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Diffstat (limited to 'gfx/ots/src/kern.cc')
| -rw-r--r-- | gfx/ots/src/kern.cc | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/gfx/ots/src/kern.cc b/gfx/ots/src/kern.cc new file mode 100644 index 0000000000..ec41dfb9c0 --- /dev/null +++ b/gfx/ots/src/kern.cc @@ -0,0 +1,177 @@ +// Copyright (c) 2009-2017 The OTS Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#include "kern.h" + +// kern - Kerning +// http://www.microsoft.com/typography/otspec/kern.htm + +namespace ots { + +bool OpenTypeKERN::Parse(const uint8_t *data, size_t length) { + Buffer table(data, length); + + uint16_t num_tables = 0; + if (!table.ReadU16(&this->version) || + !table.ReadU16(&num_tables)) { + return Error("Failed to read table header"); + } + + if (this->version > 0) { + return Drop("Unsupported table version: %d", this->version); + } + + if (num_tables == 0) { + return Drop("nTables is zero"); + } + + this->subtables.reserve(num_tables); + for (unsigned i = 0; i < num_tables; ++i) { + OpenTypeKERNFormat0 subtable; + uint16_t sub_length = 0; + + if (!table.ReadU16(&subtable.version) || + !table.ReadU16(&sub_length)) { + return Error("Failed to read subtable %d header", i); + } + + if (subtable.version > 0) { + Warning("Ignoring subtable %d with unsupported version: %d", + i, subtable.version); + continue; + } + + const size_t current_offset = table.offset(); + if (current_offset - 4 + sub_length > length) { + return Error("Bad subtable %d offset %ld", i, current_offset); + } + + if (!table.ReadU16(&subtable.coverage)) { + return Error("Failed to read subtable %d coverage", i); + } + + if (!(subtable.coverage & 0x1)) { + Warning( + "We don't support vertical data as the renderer doesn't support it."); + continue; + } + if (subtable.coverage & 0xF0) { + return Drop("Reserved fields should be zero"); + } + const uint32_t format = (subtable.coverage & 0xFF00) >> 8; + if (format != 0) { + Warning("Ignoring subtable %d with unsupported format: %d", i, format); + continue; + } + + // Parse the format 0 field. + uint16_t num_pairs = 0; + if (!table.ReadU16(&num_pairs) || + !table.ReadU16(&subtable.search_range) || + !table.ReadU16(&subtable.entry_selector) || + !table.ReadU16(&subtable.range_shift)) { + return Error("Failed to read subtable %d format 0 fields", i); + } + + if (!num_pairs) { + return Drop("Zero length subtable is found"); + } + + // Sanity checks for search_range, entry_selector, and range_shift. See the + // comment in ots.cc for details. + const size_t kFormat0PairSize = 6; // left, right, and value. 2 bytes each. + if (num_pairs > (65536 / kFormat0PairSize)) { + // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923. + return Drop("Too large subtable"); + } + unsigned max_pow2 = 0; + while (1u << (max_pow2 + 1) <= num_pairs) { + ++max_pow2; + } + const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize; + if (subtable.search_range != expected_search_range) { + Warning("bad search range"); + subtable.search_range = expected_search_range; + } + if (subtable.entry_selector != max_pow2) { + return Error("Bad subtable %d entry selector %d", i, subtable.entry_selector); + } + const uint16_t expected_range_shift = + kFormat0PairSize * num_pairs - subtable.search_range; + if (subtable.range_shift != expected_range_shift) { + Warning("bad range shift"); + subtable.range_shift = expected_range_shift; + } + + // Read kerning pairs. + subtable.pairs.reserve(num_pairs); + uint32_t last_pair = 0; + for (unsigned j = 0; j < num_pairs; ++j) { + OpenTypeKERNFormat0Pair kerning_pair; + if (!table.ReadU16(&kerning_pair.left) || + !table.ReadU16(&kerning_pair.right) || + !table.ReadS16(&kerning_pair.value)) { + return Error("Failed to read subtable %d kerning pair %d", i, j); + } + const uint32_t current_pair + = (kerning_pair.left << 16) + kerning_pair.right; + if (j != 0 && current_pair <= last_pair) { + // Many free fonts don't follow this rule, so we don't call OTS_FAILURE + // in order to support these fonts. + return Drop("Kerning pairs are not sorted"); + } + last_pair = current_pair; + subtable.pairs.push_back(kerning_pair); + } + + this->subtables.push_back(subtable); + } + + if (!this->subtables.size()) { + return Drop("All subtables were removed"); + } + + return true; +} + +bool OpenTypeKERN::Serialize(OTSStream *out) { + const uint16_t num_subtables = static_cast<uint16_t>(this->subtables.size()); + if (num_subtables != this->subtables.size() || + !out->WriteU16(this->version) || + !out->WriteU16(num_subtables)) { + return Error("Failed to write kern table header"); + } + + for (uint16_t i = 0; i < num_subtables; ++i) { + const size_t length = 14 + (6 * this->subtables[i].pairs.size()); + if (length > std::numeric_limits<uint16_t>::max() || + !out->WriteU16(this->subtables[i].version) || + !out->WriteU16(static_cast<uint16_t>(length)) || + !out->WriteU16(this->subtables[i].coverage) || + !out->WriteU16( + static_cast<uint16_t>(this->subtables[i].pairs.size())) || + !out->WriteU16(this->subtables[i].search_range) || + !out->WriteU16(this->subtables[i].entry_selector) || + !out->WriteU16(this->subtables[i].range_shift)) { + return Error("Failed to write kern subtable %d", i); + } + for (unsigned j = 0; j < this->subtables[i].pairs.size(); ++j) { + if (!out->WriteU16(this->subtables[i].pairs[j].left) || + !out->WriteU16(this->subtables[i].pairs[j].right) || + !out->WriteS16(this->subtables[i].pairs[j].value)) { + return Error("Failed to write kern pair %d for subtable %d", j, i); + } + } + } + + return true; +} + +bool OpenTypeKERN::ShouldSerialize() { + return Table::ShouldSerialize() && + // this table is not for CFF fonts. + GetFont()->GetTable(OTS_TAG_GLYF) != NULL; +} + +} // namespace ots |