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// Copyright (c) 2009 The Chromium 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
#define TABLE_NAME "kern"
#define DROP_THIS_TABLE(msg_) \
do { \
OTS_FAILURE_MSG(msg_ ", table discarded"); \
delete font->kern; \
font->kern = 0; \
} while (0)
namespace ots {
bool ots_kern_parse(Font *font, const uint8_t *data, size_t length) {
Buffer table(data, length);
OpenTypeKERN *kern = new OpenTypeKERN;
font->kern = kern;
uint16_t num_tables = 0;
if (!table.ReadU16(&kern->version) ||
!table.ReadU16(&num_tables)) {
return OTS_FAILURE_MSG("Failed to read kern header");
}
if (kern->version > 0) {
DROP_THIS_TABLE("bad table version");
return true;
}
if (num_tables == 0) {
DROP_THIS_TABLE("num_tables is zero");
return true;
}
kern->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 OTS_FAILURE_MSG("Failed to read kern subtable %d header", i);
}
if (subtable.version > 0) {
OTS_WARNING("Bad subtable version: %d", subtable.version);
continue;
}
const size_t current_offset = table.offset();
if (current_offset - 4 + sub_length > length) {
return OTS_FAILURE_MSG("Bad kern subtable %d offset %ld", i, current_offset);
}
if (!table.ReadU16(&subtable.coverage)) {
return OTS_FAILURE_MSG("Cailed to read kern subtable %d coverage", i);
}
if (!(subtable.coverage & 0x1)) {
OTS_WARNING(
"We don't support vertical data as the renderer doesn't support it.");
continue;
}
if (subtable.coverage & 0xF0) {
DROP_THIS_TABLE("Reserved fields should zero-filled");
return true;
}
const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
if (format != 0) {
OTS_WARNING("Format %d is not supported.", 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 OTS_FAILURE_MSG("Failed to read kern subtable %d format 0 fields", i);
}
if (!num_pairs) {
DROP_THIS_TABLE("Zero length subtable is found");
return true;
}
// 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.
DROP_THIS_TABLE("Too large subtable");
return true;
}
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) {
OTS_WARNING("bad search range");
subtable.search_range = expected_search_range;
}
if (subtable.entry_selector != max_pow2) {
return OTS_FAILURE_MSG("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) {
OTS_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 OTS_FAILURE_MSG("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.
DROP_THIS_TABLE("Kerning pairs are not sorted");
return true;
}
last_pair = current_pair;
subtable.pairs.push_back(kerning_pair);
}
kern->subtables.push_back(subtable);
}
if (!kern->subtables.size()) {
DROP_THIS_TABLE("All subtables are removed");
return true;
}
return true;
}
bool ots_kern_should_serialise(Font *font) {
if (!font->glyf) return false; // this table is not for CFF fonts.
return font->kern != NULL;
}
bool ots_kern_serialise(OTSStream *out, Font *font) {
const OpenTypeKERN *kern = font->kern;
const uint16_t num_subtables = static_cast<uint16_t>(kern->subtables.size());
if (num_subtables != kern->subtables.size() ||
!out->WriteU16(kern->version) ||
!out->WriteU16(num_subtables)) {
return OTS_FAILURE_MSG("Can't write kern table header");
}
for (uint16_t i = 0; i < num_subtables; ++i) {
const size_t length = 14 + (6 * kern->subtables[i].pairs.size());
if (length > std::numeric_limits<uint16_t>::max() ||
!out->WriteU16(kern->subtables[i].version) ||
!out->WriteU16(static_cast<uint16_t>(length)) ||
!out->WriteU16(kern->subtables[i].coverage) ||
!out->WriteU16(
static_cast<uint16_t>(kern->subtables[i].pairs.size())) ||
!out->WriteU16(kern->subtables[i].search_range) ||
!out->WriteU16(kern->subtables[i].entry_selector) ||
!out->WriteU16(kern->subtables[i].range_shift)) {
return OTS_FAILURE_MSG("Failed to write kern subtable %d", i);
}
for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
!out->WriteU16(kern->subtables[i].pairs[j].right) ||
!out->WriteS16(kern->subtables[i].pairs[j].value)) {
return OTS_FAILURE_MSG("Failed to write kern pair %d for subtable %d", j, i);
}
}
}
return true;
}
void ots_kern_reuse(Font *font, Font *other) {
font->kern = other->kern;
font->kern_reused = true;
}
void ots_kern_free(Font *font) {
delete font->kern;
}
} // namespace ots
#undef TABLE_NAME
#undef DROP_THIS_TABLE
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