1 /****************************************************************************
2 *
3 * ttkern.c
4 *
5 * Load the basic TrueType kerning table. This doesn't handle
6 * kerning data within the GPOS table at the moment.
7 *
8 * Copyright (C) 1996-2019 by
9 * David Turner, Robert Wilhelm, and Werner Lemberg.
10 *
11 * This file is part of the FreeType project, and may only be used,
12 * modified, and distributed under the terms of the FreeType project
13 * license, LICENSE.TXT. By continuing to use, modify, or distribute
14 * this file you indicate that you have read the license and
15 * understand and accept it fully.
16 *
17 */
18
19
20 #include <ft2build.h>
21 #include FT_INTERNAL_DEBUG_H
22 #include FT_INTERNAL_STREAM_H
23 #include FT_TRUETYPE_TAGS_H
24 #include "ttkern.h"
25
26 #include "sferrors.h"
27
28
29 /**************************************************************************
30 *
31 * The macro FT_COMPONENT is used in trace mode. It is an implicit
32 * parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log
33 * messages during execution.
34 */
35 #undef FT_COMPONENT
36 #define FT_COMPONENT ttkern
37
38
39 #undef TT_KERN_INDEX
40 #define TT_KERN_INDEX( g1, g2 ) ( ( (FT_ULong)(g1) << 16 ) | (g2) )
41
42
43 FT_LOCAL_DEF( FT_Error )
44 tt_face_load_kern( TT_Face face,
45 FT_Stream stream )
46 {
47 FT_Error error;
48 FT_ULong table_size;
49 FT_Byte* p;
50 FT_Byte* p_limit;
51 FT_UInt nn, num_tables;
52 FT_UInt32 avail = 0, ordered = 0;
53
54
55 /* the kern table is optional; exit silently if it is missing */
56 error = face->goto_table( face, TTAG_kern, stream, &table_size );
57 if ( error )
58 goto Exit;
59
60 if ( table_size < 4 ) /* the case of a malformed table */
61 {
62 FT_ERROR(( "tt_face_load_kern:"
63 " kerning table is too small - ignored\n" ));
64 error = FT_THROW( Table_Missing );
65 goto Exit;
66 }
67
68 if ( FT_FRAME_EXTRACT( table_size, face->kern_table ) )
69 {
70 FT_ERROR(( "tt_face_load_kern:"
71 " could not extract kerning table\n" ));
72 goto Exit;
73 }
74
75 face->kern_table_size = table_size;
76
77 p = face->kern_table;
78 p_limit = p + table_size;
79
80 p += 2; /* skip version */
81 num_tables = FT_NEXT_USHORT( p );
82
83 if ( num_tables > 32 ) /* we only support up to 32 sub-tables */
84 num_tables = 32;
85
86 for ( nn = 0; nn < num_tables; nn++ )
87 {
88 FT_UInt num_pairs, length, coverage, format;
89 FT_Byte* p_next;
90 FT_UInt32 mask = (FT_UInt32)1UL << nn;
91
92
93 if ( p + 6 > p_limit )
94 break;
95
96 p_next = p;
97
98 p += 2; /* skip version */
99 length = FT_NEXT_USHORT( p );
100 coverage = FT_NEXT_USHORT( p );
101
102 if ( length <= 6 + 8 )
103 break;
104
105 p_next += length;
106
107 if ( p_next > p_limit ) /* handle broken table */
108 p_next = p_limit;
109
110 format = coverage >> 8;
111
112 /* we currently only support format 0 kerning tables */
113 if ( format != 0 )
114 goto NextTable;
115
116 /* only use horizontal kerning tables */
117 if ( ( coverage & 3U ) != 0x0001 ||
118 p + 8 > p_next )
119 goto NextTable;
120
121 num_pairs = FT_NEXT_USHORT( p );
122 p += 6;
123
124 if ( ( p_next - p ) < 6 * (int)num_pairs ) /* handle broken count */
125 num_pairs = (FT_UInt)( ( p_next - p ) / 6 );
126
127 avail |= mask;
128
129 /*
130 * Now check whether the pairs in this table are ordered.
131 * We then can use binary search.
132 */
133 if ( num_pairs > 0 )
134 {
135 FT_ULong count;
136 FT_ULong old_pair;
137
138
139 old_pair = FT_NEXT_ULONG( p );
140 p += 2;
141
142 for ( count = num_pairs - 1; count > 0; count-- )
143 {
144 FT_UInt32 cur_pair;
145
146
147 cur_pair = FT_NEXT_ULONG( p );
148 if ( cur_pair <= old_pair )
149 break;
150
151 p += 2;
152 old_pair = cur_pair;
153 }
154
155 if ( count == 0 )
156 ordered |= mask;
157 }
158
159 NextTable:
160 p = p_next;
161 }
162
163 face->num_kern_tables = nn;
164 face->kern_avail_bits = avail;
165 face->kern_order_bits = ordered;
166
167 Exit:
168 return error;
169 }
170
171
172 FT_LOCAL_DEF( void )
173 tt_face_done_kern( TT_Face face )
174 {
175 FT_Stream stream = face->root.stream;
176
177
178 FT_FRAME_RELEASE( face->kern_table );
179 face->kern_table_size = 0;
180 face->num_kern_tables = 0;
181 face->kern_avail_bits = 0;
182 face->kern_order_bits = 0;
183 }
184
185
186 FT_LOCAL_DEF( FT_Int )
187 tt_face_get_kerning( TT_Face face,
188 FT_UInt left_glyph,
189 FT_UInt right_glyph )
190 {
191 FT_Int result = 0;
192 FT_UInt count, mask;
193 FT_Byte* p = face->kern_table;
194 FT_Byte* p_limit = p + face->kern_table_size;
195
196
197 p += 4;
198 mask = 0x0001;
199
200 for ( count = face->num_kern_tables;
201 count > 0 && p + 6 <= p_limit;
202 count--, mask <<= 1 )
203 {
204 FT_Byte* base = p;
205 FT_Byte* next;
206 FT_UInt version = FT_NEXT_USHORT( p );
207 FT_UInt length = FT_NEXT_USHORT( p );
208 FT_UInt coverage = FT_NEXT_USHORT( p );
209 FT_UInt num_pairs;
210 FT_Int value = 0;
211
212 FT_UNUSED( version );
213
214
215 next = base + length;
216
217 if ( next > p_limit ) /* handle broken table */
218 next = p_limit;
219
220 if ( ( face->kern_avail_bits & mask ) == 0 )
221 goto NextTable;
222
223 FT_ASSERT( p + 8 <= next ); /* tested in tt_face_load_kern */
224
225 num_pairs = FT_NEXT_USHORT( p );
226 p += 6;
227
228 if ( ( next - p ) < 6 * (int)num_pairs ) /* handle broken count */
229 num_pairs = (FT_UInt)( ( next - p ) / 6 );
230
231 switch ( coverage >> 8 )
232 {
233 case 0:
234 {
235 FT_ULong key0 = TT_KERN_INDEX( left_glyph, right_glyph );
236
237
238 if ( face->kern_order_bits & mask ) /* binary search */
239 {
240 FT_UInt min = 0;
241 FT_UInt max = num_pairs;
242
243
244 while ( min < max )
245 {
246 FT_UInt mid = ( min + max ) >> 1;
247 FT_Byte* q = p + 6 * mid;
248 FT_ULong key;
249
250
251 key = FT_NEXT_ULONG( q );
252
253 if ( key == key0 )
254 {
255 value = FT_PEEK_SHORT( q );
256 goto Found;
257 }
258 if ( key < key0 )
259 min = mid + 1;
260 else
261 max = mid;
262 }
263 }
264 else /* linear search */
265 {
266 FT_UInt count2;
267
268
269 for ( count2 = num_pairs; count2 > 0; count2-- )
270 {
271 FT_ULong key = FT_NEXT_ULONG( p );
272
273
274 if ( key == key0 )
275 {
276 value = FT_PEEK_SHORT( p );
277 goto Found;
278 }
279 p += 2;
280 }
281 }
282 }
283 break;
284
285 /*
286 * We don't support format 2 because we haven't seen a single font
287 * using it in real life...
288 */
289
290 default:
291 ;
292 }
293
294 goto NextTable;
295
296 Found:
297 if ( coverage & 8 ) /* override or add */
298 result = value;
299 else
300 result += value;
301
302 NextTable:
303 p = next;
304 }
305
306 return result;
307 }
308
309 #undef TT_KERN_INDEX
310
311 /* END */