The problem with applying the filter manually is that you lose the original paths. However, there is a way to round your corners non-destructively. Here’s how:
First, select the filter ‘Round Corners’ at Filter > Round Corners and enter your radius value. You will see a preview right away.
Pro tip: Use the Visual Corrections option to create a more natural looking corner rounding. This option increases the corner radius at obtuse angles, and reduces the radius at acute angles, yielding a more natural shape.
Do not click OK. Instead, click the gear wheel and select Copy Custom Parameter:
Now, press Cancel, and open File > Font Info > Instances (Cmd-I). Then, add a new instance via the plus button in the bottom left corner of the Font Info window. Choose your settings to your liking: you may want to give it a Style Name like ‘Rounded Regular’. Now, add the Parameter you copied before by first clicking into the Custom Parameters field and then pasting it with Cmd-V, and voilà:
You can see that a Filter parameter is added, and as its value, it carries
RoundedCorner; followed by two semicolon-separated numbers. The first number is the rounding radius, while the second number is either zero, representing visual corrections off, or one, meaning visual corrections on. For example:
RoundedCorner; 30; 1 means corner-rounding with a radius of 30 units, and with visual corrections as described above.
The next time you export your font family, you will get an additional font with rounded corners! That’s cool.
Rounding Inside Corners
You probably noticed that only the outside corners of the shapes are rounded, while the counters, or the ‘white’ corners at the crossbar, are left as they are:
That is right. Round Corners only applies rounding outside or ‘black’ corners. In order to round the inner ‘white’ corners as well, you would have to remove overlaps first, then select the points, and apply the filter.
But how do you do that if you are automating the rounding with a custom parameter as shown above? There is a special trick to apply the inner rounding with the custom parameter:
- Copy and paste the parameter.
- In the parameter value string, change the rounding radius value to negative.
Consider adjusting the radius value as well, because inner rounding appear bigger than they are. So, in most cases, you will want to reduce the radius a little. Experiment with the value and see for yourself which one fits best. Here is the same row of A’s with the same rounding radiuses for inner and outer corners:
Rounded Font vs. Rounded Corners
You may have spotted that other entry in there Filter menu, Rounded Font. It seems to have no options and just round the whole shape right away:
The difference is that it applies elliptical rounding to the stem rather than just corners. To achieve that, it relies on the standard stems you entered in File > Font Info > Masters. It reads the first vertical stem of the master, and tries to apply appropriate corner rounding with overshoots to the selected glyphs.
You can also apply it as a custom parameter, of course: Simply add a Filter parameter to the instance in question, and add
RoundedFont as value string. With the parameter, you can also specify a differing stem thickness by adding the stem value after a semicolon, e.g:
RoundedFont; 36 will use 36 as stem thickness for rounding rather than whatever is entered, or interpolated as, the first vertical standard stem.
More on Custom Parameters
Read the Custom Parameters tutorial for more stuff you can do. E.g., you can limit the effect of the parameter to only certain glyphs with the
include directive in your parameter string.
Update 2016-02-19: Easier way to add Filter and updated for Glyphs 2.
Update 2018-10-16: Added Rounding Inside Corners and Rounded Font filter.