Module: Fontisan::Ufo::Compile::Gvar

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

Overview

Builds the OpenType gvar (Glyph Variation Data) table from per-glyph deltas computed between a default master and one or more extreme masters.

This is the hardest table in the variable-font specification. It stores, for every glyph, how each outline point moves between the default master and each extreme master.

This builder produces a minimal-but-valid gvar:

- One tuple per master (no shared tuples)
- Explicit per-point deltas (no IUP compression)
- Delta values encoded as int8 when possible, int16 otherwise

See Also:

Constant Summary collapse

VERSION_MAJOR = 
1
VERSION_MINOR = 
0
TUPLE_SHARED =

TupleIndex flags

0x8000
TUPLE_PRIVATE = 
0x4000
TUPLE_AXIS_COUNT_MASK = 
0x0FFF
DELTAS_ARE_ZERO =

Delta encoding flags (in the delta data header)

0x80
DELTAS_ARE_INT8 = 
0x40
POINT_COUNT_MASK = 
0x3FFF

Class Method Summary collapse

Class Method Details

.build(default_glyphs:, masters:, axis_count:) ⇒ String

Returns gvar table bytes.

Parameters:

  • default_glyphs (Array<Fontisan::Ufo::Glyph>) —

    default master

  • masters (Array<Hash>) —

    extreme masters Each hash: { axes: { tag: peak_value }, glyphs: [Glyph, ...] }

  • axis_count (Integer) —

    number of axes

Returns:

  • (String) —

    gvar table bytes



39
40
41
42
43
44
45
46
47
48
49
 
# File 'lib/fontisan/ufo/compile/gvar.rb', line 39

def self.build(default_glyphs:, masters:, axis_count:)
  glyph_count = default_glyphs.size
  return build_empty(glyph_count) if masters.empty? || glyph_count.zero?

  # Compute per-glyph variation data
  glyph_data = Array.new(glyph_count) do |gid|
    build_glyph_variation(default_glyphs[gid], masters, gid, axis_count)
  end

  assemble(glyph_count, axis_count, glyph_data)
end