Curves are of two types: PostScript curves segment or TrueType curve segments.
PostScript curves (also called Type 1 curves) are Bézier curves (3rd order, cubic B-splines). To modify the form of the curves two additional points (handles) are used:
These points are called handles or control points and the vectors that connect the control points with the curve’s ends are called control vectors. In the Glyph window straight segments end in square (in black-white mode) or red (in color mode) dots and curves end with round or green dots. Note that the contour direction plays a role here: it is always the element or color of the final node of a segment that tells you about the type of the segment.
TrueType curves are 2nd-order curves (quadratic B-splines) that have one control point, called the “off-curve” point:
Some TrueType curves may appear linked together and form a long curve with off-curve points only. In such curves, the intermediate nodes do not exist explicitly, but are implied by the rasterizer:
Off-curve points of the TrueType curves are light-blue in color mode appearance.