Class: Fontisan::Tables::CblcIndexSubTableFormatParser

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/tables/cblc_index_subtable_format_parser.rb

Overview

Per-format CBLC IndexSubTable parser. Extracted as a sibling class so that CblcIndexSubTable remains a pure data model.

The five OpenType formats differ in how the offset array encodes glyph lengths and CBDT offsets. This class hides that arithmetic behind a uniform [.locations] entry point that returns a flat list of CblcGlyphBitmapLocation objects (one per glyph in the range).

Reference: OpenType CBLC spec, IndexSubTable formats 1–5.

Defined Under Namespace

Classes: UnsupportedFormat

Class Method Summary collapse

Class Method Details

.locations(header:, bytes:, base:, first:, last:) ⇒ Array<CblcGlyphBitmapLocation>

Returns an Array of CblcGlyphBitmapLocation, one per glyph in the IndexSubTable's glyph range.

Parameters:

  • header (CblcIndexSubTableHeader) —

    the 8-byte IndexSubTable header

  • bytes (String) —

    the full CBLC table bytes

  • base (Integer) —

    absolute offset of this IndexSubTable within CBLC

  • first (Integer) —

    first glyph ID covered

  • last (Integer) —

    last glyph ID covered

Returns:



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# File 'lib/fontisan/tables/cblc_index_subtable_format_parser.rb', line 28

def locations(header:, bytes:, base:, first:, last:)
  case header.index_format
  when 1 then format_1(header, bytes, base, first, last)
  when 2 then format_2(header, bytes, base, first, last)
  when 3 then format_3(header, bytes, base, first, last)
  when 5 then format_5(header, bytes, base, first, last)
  when 4
    raise UnsupportedFormat,
          "CBLC IndexSubTable format 4 (bit-packed) is unsupported"
  else
    raise UnsupportedFormat,
          "Unknown CBLC IndexSubTable format: #{header.index_format}"
  end
end

.raw_bytes(header:, bytes:, base:, first:, last:) ⇒ String

Returns the raw bytes the IndexSubTable occupies in CBLC.

Returns:

  • (String) 


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# File 'lib/fontisan/tables/cblc_index_subtable_format_parser.rb', line 46

def raw_bytes(header:, bytes:, base:, first:, last:)
  count = last - first + 1
  length = byte_length(header.index_format, count, bytes, base)
  bytes[base, length]
end