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LibTTF: Parse OS/2 tables

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The OS/2 table contains nice typographic ascent/descent information.
This commit is contained in:
Andreas Kling 2021-07-20 01:31:00 +02:00
parent 3b1e05f714
commit e984200206
3 changed files with 48 additions and 2 deletions
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25
Userland/Libraries/LibTTF/Font.cpp
View file

@ -274,6 +274,7 @@ Result<NonnullRefPtr<Font>, String> Font::try_load_from_offset(ReadonlyBytes buf
Optional<ReadonlyBytes> opt_cmap_slice = {};
Optional<ReadonlyBytes> opt_loca_slice = {};
Optional<ReadonlyBytes> opt_glyf_slice = {};
Optional<ReadonlyBytes> opt_os2_slice = {};
Optional<Head> opt_head = {};
Optional<Name> opt_name = {};
@ -282,6 +283,7 @@ Result<NonnullRefPtr<Font>, String> Font::try_load_from_offset(ReadonlyBytes buf
Optional<Hmtx> opt_hmtx = {};
Optional<Cmap> opt_cmap = {};
Optional<Loca> opt_loca = {};
Optional<OS2> opt_os2 = {};
auto num_tables = be_u16(buffer.offset_pointer(offset + (u32)Offsets::NumTables));
if (buffer.size() < offset + (u32)Sizes::OffsetTable + num_tables * (u32)Sizes::TableRecord)
@ -318,6 +320,8 @@ Result<NonnullRefPtr<Font>, String> Font::try_load_from_offset(ReadonlyBytes buf
opt_loca_slice = buffer_here;
} else if (tag == tag_from_str("glyf")) {
opt_glyf_slice = buffer_here;
} else if (tag == tag_from_str("OS/2")) {
opt_os2_slice = buffer_here;
}
}
@ -353,6 +357,10 @@ Result<NonnullRefPtr<Font>, String> Font::try_load_from_offset(ReadonlyBytes buf
return String { "Could not load Glyf" };
auto glyf = Glyf(opt_glyf_slice.value());
if (!opt_os2_slice.has_value())
return String { "Could not load OS/2" };
auto os2 = OS2(opt_os2_slice.value());
// Select cmap table. FIXME: Do this better. Right now, just looks for platform "Windows"
// and corresponding encoding "Unicode full repertoire", or failing that, "Unicode BMP"
for (u32 i = 0; i < cmap.num_subtables(); i++) {
@ -373,7 +381,7 @@ Result<NonnullRefPtr<Font>, String> Font::try_load_from_offset(ReadonlyBytes buf
}
}
return adopt_ref(*new Font(move(buffer), move(head), move(name), move(hhea), move(maxp), move(hmtx), move(cmap), move(loca), move(glyf)));
return adopt_ref(*new Font(move(buffer), move(head), move(name), move(hhea), move(maxp), move(hmtx), move(cmap), move(loca), move(glyf), move(os2)));
}
ScaledFontMetrics Font::metrics(float x_scale, float y_scale) const
@ -551,4 +559,19 @@ u8 ScaledFont::glyph_fixed_width() const
return glyph_metrics(glyph_id_for_code_point(' ')).advance_width;
}
i16 OS2::typographic_ascender() const
{
return be_i16(m_slice.offset_pointer((u32)Offsets::TypographicAscender));
}
i16 OS2::typographic_descender() const
{
return be_i16(m_slice.offset_pointer((u32)Offsets::TypographicDescender));
}
i16 OS2::typographic_line_gap() const
{
return be_i16(m_slice.offset_pointer((u32)Offsets::TypographicLineGap));
}
}

4
Userland/Libraries/LibTTF/Font.h
View file

@ -73,7 +73,7 @@ private:
static Result<NonnullRefPtr<Font>, String> try_load_from_offset(ReadonlyBytes, unsigned index = 0);
Font(ReadonlyBytes bytes, Head&& head, Name&& name, Hhea&& hhea, Maxp&& maxp, Hmtx&& hmtx, Cmap&& cmap, Loca&& loca, Glyf&& glyf)
Font(ReadonlyBytes bytes, Head&& head, Name&& name, Hhea&& hhea, Maxp&& maxp, Hmtx&& hmtx, Cmap&& cmap, Loca&& loca, Glyf&& glyf, OS2&& os2)
: m_buffer(move(bytes))
, m_head(move(head))
, m_name(move(name))
@ -83,6 +83,7 @@ private:
, m_loca(move(loca))
, m_glyf(move(glyf))
, m_cmap(move(cmap))
, m_os2(move(os2))
{
}
@ -99,6 +100,7 @@ private:
Loca m_loca;
Glyf m_glyf;
Cmap m_cmap;
OS2 m_os2;
};
class ScaledFont : public Gfx::Font {

21
Userland/Libraries/LibTTF/Tables.h
View file

@ -126,6 +126,27 @@ private:
u32 m_number_of_h_metrics { 0 };
};
class OS2 {
public:
enum class Offsets {
TypographicAscender = 68,
TypographicDescender = 70,
TypographicLineGap = 72,
};
i16 typographic_ascender() const;
i16 typographic_descender() const;
i16 typographic_line_gap() const;
explicit OS2(ReadonlyBytes const& slice)
: m_slice(slice)
{
}
private:
ReadonlyBytes m_slice;
};
class Name {
public:
enum class Platform {