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LibGfx: Remove bit casting in OpenType Hmtx table after construction

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Store the variable-length data in Spans instead.
This commit is contained in:
Sam Atkins 2023-10-26 17:16:40 +01:00 • committed by Andreas Kling
parent cef4d4821b
commit 75376d6834
Notes: sideshowbarker 2024-07-17 03:35:24 +09:00
2 changed files with 23 additions and 17 deletions
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28
Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp
View file

@ -145,27 +145,35 @@ u16 Maxp::num_glyphs() const
ErrorOr<Hmtx> Hmtx::from_slice(ReadonlyBytes slice, u32 num_glyphs, u32 number_of_h_metrics)
{
if (slice.size() < number_of_h_metrics * sizeof(LongHorMetric) + (num_glyphs - number_of_h_metrics) * sizeof(u16)) {
if (slice.size() < number_of_h_metrics * sizeof(LongHorMetric) + (num_glyphs - number_of_h_metrics) * sizeof(i16))
return Error::from_string_literal("Could not load Hmtx: Not enough data");
// The Horizontal Metrics table is LongHorMetric[number_of_h_metrics] followed by i16[num_glyphs - number_of_h_metrics];
ReadonlySpan<LongHorMetric> long_hor_metrics { bit_cast<LongHorMetric*>(slice.data()), number_of_h_metrics };
ReadonlySpan<i16> left_side_bearings {};
auto number_of_left_side_bearings = num_glyphs - number_of_h_metrics;
if (number_of_left_side_bearings > 0) {
left_side_bearings = {
bit_cast<i16*>(slice.offset(number_of_h_metrics * sizeof(LongHorMetric))),
number_of_left_side_bearings
};
}
return Hmtx(slice, num_glyphs, number_of_h_metrics);
return Hmtx(long_hor_metrics, left_side_bearings);
}
GlyphHorizontalMetrics Hmtx::get_glyph_horizontal_metrics(u32 glyph_id) const
{
VERIFY(glyph_id < m_num_glyphs);
auto const* long_hor_metrics = bit_cast<LongHorMetric const*>(m_slice.data());
if (glyph_id < m_number_of_h_metrics) {
VERIFY(glyph_id < m_long_hor_metrics.size() + m_left_side_bearings.size());
if (glyph_id < m_long_hor_metrics.size()) {
return GlyphHorizontalMetrics {
.advance_width = static_cast<u16>(long_hor_metrics[glyph_id].advance_width),
.left_side_bearing = static_cast<i16>(long_hor_metrics[glyph_id].lsb),
.advance_width = m_long_hor_metrics[glyph_id].advance_width,
.left_side_bearing = m_long_hor_metrics[glyph_id].lsb,
};
}
auto const* left_side_bearings = bit_cast<BigEndian<u16> const*>(m_slice.offset(m_number_of_h_metrics * sizeof(LongHorMetric)));
return GlyphHorizontalMetrics {
.advance_width = static_cast<u16>(long_hor_metrics[m_number_of_h_metrics - 1].advance_width),
.left_side_bearing = static_cast<i16>(left_side_bearings[glyph_id - m_number_of_h_metrics]),
.advance_width = m_long_hor_metrics.last().advance_width,
.left_side_bearing = m_left_side_bearings[glyph_id - m_long_hor_metrics.size()],
};
}

12
Userland/Libraries/LibGfx/Font/OpenType/Tables.h
View file

@ -260,16 +260,14 @@ private:
};
static_assert(AssertSize<LongHorMetric, 4>());
Hmtx(ReadonlyBytes slice, u32 num_glyphs, u32 number_of_h_metrics)
: m_slice(slice)
, m_num_glyphs(num_glyphs)
, m_number_of_h_metrics(number_of_h_metrics)
Hmtx(ReadonlySpan<LongHorMetric> long_hor_metrics, ReadonlySpan<i16> left_side_bearings)
: m_long_hor_metrics(long_hor_metrics)
, m_left_side_bearings(left_side_bearings)
{
}
ReadonlyBytes m_slice;
u32 m_num_glyphs { 0 };
u32 m_number_of_h_metrics { 0 };
ReadonlySpan<LongHorMetric> m_long_hor_metrics;
ReadonlySpan<i16> m_left_side_bearings;
};
// https://learn.microsoft.com/en-us/typography/opentype/spec/os2