Class: Pdfrb::Font::CFF::Subsetter

Inherits:
Object
  • Object
show all
Defined in:
lib/pdfrb/font/cff/subsetter.rb

Overview

Safe CFF subsetter (TN5176). Given the used glyph IDs, produces a smaller CFF with:

* a CharStrings INDEX holding only .notdef + the used
glyphs (original order, .notdef forced to gid 0);
* a format-0 charset remapping SIDs to the new gids —
unless the source charset was range-encoded or implicit,
in which case the original charset bytes are copied
verbatim (only safe when every glyph is kept);
* the Global Subr INDEX, Private DICT, and Local Subr INDEX
copied verbatim — subr references inside charstrings use
biased absolute indices, which stay valid unchanged;
* Name/String INDEXes and all other Top DICT data copied;
the CharStrings / charset / Private offsets are
re-encoded.

Constant Summary collapse

NOTDEF_GID = 
0

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(cff, glyph_ids) ⇒ Subsetter

Returns a new instance of Subsetter.



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 26

def initialize(cff, glyph_ids)
  @cff = cff
  @glyph_ids = ([NOTDEF_GID] + glyph_ids).sort.uniq
end

Instance Attribute Details

#cff ⇒ Object (readonly)

Returns the value of attribute cff.



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 24

def cff
  @cff
end

#glyph_ids ⇒ Object (readonly)

Returns the value of attribute glyph_ids.



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 24

def glyph_ids
  @glyph_ids
end

Class Method Details

.subset_otf(otf_bytes, glyph_ids) ⇒ Object

Subset the 'CFF ' table of an OTF (sfnt) byte string and rebuild the container directory; other tables are copied verbatim. Returns the new OTF bytes (or the original when subsetting is not possible).



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 133

def subset_otf(otf_bytes, glyph_ids)
  cff_table = table_bytes(otf_bytes, "CFF ")
  return otf_bytes unless cff_table

  subset = new(Pdfrb::Font::CFF::File.new(cff_table), glyph_ids).subset
  return otf_bytes if subset.bytesize >= cff_table.bytesize

  tables = directory(otf_bytes).map do |entry|
    data = entry[:tag] == "CFF " ? subset : otf_bytes.byteslice(entry[:offset], entry[:length])
    { tag: entry[:tag], data: data }
  end
  rebuild_sfnt(otf_bytes, tables)
end

Instance Method Details

#glyph_map ⇒ Object 



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 35

def glyph_map
  @glyph_map ||= glyph_ids.each_with_index.to_h { |old, new| [old, new] }
end

#subset ⇒ Object 



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# File 'lib/pdfrb/font/cff/subsetter.rb', line 31

def subset
  @subset ||= build
end