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