Contours, Nodes, and Handles
A filled letter looks continuous, but its outline is built from a small set of points and the segments between them. Learning to read that structure makes drawing and editing more predictable: you can identify what controls a shape before you try to change it.
Contour Anatomy
Open an existing o in the Glyph window and select the Contour tool. With the default detailed editing view, its drawing shows points and connecting segments. Use a simple outline o for this inspection; a decorative or layered design can contain additional structure.
A typical o has two closed contours: one around the outside and one around the counter, the open area inside the letter. A contour, also called a path, is a continuous sequence of segments. Each contour is independent; the inner and outer contours do not need a connecting line.
A segment is the portion between two neighboring nodes. It can be a straight line or a curve. Follow one side of the o: a small number of curved segments usually describes what appears to be one continuous oval.
A node is an on-curve point. It lies on the path and joins adjacent segments, or marks an endpoint of an open contour. Its x and y coordinates place it in the glyph's font-unit coordinate system.
A handle is an off-curve point that controls a curve's shape. You may also see it called a Bézier control point, or BCP. In a cubic curve, a line from a node to its handle indicates the direction in which the curve leaves or approaches the node. The handle's distance from the node influences how strongly the curve follows that direction. The curve does not normally pass through the handle itself.
“Outline” has two common uses: it can mean the visible edge of one contour, or the complete set of contours defining a glyph. In either case, the point structure, rather than the screen pixels, defines the scalable drawing.
Visible contour structure
Choose View > Contours > Nodes to show all nodes. Choose View > Contours > Handles to show handles. With these displays reduced, points can appear only near the pointer; move the pointer toward a contour to distinguish a proximity display from a drawing with no points.
The Handles toggle shows all handles when on; when off, it limits them to the pointer’s highlight distance. With Nodes also off, nearby handles remain visible regardless. This inspection assumes the default settings, with both Nodes and Handles on; enable them if you changed those defaults. Release Quick Preview if you are holding it, and make sure the glyph you want to inspect is current.
Node Types
Node types describe how adjoining segments meet. The tangent direction is the direction a curve follows at a particular point. The three ordinary node types are corner, smooth, and tangent. Their marker shapes help you read the intended relationship without moving anything.
| Node type | Marker | Relationship at the join |
|---|---|---|
| Corner | Square | Adjacent directions can differ; handles are independent |
| Smooth | Circle | The handles align through the node, maintaining a common tangent |
| Tangent | Triangle | A curve joins a straight segment with its curve-side handle aligned to the line |
A corner node, sometimes called a sharp node in older material, permits an abrupt change in direction. It is natural at a rectangle's corner. It can also join curves whose directions need to be controlled independently; the type does not require the corner to look visibly sharp in every position.
A smooth node keeps its handles on one line through the node. Their lengths can differ. This alignment prevents a change of tangent direction at the join, but it does not by itself guarantee an even change in curvature. A curve can still appear lumpy on either side of a smooth node.
A tangent node serves the transition between a straight segment and a curve. Its curve-side handle follows the adjoining straight segment's direction, allowing the curve to leave the straight section without a kink.
These descriptions apply most directly to the cubic curve model. TrueType curves use a different arrangement of off-curve points, including implied on-curve positions. The distinction concerns how the path is represented; both kinds still produce a continuous outline from points and segments.
Open and Closed Contours, and the Start Point
A closed contour has a segment from its last node back to its first. It defines a complete boundary. An open contour has two endpoints and no closing segment between them.
Open contours are useful while drawing. For ordinary filled font outlines, finish them as closed contours before export. An apparent fill in the editor is not proof that a path is closed: a display can fill the area as though an implicit connection existed between its endpoints. Inspect the endpoints themselves.
FontLab distinguishes open-contour endpoints with arrow-like markers. Every contour also has a start point, the first node in its stored sequence. An open contour begins there; a closed contour returns there after its final segment.
A closed contour's visible shape can remain the same when a different node becomes its start point, but the ordering of its points changes. That order matters for interpolation stability and for TrueType hinting programs or feature-related data that refers to particular points. Treat start points as part of the drawing's structure. Point states are taught in Selecting and the Contour Tool, and Set Start Point is taught in Basic Node and Handle Operations.
For this inspection, locate each contour's start point and follow its segments back to the beginning. You can now distinguish the outer and inner paths, their on-curve nodes, and the off-curve controls that shape them.