Class: Fontisan::Woff2::GlyfLocaTransform

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/woff2/glyf_loca_transform.rb

Overview

Encodes glyf + loca into the WOFF2 transformed glyf table format per WOFF2 spec section 5.1.

The loca table is reconstructed by the decoder (its data is omitted from the brotli-compressed stream). Its directory entry keeps origLength and sets transformLength = 0 per spec section 5.3.

Output layout (spec section 5.1):

uint16 version              # always 0
uint16 optionFlags          # bit 0 = overlapSimpleBitmap present
uint16 numGlyphs
uint16 indexFormat          # loca format (0=short, 1=long)
uint32 × 7 stream sizes
nContourStream:   int16[numGlyphs]
nPointsStream:    255UInt16 per contour (point count, not endpoint)
flagStream:       uint8[numPoints] (triplet flags)
glyphStream:      triplet payloads + 255UInt16 instructionLength per glyph
compositeStream:  raw component bytes per composite glyph
bboxStream:       bboxBitmap + explicit bbox int16[4] entries
instructionStream: raw instruction bytes
overlapSimpleBitmap (optional)

Defined Under Namespace

Classes: Streams

Constant Summary collapse

FLAG_ON_CURVE =

TrueType simple-glyph flag bits per OpenType spec.

0x01
FLAG_OVERLAP_SIMPLE = 
0x40
ARG_1_AND_2_ARE_WORDS =

TrueType composite-glyph flag bits.

0x0001
WE_HAVE_A_SCALE = 
0x0008
MORE_COMPONENTS = 
0x0020
WE_HAVE_AN_X_AND_Y_SCALE = 
0x0040
WE_HAVE_A_TWO_BY_TWO = 
0x0080
WE_HAVE_INSTRUCTIONS = 
0x0100
SIMPLE_HEADER_SIZE =

Simple glyph records start with int16 numberOfContours + 4 int16 bbox.

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Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(glyf_data:, loca_data:, num_glyphs:, index_format:) ⇒ GlyfLocaTransform

Returns a new instance of GlyfLocaTransform.

Parameters:

  • glyf_data (String) —

    raw glyf table bytes

  • loca_data (String) —

    raw loca table bytes

  • num_glyphs (Integer) —

    from maxp

  • index_format (Integer) —

    0 (short) or 1 (long), from head. Used to parse the source loca; the WOFF2 transformed glyf always emits indexFormat=0 (Chrome OTS silently rejects any other value, even though WOFF2 spec section 5.1 allows the source's indexToLocFormat).



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# File 'lib/fontisan/woff2/glyf_loca_transform.rb', line 54

def initialize(glyf_data:, loca_data:, num_glyphs:, index_format:)
  @glyf_data = glyf_data
  @loca_data = loca_data
  @num_glyphs = num_glyphs
  @source_index_format = index_format
end

Instance Attribute Details

#num_glyphs ⇒ Object (readonly)

Returns the value of attribute num_glyphs.



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# File 'lib/fontisan/woff2/glyf_loca_transform.rb', line 44

def num_glyphs
  @num_glyphs
end

#source_index_format ⇒ Object (readonly)

Returns the value of attribute source_index_format.



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# File 'lib/fontisan/woff2/glyf_loca_transform.rb', line 44

def source_index_format
  @source_index_format
end

Instance Method Details

#transform ⇒ String

Encode the glyf/loca transform, returning the transformed glyf bytes.

Returns:

  • (String) —

    transformed glyf bytes per spec section 5.1



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# File 'lib/fontisan/woff2/glyf_loca_transform.rb', line 64

def transform
  s = Streams.new(@num_glyphs)
  offsets = parse_loca_offsets

  num_glyphs.times do |glyph_id|
    start_off = offsets[glyph_id]
    end_off = offsets[glyph_id + 1]
    glyph_bytes = @glyf_data[start_off...end_off]

    if glyph_bytes.nil? || glyph_bytes.empty? || glyph_bytes.bytesize.zero?
      s.n_contour << [0].pack("s>")
      next
    end

    num_contours = read_int16(glyph_bytes, 0)
    bbox = read_bbox(glyph_bytes, 2)

    case num_contours
    when 0
      s.n_contour << [0].pack("s>")
    when -1
      encode_composite(s:, glyph_bytes:, bbox:, glyph_id:)
    else
      encode_simple(s:, glyph_bytes:, num_contours:, bbox:, glyph_id:)
    end
  end

  assemble(s)
end