Types of points

mauro sacchetto

On Linux I use FontForge, which has three types of points: corner points, curve points and tangent points.

Now, in my (new) MacBook I've installed Glyphs, and I'm trying now to figure out how it works.

I note that in Glyphs the types of points allowed are however only two: in fact the tangent points are not counted.

What is the cause of this difference, and what can it lead to 1) drawing a glyph and 2) opening (import)) a file drawn with FontForge within Glyphs?

Thank you

m

John Hudson

Tangent, curve, and corner points can be simplified to smooth and non-smooth, which is how many font tools handle them. A tangent point is a smooth connection between a straight line and a curve segment, a curve point is smooth connection between two curve segments, and a corner point is any non-smooth connection. Smooth simply means that the control handle on a curve is aligned through the point to the line segment in a tangent node or to the opposite control handle in a curve node. So when editing outlines, a designer shouldn’t need to be concerned with whether a smooth point is a tangent or a curve because that is defined by what is on either side of the point: the only thing the designer needs to decide is whether the point is smooth or non-smooth.

Mark Simonson

Paths in both PostScript fonts (cubic Bézier) and TrueType fonts (quadratic Bézier) are encoded in the font as segments, with an "on-curve" node at the start and end and zero or more "off-curve" nodes between them. If it's zero, it's a straight line segment. If it's more than zero (two in cubic and one in quadratic paths*), it's a curve segment.

But this low-level fact is usually abstracted away in font editors and drawing apps since it's easier for users to think in terms of the nodes (on-curve points) and handles (off-curve points) along continuous paths. Restricting handles to be aligned with straight paths or other handles is a function of the app, not the font format. What you're noticing is that the way this abstraction is handled in terms of UI and terminology differs among apps.

* You don't necessarily have to explicitly define on-curve nodes with TrueType paths in some situations. If you define two or more off-curve nodes in a row, virtual on-curve nodes between them are, in effect, created.

steven

No matter what type of point drawing you use, the final imported glyphs can be converted, so you can get better compatibility.

Glyphs tool ➡️ route ➡️ other ➡️ You can convert to conic or cubic.

Different software has different definitions of point types and other aspects, which is the case for most software.

mauro sacchetto

"Tangent, curve, and corner points can be simplified to smooth and non-smooth". Ok, so it's not so relevant the differentation present in FF. And in any case it is something not to worry about in these terms. Thank you!