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 1996-2018 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 trace_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 */ 312
