Spacing States format

version 0.1.5

A format to store various sets of glyph metrics and kerning values inside the same font.

• Spacing State definition
  • Libs overview
• Spacing lib
  • Python example
  • XML example
• Kerning lib
  • Python example
  • XML example
• JSON format

Spacing State definition

A spacing state is a description of all spacing values in the font.

A single set of glyph contours can contain multiple spacing states, for example: default, tight and loose.

A spacing state is defined by:

• the left margin and advance width of all glyphs
• all kerning pairs and kerning values in the font

Libs overview

The data to enable spacing states in UFO sources is stored in 2 custom font-level libs under the prefix com.fontbureau.variableSpacing:

Spacing lib

The spacing lib contains a record of the left margin and advance width of all glyphs in a font, for each spacing state.

Empty glyphs have no margins, and are described only by their advance width.

Python example

font.lib[f'com.fontbureau.variableSpacing.spacing'] = {
    'default' : {
        'a': {'width': 543, 'leftMargin': 75},
        'space': {'width': 270},
    }
    'tight' : {
        'a': {
            # etc.
        },
    },
    'loose' : {
        'a': {
            # etc.
        },
    },
}

XML example

<key>com.fontbureau.variableSpacing.spacing</key>
<dict>
  <key>default</key>
  <dict>
    <key>a</key>
    <dict>
      <key>leftMargin</key>
      <real>75</real>
      <key>width</key>
      <integer>543</integer>
    </dict>
    <key>space</key>
    <dict>
      <key>width</key>
      <integer>270</integer>
    </dict>
  </dict>
  <key>tight</key>
  <dict>
    <key>a</key>
    <dict>
      <!-- etc. -->
    </dict>
  </dict>
  <key>loose</key>
  <dict>
    <key>a</key>
    <dict>
      <!-- etc. -->
    </dict>
  </dict>
</dict>

Kerning lib

The kerning lib contains a record of all kerning values in a font, for each spacing state.

Each kerning pair is stored as a tuple of first glyph or group, second glyph or group, and the kern value.

Python example

font.lib['com.fontbureau.variableSpacing.kerning'] = {
    'default' : [
        ('public.kern1.A', 'public.kern2.V', -40),
        ('B', 'J', -20),
    ],
    'tight' : [
        # etc.
    ],
    'loose' : [
        # etc.
    ],
}

XML example

<key>com.fontbureau.variableSpacing.kerning</key>
<dict>
  <key>default</key>
  <array>
    <array>
      <string>public.kern1.A</string>
      <string>public.kern2.V</string>
      <integer>-40</integer>
    </array>
    <array>
      <string>B</string>
      <string>J</string>
      <integer>-20</integer>
    </array>
  </array>
  <key>tight</key>
  <array>
    <!-- etc. -->
  </array>
  <key>loose</key>
  <array>
    <!-- etc. -->
  </array>
</dict>

JSON format

Spacing states can also be saved outside the UFO sources as standalone JSON files.

See the functions exportSpacingStates and importSpacingStates.