################################# DesignSpaceDocument Specification ################################# An object to read, write and edit interpolation systems for typefaces. Define sources, axes, rules and instances. - `The Python API of the objects <#python-api>`_ - `The document XML structure <#document-xml-structure>`_ ********** Python API ********** .. _designspacedocument-object: 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 <#document-xml-structure>`_ attributes are usually all lowercase. .. example-1: .. code:: python 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. .. code:: python 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) .. _instance-descriptor-object: InstanceDescriptor object ========================= .. attributes-1: 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 ------- .. code:: python 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) .. _axis-descriptor-object: 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. .. code:: python 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. .. code:: python 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: 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. .. code:: python 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. .. code:: xml .. 1-axis-element: 1. axis element =============== - Define a single axis - Child element of ``axes`` .. attributes-2: 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. .. code:: xml .. 11-labelname-element: 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-3: Attributes ---------- - ``xml:lang``: required, string. `XML language definition `__ Value ----- - The natural language name of this axis. .. example-2: Example ------- .. code:: xml قطر Wéíght .. 12-map-element: 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-3: Example ------- .. code:: xml Example of all axis elements together: -------------------------------------- .. code:: xml قطر Wéíght .. 2-location-element: 2. location element =================== - Defines a coordinate in the design space. - Dictionary of axisname: axisvalue - Used in ``source``, ``instance`` and ``glyph`` elements. .. 21-dimension-element: 2.1 dimension element ===================== - Child element of ``location`` .. attributes-4: 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-4: Example ------- .. code:: xml .. 3-source-element: 3. source element ================= - Defines a single font or layer that contributes to the designspace. - Child element of ``sources`` - Location in designspace coordinates. .. attributes-5: 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. .. 31-lib-element: 3.1 lib element =============== There are two meanings for the ``lib`` element: 1. Source lib - Example: ```` - 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: .. code:: xml ... The contents use the PLIST format. - 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** __ .. 32-info-element: 3.2 info element ================ - ```` - Child element of ``source`` - Defines if the instances can inherit the non-interpolating font info from this source. - MutatorMath .. 33-features-element: 3.3 features element ==================== - ```` - Defines if the instances can inherit opentype feature text from this source. - Child element of ``source`` - MutatorMath only .. 34-glyph-element: 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-6: Attributes ---------- - ``mute``: optional attribute, number 1 or 0. Indicate if this glyph should be ignored as a master. - ```` - MutatorMath only .. 35-kerning-element: 3.5 kerning element =================== - ```` - Can appear in ``source`` as well as in ``instance`` elements. .. attributes-7: 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-5: Example ------- .. code:: xml .. 4-instance-element: 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-8: 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 ------------------ .. code:: xml com.coolDesignspaceApp.specimenText Hamburgerwhatever .. 41-glyphs-element: 4.1 glyphs element ================== - Container for ``glyph`` elements. - Optional - MutatorMath only. .. 42-glyph-element: 4.2 glyph element ================= - Child element of ``glyphs`` - May contain a ``location`` element. .. attributes-9: 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. .. 421-note-element: 4.2.1 note element ================== - String. The value corresponds to glyph.note in UFO. .. 422-masters-element: 4.2.2 masters element ===================== - Container for ``master`` elements - These ``master`` elements define an alternative set of glyph masters for this glyph. .. 4221-master-element: 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-6: Example ------- .. code:: xml Demigras 半ば Montserrat モンセラート Standard Montserrat Halbfett モンセラート SemiBold .. attributes-10: 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-7: Example ------- .. code:: xml A note about this glyph com.coolDesignspaceApp.specimenText Hamburgerwhatever .. 50-rules-element: 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-11: 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`. .. 51-rule-element: 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-11: 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. .. 512-condition-element: 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-12: 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. .. 513-sub-element: 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-13: 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-8: Example ------- Example with an implied ``conditionset``. Here the conditions are not contained in a conditionset. .. code:: xml Example with ``conditionsets``. All conditions in a conditionset must be true. .. code:: xml .. 6-notes: 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: 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: 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 9 This document =============== - Changes are to be expected.