These examples supplement Guido Ferreyra’s talk on Variable Fonts for Type Network on 2022-03-03.

They use Mutator Sans by Erik van Blokland.

Salon video recording

This example uses UFO and designspace, and is designed to be exported using fontmake.

To do a simple build, follow these steps in Terminal:

1. Change your working directory to the folder containing the designspace

$ cd /path/to/MutatorUFO

2. Run fontmake to generate the variable font. -f flattens components to a single level.

$ fontmake -o variable -m MutatorSans.designspace -f

To build static fonts for the instances, it’s a similar command, adding -i to build instances:

$ fontmake -o variable -m MutatorSans.designspace -f -i

A more complex build can be done with the shell script buildMutatorSans.sh. It builds both static and variable font files, and gives an example of postprocessing done with gftools.

$ bash buildMutatorSans.sh

This example uses Glyphs 3. They can be exported using File > Export in Glyphs.

It is also possible to export Glyphs files with fontmake using -g, but not all features may apply.

$ fontmake -o variable -g MutatorSans.glyphs -f -i

This technique allows you to map internal coordinates to external coordinates. This means you can use 0-1000 or stem weights or whatever your preferred values are inside the font, and still offer users axis locations that are more in-line with their expectations or the spec.

This is also an easy way to “warp” axes like opsz so that the rate of interpolation varies is not linear. (Not that this is different than HOI which is more advanced).

In a designspace, these can be added <map> tags to an <axis>. Note that this involves changing a self-closing <axis .../> tag to an open/close pair <axis>...</axis>.

    <axis tag="wght" name="Weight" minimum="100" maximum="900" default="100">
      <map input="100" output="1"/>
      <map input="400" output="440"/>
      <map input="700" output="760"/>
      <map input="900" output="1000"/>
    </axis>

In a Glyphs file, you can set the Axis Location custom parameter for “Masters” and “Exports” to set the external user coordinates. More info.

Glyphs also offers a font-level Axis Mappings custom parameter, but as of this writing this does not appear to be fully functional in exported variable fonts.

In instances where only a few glyphs need retouching, it doesn’t make sense to add a whole new “Source” or “Master”. Instead you can add an Intermediate Layer or Support to add additional control to an interpolation.

Not shown in this demo yet, but possible with Skateboard “supports”.

In the Glyphs examples, the horizontals of B, E, F, and G have intermediate layers (aka brace layers). More info.

Feature variations allow glyphs to swap to an alternate at certain points in the designspace. They typically use the OpenType features rvrn or rlig in the final font, but can be expressed differently in the source files.

In these examples, I and J are substituted with alternate glyphs which are narrower.

For UFOs, this be done using in a designspace using rules

<rules>
    <rule name="narrow_letters">
      <conditionset>
        <condition name="Width" minimum="50" maximum="75"/>
        <condition name="Weight" minimum="1" maximum="900"/>
      </conditionset>
      <sub name="I" with="I.narrow"/>
      <sub name="J" with="J.narrow"/>
    </rule>
</rules>

In Glyphs 3, this can be accomplished in one of two ways:

In MutatorSans-TrickLayers.glyphs, you can see these layers for I, J, and S. Double click on the layer to change the location of the swap; right click on layer to change layer type.

In MutatorSans.glyphs, the alternates are stored as separate glyphs (I.narrow, J.narrow S.closed). In the OpenType features, the rvrn or rlig OpenType feature is added with conditions.

#ifdef VARIABLE
condition 50 < wdth < 75;
sub I by I.narrow;
sub J by J.narrow;
#endif

As of this writing, this is a Glyphs 3-specific technique and it only works when exporting directly from Glyphs (not through fontmake).

More info on these approaches.

Either approach works! DJR finds it less confusing to work with feature variations as separate glyphs, rather than as layers.

Demo coming soon.

At the moment of writing this document, most font editors/building methods can not create complete/correct STAT table for some axes setups. Therefore, STAT table need to be patched after font building.

There are several methods for patching the STAT table after building but we recommend using gftools gen-stat tool since is the simplest one.

To understand better what is the STAT table and what are the expected values please read more here and also you can check how the STAT table is made on other fonts to understand how it should be for your font.

Pre requisites:

• The compiled font you want to patch (.ttf, .otf)
• A .yml file with the description of the font axes and axis values (Check sample-stat.yml)
• Python 3 installed

To patch the fonts open your terminal and follow these steps:

• Install gftools (only the first time):
  pip install gftools
• Patch the STAT table with:
  gftools gen-stat path/to/the/font --src path/to/the/yml