I assume you already have fractions. We will reuse them for the superscript and subscript figures.
Superscript: the sups feature
Imagine m squared for square meter, imagine x to the third power. This is the height the superscript figures ought to have. Depending on your design, exact copies of the numerators may do. Many designs need them shifted a little higher, though:
So, how do we do that? Go to Glyph > Add Glyphs… (Cmd-Shift-G) and create component copies of your denominators with a simple recipe:
zero.dnom=zerosuperior one.dnom=onesuperior two.dnom=twosuperior three.dnom=threesuperior four.dnom=foursuperior five.dnom=fivesuperior six.dnom=sixsuperior seven.dnom=sevensuperior eight.dnom=eightsuperior nine.dnom=ninesuperior
Then select the
superior glyphs (in Font or Edit view, it does not matter) and shift them up: You can push them all up in one go with Filter > Transformations > Transform. Enter an appropriate value in the Translate Y field and you’re good to go:
In File > Font Info > Features, push the Update button, and Glyphs will generate the
sups (superscript) feature:
This can include a change of semantic value. Besides the original character codes, the application should store the code for the new character.
The magic word here is ‘change of semantic value.’ OpenType features usually are not supposed to do that, i.e., change the Unicode value, and thus, change the semantic value. There are, however, a few exceptions, and luckily,
sups is one of them. So, our feature code is OK, and that is why we recommend this method whole-heartedly.
Subscript: subs vs. sinf
What? Two different OpenType features for subscripts? In the official wording,
subs (subscript) is for:
The ‘subs’ feature may replace a default glyph with a subscript glyph, or it may combine a glyph substitution with positioning adjustments for proper placement. […] Note: This is a change of semantic value. Besides the original character codes, the application should store the code for the new character.
The point, again, is that
subs can trigger a ‘change of semantic value’, i.e. fiddle around on the character level. Theoretically, OpenType features are not supposed to do that, but in this case, Unicode already had subscript figures encoded, so we might as well reuse them for the feature.
sinf (scientific inferiors) is intended for scientific use:
Replaces lining or oldstyle figures with inferior figures (smaller glyphs which sit lower than the standard baseline, primarily for chemical or mathematical notation). May also replace lowercase characters with alphabetic inferiors.
So, when the chemical formulae for carbon-dioxide and water need inferior twos, this is a job for
It is totally legit that you want your
subs figures to be identical to your
sinf figures. However,
sinf officially does not condone a semantic change. It is not a problem to do that anyway, and simply use the same set of inferior figures for both. That is also what we recommend.
You can achieve that if you employ figures with an
inferior suffix, without the dot. To create them, paste this in the dialog that appears after you call Glyph > Add Glyphs…:
zero.dnom=zeroinferior one.dnom=oneinferior two.dnom=twoinferior three.dnom=threeinferior four.dnom=fourinferior five.dnom=fiveinferior six.dnom=sixinferior seven.dnom=seveninferior eight.dnom=eightinferior nine.dnom=nineinferior
Press Generate and Glyphs will create the new glyphs as component copies of the denominators. Then, push them down with Filter > Transformations, just this time with a negative Translate Y value.
Proceed to File > Font Info > Features and press the Update button, and Glyphs generate both the
subs and the
sinf feature with them. And you’re done, congratulations!
Avoiding a Semantic Change
If, for whatever reason, you want to avoid the semantic changes we mentioned above, or you need to keep semantic superiors apart from pure OpenType superiors, then use the
.sups suffix for your superior figures. Why? Because glyphs with dot suffixes do not get Unicode values. Here is a recipe for that:
zero.dnom=zero.sups one.dnom=one.sups two.dnom=two.sups three.dnom=three.sups four.dnom=four.sups five.dnom=five.sups six.dnom=six.sups seven.dnom=seven.sups eight.dnom=eight.sups nine.dnom=nine.sups
Attention: We do not recommend that. The method with
superiorfigures is OK and works fine. Only do that if you need to solve a technical problem.
Similarly, if you need to differentiate between
sinf, or avoid the semantic change mentioned above, use both the
.subs suffixes, including the periods. Instead of the undotted
inferior figures, that is. To get the party started, here is the glyph recipe for Glyph > Add Glyphs…:
zero.dnom=zero.sinf one.dnom=one.sinf two.dnom=two.sinf three.dnom=three.sinf four.dnom=four.sinf five.dnom=five.sinf six.dnom=six.sinf seven.dnom=seven.sinf eight.dnom=eight.sinf nine.dnom=nine.sinf zero.dnom=zero.subs one.dnom=one.subs two.dnom=two.subs three.dnom=three.subs four.dnom=four.subs five.dnom=five.subs six.dnom=six.subs seven.dnom=seven.subs eight.dnom=eight.subs nine.dnom=nine.subs
Then, Filter > Transformations > Transform will help you move the figures into the right position again. Do not forget to update your features in File > Font Info > Features before you export your font.
SAMPLE FONT: MARTHA, COURTESY OF LISA SCHULTZ.
Update 2019-05-06: Updated instructions for Glyphs 2.6. Thx @madigens. Also updated links and explained semantic change.