Module: Fontisan::Ufo::Compile::Sbix

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

Overview

Builds the OpenType sbix (Apple Bitmap) table.

sbix stores bitmap strikes (PNG/JPEG) at multiple sizes. Each strike is a set of glyph-to-bitmap mappings at a specific ppem and resolution.

Layout:

Header (8 bytes):
uint16 version (= 1)
uint16 flags
uint32 numStrikes
Offset32 strikeOffsets[numStrikes]

Strike (per ppem):
uint16 ppem
uint16 resolution (ppi)
Offset32 glyphDataOffsets[numGlyphs + 1]

Glyph Data (per glyph):
int16 originOffsetX
int16 originOffsetY
uint16 graphicType ("png " or "jpeg")
uint8 bitmapData[]

See Also:

Constant Summary collapse

VERSION = 
1
PNG_TYPE = 
"png "
JPEG_TYPE = 
"jpeg"

Class Method Summary collapse

Class Method Details

.build(strikes:, num_glyphs:) ⇒ String?

Returns sbix bytes, or nil if no strikes.

Parameters:

  • strikes (Array<Hash>) —

    each with :ppem, :resolution, and :glyphs (Array with :origin_x, :origin_y, :graphic_type, :data per glyph)

  • num_glyphs (Integer) —

    total glyph count

Returns:

  • (String, nil) —

    sbix bytes, or nil if no strikes



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# File 'lib/fontisan/ufo/compile/sbix.rb', line 41

def self.build(strikes:, num_glyphs:)
  return nil if strikes.nil? || strikes.empty?

  num_strikes = strikes.size
  header_size = 4 + 4 + (num_strikes * 4) # version + flags + offsets

  strike_bytes = strikes.map { |s| build_strike(s, num_glyphs) }

  io = +""
  io << [VERSION, 0, num_strikes].pack("nnN")

  offset = header_size
  strike_bytes.each do |s|
    io << [offset].pack("N")
    offset += s.bytesize
    io << s
  end
  io
end