You could use Glyphs without it...
Bézier paths are made by joining together a series of Bézier curves. When two curves meet at a point, the incoming curve has a certain speed and direction, and the outgoing curve has another. If those two speeds and directions are different, the curve looks lumpy and bumpy - it's “discontinuous”. If they’re the same, the curve looks smooth - it has “continuous curvature”.
"Show Curvature" gives you a visual representation of the speed and direction of the curves, so you can see at a glance if they’re going to look bumpy or smooth.
Of course, now that you know when your curves aren’t continuous, you could tune them by hand until they are.
But this isn’t why we use computers. We use computers to do stuff for us. So it’s only right that SuperTool shouldn’t just show you what’s wrong, but also fix it for you. "Harmonize" tries to subtly shift your handles around until the two Béziers meet at a consistent speed and direction, guaranteeing you a smooth
shave curve every time.
In 2003, Eduardo Tunni came up with a new way of specifying the tension of a curve.
If you extend two handles out indefinitely, you'll find that they cross at a point; let's call that the “Tunni Point.” The location of a handle between its oncurve and the Tunni Point gives you the tension - circles have their handles about 55% of the way to the Tunni Point; pushing the handles out to 100% will give you a rounded square. If both handles have the same ratio, the curve is balanced, which helps make your interpolations much more predictable.
Glyphs lets you set the tension manually with its "Fit Curve" feature, but SuperTool also allows you to move the two handles interactively by dragging the “Tunni line” connecting the handles. It'll also balance the handles for you, much like mekkablue's Tunnify script.
We've all done it. You've just pasted in a shape from Illustrator, and there are control points everywhere.
Wouldn't it be great if Glyphs could tidy up the path, removing the nodes but keeping the shape, to a variable degree of precision, just like Illustrator could?
Curves are annoying. I mean, seriously. Can't we just use straight lines for everything? One of the annoying things about curves is that it's very hard to maintain a consistent thickness between two curves, and it's even harder to make a nice smooth transition between two thicknesses around a curve.
SuperTool doesn't do that for you, but it helps you to visualize how your stem thickness is changing around a curve: yellows and reds for thicker areas, greens for average thickness, and blues for thinner ones.
Callipers works wonderfully with Rafael Buchner's "Show Stem Thickness" plugin, as shown here. It's available from the Glyphs plugin manager. Thanks, Rafael!
SuperTool is yours for
€49.99 free, thanks to support from Google Fonts! Go get it from the Glyphs Plugin Manager.
First, have a look at the manual.