third_party/ots/src/kern.cc

   1 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "kern.h"
   6
   7 // kern - Kerning
   8 // http://www.microsoft.com/typography/otspec/kern.htm
   9
  10 #define TABLE_NAME "kern"
  11
  12 #define DROP_THIS_TABLE(msg_) \
  13   do { \
  14     OTS_FAILURE_MSG(msg_ ", table discarded"); \
  15     delete font->kern; \
  16     font->kern = 0; \
  17   } while (0)
  18
  19 namespace ots {
  20
  21 bool ots_kern_parse(Font *font, const uint8_t *data, size_t length) {
  22   Buffer table(data, length);
  23
  24   OpenTypeKERN *kern = new OpenTypeKERN;
  25   font->kern = kern;
  26
  27   uint16_t num_tables = 0;
  28   if (!table.ReadU16(&kern->version) ||
  29       !table.ReadU16(&num_tables)) {
  30     return OTS_FAILURE_MSG("Failed to read kern header");
  31   }
  32
  33   if (kern->version > 0) {
  34     DROP_THIS_TABLE("bad table version");
  35     return true;
  36   }
  37
  38   if (num_tables == 0) {
  39     DROP_THIS_TABLE("num_tables is zero");
  40     return true;
  41   }
  42
  43   kern->subtables.reserve(num_tables);
  44   for (unsigned i = 0; i < num_tables; ++i) {
  45     OpenTypeKERNFormat0 subtable;
  46     uint16_t sub_length = 0;
  47
  48     if (!table.ReadU16(&subtable.version) ||
  49         !table.ReadU16(&sub_length)) {
  50       return OTS_FAILURE_MSG("Failed to read kern subtable %d header", i);
  51     }
  52
  53     if (subtable.version > 0) {
  54       OTS_WARNING("Bad subtable version: %d", subtable.version);
  55       continue;
  56     }
  57
  58     const size_t current_offset = table.offset();
  59     if (current_offset - 4 + sub_length > length) {
  60       return OTS_FAILURE_MSG("Bad kern subtable %d offset %ld", i, current_offset);
  61     }
  62
  63     if (!table.ReadU16(&subtable.coverage)) {
  64       return OTS_FAILURE_MSG("Cailed to read kern subtable %d coverage", i);
  65     }
  66
  67     if (!(subtable.coverage & 0x1)) {
  68       OTS_WARNING(
  69           "We don't support vertical data as the renderer doesn't support it.");
  70       continue;
  71     }
  72     if (subtable.coverage & 0xF0) {
  73       DROP_THIS_TABLE("Reserved fields should zero-filled");
  74       return true;
  75     }
  76     const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
  77     if (format != 0) {
  78       OTS_WARNING("Format %d is not supported.", format);
  79       continue;
  80     }
  81
  82     // Parse the format 0 field.
  83     uint16_t num_pairs = 0;
  84     if (!table.ReadU16(&num_pairs) ||
  85         !table.ReadU16(&subtable.search_range) ||
  86         !table.ReadU16(&subtable.entry_selector) ||
  87         !table.ReadU16(&subtable.range_shift)) {
  88       return OTS_FAILURE_MSG("Failed to read kern subtable %d format 0 fields", i);
  89     }
  90
  91     if (!num_pairs) {
  92       DROP_THIS_TABLE("Zero length subtable is found");
  93       return true;
  94     }
  95
  96     // Sanity checks for search_range, entry_selector, and range_shift. See the
  97     // comment in ots.cc for details.
  98     const size_t kFormat0PairSize = 6;  // left, right, and value. 2 bytes each.
  99     if (num_pairs > (65536 / kFormat0PairSize)) {
 100       // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
 101       DROP_THIS_TABLE("Too large subtable");
 102       return true;
 103     }
 104     unsigned max_pow2 = 0;
 105     while (1u << (max_pow2 + 1) <= num_pairs) {
 106       ++max_pow2;
 107     }
 108     const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
 109     if (subtable.search_range != expected_search_range) {
 110       OTS_WARNING("bad search range");
 111       subtable.search_range = expected_search_range;
 112     }
 113     if (subtable.entry_selector != max_pow2) {
 114       return OTS_FAILURE_MSG("Bad subtable %d entry selector %d", i, subtable.entry_selector);
 115     }
 116     const uint16_t expected_range_shift =
 117         kFormat0PairSize * num_pairs - subtable.search_range;
 118     if (subtable.range_shift != expected_range_shift) {
 119       OTS_WARNING("bad range shift");
 120       subtable.range_shift = expected_range_shift;
 121     }
 122
 123     // Read kerning pairs.
 124     subtable.pairs.reserve(num_pairs);
 125     uint32_t last_pair = 0;
 126     for (unsigned j = 0; j < num_pairs; ++j) {
 127       OpenTypeKERNFormat0Pair kerning_pair;
 128       if (!table.ReadU16(&kerning_pair.left) ||
 129           !table.ReadU16(&kerning_pair.right) ||
 130           !table.ReadS16(&kerning_pair.value)) {
 131         return OTS_FAILURE_MSG("Failed to read subtable %d kerning pair %d", i, j);
 132       }
 133       const uint32_t current_pair
 134           = (kerning_pair.left << 16) + kerning_pair.right;
 135       if (j != 0 && current_pair <= last_pair) {
 136         // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
 137         // in order to support these fonts.
 138         DROP_THIS_TABLE("Kerning pairs are not sorted");
 139         return true;
 140       }
 141       last_pair = current_pair;
 142       subtable.pairs.push_back(kerning_pair);
 143     }
 144
 145     kern->subtables.push_back(subtable);
 146   }
 147
 148   if (!kern->subtables.size()) {
 149     DROP_THIS_TABLE("All subtables are removed");
 150     return true;
 151   }
 152
 153   return true;
 154 }
 155
 156 bool ots_kern_should_serialise(Font *font) {
 157   if (!font->glyf) return false;  // this table is not for CFF fonts.
 158   return font->kern != NULL;
 159 }
 160
 161 bool ots_kern_serialise(OTSStream *out, Font *font) {
 162   const OpenTypeKERN *kern = font->kern;
 163
 164   const uint16_t num_subtables = static_cast<uint16_t>(kern->subtables.size());
 165   if (num_subtables != kern->subtables.size() ||
 166       !out->WriteU16(kern->version) ||
 167       !out->WriteU16(num_subtables)) {
 168     return OTS_FAILURE_MSG("Can't write kern table header");
 169   }
 170
 171   for (uint16_t i = 0; i < num_subtables; ++i) {
 172     const size_t length = 14 + (6 * kern->subtables[i].pairs.size());
 173     if (length > std::numeric_limits<uint16_t>::max() ||
 174         !out->WriteU16(kern->subtables[i].version) ||
 175         !out->WriteU16(static_cast<uint16_t>(length)) ||
 176         !out->WriteU16(kern->subtables[i].coverage) ||
 177         !out->WriteU16(
 178             static_cast<uint16_t>(kern->subtables[i].pairs.size())) ||
 179         !out->WriteU16(kern->subtables[i].search_range) ||
 180         !out->WriteU16(kern->subtables[i].entry_selector) ||
 181         !out->WriteU16(kern->subtables[i].range_shift)) {
 182       return OTS_FAILURE_MSG("Failed to write kern subtable %d", i);
 183     }
 184     for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
 185       if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
 186           !out->WriteU16(kern->subtables[i].pairs[j].right) ||
 187           !out->WriteS16(kern->subtables[i].pairs[j].value)) {
 188         return OTS_FAILURE_MSG("Failed to write kern pair %d for subtable %d", j, i);
 189       }
 190     }
 191   }
 192
 193   return true;
 194 }
 195
 196 void ots_kern_reuse(Font *font, Font *other) {
 197   font->kern = other->kern;
 198   font->kern_reused = true;
 199 }
 200
 201 void ots_kern_free(Font *font) {
 202   delete font->kern;
 203 }
 204
 205 }  // namespace ots
 206
 207 #undef TABLE_NAME
 208 #undef DROP_THIS_TABLE