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LibGfx/OpenType: Clean up "kern" table reading
- Use C++ structs for the header and subtable headers. - Use AK::binary_search to search for kerning pairs.
This commit is contained in:
Andreas Kling
parent
afba67f3a2
commit
2185a98b36
2 changed files with 59 additions and 44 deletions
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@ -1,11 +1,12 @@
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/*
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* Copyright (c) 2020, Srimanta Barua <srimanta.barua1@gmail.com>
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* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/BinarySearch.h>
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#include <AK/Checked.h>
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#include <AK/Try.h>
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#include <LibCore/MappedFile.h>
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@ -166,12 +167,13 @@ Optional<Name> Name::from_slice(ReadonlyBytes slice)
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ErrorOr<Kern> Kern::from_slice(ReadonlyBytes slice)
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{
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if (slice.size() < sizeof(u32))
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if (slice.size() < sizeof(Header))
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return Error::from_string_literal("Invalid kern table header");
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// We only support the old (2x u16) version of the header
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auto version = be_u16(slice.data());
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auto number_of_subtables = be_u16(slice.offset(sizeof(u16)));
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auto const& header = *bit_cast<Header const*>(slice.data());
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auto version = header.version;
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auto number_of_subtables = header.n_tables;
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if (version != 0)
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return Error::from_string_literal("Unsupported kern table version");
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if (number_of_subtables == 0)
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@ -179,14 +181,13 @@ ErrorOr<Kern> Kern::from_slice(ReadonlyBytes slice)
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// Read all subtable offsets
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auto subtable_offsets = TRY(FixedArray<size_t>::try_create(number_of_subtables));
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size_t offset = 2 * sizeof(u16);
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size_t offset = sizeof(Header);
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for (size_t i = 0; i < number_of_subtables; ++i) {
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if (slice.size() < offset + Sizes::SubtableHeader)
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if (slice.size() < offset + sizeof(SubtableHeader))
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return Error::from_string_literal("Invalid kern subtable header");
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auto const& subtable_header = *bit_cast<SubtableHeader const*>(slice.offset_pointer(offset));
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subtable_offsets[i] = offset;
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auto subtable_size = be_u16(slice.offset(offset + sizeof(u16)));
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offset += subtable_size;
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offset += subtable_header.length;
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}
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return Kern(slice, move(subtable_offsets));
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@ -199,10 +200,11 @@ i16 Kern::get_glyph_kerning(u16 left_glyph_id, u16 right_glyph_id) const
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i16 glyph_kerning = 0;
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for (auto subtable_offset : m_subtable_offsets) {
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auto subtable_slice = m_slice.slice(subtable_offset);
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auto const& subtable_header = *bit_cast<SubtableHeader const*>(subtable_slice.data());
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auto version = be_u16(subtable_slice.data());
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auto length = be_u16(subtable_slice.offset(sizeof(u16)));
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auto coverage = be_u16(subtable_slice.offset(2 * sizeof(u16)));
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auto version = subtable_header.version;
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auto length = subtable_header.version;
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auto coverage = subtable_header.coverage;
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if (version != 0) {
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dbgln("OpenType::Kern: unsupported subtable version {}", version);
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@ -231,7 +233,7 @@ i16 Kern::get_glyph_kerning(u16 left_glyph_id, u16 right_glyph_id) const
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Optional<i16> subtable_kerning;
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switch (format) {
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case 0:
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subtable_kerning = read_glyph_kerning_format0(subtable_slice.slice(Sizes::SubtableHeader), left_glyph_id, right_glyph_id);
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subtable_kerning = read_glyph_kerning_format0(subtable_slice.slice(sizeof(SubtableHeader)), left_glyph_id, right_glyph_id);
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break;
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default:
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dbgln("OpenType::Kern: FIXME: subtable format {} is unsupported", format);
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@ -251,48 +253,39 @@ i16 Kern::get_glyph_kerning(u16 left_glyph_id, u16 right_glyph_id) const
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Optional<i16> Kern::read_glyph_kerning_format0(ReadonlyBytes slice, u16 left_glyph_id, u16 right_glyph_id)
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{
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if (slice.size() < 4 * sizeof(u16))
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if (slice.size() < sizeof(Format0))
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return {};
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u16 number_of_pairs = be_u16(slice.data());
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u16 search_range = be_u16(slice.offset_pointer(sizeof(u16)));
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u16 entry_selector = be_u16(slice.offset_pointer(2 * sizeof(u16)));
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u16 range_shift = be_u16(slice.offset_pointer(3 * sizeof(u16)));
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auto const& format0 = *bit_cast<Format0 const*>(slice.data());
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u16 number_of_pairs = format0.n_pairs;
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u16 search_range = format0.search_range;
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u16 entry_selector = format0.entry_selector;
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u16 range_shift = format0.range_shift;
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// Sanity checks for this table format
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auto pairs_in_search_range = search_range / Sizes::Format0Entry;
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auto pairs_in_search_range = search_range / sizeof(Format0Pair);
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if (number_of_pairs == 0)
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return {};
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if (pairs_in_search_range > number_of_pairs)
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return {};
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if ((1 << entry_selector) * Sizes::Format0Entry != search_range)
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if ((1 << entry_selector) * sizeof(Format0Pair) != search_range)
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return {};
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if ((number_of_pairs - pairs_in_search_range) * Sizes::Format0Entry != range_shift)
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if ((number_of_pairs - pairs_in_search_range) * sizeof(Format0Pair) != range_shift)
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return {};
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// FIXME: implement a possibly slightly more efficient binary search using the parameters above
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auto search_slice = slice.slice(4 * sizeof(u16));
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size_t left_idx = 0;
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size_t right_idx = number_of_pairs - 1;
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for (auto i = 0; i < 16; ++i) {
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size_t pivot_idx = (left_idx + right_idx) / 2;
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Span<Format0Pair const> pairs { bit_cast<Format0Pair const*>(slice.slice(sizeof(Format0)).data()), number_of_pairs };
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u16 pivot_left_glyph_id = be_u16(search_slice.offset(pivot_idx * Sizes::Format0Entry + 0));
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u16 pivot_right_glyph_id = be_u16(search_slice.offset(pivot_idx * Sizes::Format0Entry + 2));
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// The left and right halves of the kerning pair make an unsigned 32-bit number, which is then used to order the kerning pairs numerically.
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auto needle = (static_cast<u32>(left_glyph_id) << 16u) | static_cast<u32>(right_glyph_id);
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auto* pair = binary_search(pairs, nullptr, nullptr, [&](void*, Format0Pair const& pair) {
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auto as_u32 = (static_cast<u32>(pair.left) << 16u) | static_cast<u32>(pair.right);
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return needle - as_u32;
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});
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// Match
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if (pivot_left_glyph_id == left_glyph_id && pivot_right_glyph_id == right_glyph_id)
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return be_i16(search_slice.offset(pivot_idx * Sizes::Format0Entry + 4));
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// Narrow search area
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if (pivot_left_glyph_id < left_glyph_id || (pivot_left_glyph_id == left_glyph_id && pivot_right_glyph_id < right_glyph_id))
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left_idx = pivot_idx + 1;
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else if (pivot_idx == left_idx)
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break;
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else
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right_idx = pivot_idx - 1;
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}
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return 0;
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if (!pair)
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return 0;
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return pair->value;
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}
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DeprecatedString Name::string_for_id(NameId id) const
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@ -327,11 +327,33 @@ public:
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i16 get_glyph_kerning(u16 left_glyph_id, u16 right_glyph_id) const;
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private:
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enum Sizes : size_t {
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SubtableHeader = 6,
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Format0Entry = 6,
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struct Header {
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BigEndian<u16> version;
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BigEndian<u16> n_tables;
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};
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struct SubtableHeader {
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BigEndian<u16> version;
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BigEndian<u16> length;
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BigEndian<u16> coverage;
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};
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// https://learn.microsoft.com/en-us/typography/opentype/spec/kern#format-0
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struct Format0 {
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BigEndian<u16> n_pairs;
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BigEndian<u16> search_range;
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BigEndian<u16> entry_selector;
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BigEndian<u16> range_shift;
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};
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struct Format0Pair {
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BigEndian<u16> left;
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BigEndian<u16> right;
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FWord value;
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};
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Header const& header() const { return *bit_cast<Header const*>(m_slice.data()); }
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Kern(ReadonlyBytes slice, FixedArray<size_t> subtable_offsets)
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: m_slice(slice)
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, m_subtable_offsets(move(subtable_offsets))
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