AFDKO Python Modules

Installation

pip3 install git+https://github.com/adobe-type-tools/python-modules

kernFeatureWriter.py

This tool exports the kerning and groups data within a UFO to a makeotf-compatible GPOS kern feature file.

Default functionality:

• writing of a sorted kern.fea file, which organizes pairs in order of specificity (exceptions first, then glyph-to-glyph, then group pairs)
• filtering of small pairs (often results of interpolation).
  Exceptions (even though they may be small) are not filtered.
• processing of right-to-left pairs (given that kerning groups containing those glyphs are suffixed with _ARA, _HEB, or _RTL)

Optional functionality:

• dissolving single-element groups into glyph pairs – this helps with subtable optimization, and can be seen as a means to avoid kerning overflow
• subtable measuring and automatic insertion of subtable breaks
• specifying a maximum subtable size
• identification of glyph-to-glyph RTL pairs by way of a global RTL_KERNING reference group
• specifying a glyph name suffix for glyphs to be ignored when writing the kern feature

Usage:

    # write a basic kern feature file
    python kernFeatureWriter.py font.ufo

    # write a kern feature file with minimum absolute kerning value of 5
    python kernFeatureWriter.py -min 5 font.ufo

    # write a kern feature with subtable breaks
    python kernFeatureWriter.py -s font.ufo

    # further usage information
    python kernFeatureWriter.py -h

markFeatureWriter.py

This tool interprets glyphs and anchor points within a UFO to write a makeotf-compatible GPOS mark feature file.

The input UFO file needs to have base glyphs and zero-width combining marks. Base- and mark glyphs attach via anchor pairs (e.g. above and _above, or top, and _top). Combining marks must be members of a COMBINING_MARKS reference group.

Default functionality:

• writing a mark.fea file, which contains mark classes/groups, and per-anchor mark-to-base positioning lookups (GPOS lookup type 4)
• writing mark-to-ligature positioning lookups (GPOS lookup type 5). This requires anchor names to be suffixed with an ordinal (1ST, 2ND, 3RD, etc). For example – if a mark with an _above anchor is to be attached to a ligature, the ligature’s anchor names would be above1ST, above2ND, etc – depending on the amount of ligature elements.

Optional functionality:

• writing mkmk.fea, for mark-to-mark positioning (GPOS lookup type 6)

• writing abvm.fea/blwm.fea files, as used in Indic scripts (anchor pairs are abvm, _abvm, and blwm, _blwm, respectively)

• writing mark classes into a separate file (in case classes need to be shared across multiple lookup types)

• trimming casing tags (UC, LC, or SC)

  Trimming tags is a somewhat specific feature, but it is quite essential: In a UFO, anchors can be used to build composite glyphs – for example aacute, and Aacute. Since those glyphs would often receive a differently-shaped accent, the anchor pairs (on bases a/A and marks acutecmb/acutecmb.cap) would be aboveLC/_aboveLC, and aboveUC/_aboveUC, respectively.

  When writing the mark feature, we care more about which group of combining marks triggers a certain behavior, so removing those casing tags allows grouping all _above marks together, hence attaching to a base glyph – no matter if it is upper- or lowercase. The aesthetic substitution of the mark (e.g. smaller mark on the uppercase letter) can happen later, in the ccmp feature.

Usage:

    # write a basic mark feature
    python markFeatureWriter.py font.ufo

    # write mark and mkmk feature files
    python markFeatureWriter.py -m font.ufo

    # trim casing tags
    python markFeatureWriter.py -t font.ufo

    # further usage information
    python markFeatureWriter.py -h

Both kern- and mark feature writers export raw feature data, which still needs to be wrapped with feature “fence”. This is easily achieved with an include statement:

feature kern{
    include(kern.fea);

} kern;

The benefit of this is that different feature flags can be used (example), or that mark groups can be shared across mark/mkmk features. Also, the (sometimes volatile) GPOS feature data can be re-generated periodically without affecting the overall structure of the feature tree.

utilities (folder /utilities)

• flKernExport.py
  FLS5 script to export class kerning to UFO. Superseded by vfb3ufo.

other modules (folder /vintage)

Other modules are FontLab scripts which were used in pre-UFO days in a FLS5 environment. Those modules are not in active development.

• AdobeFontLabUtils.py
  Support module for FontLab scripts. Defines commonly used functions and globals.

• BezChar.py
  This module converts between a FontLab glyph and a bez file data string. Used by the OutlineCheck and AutoHint scripts, to convert FL glyphs to bez programs as needed by C libraries that do the hard work.

• WriteFeaturesKernFDK.py
  Former kern feature writer.

• WriteFeaturesMarkFDK.py
  Former mark feature writer.