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LibGfx/OpenType: Add named constants for header tags

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...together with spec comments.

No behavior change.
This commit is contained in:
Nico Weber 2024-02-28 08:57:47 -05:00 • committed by Tim Flynn
parent 36bbf12b73
commit 41e0a0f0aa
Notes: sideshowbarker 2024-07-17 07:06:47 +09:00
2 changed files with 16 additions and 3 deletions
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6
Userland/Libraries/LibGfx/Font/OpenType/Font.cpp
View file

@ -165,7 +165,7 @@ static ErrorOr<Tag> read_tag(ReadonlyBytes buffer)
ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_externally_owned_memory(ReadonlyBytes buffer, Options options)
{
auto tag = TRY(read_tag(buffer));
if (tag == Tag("ttcf")) {
if (tag == HeaderTag_FontCollection) {
// It's a font collection
FixedMemoryStream stream { buffer };
auto ttc_header_v1 = TRY(stream.read_in_place<TTCHeaderV1>());
@ -178,10 +178,10 @@ ErrorOr<NonnullRefPtr<Font>> Font::try_load_from_externally_owned_memory(Readonl
auto offset = TRY(stream.read_value<BigEndian<u32>>());
return try_load_from_offset(buffer, offset, move(options));
}
if (tag == Tag("OTTO"))
if (tag == HeaderTag_CFFOutlines)
return Error::from_string_literal("CFF fonts not supported yet");
if (tag.to_u32() != 0x00010000 && tag != Tag("true"))
if (tag != HeaderTag_TrueTypeOutlines && tag != HeaderTag_TrueTypeOutlinesApple)
return Error::from_string_literal("Not a valid font");
return try_load_from_offset(buffer, 0, move(options));

13
Userland/Libraries/LibGfx/Font/OpenType/Font.h
View file

@ -72,6 +72,19 @@ public:
Optional<ReadonlyBytes> control_value_program() const;
Optional<ReadonlyBytes> glyph_program(u32 glyph_id) const;
// https://learn.microsoft.com/en-us/typography/opentype/spec/otff
// "OpenType fonts that contain TrueType outlines should use the value of 0x00010000 for the sfntVersion.
// OpenType fonts containing CFF data (version 1 or 2) should use 0x4F54544F ('OTTO', when re-interpreted as a Tag) for sfntVersion.
// Note: The Apple specification for TrueType fonts allows for 'true' and 'typ1' for sfnt version.
// These version tags should not be used for OpenType fonts."
// "Font Collection ID string: 'ttcf' (used for fonts with CFF or CFF2 outlines as well as TrueType outlines)"
// The old Apple TrueType spec said "Fonts with TrueType outlines produced for OS X or iOS only are encouraged to use 'true'",
// so 'true' is somewhat common, especially in PDFs.
static constexpr Tag HeaderTag_TrueTypeOutlines = Tag::from_u32(0x00010000);
static constexpr Tag HeaderTag_TrueTypeOutlinesApple = Tag { "true" };
static constexpr Tag HeaderTag_CFFOutlines = Tag { "OTTO" };
static constexpr Tag HeaderTag_FontCollection = Tag { "ttcf" };
private:
struct AscenderAndDescender {
i16 ascender;