independent distance |
| Visual Result | Sharp angle or sudden directional shift | Continuous, smooth curvature without creases |
| Common Use Cases | Line intersections, serifs, stems, sharp turns | Arcs, bowls, loops, wave transitions |
| Canvas Symbol | Square | Circle |
Switching Between Point Types
FontForge allows you to convert an existing point from one type to another at any time. Selecting a point and opening the Point menu provides options to designate it as a Corner Point or a Smooth Point. Alternatively, you can use the keyboard shortcuts or double-click the point to open the Point Info dialogue window to set the type explicitly and adjust numerical coordinates for both the point and its control vectors.