1 // Copyright (c) 2009-2017 The OTS 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 namespace ots {
11
Parse(const uint8_t * data,size_t length)12 bool OpenTypeKERN::Parse(const uint8_t *data, size_t length) {
13 Buffer table(data, length);
14
15 uint16_t num_tables = 0;
16 if (!table.ReadU16(&this->version) ||
17 !table.ReadU16(&num_tables)) {
18 return Error("Failed to read table header");
19 }
20
21 if (this->version > 0) {
22 return Drop("Unsupported table version: %d", this->version);
23 }
24
25 if (num_tables == 0) {
26 return Drop("nTables is zero");
27 }
28
29 this->subtables.reserve(num_tables);
30 for (unsigned i = 0; i < num_tables; ++i) {
31 OpenTypeKERNFormat0 subtable;
32 uint16_t sub_length = 0;
33
34 if (!table.ReadU16(&subtable.version) ||
35 !table.ReadU16(&sub_length)) {
36 return Error("Failed to read subtable %d header", i);
37 }
38
39 if (subtable.version > 0) {
40 Warning("Ignoring subtable %d with unsupported version: %d",
41 i, subtable.version);
42 continue;
43 }
44
45 const size_t current_offset = table.offset();
46 if (current_offset - 4 + sub_length > length) {
47 return Error("Bad subtable %d offset %ld", i, current_offset);
48 }
49
50 if (!table.ReadU16(&subtable.coverage)) {
51 return Error("Failed to read subtable %d coverage", i);
52 }
53
54 if (!(subtable.coverage & 0x1)) {
55 Warning(
56 "We don't support vertical data as the renderer doesn't support it.");
57 continue;
58 }
59 if (subtable.coverage & 0xF0) {
60 return Drop("Reserved fields should be zero");
61 }
62 const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
63 if (format != 0) {
64 Warning("Ignoring subtable %d with unsupported format: %d", i, format);
65 continue;
66 }
67
68 // Parse the format 0 field.
69 uint16_t num_pairs = 0;
70 if (!table.ReadU16(&num_pairs) ||
71 !table.ReadU16(&subtable.search_range) ||
72 !table.ReadU16(&subtable.entry_selector) ||
73 !table.ReadU16(&subtable.range_shift)) {
74 return Error("Failed to read subtable %d format 0 fields", i);
75 }
76
77 if (!num_pairs) {
78 return Drop("Zero length subtable is found");
79 }
80
81 // Sanity checks for search_range, entry_selector, and range_shift. See the
82 // comment in ots.cc for details.
83 const size_t kFormat0PairSize = 6; // left, right, and value. 2 bytes each.
84 if (num_pairs > (65536 / kFormat0PairSize)) {
85 // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
86 return Drop("Too large subtable");
87 }
88 unsigned max_pow2 = 0;
89 while (1u << (max_pow2 + 1) <= num_pairs) {
90 ++max_pow2;
91 }
92 const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
93 if (subtable.search_range != expected_search_range) {
94 Warning("bad search range");
95 subtable.search_range = expected_search_range;
96 }
97 if (subtable.entry_selector != max_pow2) {
98 return Error("Bad subtable %d entry selector %d", i, subtable.entry_selector);
99 }
100 const uint16_t expected_range_shift =
101 kFormat0PairSize * num_pairs - subtable.search_range;
102 if (subtable.range_shift != expected_range_shift) {
103 Warning("bad range shift");
104 subtable.range_shift = expected_range_shift;
105 }
106
107 // Read kerning pairs.
108 subtable.pairs.reserve(num_pairs);
109 uint32_t last_pair = 0;
110 for (unsigned j = 0; j < num_pairs; ++j) {
111 OpenTypeKERNFormat0Pair kerning_pair;
112 if (!table.ReadU16(&kerning_pair.left) ||
113 !table.ReadU16(&kerning_pair.right) ||
114 !table.ReadS16(&kerning_pair.value)) {
115 return Error("Failed to read subtable %d kerning pair %d", i, j);
116 }
117 const uint32_t current_pair
118 = (kerning_pair.left << 16) + kerning_pair.right;
119 if (j != 0 && current_pair <= last_pair) {
120 // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
121 // in order to support these fonts.
122 return Drop("Kerning pairs are not sorted");
123 }
124 last_pair = current_pair;
125 subtable.pairs.push_back(kerning_pair);
126 }
127
128 this->subtables.push_back(subtable);
129 }
130
131 if (!this->subtables.size()) {
132 return Drop("All subtables were removed");
133 }
134
135 return true;
136 }
137
Serialize(OTSStream * out)138 bool OpenTypeKERN::Serialize(OTSStream *out) {
139 const uint16_t num_subtables = static_cast<uint16_t>(this->subtables.size());
140 if (num_subtables != this->subtables.size() ||
141 !out->WriteU16(this->version) ||
142 !out->WriteU16(num_subtables)) {
143 return Error("Failed to write kern table header");
144 }
145
146 for (uint16_t i = 0; i < num_subtables; ++i) {
147 const size_t length = 14 + (6 * this->subtables[i].pairs.size());
148 if (length > std::numeric_limits<uint16_t>::max() ||
149 !out->WriteU16(this->subtables[i].version) ||
150 !out->WriteU16(static_cast<uint16_t>(length)) ||
151 !out->WriteU16(this->subtables[i].coverage) ||
152 !out->WriteU16(
153 static_cast<uint16_t>(this->subtables[i].pairs.size())) ||
154 !out->WriteU16(this->subtables[i].search_range) ||
155 !out->WriteU16(this->subtables[i].entry_selector) ||
156 !out->WriteU16(this->subtables[i].range_shift)) {
157 return Error("Failed to write kern subtable %d", i);
158 }
159 for (unsigned j = 0; j < this->subtables[i].pairs.size(); ++j) {
160 if (!out->WriteU16(this->subtables[i].pairs[j].left) ||
161 !out->WriteU16(this->subtables[i].pairs[j].right) ||
162 !out->WriteS16(this->subtables[i].pairs[j].value)) {
163 return Error("Failed to write kern pair %d for subtable %d", j, i);
164 }
165 }
166 }
167
168 return true;
169 }
170
ShouldSerialize()171 bool OpenTypeKERN::ShouldSerialize() {
172 return Table::ShouldSerialize() &&
173 // this table is not for CFF fonts.
174 GetFont()->GetTable(OTS_TAG_GLYF) != NULL;
175 }
176
177 } // namespace ots
178