Class: Skrift::Font

Inherits:
Object
  • Object
show all
Includes:
Geometry
Defined in:
lib/skrift/font.rb

Constant Summary collapse

FILE_MAGIC =

TrueType, TrueType, OpenType

["\0\1\0\0", "true", "OTTO"]
CMAP_UNICODE_BMP =

cmap subtable selector, packed as platformID * 64 + encodingID.

0 * 64 + 3
CMAP_UNICODE_FULL =

Unicode platform, BMP only

0 * 64 + 4
CMAP_WIN_BMP =

Unicode platform, full repertoire

3 * 64 + 1
CMAP_WIN_UCS4 =

Windows platform, Unicode BMP

3 * 64 + 10
VS_TEXT =

Unicode variation selectors. VS15 requests text, VS16 emoji presentation; a sequence <base, selector> can map to a different glyph via cmap format 14 (see #variation_glyph_id).

0xFE0E
VS_EMOJI =

VS15 — text presentation

0xFE0F
REPEAT_FLAG = 
0x08
X_CHANGE_IS_SMALL =

x2 for Y

0x02
X_CHANGE_IS_ZERO =

x2 for Y

0x10
X_CHANGE_IS_POSITIVE =

x2 for Y

0x10
POINT_IS_ON_CURVE = 
0x01
OFFSETS_ARE_LARGE = 
0x001
ACTUAL_XY_OFFSETS = 
0x002
GOT_A_SINGLE_SCALE = 
0x008
THERE_ARE_MORE_COMPONENTS = 
0x020
GOT_AN_X_AND_Y_SCALE = 
0x040
GOT_A_SCALE_MATRIX = 
0x080
HORIZONTAL_KERNING = 
0x01
MINIMUM_KERNING = 
0x02
CROSS_STREAM_KERNING = 
0x04
OVERRIDE_KERNING = 
0x08

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Geometry

midpoint, transform_points

Constructor Details

#initialize(memory) ⇒ Font

Returns a new instance of Font.



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# File 'lib/skrift/font.rb', line 10

def initialize(memory)
  @memory = memory
  raise "Unsupported format (magic value: #{at(0,4).inspect})" if !FILE_MAGIC.member?(at(0,4))
  head = reqtable("head")
  @units_per_em  = getu16(head + 18)
  @loca_format   = geti16(head + 50)
  hhea = reqtable("hhea")
  @num_long_hmtx = getu16(hhea + 34)
end

Instance Attribute Details

#memory ⇒ Object (readonly)

Returns the value of attribute memory.



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# File 'lib/skrift/font.rb', line 8

def memory
  @memory
end

#units_per_em ⇒ Object (readonly)

Returns the value of attribute units_per_em.



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# File 'lib/skrift/font.rb', line 8

def units_per_em
  @units_per_em
end

Class Method Details

.load(filename) ⇒ Object

loadfile, 103



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# File 'lib/skrift/font.rb', line 20

def Font.load(filename) # loadfile, 103
  memory = File.read(filename).force_encoding("ASCII-8BIT")
  Font.new(memory)
end

.variation_selector?(cp) ⇒ Boolean

True if cp is a Unicode variation selector (the VS1–VS16 block or the supplementary VS17–VS256 block).

Returns:

  • (Boolean) 


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# File 'lib/skrift/font.rb', line 79

def self.variation_selector?(cp)
  (0xFE00..0xFE0F).cover?(cp) || (0xE0100..0xE01EF).cover?(cp)
end

Instance Method Details

#at(offset, len = 1) ⇒ Object 



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# File 'lib/skrift/font.rb', line 25

def at(offset, len=1)
  raise "Out of bounds #{offset} / len #{len} (max: #{@memory.size})" if offset.to_i + len.to_i > @memory.size
  @memory[offset..(offset+len-1)]
end

#cmap_fmt12_13(table, char_code, which) ⇒ Object 



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# File 'lib/skrift/font.rb', line 173

def cmap_fmt12_13(table, char_code, which)
  getu32(table + 12).times do |i|
    first_code, last_code, glyph_offset = at(table + (i*12) + 16, 12).unpack("N*")
    next if char_code < first_code || char_code > last_code
    glyph_offset += char_code-first_code if which == 12
    return glyph_offset
  end
  return nil
end

#cmap_fmt14(table, base, selector) ⇒ Object

Look up <base, selector> in one format-14 subtable. Returns a glyph id, the symbol :default if the sequence uses the base font’s default glyph, or nil if this subtable does not map the sequence. cmap-14 has two per-selector tables: a non-default list mapping a base to a specific glyph, and a default list of base ranges that fall through to the regular glyph.



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# File 'lib/skrift/font.rb', line 202

def cmap_fmt14(table, base, selector)
  num_records = getu32(table + 6)
  num_records.times do |i|
    rec = table + 10 + i * 11
    next unless getu24(rec) == selector       # records sorted by selector
    nondef = getu32(rec + 7)
    if nondef != 0 && (gid = uvs_nondefault(table + nondef, base))
      return gid
    end
    default = getu32(rec + 3)
    return :default if default != 0 && uvs_default?(table + default, base)
    return nil                                # selector present, base not in it
  end
  nil
end

#cmap_fmt4(table, char_code) ⇒ Object

572



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# File 'lib/skrift/font.rb', line 131

def cmap_fmt4(table, char_code) # 572
  # cmap format 4 only supports the Unicode BMP
  return nil if char_code > 0xffff
  seg_count_x2 = getu16(table)
  raise "Error" if (seg_count_x2 & 1) != 0 or seg_count_x2 == 0
  # Find starting positions of the relevant arrays
  end_codes        = table + 8
  start_codes      = end_codes   + seg_count_x2 + 2
  id_deltas        = start_codes + seg_count_x2
  id_range_offsets = id_deltas   + seg_count_x2

  @ecodes ||= at(end_codes, seg_count_x2).unpack("n*")
  seg_id_x_x2 = @ecodes.bsearch_index {|i| i >= char_code }.to_i * 2

  # Look up segment info from the arrays & short circuit if the spec requires
  start_code = getu16(start_codes + seg_id_x_x2)
  return 0 if start_code > char_code
  id_delta = getu16(id_deltas + seg_id_x_x2)
  if (id_range_offset = getu16(id_range_offsets + seg_id_x_x2)) == 0
    # Intentional integer under- and overflow
    return (char_code + id_delta) & 0xffff
  end
  # Calculate offset into glyph array and determine ultimate value
  id = getu16(id_range_offsets + seg_id_x_x2 + id_range_offset + 2 * (char_code - start_code))
  return id ? (id + id_delta) & 0xffff : 0
end

#cmap_fmt6(table, char_code) ⇒ Object

621



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# File 'lib/skrift/font.rb', line 165

def cmap_fmt6(table, char_code) # 621
  first_code, entry_count  = at(table,4).unpack("S>*")
  return nil if !char_code.between?(first_code, 0xffff)
  char_code -= first_code
  return nil if (char_code >= entry_count)
  return getu16(table + 4 + 2 * char_code)
end

#compound_outline(offset, rec_depth, outl) ⇒ Object

1057



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# File 'lib/skrift/font.rb', line 364

def compound_outline(offset, rec_depth, outl) # 1057
  # Guard against infinite recursion (compound glyphs that have themselves as component).
  return nil if rec_depth >= 4
  flags = THERE_ARE_MORE_COMPONENTS
  while flags.allbits?(THERE_ARE_MORE_COMPONENTS)
    flags, glyph = at(offset,4).unpack("S>*")
    offset += 4
    # We don't implement point matching, and neither does stb truetype
    return nil if (flags & ACTUAL_XY_OFFSETS) == 0
    # Read additional X and Y offsets (in FUnits) of this component.
    if (flags & OFFSETS_ARE_LARGE) != 0
      local = [[1.0, 0.0, geti16(offset)], [0.0,1.0, geti16(offset+2)]]
      offset += 4
    else
      local = [[1.0, 0.0, geti8(offset)], [0.0, 1.0, geti8(offset+1)]]
      offset += 2
    end

    if flags.allbits?(GOT_A_SINGLE_SCALE)
      local[0][0] = local[1][0] = geti16(offset) / 16384.0
      offset += 2
    elsif flags.allbits?(GOT_AN_X_AND_Y_SCALE)
      local[0][0] = geti16(offset + 0) / 16384.0
      local[1][0] = geti16(offset + 2) / 16384.0
      offset += 4
    elsif flags.allbits?(GOT_A_SCALE_MATRIX)
      local[0][0] = geti16(offset + 0) / 16384.0
      local[0][1] = geti16(offset + 2) / 16384.0
      local[1][0] = geti16(offset + 4) / 16384.0
      local[1][1] = geti16(offset + 6) / 16384.0
      offset += 8
    end

    outline = outline_offset(glyph)
    return nil if outline.nil?
    base_point = outl.points.length
    return nil if decode_outline(outline, rec_depth + 1, outl).nil?
    transform_points(local,outl.points[base_point..-1])
  end
  return outl
end

#decode_contour(outl, flags, off, base_point, count) ⇒ Object 



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# File 'lib/skrift/font.rb', line 320

def decode_contour(outl, flags, off, base_point, count)
  return true if count < 2 # Invisible (no area)

  if flags[off].allbits?(POINT_IS_ON_CURVE)
    loose_end = base_point
    base_point+= 1
    off += 1
    count -= 1
  elsif flags[off + count - 1].allbits?(POINT_IS_ON_CURVE)
    count -= 1
    loose_end = base_point + count
  else
    loose_end = outl.points.length
    outl.points << midpoint(outl.points[base_point], outl.points[base_point + count - 1])
  end
  beg  = loose_end
  ctrl = nil
  count.times do |i|
    cur = base_point + i
    if flags[off+i].allbits?(POINT_IS_ON_CURVE)
      outl.segments << Outline::Segment.new(beg, cur, ctrl)
      beg = cur
      ctrl = nil
    else
      if ctrl # 2x control points in a row -> insert midpoint
        center = outl.points.length
        outl.points << midpoint(outl.points[ctrl], outl.points[cur])
        outl.segments << Outline::Segment.new(beg, center, ctrl)
        beg = center
      end
      ctrl = cur
    end
  end
  outl.segments << Outline::Segment.new(beg, loose_end, ctrl)
  return true
end

#decode_outline(offset, rec_depth = 0, outl = Outline.new) ⇒ Object 



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# File 'lib/skrift/font.rb', line 158

def decode_outline(offset, rec_depth = 0, outl = Outline.new)
  num_contours = geti16(offset)
  return nil if num_contours == 0
  return simple_outline(offset + 10, num_contours, outl) if num_contours > 0
  return compound_outline(offset + 10, rec_depth, outl)
end

#each_cmap_entry ⇒ Object 



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# File 'lib/skrift/font.rb', line 83

def each_cmap_entry
  cmap = reqtable("cmap")
  getu16(cmap + 2).times do |idx|
    entry  = cmap + 4 + idx * 8
    type   = getu16(entry) * 64 + getu16(entry + 2)
    table  = cmap + getu32(entry + 4)
    format = getu16(table)
    yield(type, table, format)
  end
end

#geti16(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 33

def geti16(offset); at(offset,2).unpack1("s>"); end

#geti8(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 31

def geti8(offset); at(offset).unpack1("c"); end

#getu16(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 32

def getu16(offset); at(offset,2).unpack1("S>"); end

#getu24(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 35

def getu24(offset); (getu16(offset) << 8) | getu8(offset + 2); end

#getu32(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 34

def getu32(offset); at(offset,4).unpack1("N"); end

#getu8(offset) ⇒ Object 



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# File 'lib/skrift/font.rb', line 30

def getu8(offset); at(offset).ord; end

#glyph_bbox(outline) ⇒ Object 



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# File 'lib/skrift/font.rb', line 45

def glyph_bbox(outline)
  box = at(outline+2, 8).unpack("s>*")
  raise "Broken bbox #{box.inspect}" if box[2] < box[0] || box[3] < box[1]
  return box
end

#glyph_id(char_code) ⇒ Object

Maps unicode code points to glyph indices



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# File 'lib/skrift/font.rb', line 95

def glyph_id(char_code)
  each_cmap_entry do |type, table, format|
    if type == CMAP_UNICODE_FULL || type == CMAP_WIN_UCS4
      return cmap_fmt12_13(table, char_code, 12) if format == 12
      return nil
    end
  end

  # If no full repertoire cmap was found, try looking for a Unicode BMP map
  each_cmap_entry do |type, table, format|
    if type == CMAP_UNICODE_BMP || type == CMAP_WIN_BMP
      return cmap_fmt4(table + 6, char_code) if format == 4
      return cmap_fmt6(table + 6, char_code) if format == 6
      return nil
    end
  end
  return nil
end

#hor_metrics(glyph) ⇒ Object 



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# File 'lib/skrift/font.rb', line 114

def hor_metrics(glyph)
  hmtx = reqtable("hmtx")
  return nil if hmtx.nil?
  if glyph < @num_long_hmtx # In long metrics segment?
    offset = hmtx + 4 * glyph
    return getu16(offset), geti16(offset + 2)
  end
  # Glyph is inside short metrics segment
  boundary = hmtx + 4 * @num_long_hmtx
  return nil if boundary < 4
  offset = boundary - 4
  advance_width = getu16(offset)
  offset = boundary + 2 * (glyph - @num_long_hmtx)
  return advance_width, geti16(offset)
end

#kerning ⇒ Object 



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# File 'lib/skrift/font.rb', line 411

def kerning
  return @kerning if @kerning
  offset = tables["kern"]
  return nil if offset.nil? || getu16(offset) != 0
  offset += 4
  @kerning = {}
  getu16(offset - 2).times do
    length,format,flags = at(offset+2,6).unpack("S>CC")
    offset += 6
    if format == 0 && flags.allbits?(HORIZONTAL_KERNING) && flags.nobits?(MINIMUM_KERNING)
      offset += 8
      getu16(offset-8).times do |i|
        v = geti16(offset+i*6+4)
        @kerning[at(offset+i*6,4)] =
          Kerning.new(* flags.allbits?(CROSS_STREAM_KERNING) ? [0,v] : [v,0])
      end
    end
    offset += length
  end
  @kerning
end

#outline_offset(glyph) ⇒ Object

Returns the offset into the font that the glyph’s outline is stored at



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# File 'lib/skrift/font.rb', line 52

def outline_offset(glyph) # 806
  loca = reqtable("loca")
  glyf = reqtable("glyf")
  if @loca_format == 0
    base = loca + 2 * glyph
    this  = 2 * getu16(base)
    next_ = 2 * getu16(base + 2)
  else
    this, next_ = at(loca + 4 * glyph,8).unpack("NN")
  end
  return this == next_ ? nil : glyf + this
end

#reqtable(tag) ⇒ Object 



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# File 'lib/skrift/font.rb', line 43

def reqtable(tag) = (tables[tag] or raise "Unable to get table '#{tag}'")

#simple_flags(off, num_pts, flags) ⇒ Object

For a simple outline, determines each point of the outline with a set of flags



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# File 'lib/skrift/font.rb', line 253

def simple_flags(off, num_pts, flags)
  value  = 0
  repeat = 0
  num_pts.times do |i|
    if repeat > 0
      repeat -= 1
    else
      value = getu8(off)
      off += 1
      if value.allbits?(REPEAT_FLAG)
        repeat = getu8(off)
        off += 1
      end
    end
    flags[i] = value
  end
  return off
end

#simple_outline(offset, num_contours, outl = Outline.new) ⇒ Object 



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# File 'lib/skrift/font.rb', line 299

def simple_outline(offset, num_contours, outl = Outline.new)
  base_points = outl.points.length
  num_pts = getu16(offset + (num_contours - 1) *2) + 1
  end_pts = at(offset, num_contours*2).unpack("S>*")
  offset += 2*num_contours
  # Falling end_pts have no sensible interpretation, so treat as error
  end_pts.each_cons(2) { |a, b| raise if b < a + 1 }
  offset += 2 + getu16(offset)

  flags = simple_points(offset, num_pts, outl.points, base_points)

  beg = 0
  num_contours.times do |i|
    decode_contour(outl, flags, beg, base_points+beg, end_pts[i] - beg + 1)
    beg = end_pts[i] + 1
  end
  outl
end

#simple_points(offset, num_pts, points, base_point) ⇒ Object 



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# File 'lib/skrift/font.rb', line 276

def simple_points(offset, num_pts, points, base_point)
  [].tap do |flags|
    offset = simple_flags(offset, num_pts, flags)

    accum = 0.0
    accumulate = ->(i, factor) do
      if flags[i].allbits?(X_CHANGE_IS_SMALL * factor)
        offset += 1
        bit = flags[i].allbits?(X_CHANGE_IS_POSITIVE * factor) ? 1 : 0
        accum -= (getu8(offset-1) ^ -bit) + bit
      elsif flags[i].nobits?(X_CHANGE_IS_ZERO * factor)
        offset += 2
        accum += geti16(offset-2)
      end
      accum
    end

    num_pts.times {|i| points << Raster::Vector.new(accumulate.call(i,1), 0.0) }
    accum = 0.0
    num_pts.times {|i| points[base_point+i][1] = accumulate.call(i,2) }
  end
end

#tables ⇒ Object 



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# File 'lib/skrift/font.rb', line 37

def tables
  @tables ||= Hash[*
    getu16(4).times.map {|t| [at(t*16 + 12,4),getu32(t*16 + 20)] }.flatten
  ]
end

#uvs_default?(t, base) ⇒ Boolean

Default UVS table: numRanges (u32) then sorted 4-byte ranges of <startUnicodeValue: u24, additionalCount: u8>. True if base is covered.

Returns:

  • (Boolean) 


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# File 'lib/skrift/font.rb', line 236

def uvs_default?(t, base)
  lo, hi = 0, getu32(t) - 1
  while lo <= hi
    mid = (lo + hi) / 2
    r = t + 4 + mid * 4
    start = getu24(r)
    if    base < start            then hi = mid - 1
    elsif base > start + getu8(r + 3) then lo = mid + 1
    else  return true
    end
  end
  false
end

#uvs_nondefault(t, base) ⇒ Object

Non-default UVS table: numMappings (u32) then sorted 5-byte records of <unicodeValue: u24, glyphID: u16>. Binary search for base.



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# File 'lib/skrift/font.rb', line 220

def uvs_nondefault(t, base)
  lo, hi = 0, getu32(t) - 1
  while lo <= hi
    mid = (lo + hi) / 2
    m = t + 4 + mid * 5
    u = getu24(m)
    if    base < u then hi = mid - 1
    elsif base > u then lo = mid + 1
    else  return getu16(m + 3)
    end
  end
  nil
end

#variation_glyph_id(base, selector) ⇒ Object

Glyph for the variation sequence <base, selector> (e.g. an emoji base plus VS16), via the cmap format 14 subtable. Returns the mapped glyph id, or nil if the font does not define that sequence — in which case the caller should fall back to #glyph_id(base). A sequence that the font lists as using the default presentation resolves to the base glyph.



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# File 'lib/skrift/font.rb', line 188

def variation_glyph_id(base, selector)
  each_cmap_entry do |_type, table, format|
    next unless format == 14
    r = cmap_fmt14(table, base, selector)
    return r == :default ? glyph_id(base) : r
  end
  nil
end