Module: Fontisan::Ufo::Compile::Hvar

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

Overview

Builds the OpenType HVAR (Horizontal Metrics Variation) table.

Stores advance-width variation deltas per glyph, enabling variable-font renderers to adjust spacing without loading gvar.

See Also:

Class Method Summary collapse

Class Method Details

.build(default_widths:, master_widths:, axis_count:) ⇒ String

Returns HVAR table bytes.

Parameters:

  • default_widths (Array<Integer>) —

    advance widths for default master

  • master_widths (Array<Array<Integer>>) —

    advance widths per master

  • axis_count (Integer)

Returns:

  • (String) —

    HVAR table bytes



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# File 'lib/fontisan/ufo/compile/hvar.rb', line 17

def self.build(default_widths:, master_widths:, axis_count:)
  glyph_count = default_widths.size
  master_count = master_widths.size

  # Compute deltas: deltas[glyph][master] = master_width - default_width
  deltas = Array.new(glyph_count) do |gid|
    Array.new(master_count) do |mid|
      master_widths.dig(mid, gid).to_i - default_widths[gid].to_i
    end
  end

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

  # HVAR header: version(4) + itemVariationStoreOffset(4) +
  # advanceWidthMappingOffset(4) + lsbMappingOffset(4) + rsbMappingOffset(4)
  [0x00010000, 20].pack("NN") + [0, 0, 0].pack("NNN") + store
end