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LibPDF: Add spec comments to CFF

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Nico Weber 2023-10-12 10:18:15 -04:00 • committed by Andreas Kling
parent 9d31fc3ea3
commit d451197d3d
3 changed files with 30 additions and 6 deletions
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30
Userland/Libraries/LibPDF/Fonts/CFF.cpp
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@ -4,6 +4,8 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
// CFF spec: https://adobe-type-tools.github.io/font-tech-notes/pdfs/5176.CFF.pdf
#include <AK/Endian.h>
#include <AK/String.h>
#include <LibGfx/Forward.h>
@ -18,7 +20,7 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
{
Reader reader(cff_bytes);
// Header
// CFF spec, "6 Header"
// skip major, minor version
reader.consume(2);
auto header_size = TRY(reader.try_read<Card8>());
@ -26,7 +28,7 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
reader.consume(1);
reader.move_to(header_size);
// Name INDEX
// CFF spec, "7 Name INDEX"
Vector<String> font_names;
TRY(parse_index(reader, [&](ReadonlyBytes const& data) -> PDFErrorOr<void> {
auto string = TRY(String::from_utf8(data));
@ -36,7 +38,7 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
auto cff = adopt_ref(*new CFF());
cff->set_font_matrix({ 0.001f, 0.0f, 0.0f, 0.001f, 0.0f, 0.0f });
// Top DICT INDEX
// CFF spec, "8 Top DICT INDEX"
int charset_offset = 0;
Vector<u8> encoding_codes;
auto charstrings_offset = 0;
@ -71,6 +73,8 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
TRY(parse_dict<PrivDictOperator>(priv_dict_reader, [&](PrivDictOperator op, Vector<DictOperand> const& operands) -> PDFErrorOr<void> {
switch (op) {
case PrivDictOperator::Subrs: {
// CFF spec, "16 Local/Global Subrs INDEXes"
// "Local subrs are stored in an INDEX structure which is located via the offset operand of the Subrs operator in the Private DICT."
auto subrs_offset = operands[0].get<int>();
Reader subrs_reader { cff_bytes.slice(private_dict_offset + subrs_offset) };
dbgln("Parsing Subrs INDEX");
@ -98,6 +102,10 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
});
}));
// FIXME: CFF spec "10 String Index"
// FIXME: CFF spec "16 Local/Global Subrs INDEXes"
// "Global subrs are stored in an INDEX structure which follows the String INDEX."
// Create glyphs (now that we have the subroutines) and associate missing information to store them and their encoding
auto glyphs = TRY(parse_charstrings(Reader(cff_bytes.slice(charstrings_offset)), subroutines));
auto charset = TRY(parse_charset(Reader { cff_bytes.slice(charset_offset) }, glyphs.size()));
@ -375,6 +383,7 @@ static constexpr Array s_cff_builtin_names {
PDFErrorOr<Vector<DeprecatedFlyString>> CFF::parse_charset(Reader&& reader, size_t glyph_count)
{
// CFF spec, "13 Charsets"
Vector<DeprecatedFlyString> names;
auto resolve = [](SID sid) {
if (sid < s_cff_builtin_names.size())
@ -402,6 +411,7 @@ PDFErrorOr<Vector<DeprecatedFlyString>> CFF::parse_charset(Reader&& reader, size
PDFErrorOr<Vector<CFF::Glyph>> CFF::parse_charstrings(Reader&& reader, Vector<ByteBuffer> const& subroutines)
{
// CFF spec, "14 CharStrings INDEX"
Vector<Glyph> glyphs;
TRY(parse_index(reader, [&](ReadonlyBytes const& charstring_data) -> PDFErrorOr<void> {
GlyphParserState state;
@ -413,6 +423,7 @@ PDFErrorOr<Vector<CFF::Glyph>> CFF::parse_charstrings(Reader&& reader, Vector<By
PDFErrorOr<Vector<u8>> CFF::parse_encoding(Reader&& reader)
{
// CFF spec, "12 Encodings"
Vector<u8> encoding_codes;
auto format_raw = TRY(reader.try_read<Card8>());
// TODO: support encoding supplements when highest bit is set
@ -425,6 +436,7 @@ PDFErrorOr<Vector<u8>> CFF::parse_encoding(Reader&& reader)
} else if (format == 1) {
auto n_ranges = TRY(reader.try_read<Card8>());
for (u8 i = 0; i < n_ranges; i++) {
// CFF spec, "Table 13 Range1 Format (Encoding)"
auto first_code = TRY(reader.try_read<Card8>());
int left = TRY(reader.try_read<Card8>());
for (u8 code = first_code; left >= 0; left--, code++)
@ -438,10 +450,11 @@ PDFErrorOr<Vector<u8>> CFF::parse_encoding(Reader&& reader)
template<typename OperatorT>
PDFErrorOr<void> CFF::parse_dict(Reader& reader, DictEntryHandler<OperatorT>&& handler)
{
// CFF spec, "4 DICT data"
Vector<DictOperand> operands;
while (reader.remaining() > 0) {
auto b0 = reader.read<u8>();
// A command
// "Operators and operands may be distinguished by inspection of their first byte: 0-21 specify operators"
if (b0 <= 21) {
auto op = TRY(parse_dict_operator<OperatorT>(b0, reader));
TRY(handler(op, operands));
@ -460,7 +473,10 @@ template PDFErrorOr<void> CFF::parse_dict<CFF::PrivDictOperator>(Reader&, DictEn
template<typename OperatorT>
PDFErrorOr<OperatorT> CFF::parse_dict_operator(u8 b0, Reader& reader)
{
// CFF spec, "4 DICT data"
VERIFY(b0 <= 21);
// "Two-byte operators have an initial escape byte of 12."
if (b0 != 12)
return OperatorT { (int)b0 };
auto b1 = TRY(reader.try_read<u8>());
@ -471,6 +487,7 @@ template PDFErrorOr<CFF::TopDictOperator> CFF::parse_dict_operator(u8, Reader&);
PDFErrorOr<void> CFF::parse_index(Reader& reader, IndexDataHandler&& data_handler)
{
// CFF spec, "5 INDEX Data"
Card16 count = TRY(reader.try_read<BigEndian<Card16>>());
if (count == 0)
return {};
@ -487,6 +504,7 @@ PDFErrorOr<void> CFF::parse_index(Reader& reader, IndexDataHandler&& data_handle
template<typename OffsetType>
PDFErrorOr<void> CFF::parse_index_data(Card16 count, Reader& reader, IndexDataHandler& handler)
{
// CFF spec, "5 INDEX Data"
OffsetType last_data_end = 1;
auto offset_refpoint = reader.offset() + sizeof(OffsetType) * (count + 1) - 1;
for (u16 i = 0; i < count; i++) {
@ -507,9 +525,9 @@ template PDFErrorOr<void> CFF::parse_index_data<u8>(Card16, Reader&, IndexDataHa
template PDFErrorOr<void> CFF::parse_index_data<u16>(Card16, Reader&, IndexDataHandler&);
template PDFErrorOr<void> CFF::parse_index_data<u32>(Card16, Reader&, IndexDataHandler&);
// 4 DICT DATA, Table 3 Operand Encoding
int CFF::load_int_dict_operand(u8 b0, Reader& reader)
{
// CFF spec, "Table 3 Operand Encoding"
if (b0 >= 32 && b0 <= 246) {
return b0 - 139;
}
@ -538,6 +556,7 @@ int CFF::load_int_dict_operand(u8 b0, Reader& reader)
float CFF::load_float_dict_operand(Reader& reader)
{
// CFF spec, "Table 5 Nibble Definitions"
StringBuilder sb;
auto add_nibble = [&](char nibble) {
if (nibble < 0xa)
@ -568,6 +587,7 @@ float CFF::load_float_dict_operand(Reader& reader)
PDFErrorOr<CFF::DictOperand> CFF::load_dict_operand(u8 b0, Reader& reader)
{
// CFF spec, "4 DICT data"
if (b0 == 30)
return load_float_dict_operand(reader);
if (b0 >= 28)