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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
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@ -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));
}
}