"No default source" when I have a discrete axis map AND split variable fonts defined

[arrowtype]

I’m currently using FontMake 3.6.0 (the current release).

I have a designspace which is building well with:

• An ital axis with a mapping to make it a discrete, binary, on/off axis
• A single variable font, including the full ital range

However, if I also add variable-font elements that use just one side or the other of the ital range (e.g. split roman vs italic VFs), I get an error.

INFO:fontmake.font_project:Building variable fonts variable_ttf/AT-NameSansVariable.ttf, variable_ttf/AT-NameSansVariable-Roman.ttf, variable_ttf/AT-NameSansVariable-Italic.ttf
fontmake: Error: In 'source/ArrowType-NameSans-Prep-v011/name_sans-wght_1_1000-opsz_12_96-ital_0_1--w_sparse_supports--unified.designspace': Generating fonts from Designspace failed: No default source; expected default master at Optical Size=8, Weight=700. Found master locations:

However, I do have a source at Optical Size=8, Weight=700:

    <source filename="Name_Sans-Text_Bold.ufo" familyname="AT Name Sans" stylename="Text Bold">
      <location>
        <dimension name="Optical Size" xvalue="8"/>
        <dimension name="Weight" xvalue="700"/>
        <dimension name="Italic" xvalue="0"/>
      </location>
    </source>

Here’s my ital axis and map:

    <axis tag="ital" name="Italic" minimum="0" maximum="1" default="0">
      <map input="1" output="1"/>
      <map input="0.5" output="1"/>
      <map input="0.49994" output="0"/>
      <map input="0" output="0"/>
      <labels>
        <label uservalue="0" name="Roman" elidable="true"/>
        <label uservalue="1" name="Italic"/>
      </labels>
    </axis>

Here’s my variable-fonts element:

  <variable-fonts>
    <variable-font name="AT-NameSansVariable">
      <axis-subsets>
        <axis-subset name="Optical Size"/>
        <axis-subset name="Weight"/>
        <axis-subset name="Italic"/>
      </axis-subsets>
    </variable-font>
    <variable-font name="AT-NameSansVariable-Roman">
      <axis-subsets>
        <axis-subset name="Optical Size"/>
        <axis-subset name="Weight"/>
        <axis-subset name="Italic" uservalue="0"/>
      </axis-subsets>
    </variable-font>
    <variable-font name="AT-NameSansVariable-Italic">
      <axis-subsets>
        <axis-subset name="Optical Size"/>
        <axis-subset name="Weight"/>
        <axis-subset name="Italic" uservalue="1"/>
      </axis-subsets>
    </variable-font>
  </variable-fonts>

If my variable fonts element is only the first font, things work fine, and that font compiles as expected:

  <variable-fonts>
    <variable-font name="AT-NameSansVariable">
      <axis-subsets>
        <axis-subset name="Optical Size"/>
        <axis-subset name="Weight"/>
        <axis-subset name="Italic"/>
      </axis-subsets>
    </variable-font>
  </variable-fonts>

Or, if I remove the mapping from my ital axis, all three variable fonts build as expected:

    <axis tag="ital" name="Italic" minimum="0" maximum="1" default="0">
      <labels>
        <label uservalue="0" name="Roman" elidable="true"/>
        <label uservalue="1" name="Italic"/>
      </labels>
    </axis>

As far as I understand things, this should all be working, with both the ital mapping and all three variable font outputs.

Here’s my full `axes` element, in case that is helpful. (Click to expand)

  <axes elidedfallbackname="Regular">
    <axis tag="opsz" name="Optical Size" minimum="8" maximum="72" default="8">
      <labelname xml:lang="en">Optical Size</labelname>
      <map input="72" output="72"/>
      <map input="20" output="40"/>
      <map input="8" output="8"/>
    </axis>
    <axis tag="wght" name="Weight" minimum="1" maximum="1000" default="700">
      <labelname xml:lang="en">Weight</labelname>
      <map input="1000" output="1000"/>
      <map input="900" output="850"/>
      <map input="800" output="775"/>
      <map input="700" output="700"/>
      <map input="600" output="600"/>
      <map input="500" output="500"/>
      <map input="400" output="400"/>
      <map input="300" output="300"/>
      <map input="200" output="200"/>
      <map input="100" output="100"/>
      <map input="50" output="50"/>
      <map input="1" output="1"/>
      <labels>
        <label uservalue="25" name="Hairline"/>
        <label uservalue="50" name="ExtraThin"/>
        <label uservalue="100" name="Thin"/>
        <label uservalue="200" name="ExtraLight"/>
        <label uservalue="300" name="Light"/>
        <label uservalue="400" name="Regular" elidable="true" linkeduservalue="700"/>
        <label uservalue="500" name="Medium"/>
        <label uservalue="600" name="SemiBold"/>
        <label uservalue="700" name="Bold" linkeduservalue="400"/>
        <label uservalue="800" name="ExtraBold"/>
        <label uservalue="900" name="Black"/>
        <label uservalue="1000" name="Ultra"/>
      </labels>
    </axis>
    <axis tag="ital" name="Italic" minimum="0" maximum="1" default="0">
      <map input="1" output="1"/>
      <map input="0.5" output="1"/>
      <map input="0.49994" output="0"/>
      <map input="0" output="0"/>
      <labels>
        <label uservalue="0" name="Roman" elidable="true"/>
        <label uservalue="1" name="Italic"/>
      </labels>
    </axis>
  </axes>

Am I doing something wrong, or missing something?

Thanks so much for any insights here!

[arrowtype]

This seems related to #920, but slightly different. There, a variable font output is specified as having a location that doesn’t have a source at all (which should still work, IMO). While here, the location does have a source, but it’s just not the default location for the full designspace.

[belluzj]

In the error message from fontmake, after "Found master locations:" there's nothing, so it sounds like a bug in the function splitVariableFonts that may not preserve the correct sources in the italic-only designspace.

Could you either share your designspace file (axes + sources) or check on your side the following:

• load your designspace in Python doc = DesignSpaceDocument.fromfile("some/path/to/my.designspace")

• split it by variable font vfs = list(splitVariableFonts(doc))

• inspect the vfs variable, which should be a list of 3 tuples, each tuple has in its second element a sub-designspace for the variable-font element from your input file. Each of these sub-designspaces should have the correct number of sources, that is:

  • all of them for the big VF
  • half of them for each of the uprights-only, italic-only VFs

  for vf in vfs:
      print("vf name = ", vf[0], "sources = ", vf[1].sources)

  From the error message I suspect you'll find the italic-only VF sub-designspace has no sources at all. Can you confirm?