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