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README.builder.md

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glyphsLib.builder sketch

Here is an of overview of how glyphsLib.builder converts a Glyphs GSFont object into a set of UFO and Designspace files.

To convert each master

  • Create base UFOs using the GSFont metadata and per-master metadata
    • Also store names, user data, custom parameters, custom filters
  • Convert the main layer of each master; convert also bracket/brace layers. (See To convert each layer below)
  • Propagate anchors. How we should do this is… disputed.
  • Store font and master userData in “layerLib” (why?)
  • Convert color layer IDs into layer names if there is a mapping in com.github.googlei18n.ufo2ft.colorLayerMapping (how would there be one here at this point?)
  • Convert the features into a feature file
  • Apply any custom parameters to the lib, including:
    • codePageRanges/openTypeOS2CodePageRanges/codePageRangesUnsupportedBits
    • GASP table
    • Color Palettes (converted and stored in a ufo2ft key)
    • Name records
    • Don't use Production Names
    • disablesNiceNames/useNiceNames
    • "Use Typo Metrics"/"Has WWS Names" /"openTypeOS2SelectionUnsupportedBits"
    • glyphOrder
    • Filters
    • Replace Prefix / Replace Feature (modifies feature file)
    • Reencode Glyphs
  • Fix up color layers:
    • Create color palette layers of {glyphname}.color{i}, convert UFO glyphs for each
    • Create COLRv1 layers, convert UFO glyphs for each and apply paint/stroke
  • Write out any skipExportGlyphs list gathered when converting glyphs
  • Convert feature groups and kerning groups
  • Convert kerning

To convert each layer

  • For each glyph, look at all its Glyphs layers and, for master layers only, create/select appropriate UFO layers. Then convert each glyph. (See To convert each glyph below)
  • For non-master layers, collect a list of Glyphs layers and glyphs associated with them.
  • Out of that list, discard those which have no master associated with them and no name; gather up bracket layers (which will be processed during designspace generation); discard other irrelevant layers; convert other glyphs to glyphs in appropriate UFO layers.

To convert each glyph

  • For color glyphs, create a mapping between layers and palette IDs; clone any layers with components shared between them; gather into a list of color layers.
  • Set unicodes
  • Add to skipExportGlyphs if not exported
  • Determine production name, category and subcategory; write production name into lib.
  • Use category to zero out width if it’s a mark glyph; otherwise, check if the width is determined from the “Link Metrics With Master”/Link Metrics With First Master custom parameters.
  • Convert hints.
  • Stash any user data (is this necessary?)
  • Resolve/decompose smart components (currently we just store this info - don’t do anything with it?)
  • Draw paths with a pen onto the UFO glyph
  • Convert any components to UFO
  • Convert any anchors to UFO
  • If the font is vertical, set the height and vertical origin in the UFO

To create the designspace file

  • Convert Glyphs axes to designspace axes (Looking carefully at the custom parameters “Axis Mappings”, “Axes” - for older Glyphs versions - “Axis Location”, and “Variable Font Origin”/”Variation Font Origin” (again for older Glyphs)
  • Convert Glyphs masters to designspace sources
  • Convert Glyphs instances to designspace instances
  • Copy userdata into the designspace lib, add feature writers unless there is a manual kern feature. (this may be a bug - googlefonts#764 )
  • Extract bracket layers into free-standing UFO glyphs with Designspace substitution rules. Check the “Feature for Feature Variations” custom parameter to set the OT feature for the rule.