The curves and lines that define the shapes of letters are controlled by points. The points that lie on segments are called nodes; and off-curve points are handles (also called TrueType Control Points or Bézier Control Points (BCPs)).
FontLab VI has several types of nodes with different symbols, indicating both the type of segment (straight or curve) that the node connects, and the type of connection (sharp or smooth).
|Smooth node (or Curve node) represented by a green, round node symbol indicates a smooth connection between two curve segments.|
|Tangent node represented by a violet, triangular node symbol indicates a smooth connection between a curve segment and a straight segment.|
|Sharp node (or Corner node) represented by a red, square node symbol indicates a sharp connection between any segment types.|
A blue node with an arrow indicates the start point of a contour. To display the nodes similar to Fontographer, in black-and-white only, change the node color on the Glyph Window page of the Preferences dialog.
The type of connection between segments is very important if you want to keep the contour smooth at appropriate nodes. There are two types of connections: sharp (corner) and smooth.
At a sharp connection, the two connected segments (curve and curve or straight segment and curve) are absolutely free in their angle relative to each other at the connecting node.
At a smooth connection, the direction of the straight segment and the control vector of a curve or the control vectors of two sequential curves are kept collinear (lie on the same straight line). I.e. the angle between the two segments at the node is fixed at 180 degrees.
It is very important to maintain the smoothness of the glyph’s contours at the appropriate places. Small corners (sharp connections that are invisible when glyphs are small) become visible (and ugly) when you print large text. Furthermore, rasterizing programs that convert outline glyphs into bitmap images on paper do not like outlines where sharp connections are present in places where the outline should be smooth.
A quick way to change the connection type is to double-click on a node. More detailed control is available on the Node panel.
Servant is an additional property of a node. You can make any node a servant node.
Servant nodes have their X or Y coordinate (or both) interpolated between the positions of neighboring (non-Servant) nodes. So if you make the top node of a circle an X-Servant, and move the right-most node by 100 units, the X-Servant node will move by 50 units, and its control points will move and scale appropriately as well. It is a bit like “interpolated nudge,” but for nodes.
A Genius node is a PostScript node that always retains G2 continuity or ultra-smoothness. This means not only is the angle (direction) of the handles on both sides of the node same, but also the curvature. The curvature of a node can be visualized via View > Show > Curvature. This will display a “curvature comb” that shows the speed at which the shape of the curve progresses at each point. You can tell that a node has G2 continuity if the height of the curvature comb on either side of the node is the same. Wherever the control handles are, the position of a Genius node will be automatically calculated between them in such a way that the curve stays as smooth as possible. As a result, moving the control handles of a genius node could potentially move the node as well.
To make a node genius, select the node and choose Genius in the Contour > Nodes menu, or do a context-click (right-click) and choose Genius. Note that when you do this, the node could change its position to retain the curve’s smoothness.
Genius nodes have a circle around their node symbol:
G2 continuity can also be achieved by using Harmonize, which makes the curvature on both sides of a node same, but only as a one-time operation. One could say that Genius nodes are permanently Harmonized.
Harmonize and Genius are largely unrelated to fixed handles, which maintains pre-existing angles of control handles on the curve when a curve is being dragged or altered.
PostScript off-curve points are called handles (or Bézier Control Points, or BCPs).
Any PostScript curve segment has two handles. Removing any of these handles turns the curve into a line immediately.
When dragging a curve to alter the curve segment, use the Shift key to maintain pre-existing angles of control handles on the curve. (This was a preference setting in FontLab Studio 5: All BCPs are fixed).
Under Preferences > Glyph Window there is a middle Node Style option. When this option is selected, any node whose handles are aligned perfectly vertically or horizontally (or corner node whose adjacent line is almost vertical/horizontal) will be a darker solid color. Any node that does not meet such a test will be lighter and outlined. This helps identify points that are not quite where you intended, or are not quite proper extrema.
TrueType Control Points»
TrueType off-curve points are called TrueType Control Points (or TT Control Points, or TTCPs).
Any of the TT curves may have one or more off-curve points.