Module: Fontisan::Ufo::Compile::Colr

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

Overview

Builds the OpenType COLR (Color) table (version 0).

COLR v0 maps glyph IDs to layers. Each layer is a reference to another glyph painted in a specific color. This produces multi-color glyphs (e.g., emoji) using simple flat layers.

Header (14 bytes):

uint16 version (= 0)
uint16 numBaseGlyphRecords
Offset32 baseGlyphRecordsOffset
Offset32 layerRecordsOffset
uint16 numLayerRecords

BaseGlyphRecord (6 bytes):

uint16 glyphID
uint16 firstLayerIndex
uint16 numLayers

LayerRecord (3 bytes):

uint16 layerGlyphID
uint8 paletteIndex

See Also:

Constant Summary collapse

VERSION = 
0
HEADER_SIZE = 
14
BASE_GLYPH_RECORD_SIZE = 
6
LAYER_RECORD_SIZE = 
3

Class Method Summary collapse

Class Method Details

.build(base_glyphs:) ⇒ String?

Returns COLR table bytes, or nil if no base glyphs.

Parameters:

  • base_glyphs (Array<Hash>) —

    each with :gid (Integer) and :layers (Array with :layer_gid and :palette_index)

Returns:

  • (String, nil) —

    COLR table bytes, or nil if no base glyphs



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# File 'lib/fontisan/ufo/compile/colr.rb', line 38

def self.build(base_glyphs:)
  return nil if base_glyphs.nil? || base_glyphs.empty?

  base_records = +""
  layer_records = +""
  first_layer_index = 0

  base_glyphs.each do |bg|
    layers = bg[:layers] || []
    num_layers = layers.size

    base_records << [
      bg[:gid] || 0,
      first_layer_index,
      num_layers,
    ].pack("nnn")

    layers.each do |layer|
      layer_records << [
        layer[:layer_gid] || 0,
        layer[:palette_index] || 0,
      ].pack("nC")
    end

    first_layer_index += num_layers
  end

  num_base = base_glyphs.size
  base_offset = HEADER_SIZE
  layer_offset = base_offset + (num_base * BASE_GLYPH_RECORD_SIZE)
  num_layer_records = layer_records.bytesize / LAYER_RECORD_SIZE

  io = +""
  io << [VERSION, num_base, base_offset, layer_offset,
         num_layer_records].pack("nnNNn")
  io << base_records
  io << layer_records
  io
end