Curves, Direction, and Fill

The points in a contour determine its geometry. The order of those points also matters: it gives the contour a direction, which helps determine which areas of a glyph are filled. Read both the point structure and the fill when checking a drawing.

Cubic and Quadratic Curves

FontLab supports two curve models: PostScript, or PS, curves and TrueType, or TT, curves. Both describe scalable paths between on-curve points, but they use different off-curve controls.

PostScript curves

A PS curve is a cubic Bézier segment. It has two endpoint nodes and two control positions, normally shown as handles attached to the endpoints. One handle controls how the curve leaves the first node; the other controls how it arrives at the second.

A handle can be retracted to its node, so not every control position produces a visible handle arm. The node remains on the contour; a handle normally lies off it. The arrangement gives you separate control over the two ends of the segment.

Straight segments connect their endpoint nodes directly and do not need visible off-curve handles. Curve and line segments can meet at a corner or at a tangent transition, depending on their geometry and node types.

TrueType curves

A TT curve is a quadratic Bézier segment. Between its two on-curve endpoints, it uses one off-curve control point. That point shapes the segment as a whole; it is not one of a pair of independently attached PS handles.

A TT contour can store consecutive off-curve points. An on-curve point is then implied at the midpoint between each neighboring pair. The renderer uses that midpoint to join the quadratic segments even when it is not stored as an explicit point.

This is why a TT outline can look different structurally from a PS outline of the same letter. A complex curve may require a different number and arrangement of points in the two models.

Drawing model and output format

FontLab permits PS and TT segments during design, including mixed contours. Export resolves the outlines to the geometry required by the chosen format: CFF output uses cubic curves, while ordinary TrueType outlines use quadratic curves.

You do not have to choose a separate drawing application for each output geometry. You do need to check the converted result. Conversion can change point counts and approximate the original shape, so a good source outline is not a substitute for inspecting the exported font.

Contour Direction and Fill

A closed contour runs clockwise or counterclockwise according to the order of its nodes. Imagine walking along its segments from the start point and back again: the direction of that journey is its winding direction.

For a simple glyph with one boundary inside another, opposite directions create a counter. In an ordinary o, the outer contour runs one way and the inner contour runs the other. Their relationship leaves the inside open while the band between them remains filled.

A contour is not intrinsically “white.” The same contour can bound a filled region or create a counter depending on its direction and its relationship to surrounding contours. Nesting is important; an opposite-direction contour elsewhere on the canvas does not automatically act as a white object painted over everything behind it.

The customary outer direction differs by output model: PS outlines use counterclockwise outer contours, while TT outlines use clockwise outer contours. FontLab handles the required direction during export. While drawing, concentrate on a consistent relationship between outer boundaries and their counters. Ordinary outline-font production expects consistently wound outlines without unwanted overlaps. Overlapping or self-intersecting paths need additional inspection; overlap removal is taught in Overlaps and Boolean Operations.

Inspect and reverse a contour

Choose View > Contours > Contour Direction to show the direction indicator at each contour's start point. In a simple o, compare the outer and inner arrows.

To reverse one contour, use the Contour tool to select a node belonging to it, with no nodes selected on other contours, then choose Contour > Reverse Contour. The command reverses the contour containing the selected node; it does not reverse only a short segment. If your selection reaches several contours, those contours can be affected together.

Check the fill afterward. For a simple counter whose direction matched its outer contour, reversing the inner contour should open the counter. If the result is unexpected, undo and inspect the contour selection, closure, nesting, and any overlapping paths before proceeding.

Inspect the filled result

The normal editing view can show a subdued fill preview alongside the outline structure. The default fill preview’s opacity is controlled by Fill preview under Preferences > Glyph Window. A light fill is an editing display; it does not mean the exported glyph will print gray.

With a drawing tool active and the canvas in focus, hold Space for Quick Preview. FontLab emphasizes the filled result and hides structural details until you release the key. Use it frequently to judge the silhouette and counters without the distraction of points and handles.

Choose View > True Fill, or press Shift+Space in the editing context, for a persistent full-opacity fill while retaining the structural details enabled in the view. Quick Preview is a held-key view; True Fill is a toggle. Neither command changes contour direction or repairs an outline.

Before treating a drawing as finished, inspect both views: structure reveals how the outline is built, while fill reveals whether it produces the intended shape.