Module: Fontisan::Ufo::Compile::Mvar

Defined in:
lib/fontisan/ufo/compile/mvar.rb

Overview

Builds the OpenType MVAR (Metrics Variation) table.

Stores deltas for font-wide metrics (ascender, descender, etc.) so they can vary across the design space.

See Also:

Constant Summary collapse

HEADER_SIZE =

majorVersion(2) + minorVersion(2) + valueRecordSize(2) +

10
VALUE_RECORD_SIZE =

valueRecordCount(2) + itemVariationStoreOffset(2)

8

Class Method Summary collapse

Class Method Details

.build(default_metrics:, master_metrics:, axis_count:) ⇒ String

Returns MVAR table bytes.

Parameters:

  • default_metrics (Hash<Symbol, Integer>) —

    e.g. { hasc: 800, hdsc: -200 }

  • master_metrics (Array<Hash<Symbol, Integer>>) —

    per master

  • axis_count (Integer)

Returns:

  • (String) —

    MVAR table bytes



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# File 'lib/fontisan/ufo/compile/mvar.rb', line 21

def self.build(default_metrics:, master_metrics:, axis_count:)
  tags = default_metrics.keys
  return nil if tags.empty?

  master_count = master_metrics.size

  deltas = []
  records = +""
  tags.each_with_index do |tag, idx|
    tag_bytes = tag.to_s.ljust(4, " ")[0, 4]
    delta = master_metrics.dig(0, tag).to_i - default_metrics[tag].to_i
    records << tag_bytes
    records << [0, idx].pack("nn") # outerIndex=0, innerIndex=idx
    deltas << [delta]
  end

  store = ItemVariationStore.build(
    axis_count: axis_count,
    master_count: master_count,
    item_count: tags.size,
    deltas: deltas,
  )

  store_offset = HEADER_SIZE + records.bytesize

  io = +""
  io << [1].pack("n")                # majorVersion
  io << [0].pack("n")                # minorVersion
  io << [VALUE_RECORD_SIZE].pack("n")
  io << [tags.size].pack("n")        # valueRecordCount
  io << [store_offset].pack("n")     # itemVariationStoreOffset (Offset16)
  io << records
  io << store
  io
end