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LibPDF: Implement reading of CFF String Index

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Only really useful for reading SIDs in the Top DICT (copyright
text etc), which we currently don't do.

I haven't seen a difference from looking things up in the string
table. The only real effect from the commit that I need is that
it pulls a local resolve() labmda into a real function
resolve_sid(), which I want to call in a future commit.

But it makes things more spec-compliant, and if we ever want to
read SIDs in metadata in the future, now we can.
This commit is contained in:
Nico Weber 2023-10-12 10:53:01 -04:00 • committed by Andreas Kling
parent 9e3ee0e2b5
commit aba787a441
2 changed files with 32 additions and 14 deletions
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41
Userland/Libraries/LibPDF/Fonts/CFF.cpp
View file

@ -104,13 +104,14 @@ PDFErrorOr<NonnullRefPtr<CFF>> CFF::create(ReadonlyBytes const& cff_bytes, RefPt
});
}));
// FIXME: CFF spec "10 String Index"
auto strings = TRY(parse_strings(reader));
// 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()));
auto charset = TRY(parse_charset(Reader { cff_bytes.slice(charset_offset) }, glyphs.size(), strings));
// Adjust glyphs' widths as they are deltas from nominalWidthX
for (auto& glyph : glyphs) {
@ -385,30 +386,44 @@ static constexpr Array s_cff_builtin_names {
"zcaron"sv,
};
PDFErrorOr<Vector<DeprecatedFlyString>> CFF::parse_charset(Reader&& reader, size_t glyph_count)
PDFErrorOr<Vector<StringView>> CFF::parse_strings(Reader& reader)
{
// CFF spec "10 String Index"
Vector<StringView> strings;
TRY(parse_index(reader, [&](ReadonlyBytes const& string) -> PDFErrorOr<void> {
return TRY(strings.try_append(string));
}));
return strings;
}
DeprecatedFlyString CFF::resolve_sid(SID sid, Vector<StringView> const& strings)
{
if (sid < s_cff_builtin_names.size())
return DeprecatedFlyString(s_cff_builtin_names[sid]);
if (sid - s_cff_builtin_names.size() < strings.size())
return DeprecatedFlyString(strings[sid - s_cff_builtin_names.size()]);
dbgln("Couldn't find string for SID {}, going with space", sid);
return DeprecatedFlyString("space");
}
PDFErrorOr<Vector<DeprecatedFlyString>> CFF::parse_charset(Reader&& reader, size_t glyph_count, Vector<StringView> const& strings)
{
// CFF spec, "13 Charsets"
Vector<DeprecatedFlyString> names;
auto resolve = [](SID sid) {
if (sid < s_cff_builtin_names.size())
return DeprecatedFlyString(s_cff_builtin_names[sid]);
// FIXME: Read from String INDEX instead.
dbgln("Cound't find string for SID {}, going with space", sid);
return DeprecatedFlyString("space");
};
auto format = TRY(reader.try_read<Card8>());
if (format == 0) {
for (u8 i = 0; i < glyph_count - 1; i++) {
SID sid = TRY(reader.try_read<BigEndian<SID>>());
TRY(names.try_append(resolve(sid)));
TRY(names.try_append(resolve_sid(sid, strings)));
}
} else if (format == 1) {
while (names.size() < glyph_count - 1) {
auto first_sid = TRY(reader.try_read<BigEndian<SID>>());
int left = TRY(reader.try_read<Card8>());
for (u8 sid = first_sid; left >= 0; left--, sid++)
TRY(names.try_append(resolve(sid)));
TRY(names.try_append(resolve_sid(sid, strings)));
}
}
return names;

5
Userland/Libraries/LibPDF/Fonts/CFF.h
View file

@ -85,9 +85,12 @@ public:
template<typename OperatorT>
static PDFErrorOr<OperatorT> parse_dict_operator(u8, Reader&);
static PDFErrorOr<Vector<StringView>> parse_strings(Reader&);
static PDFErrorOr<Vector<CFF::Glyph>> parse_charstrings(Reader&&, Vector<ByteBuffer> const& subroutines);
static PDFErrorOr<Vector<DeprecatedFlyString>> parse_charset(Reader&&, size_t);
static DeprecatedFlyString resolve_sid(SID, Vector<StringView> const&);
static PDFErrorOr<Vector<DeprecatedFlyString>> parse_charset(Reader&&, size_t, Vector<StringView> const&);
static PDFErrorOr<Vector<u8>> parse_encoding(Reader&&);
};