DesignSpaceDocument Specification

An object to read, write and edit interpolation systems for typefaces. Define sources, axes, rules and instances.

Python API

DesignSpaceDocument object

The DesignSpaceDocument object can read and write .designspace data. It imports the axes, sources and instances to very basic descriptor objects that store the data in attributes. Data is added to the document by creating such descriptor objects, filling them with data and then adding them to the document. This makes it easy to integrate this object in different contexts.

The DesignSpaceDocument object can be subclassed to work with different objects, as long as they have the same attributes. Reader and Writer objects can be subclassed as well.

Note: Python attribute names are usually camelCased, the corresponding XML attributes are usually all lowercase.

from fontTools.designspaceLib import DesignSpaceDocument
doc = DesignSpaceDocument()
doc.read("some/path/to/my.designspace")
doc.axes
doc.sources
doc.instances

Attributes

  • axes: list of axisDescriptors

  • sources: list of sourceDescriptors

  • instances: list of instanceDescriptors

  • rules: list if ruleDescriptors

  • readerClass: class of the reader object

  • writerClass: class of the writer object

  • lib: dict for user defined, custom data that needs to be stored in the designspace. Use reverse-DNS notation to identify your own data. Respect the data stored by others.

  • rulesProcessingLast: This flag indicates whether the substitution rules should be applied before or after other glyph substitution features. False: before, True: after.

Methods

  • read(path): read a designspace file from path

  • write(path): write this designspace to path

  • addSource(aSourceDescriptor): add this sourceDescriptor to doc.sources.

  • addInstance(anInstanceDescriptor): add this instanceDescriptor to doc.instances.

  • addAxis(anAxisDescriptor): add this instanceDescriptor to doc.axes.

  • newDefaultLocation(): returns a dict with the default location in designspace coordinates.

  • updateFilenameFromPath(masters=True, instances=True, force=False): set a descriptor filename attr from the path and this document.

  • newAxisDescriptor(): return a new axisDescriptor object.

  • newSourceDescriptor(): return a new sourceDescriptor object.

  • newInstanceDescriptor(): return a new instanceDescriptor object.

  • getAxisOrder(): return a list of axisnames

  • findDefault(): return the sourceDescriptor that is on the default location. Returns None if there isn’t one.

  • normalizeLocation(aLocation): return a dict with normalized axis values.

  • normalize(): normalize the geometry of this designspace: scale all the locations of all masters and instances to the -1 - 0 - 1 value.

  • loadSourceFonts(): Ensure SourceDescriptor.font attributes are loaded, and return list of fonts.

  • tostring(encoding=None): Returns the designspace as a string. Default encoding utf-8.

Class Methods

  • fromfile(path)

  • fromstring(string)

SourceDescriptor object

Attributes

  • filename: string. A relative path to the source file, as it is in the document. MutatorMath + Varlib.

  • path: string. Absolute path to the source file, calculated from the document path and the string in the filename attr. MutatorMath + Varlib.

  • layerName: string. The name of the layer in the source to look for outline data. Default None which means foreground.

  • font: Any Python object. Optional. Points to a representation of this source font that is loaded in memory, as a Python object (e.g. a defcon.Font or a fontTools.ttFont.TTFont). The default document reader will not fill-in this attribute, and the default writer will not use this attribute. It is up to the user of designspaceLib to either load the resource identified by filename and store it in this field, or write the contents of this field to the disk and make filename point to that.

  • name: string. Optional. Unique identifier name for this source, if there is one or more instance.glyph elements in the document. MutatorMath.

  • location: dict. Axis values for this source. MutatorMath + Varlib

  • copyLib: bool. Indicates if the contents of the font.lib need to be copied to the instances. MutatorMath.

  • copyInfo bool. Indicates if the non-interpolating font.info needs to be copied to the instances. MutatorMath

  • copyGroups bool. Indicates if the groups need to be copied to the instances. MutatorMath.

  • copyFeatures bool. Indicates if the feature text needs to be copied to the instances. MutatorMath.

  • muteKerning: bool. Indicates if the kerning data from this source needs to be muted (i.e. not be part of the calculations). MutatorMath.

  • muteInfo: bool. Indicated if the interpolating font.info data for this source needs to be muted. MutatorMath.

  • mutedGlyphNames: list. Glyphnames that need to be muted in the instances. MutatorMath.

  • familyName: string. Family name of this source. Though this data can be extracted from the font, it can be efficient to have it right here. Varlib.

  • styleName: string. Style name of this source. Though this data can be extracted from the font, it can be efficient to have it right here. Varlib.

doc = DesignSpaceDocument()
s1 = SourceDescriptor()
s1.path = masterPath1
s1.name = "master.ufo1"
s1.font = defcon.Font("master.ufo1")
s1.copyLib = True
s1.copyInfo = True
s1.copyFeatures = True
s1.location = dict(weight=0)
s1.familyName = "MasterFamilyName"
s1.styleName = "MasterStyleNameOne"
s1.mutedGlyphNames.append("A")
s1.mutedGlyphNames.append("Z")
doc.addSource(s1)

InstanceDescriptor object

Attributes

  • filename: string. Relative path to the instance file, as it is in the document. The file may or may not exist. MutatorMath.

  • path: string. Absolute path to the source file, calculated from the document path and the string in the filename attr. The file may or may not exist. MutatorMath.

  • name: string. Unique identifier name of the instance, used to identify it if it needs to be referenced from elsewhere in the document.

  • location: dict. Axis values for this source. MutatorMath + Varlib.

  • familyName: string. Family name of this instance. MutatorMath + Varlib.

  • localisedFamilyName: dict. A dictionary of localised family name strings, keyed by language code.

  • styleName: string. Style name of this source. MutatorMath + Varlib.

  • localisedStyleName: dict. A dictionary of localised stylename strings, keyed by language code.

  • postScriptFontName: string. Postscript fontname for this instance. MutatorMath.

  • styleMapFamilyName: string. StyleMap familyname for this instance. MutatorMath.

  • localisedStyleMapFamilyName: A dictionary of localised style map familyname strings, keyed by language code.

  • localisedStyleMapStyleName: A dictionary of localised style map stylename strings, keyed by language code.

  • styleMapStyleName: string. StyleMap stylename for this instance. MutatorMath.

  • glyphs: dict for special master definitions for glyphs. If glyphs need special masters (to record the results of executed rules for example). MutatorMath.

  • kerning: bool. Indicates if this instance needs its kerning calculated. MutatorMath.

  • info: bool. Indicated if this instance needs the interpolating font.info calculated.

  • lib: dict. Custom data associated with this instance.

Methods

These methods give easier access to the localised names.

  • setStyleName(styleName, languageCode="en")

  • getStyleName(languageCode="en")

  • setFamilyName(familyName, languageCode="en")

  • getFamilyName(self, languageCode="en")

  • setStyleMapStyleName(styleMapStyleName, languageCode="en")

  • getStyleMapStyleName(languageCode="en")

  • setStyleMapFamilyName(styleMapFamilyName, languageCode="en")

  • getStyleMapFamilyName(languageCode="en")

Example

i2 = InstanceDescriptor()
i2.path = instancePath2
i2.familyName = "InstanceFamilyName"
i2.styleName = "InstanceStyleName"
i2.name = "instance.ufo2"
# anisotropic location
i2.location = dict(weight=500, width=(400,300))
i2.postScriptFontName = "InstancePostscriptName"
i2.styleMapFamilyName = "InstanceStyleMapFamilyName"
i2.styleMapStyleName = "InstanceStyleMapStyleName"
glyphMasters = [dict(font="master.ufo1", glyphName="BB", location=dict(width=20,weight=20)), dict(font="master.ufo2", glyphName="CC", location=dict(width=900,weight=900))]
glyphData = dict(name="arrow", unicodeValue=1234)
glyphData['masters'] = glyphMasters
glyphData['note'] = "A note about this glyph"
glyphData['instanceLocation'] = dict(width=100, weight=120)
i2.glyphs['arrow'] = glyphData
i2.glyphs['arrow2'] = dict(mute=False)
i2.lib['com.coolDesignspaceApp.specimenText'] = 'Hamburgerwhatever'
doc.addInstance(i2)

AxisDescriptor object

  • tag: string. Four letter tag for this axis. Some might be registered at the OpenType specification. Privately-defined axis tags must begin with an uppercase letter and use only uppercase letters or digits.

  • name: string. Name of the axis as it is used in the location dicts. MutatorMath + Varlib.

  • labelNames: dict. When defining a non-registered axis, it will be necessary to define user-facing readable names for the axis. Keyed by xml:lang code. Values are required to be unicode strings, even if they only contain ASCII characters.

  • minimum: number. The minimum value for this axis in user space. MutatorMath + Varlib.

  • maximum: number. The maximum value for this axis in user space. MutatorMath + Varlib.

  • default: number. The default value for this axis, i.e. when a new location is created, this is the value this axis will get in user space. MutatorMath + Varlib.

  • map: list of input / output values that can describe a warp of user space to design space coordinates. If no map values are present, it is assumed user space is the same as design space, as in [(minimum, minimum), (maximum, maximum)]. Varlib.

a1 = AxisDescriptor()
a1.minimum = 1
a1.maximum = 1000
a1.default = 400
a1.name = "weight"
a1.tag = "wght"
a1.labelNames[u'fa-IR'] = u"قطر"
a1.labelNames[u'en'] = u"Wéíght"
a1.map = [(1.0, 10.0), (400.0, 66.0), (1000.0, 990.0)]

RuleDescriptor object

  • name: string. Unique name for this rule. Can be used to reference this rule data.

  • conditionSets: a list of conditionsets

  • Each conditionset is a list of conditions.

  • Each condition is a dict with name, minimum and maximum keys.

  • subs: list of substitutions

  • Each substitution is stored as tuples of glyphnames, e.g. (“a”, “a.alt”).

  • Note: By default, rules are applied first, before other text shaping/OpenType layout, as they are part of the Required Variation Alternates OpenType feature. See 5.0 rules element § Attributes.

Evaluating rules

  • evaluateRule(rule, location): Return True if any of the rule’s conditionsets matches the given location.

  • evaluateConditions(conditions, location): Return True if all the conditions matches the given location.

  • processRules(rules, location, glyphNames): Apply all the rules to the list of glyphNames. Return a new list of glyphNames with substitutions applied.

r1 = RuleDescriptor()
r1.name = "unique.rule.name"
r1.conditionSets.append([dict(name="weight", minimum=-10, maximum=10), dict(...)])
r1.conditionSets.append([dict(...), dict(...)])
r1.subs.append(("a", "a.alt"))

Subclassing descriptors

The DesignSpaceDocument can take subclassed Reader and Writer objects. This allows you to work with your own descriptors. You could subclass the descriptors. But as long as they have the basic attributes the descriptor does not need to be a subclass.

class MyDocReader(BaseDocReader):
    ruleDescriptorClass = MyRuleDescriptor
    axisDescriptorClass = MyAxisDescriptor
    sourceDescriptorClass = MySourceDescriptor
    instanceDescriptorClass = MyInstanceDescriptor

class MyDocWriter(BaseDocWriter):
    ruleDescriptorClass = MyRuleDescriptor
    axisDescriptorClass = MyAxisDescriptor
    sourceDescriptorClass = MySourceDescriptor
    instanceDescriptorClass = MyInstanceDescriptor

myDoc = DesignSpaceDocument(KeyedDocReader, KeyedDocWriter)

Document xml structure

  • The axes element contains one or more axis elements.

  • The sources element contains one or more source elements.

  • The instances element contains one or more instance elements.

  • The rules element contains one or more rule elements.

  • The lib element contains arbitrary data.

<?xml version='1.0' encoding='utf-8'?>
<designspace format="3">
    <axes>
        <!-- define axes here -->
        <axis../>
    </axes>
    <sources>
        <!-- define masters here -->
        <source../>
    </sources>
    <instances>
        <!-- define instances here -->
        <instance../>
    </instances>
    <rules>
        <!-- define rules here -->
        <rule../>
    </rules>
    <lib>
        <dict>
            <!-- store custom data here -->
        </dict>
    </lib>
</designspace>

1. axis element

  • Define a single axis

  • Child element of axes

Attributes

  • name: required, string. Name of the axis that is used in the location elements.

  • tag: required, string, 4 letters. Some axis tags are registered in the OpenType Specification.

  • minimum: required, number. The minimum value for this axis, in user space coordinates.

  • maximum: required, number. The maximum value for this axis, in user space coordinates.

  • default: required, number. The default value for this axis, in user space coordinates.

  • hidden: optional, 0 or 1. Records whether this axis needs to be hidden in interfaces.

<axis name="weight" tag="wght" minimum="1" maximum="1000" default="400">

1.1 labelname element

  • Defines a human readable name for UI use.

  • Optional for non-registered axis names.

  • Can be localised with xml:lang

  • Child element of axis

Attributes

Value

  • The natural language name of this axis.

Example

<labelname xml:lang="fa-IR">قطر</labelname>
<labelname xml:lang="en">Wéíght</labelname>

1.2 map element

  • Defines a single node in a series of input value (user space coordinate) to output value (designspace coordinate) pairs.

  • Together these values transform the designspace.

  • Child of axis element.

Example

<map input="1.0" output="10.0" />
<map input="400.0" output="66.0" />
<map input="1000.0" output="990.0" />

Example of all axis elements together:

<axes>
    <axis default="1" maximum="1000" minimum="0" name="weight" tag="wght">
        <labelname xml:lang="fa-IR">قطر</labelname>
        <labelname xml:lang="en">Wéíght</labelname>
    </axis>
    <axis default="100" maximum="200" minimum="50" name="width" tag="wdth">
        <map input="50.0" output="10.0" />
        <map input="100.0" output="66.0" />
        <map input="200.0" output="990.0" />
    </axis>
</axes>

2. location element

  • Defines a coordinate in the design space.

  • Dictionary of axisname: axisvalue

  • Used in source, instance and glyph elements.

2.1 dimension element

  • Child element of location

Attributes

  • name: required, string. Name of the axis.

  • xvalue: required, number. The value on this axis.

  • yvalue: optional, number. Separate value for anisotropic interpolations.

Example

<location>
    <dimension name="width" xvalue="0.000000" />
    <dimension name="weight" xvalue="0.000000" yvalue="0.003" />
</location>

3. source element

  • Defines a single font or layer that contributes to the designspace.

  • Child element of sources

  • Location in designspace coordinates.

Attributes

  • familyname: optional, string. The family name of the source font. While this could be extracted from the font data itself, it can be more efficient to add it here.

  • stylename: optional, string. The style name of the source font.

  • name: required, string. A unique name that can be used to identify this font if it needs to be referenced elsewhere.

  • filename: required, string. A path to the source file, relative to the root path of this document. The path can be at the same level as the document or lower.

  • layer: optional, string. The name of the layer in the source file. If no layer attribute is given assume the foreground layer should be used.

3.1 lib element

There are two meanings for the lib element:

  1. Source lib
    • Example: <lib copy="1" />

    • Child element of source

    • Defines if the instances can inherit the data in the lib of this source.

    • MutatorMath only

  2. Document and instance lib
    • Example:

      <lib>
          <dict>
              <key>...</key>
              <string>The contents use the PLIST format.</string>
          </dict>
      </lib>
      
    • Child element of designspace and instance

    • Contains arbitrary data about the whole document or about a specific instance.

    • Items in the dict need to use reverse domain name notation <https://en.wikipedia.org/wiki/Reverse_domain_name_notation>__

3.2 info element

  • <info copy="1" />

  • Child element of source

  • Defines if the instances can inherit the non-interpolating font info from this source.

  • MutatorMath

3.3 features element

  • <features copy="1" />

  • Defines if the instances can inherit opentype feature text from this source.

  • Child element of source

  • MutatorMath only

3.4 glyph element

  • Can appear in source as well as in instance elements.

  • In a source element this states if a glyph is to be excluded from the calculation.

  • MutatorMath only

Attributes

  • mute: optional attribute, number 1 or 0. Indicate if this glyph should be ignored as a master.

  • <glyph mute="1" name="A"/>

  • MutatorMath only

3.5 kerning element

  • <kerning mute="1" />

  • Can appear in source as well as in instance elements.

Attributes

  • mute: required attribute, number 1 or 0. Indicate if the kerning data from this source is to be excluded from the calculation.

  • If the kerning element is not present, assume mute=0, yes, include the kerning of this source in the calculation.

  • MutatorMath only

Example

<source familyname="MasterFamilyName" filename="masters/masterTest1.ufo" name="master.ufo1" stylename="MasterStyleNameOne">
    <lib copy="1" />
    <features copy="1" />
    <info copy="1" />
    <glyph mute="1" name="A" />
    <glyph mute="1" name="Z" />
    <location>
        <dimension name="width" xvalue="0.000000" />
        <dimension name="weight" xvalue="0.000000" />
    </location>
</source>

4. instance element

  • Defines a single font that can be calculated with the designspace.

  • Child element of instances

  • For use in Varlib the instance element really only needs the names and the location. The glyphs element is not required.

  • MutatorMath uses the glyphs element to describe how certain glyphs need different masters, mainly to describe the effects of conditional rules in Superpolator.

  • Location in designspace coordinates.

Attributes

  • familyname: required, string. The family name of the instance font. Corresponds with font.info.familyName

  • stylename: required, string. The style name of the instance font. Corresponds with font.info.styleName

  • name: required, string. A unique name that can be used to identify this font if it needs to be referenced elsewhere.

  • filename: string. Required for MutatorMath. A path to the instance file, relative to the root path of this document. The path can be at the same level as the document or lower.

  • postscriptfontname: string. Optional for MutatorMath. Corresponds with font.info.postscriptFontName

  • stylemapfamilyname: string. Optional for MutatorMath. Corresponds with styleMapFamilyName

  • stylemapstylename: string. Optional for MutatorMath. Corresponds with styleMapStyleName

Example for varlib

<instance familyname="InstanceFamilyName" filename="instances/instanceTest2.ufo" name="instance.ufo2" postscriptfontname="InstancePostscriptName" stylemapfamilyname="InstanceStyleMapFamilyName" stylemapstylename="InstanceStyleMapStyleName" stylename="InstanceStyleName">
<location>
    <dimension name="width" xvalue="400" yvalue="300" />
    <dimension name="weight" xvalue="66" />
</location>
<kerning />
<info />
<lib>
    <dict>
        <key>com.coolDesignspaceApp.specimenText</key>
        <string>Hamburgerwhatever</string>
    </dict>
</lib>
</instance>

4.1 glyphs element

  • Container for glyph elements.

  • Optional

  • MutatorMath only.

4.2 glyph element

  • Child element of glyphs

  • May contain a location element.

Attributes

  • name: string. The name of the glyph.

  • unicode: string. Unicode values for this glyph, in hexadecimal. Multiple values should be separated with a space.

  • mute: optional attribute, number 1 or 0. Indicate if this glyph should be supressed in the output.

4.2.1 note element

  • String. The value corresponds to glyph.note in UFO.

4.2.2 masters element

  • Container for master elements

  • These master elements define an alternative set of glyph masters for this glyph.

4.2.2.1 master element

  • Defines a single alternative master for this glyph.

4.3 Localised names for instances

Localised names for instances can be included with these simple elements with an xml:lang attribute: XML language definition

  • stylename

  • familyname

  • stylemapstylename

  • stylemapfamilyname

Example

<stylename xml:lang="fr">Demigras</stylename>
<stylename xml:lang="ja">半ば</stylename>
<familyname xml:lang="fr">Montserrat</familyname>
<familyname xml:lang="ja">モンセラート</familyname>
<stylemapstylename xml:lang="de">Standard</stylemapstylename>
<stylemapfamilyname xml:lang="de">Montserrat Halbfett</stylemapfamilyname>
<stylemapfamilyname xml:lang="ja">モンセラート SemiBold</stylemapfamilyname>

Attributes

  • glyphname: the name of the alternate master glyph.

  • source: the identifier name of the source this master glyph needs to be loaded from

Example

<instance familyname="InstanceFamilyName" filename="instances/instanceTest2.ufo" name="instance.ufo2" postscriptfontname="InstancePostscriptName" stylemapfamilyname="InstanceStyleMapFamilyName" stylemapstylename="InstanceStyleMapStyleName" stylename="InstanceStyleName">
<location>
    <dimension name="width" xvalue="400" yvalue="300" />
    <dimension name="weight" xvalue="66" />
</location>
<glyphs>
    <glyph name="arrow2" />
    <glyph name="arrow" unicode="0x4d2 0x4d3">
    <location>
        <dimension name="width" xvalue="100" />
        <dimension name="weight" xvalue="120" />
    </location>
    <note>A note about this glyph</note>
    <masters>
        <master glyphname="BB" source="master.ufo1">
        <location>
            <dimension name="width" xvalue="20" />
            <dimension name="weight" xvalue="20" />
        </location>
        </master>
    </masters>
    </glyph>
</glyphs>
<kerning />
<info />
<lib>
    <dict>
        <key>com.coolDesignspaceApp.specimenText</key>
        <string>Hamburgerwhatever</string>
    </dict>
</lib>
</instance>

5.0 rules element

  • Container for rule elements

  • The rules are evaluated in this order.

Rules describe designspace areas in which one glyph should be replaced by another. A rule has a name and a number of conditionsets. The rule also contains a list of glyphname pairs: the glyphs that need to be substituted. For a rule to be triggered only one of the conditionsets needs to be true, OR. Within a conditionset all conditions need to be true, AND.

Attributes

  • processing: flag, optional. Valid values are [first, last]. This flag indicates whether the substitution rules should be applied before or after other glyph substitution features.

  • If no processing attribute is given, interpret as first, and put the substitution rule in the rvrn feature.

  • If processing is last, put it in rclt.

5.1 rule element

  • Defines a named rule.

  • Each rule element contains one or more conditionset elements.

  • Only one conditionset needs to be true to trigger the rule.

  • All conditions in a conditionset must be true to make the conditionset true.

  • For backwards compatibility a rule can contain condition elements outside of a conditionset. These are then understood to be part of a single, implied, conditionset. Note: these conditions should be written wrapped in a conditionset.

  • A rule element needs to contain one or more sub elements in order to be compiled to a variable font.

  • Rules without sub elements should be ignored when compiling a font.

  • For authoring tools it might be necessary to save designspace files without sub elements just because the work is incomplete.

Attributes

  • name: optional, string. A unique name that can be used to identify this rule if it needs to be referenced elsewhere. The name is not important for compiling variable fonts.

5.1.1 conditionset element

  • Child element of rule

  • Contains one or more condition elements.

5.1.2 condition element

  • Child element of conditionset

  • Between the minimum and maximum this condition is True.

  • minimum and maximum are in designspace coordinates.

  • If minimum is not available, assume it is axis.minimum, mapped to designspace coordinates.

  • If maximum is not available, assume it is axis.maximum, mapped to designspace coordinates.

  • The condition must contain at least a minimum or maximum or both.

Attributes

  • name: string, required. Must match one of the defined axis name attributes.

  • minimum: number, required*. The low value, in designspace coordinates.

  • maximum: number, required*. The high value, in designspace coordinates.

5.1.3 sub element

  • Child element of rule.

  • Defines which glyph to replace when the rule evaluates to True.

  • The sub element contains a pair of glyphnames. The name attribute is the glyph that should be visible when the rule evaluates to False. The with attribute is the glyph that should be visible when the rule evaluates to True.

Axis values in Conditions are in designspace coordinates.

Attributes

  • name: string, required. The name of the glyph this rule looks for.

  • with: string, required. The name of the glyph it is replaced with.

Example

Example with an implied conditionset. Here the conditions are not contained in a conditionset.

<rules processing="last">
    <rule name="named.rule.1">
        <condition minimum="250" maximum="750" name="weight" />
        <condition minimum="50" maximum="100" name="width" />
        <sub name="dollar" with="dollar.alt"/>
    </rule>
</rules>

Example with conditionsets. All conditions in a conditionset must be true.

<rules>
    <rule name="named.rule.2">
        <conditionset>
            <condition minimum="250" maximum="750" name="weight" />
            <condition minimum="50" maximum="100" name="width" />
        </conditionset>
        <conditionset>
            <condition ... />
            <condition ... />
        </conditionset>
        <sub name="dollar" with="dollar.alt"/>
    </rule>
</rules>

6 Notes

Paths and filenames

A designspace file needs to store many references to UFO files.

  • designspace files can be part of versioning systems and appear on different computers. This means it is not possible to store absolute paths.

  • So, all paths are relative to the designspace document path.

  • Using relative paths allows designspace files and UFO files to be near each other, and that they can be found without enforcing one particular structure.

  • The filename attribute in the SourceDescriptor and InstanceDescriptor classes stores the preferred relative path.

  • The path attribute in these objects stores the absolute path. It is calculated from the document path and the relative path in the filename attribute when the object is created.

  • Only the filename attribute is written to file.

  • Both filename and path must use forward slashes (/) as path separators, even on Windows.

Right before we save we need to identify and respond to the following situations:

In each descriptor, we have to do the right thing for the filename attribute. Before writing to file, the documentObject.updatePaths() method prepares the paths as follows:

Case 1

descriptor.filename == None
descriptor.path == None

Action

  • write as is, descriptors will not have a filename attr. Useless, but no reason to interfere.

Case 2

descriptor.filename == "../something"
descriptor.path == None

Action

  • write as is. The filename attr should not be touched.

Case 3

descriptor.filename == None
descriptor.path == "~/absolute/path/there"

Action

  • calculate the relative path for filename. We’re not overwriting some other value for filename, it should be fine.

Case 4

descriptor.filename == '../somewhere'
descriptor.path == "~/absolute/path/there"

Action

  • There is a conflict between the given filename, and the path. The difference could have happened for any number of reasons. Assuming the values were not in conflict when the object was created, either could have changed. We can’t guess.

  • Assume the path attribute is more up to date. Calculate a new value for filename based on the path and the document path.

Recommendation for editors

  • If you want to explicitly set the filename attribute, leave the path attribute empty.

  • If you want to explicitly set the path attribute, leave the filename attribute empty. It will be recalculated.

  • Use documentObject.updateFilenameFromPath() to explicitly set the filename attributes for all instance and source descriptors.

7 Common Lib Key Registry

public.skipExportGlyphs

This lib key works the same as the UFO lib key with the same name. The difference is that applications using a Designspace as the corner stone of the font compilation process should use the lib key in that Designspace instead of any of the UFOs. If the lib key is empty or not present in the Designspace, all glyphs should be exported, regardless of what the same lib key in any of the UFOs says.

8 Implementation and differences

The designspace format has gone through considerable development.

  • the format was originally written for MutatorMath.

  • the format is now also used in fontTools.varlib.

  • not all values are be required by all implementations.

8.1 Varlib vs. MutatorMath

There are some differences between the way MutatorMath and fontTools.varlib handle designspaces.

  • Varlib does not support anisotropic interpolations.

  • MutatorMath will extrapolate over the boundaries of the axes. Varlib can not (at the moment).

  • Varlib requires much less data to define an instance than MutatorMath.

  • The goals of Varlib and MutatorMath are different, so not all attributes are always needed.

8.2 Older versions

  • In some implementations that preceed Variable Fonts, the copyInfo flag in a source indicated the source was to be treated as the default. This is no longer compatible with the assumption that the default font is located on the default value of each axis.

  • Older implementations did not require axis records to be present in the designspace file. The axis extremes for instance were generated from the locations used in the sources. This is no longer possible.

8.3 Rules and generating static UFO instances

When making instances as UFOs from a designspace with rules, it can be useful to evaluate the rules so that the characterset of the ufo reflects, as much as possible, the state of a variable font when seen at the same location. This can be done by some swapping and renaming of glyphs.

While useful for proofing or development work, it should be noted that swapping and renaming leaves the UFOs with glyphnames that are no longer descriptive. For instance, after a swap dollar.bar could contain a shape without a bar. Also, when the swapped glyphs are part of other GSUB variations it can become complex very quickly. So proceed with caution.

  • Assuming rulesProcessingLast = True:

  • We need to swap the glyphs so that the original shape is still available. For instance, if a rule swaps a for a.alt, a glyph that references a in a component would then show the new a.alt.

  • But that can lead to unexpected results, the two glyphs may have different widths or height. So, glyphs that are not specifically referenced in a rule should not change appearance. That means that the implementation that swaps a and a.alt also swap all components that reference these glyphs in order to preserve their appearance.

  • The swap function also needs to take care of swapping the names in kerning data and any GPOS code.

9 This document

  • Changes are to be expected.