gfx/harfbuzz/src/hb-ot-shape-complex-arabic.cc

   1 /*
   2  * Copyright © 2010,2012  Google, Inc.
   3  *
   4  *  This is part of HarfBuzz, a text shaping library.
   5  *
   6  * Permission is hereby granted, without written agreement and without
   7  * license or royalty fees, to use, copy, modify, and distribute this
   8  * software and its documentation for any purpose, provided that the
   9  * above copyright notice and the following two paragraphs appear in
  10  * all copies of this software.
  11  *
  12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
  13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
  14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
  15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
  16  * DAMAGE.
  17  *
  18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
  19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
  21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
  22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
  23  *
  24  * Google Author(s): Behdad Esfahbod
  25  */
  26
  27 #include "hb.hh"
  28
  29 #ifndef HB_NO_OT_SHAPE
  30
  31 #include "hb-ot-shape-complex-arabic.hh"
  32 #include "hb-ot-shape.hh"
  33
  34
  35 /* buffer var allocations */
  36 #define arabic_shaping_action() complex_var_u8_auxiliary() /* arabic shaping action */
  37
  38 #define HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH HB_BUFFER_SCRATCH_FLAG_COMPLEX0
  39
  40 /* See:
  41  * https://github.com/harfbuzz/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516 */
  42 #define HB_ARABIC_GENERAL_CATEGORY_IS_WORD(gen_cat) \
  43         (FLAG_UNSAFE (gen_cat) & \
  44          (FLAG (HB_UNICODE_GENERAL_CATEGORY_UNASSIGNED) | \
  45           FLAG (HB_UNICODE_GENERAL_CATEGORY_PRIVATE_USE) | \
  46           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_LOWERCASE_LETTER) |*/ \
  47           FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_LETTER) | \
  48           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER) | \
  49           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_TITLECASE_LETTER) |*/ \
  50           /*FLAG (HB_UNICODE_GENERAL_CATEGORY_UPPERCASE_LETTER) |*/ \
  51           FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) | \
  52           FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) | \
  53           FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) | \
  54           FLAG (HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER) | \
  55           FLAG (HB_UNICODE_GENERAL_CATEGORY_LETTER_NUMBER) | \
  56           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_NUMBER) | \
  57           FLAG (HB_UNICODE_GENERAL_CATEGORY_CURRENCY_SYMBOL) | \
  58           FLAG (HB_UNICODE_GENERAL_CATEGORY_MODIFIER_SYMBOL) | \
  59           FLAG (HB_UNICODE_GENERAL_CATEGORY_MATH_SYMBOL) | \
  60           FLAG (HB_UNICODE_GENERAL_CATEGORY_OTHER_SYMBOL)))
  61
  62
  63 /*
  64  * Joining types:
  65  */
  66
  67 /*
  68  * Bits used in the joining tables
  69  */
  70 enum hb_arabic_joining_type_t {
  71   JOINING_TYPE_U                = 0,
  72   JOINING_TYPE_L                = 1,
  73   JOINING_TYPE_R                = 2,
  74   JOINING_TYPE_D                = 3,
  75   JOINING_TYPE_C                = JOINING_TYPE_D,
  76   JOINING_GROUP_ALAPH           = 4,
  77   JOINING_GROUP_DALATH_RISH     = 5,
  78   NUM_STATE_MACHINE_COLS        = 6,
  79
  80   JOINING_TYPE_T = 7,
  81   JOINING_TYPE_X = 8  /* means: use general-category to choose between U or T. */
  82 };
  83
  84 #include "hb-ot-shape-complex-arabic-table.hh"
  85
  86 static unsigned int get_joining_type (hb_codepoint_t u, hb_unicode_general_category_t gen_cat)
  87 {
  88   unsigned int j_type = joining_type(u);
  89   if (likely (j_type != JOINING_TYPE_X))
  90     return j_type;
  91
  92   return (FLAG_UNSAFE(gen_cat) &
  93           (FLAG(HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) |
  94            FLAG(HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
  95            FLAG(HB_UNICODE_GENERAL_CATEGORY_FORMAT))
  96          ) ?  JOINING_TYPE_T : JOINING_TYPE_U;
  97 }
  98
  99 #define FEATURE_IS_SYRIAC(tag) hb_in_range<unsigned char> ((unsigned char) (tag), '2', '3')
 100
 101 static const hb_tag_t arabic_features[] =
 102 {
 103   HB_TAG('i','s','o','l'),
 104   HB_TAG('f','i','n','a'),
 105   HB_TAG('f','i','n','2'),
 106   HB_TAG('f','i','n','3'),
 107   HB_TAG('m','e','d','i'),
 108   HB_TAG('m','e','d','2'),
 109   HB_TAG('i','n','i','t'),
 110   HB_TAG_NONE
 111 };
 112
 113
 114 /* Same order as the feature array */
 115 enum arabic_action_t {
 116   ISOL,
 117   FINA,
 118   FIN2,
 119   FIN3,
 120   MEDI,
 121   MED2,
 122   INIT,
 123
 124   NONE,
 125
 126   ARABIC_NUM_FEATURES = NONE,
 127
 128   /* We abuse the same byte for other things... */
 129   STCH_FIXED,
 130   STCH_REPEATING,
 131 };
 132
 133 static const struct arabic_state_table_entry {
 134         uint8_t prev_action;
 135         uint8_t curr_action;
 136         uint16_t next_state;
 137 } arabic_state_table[][NUM_STATE_MACHINE_COLS] =
 138 {
 139   /*   jt_U,          jt_L,          jt_R,          jt_D,          jg_ALAPH,      jg_DALATH_RISH */
 140
 141   /* State 0: prev was U, not willing to join. */
 142   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,6}, },
 143
 144   /* State 1: prev was R or ISOL/ALAPH, not willing to join. */
 145   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN2,5}, {NONE,ISOL,6}, },
 146
 147   /* State 2: prev was D/L in ISOL form, willing to join. */
 148   { {NONE,NONE,0}, {NONE,ISOL,2}, {INIT,FINA,1}, {INIT,FINA,3}, {INIT,FINA,4}, {INIT,FINA,6}, },
 149
 150   /* State 3: prev was D in FINA form, willing to join. */
 151   { {NONE,NONE,0}, {NONE,ISOL,2}, {MEDI,FINA,1}, {MEDI,FINA,3}, {MEDI,FINA,4}, {MEDI,FINA,6}, },
 152
 153   /* State 4: prev was FINA ALAPH, not willing to join. */
 154   { {NONE,NONE,0}, {NONE,ISOL,2}, {MED2,ISOL,1}, {MED2,ISOL,2}, {MED2,FIN2,5}, {MED2,ISOL,6}, },
 155
 156   /* State 5: prev was FIN2/FIN3 ALAPH, not willing to join. */
 157   { {NONE,NONE,0}, {NONE,ISOL,2}, {ISOL,ISOL,1}, {ISOL,ISOL,2}, {ISOL,FIN2,5}, {ISOL,ISOL,6}, },
 158
 159   /* State 6: prev was DALATH/RISH, not willing to join. */
 160   { {NONE,NONE,0}, {NONE,ISOL,2}, {NONE,ISOL,1}, {NONE,ISOL,2}, {NONE,FIN3,5}, {NONE,ISOL,6}, }
 161 };
 162
 163
 164 static void
 165 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
 166                        hb_font_t *font,
 167                        hb_buffer_t *buffer);
 168
 169 static void
 170 record_stch (const hb_ot_shape_plan_t *plan,
 171              hb_font_t *font,
 172              hb_buffer_t *buffer);
 173
 174 static void
 175 collect_features_arabic (hb_ot_shape_planner_t *plan)
 176 {
 177   hb_ot_map_builder_t *map = &plan->map;
 178
 179   /* We apply features according to the Arabic spec, with pauses
 180    * in between most.
 181    *
 182    * The pause between init/medi/... and rlig is required.  See eg:
 183    * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
 184    *
 185    * The pauses between init/medi/... themselves are not necessarily
 186    * needed as only one of those features is applied to any character.
 187    * The only difference it makes is when fonts have contextual
 188    * substitutions.  We now follow the order of the spec, which makes
 189    * for better experience if that's what Uniscribe is doing.
 190    *
 191    * At least for Arabic, looks like Uniscribe has a pause between
 192    * rlig and calt.  Otherwise the IranNastaliq's ALLAH ligature won't
 193    * work.  However, testing shows that rlig and calt are applied
 194    * together for Mongolian in Uniscribe.  As such, we only add a
 195    * pause for Arabic, not other scripts.
 196    *
 197    * A pause after calt is required to make KFGQPC Uthmanic Script HAFS
 198    * work correctly.  See https://github.com/harfbuzz/harfbuzz/issues/505
 199    */
 200
 201
 202   map->enable_feature (HB_TAG('s','t','c','h'));
 203   map->add_gsub_pause (record_stch);
 204
 205   map->enable_feature (HB_TAG('c','c','m','p'));
 206   map->enable_feature (HB_TAG('l','o','c','l'));
 207
 208   map->add_gsub_pause (nullptr);
 209
 210   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++)
 211   {
 212     bool has_fallback = plan->props.script == HB_SCRIPT_ARABIC && !FEATURE_IS_SYRIAC (arabic_features[i]);
 213     map->add_feature (arabic_features[i], has_fallback ? F_HAS_FALLBACK : F_NONE);
 214     map->add_gsub_pause (nullptr);
 215   }
 216
 217   /* Normally, Unicode says a ZWNJ means "don't ligate".  In Arabic script
 218    * however, it says a ZWJ should also mean "don't ligate".  So we run
 219    * the main ligating features as MANUAL_ZWJ. */
 220
 221   map->enable_feature (HB_TAG('r','l','i','g'), F_MANUAL_ZWJ | F_HAS_FALLBACK);
 222
 223   if (plan->props.script == HB_SCRIPT_ARABIC)
 224     map->add_gsub_pause (arabic_fallback_shape);
 225
 226   /* No pause after rclt.  See 98460779bae19e4d64d29461ff154b3527bf8420. */
 227   map->enable_feature (HB_TAG('r','c','l','t'), F_MANUAL_ZWJ);
 228   map->enable_feature (HB_TAG('c','a','l','t'), F_MANUAL_ZWJ);
 229   map->add_gsub_pause (nullptr);
 230
 231   /* The spec includes 'cswh'.  Earlier versions of Windows
 232    * used to enable this by default, but testing suggests
 233    * that Windows 8 and later do not enable it by default,
 234    * and spec now says 'Off by default'.
 235    * We disabled this in ae23c24c32.
 236    * Note that IranNastaliq uses this feature extensively
 237    * to fixup broken glyph sequences.  Oh well...
 238    * Test case: U+0643,U+0640,U+0631. */
 239   //map->enable_feature (HB_TAG('c','s','w','h'));
 240   map->enable_feature (HB_TAG('m','s','e','t'));
 241 }
 242
 243 #include "hb-ot-shape-complex-arabic-fallback.hh"
 244
 245 struct arabic_shape_plan_t
 246 {
 247   /* The "+ 1" in the next array is to accommodate for the "NONE" command,
 248    * which is not an OpenType feature, but this simplifies the code by not
 249    * having to do a "if (... < NONE) ..." and just rely on the fact that
 250    * mask_array[NONE] == 0. */
 251   hb_mask_t mask_array[ARABIC_NUM_FEATURES + 1];
 252
 253   hb_atomic_ptr_t<arabic_fallback_plan_t> fallback_plan;
 254
 255   unsigned int do_fallback : 1;
 256   unsigned int has_stch : 1;
 257 };
 258
 259 void *
 260 data_create_arabic (const hb_ot_shape_plan_t *plan)
 261 {
 262   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) hb_calloc (1, sizeof (arabic_shape_plan_t));
 263   if (unlikely (!arabic_plan))
 264     return nullptr;
 265
 266   arabic_plan->do_fallback = plan->props.script == HB_SCRIPT_ARABIC;
 267   arabic_plan->has_stch = !!plan->map.get_1_mask (HB_TAG ('s','t','c','h'));
 268   for (unsigned int i = 0; i < ARABIC_NUM_FEATURES; i++) {
 269     arabic_plan->mask_array[i] = plan->map.get_1_mask (arabic_features[i]);
 270     arabic_plan->do_fallback = arabic_plan->do_fallback &&
 271                                (FEATURE_IS_SYRIAC (arabic_features[i]) ||
 272                                 plan->map.needs_fallback (arabic_features[i]));
 273   }
 274
 275   return arabic_plan;
 276 }
 277
 278 void
 279 data_destroy_arabic (void *data)
 280 {
 281   arabic_shape_plan_t *arabic_plan = (arabic_shape_plan_t *) data;
 282
 283   arabic_fallback_plan_destroy (arabic_plan->fallback_plan);
 284
 285   hb_free (data);
 286 }
 287
 288 static void
 289 arabic_joining (hb_buffer_t *buffer)
 290 {
 291   unsigned int count = buffer->len;
 292   hb_glyph_info_t *info = buffer->info;
 293   unsigned int prev = UINT_MAX, state = 0;
 294
 295   /* Check pre-context */
 296   for (unsigned int i = 0; i < buffer->context_len[0]; i++)
 297   {
 298     unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
 299
 300     if (unlikely (this_type == JOINING_TYPE_T))
 301       continue;
 302
 303     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 304     state = entry->next_state;
 305     break;
 306   }
 307
 308   for (unsigned int i = 0; i < count; i++)
 309   {
 310     unsigned int this_type = get_joining_type (info[i].codepoint, _hb_glyph_info_get_general_category (&info[i]));
 311
 312     if (unlikely (this_type == JOINING_TYPE_T)) {
 313       info[i].arabic_shaping_action() = NONE;
 314       continue;
 315     }
 316
 317     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 318
 319     if (entry->prev_action != NONE && prev != UINT_MAX)
 320     {
 321       info[prev].arabic_shaping_action() = entry->prev_action;
 322       buffer->unsafe_to_break (prev, i + 1);
 323     }
 324     else
 325     {
 326       if (prev == UINT_MAX)
 327       {
 328         if (this_type >= JOINING_TYPE_R)
 329           buffer->unsafe_to_concat_from_outbuffer (0, i + 1);
 330       }
 331       else
 332       {
 333         if (this_type >= JOINING_TYPE_R ||
 334             (2 <= state && state <= 5) /* States that have a possible prev_action. */)
 335           buffer->unsafe_to_concat (prev, i + 1);
 336       }
 337     }
 338
 339     info[i].arabic_shaping_action() = entry->curr_action;
 340
 341     prev = i;
 342     state = entry->next_state;
 343   }
 344
 345   for (unsigned int i = 0; i < buffer->context_len[1]; i++)
 346   {
 347     unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
 348
 349     if (unlikely (this_type == JOINING_TYPE_T))
 350       continue;
 351
 352     const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
 353     if (entry->prev_action != NONE && prev != UINT_MAX)
 354     {
 355       info[prev].arabic_shaping_action() = entry->prev_action;
 356       buffer->unsafe_to_break (prev, buffer->len);
 357     }
 358     else if (2 <= state && state <= 5) /* States that have a possible prev_action. */
 359     {
 360       buffer->unsafe_to_concat (prev, buffer->len);
 361     }
 362     break;
 363   }
 364 }
 365
 366 static void
 367 mongolian_variation_selectors (hb_buffer_t *buffer)
 368 {
 369   /* Copy arabic_shaping_action() from base to Mongolian variation selectors. */
 370   unsigned int count = buffer->len;
 371   hb_glyph_info_t *info = buffer->info;
 372   for (unsigned int i = 1; i < count; i++)
 373     if (unlikely (hb_in_ranges<hb_codepoint_t> (info[i].codepoint, 0x180Bu, 0x180Du, 0x180Fu, 0x180Fu)))
 374       info[i].arabic_shaping_action() = info[i - 1].arabic_shaping_action();
 375 }
 376
 377 void
 378 setup_masks_arabic_plan (const arabic_shape_plan_t *arabic_plan,
 379                          hb_buffer_t               *buffer,
 380                          hb_script_t                script)
 381 {
 382   HB_BUFFER_ALLOCATE_VAR (buffer, arabic_shaping_action);
 383
 384   arabic_joining (buffer);
 385   if (script == HB_SCRIPT_MONGOLIAN)
 386     mongolian_variation_selectors (buffer);
 387
 388   unsigned int count = buffer->len;
 389   hb_glyph_info_t *info = buffer->info;
 390   for (unsigned int i = 0; i < count; i++)
 391     info[i].mask |= arabic_plan->mask_array[info[i].arabic_shaping_action()];
 392 }
 393
 394 static void
 395 setup_masks_arabic (const hb_ot_shape_plan_t *plan,
 396                     hb_buffer_t              *buffer,
 397                     hb_font_t                *font HB_UNUSED)
 398 {
 399   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 400   setup_masks_arabic_plan (arabic_plan, buffer, plan->props.script);
 401 }
 402
 403 static void
 404 arabic_fallback_shape (const hb_ot_shape_plan_t *plan,
 405                        hb_font_t *font,
 406                        hb_buffer_t *buffer)
 407 {
 408 #ifdef HB_NO_OT_SHAPE_COMPLEX_ARABIC_FALLBACK
 409   return;
 410 #endif
 411
 412   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 413
 414   if (!arabic_plan->do_fallback)
 415     return;
 416
 417 retry:
 418   arabic_fallback_plan_t *fallback_plan = arabic_plan->fallback_plan;
 419   if (unlikely (!fallback_plan))
 420   {
 421     /* This sucks.  We need a font to build the fallback plan... */
 422     fallback_plan = arabic_fallback_plan_create (plan, font);
 423     if (unlikely (!arabic_plan->fallback_plan.cmpexch (nullptr, fallback_plan)))
 424     {
 425       arabic_fallback_plan_destroy (fallback_plan);
 426       goto retry;
 427     }
 428   }
 429
 430   arabic_fallback_plan_shape (fallback_plan, font, buffer);
 431 }
 432
 433 /*
 434  * Stretch feature: "stch".
 435  * See example here:
 436  * https://docs.microsoft.com/en-us/typography/script-development/syriac
 437  * We implement this in a generic way, such that the Arabic subtending
 438  * marks can use it as well.
 439  */
 440
 441 static void
 442 record_stch (const hb_ot_shape_plan_t *plan,
 443              hb_font_t *font HB_UNUSED,
 444              hb_buffer_t *buffer)
 445 {
 446   const arabic_shape_plan_t *arabic_plan = (const arabic_shape_plan_t *) plan->data;
 447   if (!arabic_plan->has_stch)
 448     return;
 449
 450   /* 'stch' feature was just applied.  Look for anything that multiplied,
 451    * and record it for stch treatment later.  Note that rtlm, frac, etc
 452    * are applied before stch, but we assume that they didn't result in
 453    * anything multiplying into 5 pieces, so it's safe-ish... */
 454
 455   unsigned int count = buffer->len;
 456   hb_glyph_info_t *info = buffer->info;
 457   for (unsigned int i = 0; i < count; i++)
 458     if (unlikely (_hb_glyph_info_multiplied (&info[i])))
 459     {
 460       unsigned int comp = _hb_glyph_info_get_lig_comp (&info[i]);
 461       info[i].arabic_shaping_action() = comp % 2 ? STCH_REPEATING : STCH_FIXED;
 462       buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH;
 463     }
 464 }
 465
 466 static void
 467 apply_stch (const hb_ot_shape_plan_t *plan HB_UNUSED,
 468             hb_buffer_t              *buffer,
 469             hb_font_t                *font)
 470 {
 471   if (likely (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_ARABIC_HAS_STCH)))
 472     return;
 473
 474   /* The Arabic shaper currently always processes in RTL mode, so we should
 475    * stretch / position the stretched pieces to the left / preceding glyphs. */
 476
 477   /* We do a two pass implementation:
 478    * First pass calculates the exact number of extra glyphs we need,
 479    * We then enlarge buffer to have that much room,
 480    * Second pass applies the stretch, copying things to the end of buffer.
 481    */
 482
 483   int sign = font->x_scale < 0 ? -1 : +1;
 484   unsigned int extra_glyphs_needed = 0; // Set during MEASURE, used during CUT
 485   enum { MEASURE, CUT } /* step_t */;
 486
 487   for (unsigned int step = MEASURE; step <= CUT; step = step + 1)
 488   {
 489     unsigned int count = buffer->len;
 490     hb_glyph_info_t *info = buffer->info;
 491     hb_glyph_position_t *pos = buffer->pos;
 492     unsigned int new_len = count + extra_glyphs_needed; // write head during CUT
 493     unsigned int j = new_len;
 494     for (unsigned int i = count; i; i--)
 495     {
 496       if (!hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
 497       {
 498         if (step == CUT)
 499         {
 500           --j;
 501           info[j] = info[i - 1];
 502           pos[j] = pos[i - 1];
 503         }
 504         continue;
 505       }
 506
 507       /* Yay, justification! */
 508
 509       hb_position_t w_total = 0; // Total to be filled
 510       hb_position_t w_fixed = 0; // Sum of fixed tiles
 511       hb_position_t w_repeating = 0; // Sum of repeating tiles
 512       int n_fixed = 0;
 513       int n_repeating = 0;
 514
 515       unsigned int end = i;
 516       while (i &&
 517              hb_in_range<uint8_t> (info[i - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING))
 518       {
 519         i--;
 520         hb_position_t width = font->get_glyph_h_advance (info[i].codepoint);
 521         if (info[i].arabic_shaping_action() == STCH_FIXED)
 522         {
 523           w_fixed += width;
 524           n_fixed++;
 525         }
 526         else
 527         {
 528           w_repeating += width;
 529           n_repeating++;
 530         }
 531       }
 532       unsigned int start = i;
 533       unsigned int context = i;
 534       while (context &&
 535              !hb_in_range<uint8_t> (info[context - 1].arabic_shaping_action(), STCH_FIXED, STCH_REPEATING) &&
 536              (_hb_glyph_info_is_default_ignorable (&info[context - 1]) ||
 537               HB_ARABIC_GENERAL_CATEGORY_IS_WORD (_hb_glyph_info_get_general_category (&info[context - 1]))))
 538       {
 539         context--;
 540         w_total += pos[context].x_advance;
 541       }
 542       i++; // Don't touch i again.
 543
 544       DEBUG_MSG (ARABIC, nullptr, "%s stretch at (%d,%d,%d)",
 545                  step == MEASURE ? "measuring" : "cutting", context, start, end);
 546       DEBUG_MSG (ARABIC, nullptr, "rest of word:    count=%d width %d", start - context, w_total);
 547       DEBUG_MSG (ARABIC, nullptr, "fixed tiles:     count=%d width=%d", n_fixed, w_fixed);
 548       DEBUG_MSG (ARABIC, nullptr, "repeating tiles: count=%d width=%d", n_repeating, w_repeating);
 549
 550       /* Number of additional times to repeat each repeating tile. */
 551       int n_copies = 0;
 552
 553       hb_position_t w_remaining = w_total - w_fixed;
 554       if (sign * w_remaining > sign * w_repeating && sign * w_repeating > 0)
 555         n_copies = (sign * w_remaining) / (sign * w_repeating) - 1;
 556
 557       /* See if we can improve the fit by adding an extra repeat and squeezing them together a bit. */
 558       hb_position_t extra_repeat_overlap = 0;
 559       hb_position_t shortfall = sign * w_remaining - sign * w_repeating * (n_copies + 1);
 560       if (shortfall > 0 && n_repeating > 0)
 561       {
 562         ++n_copies;
 563         hb_position_t excess = (n_copies + 1) * sign * w_repeating - sign * w_remaining;
 564         if (excess > 0)
 565           extra_repeat_overlap = excess / (n_copies * n_repeating);
 566       }
 567
 568       if (step == MEASURE)
 569       {
 570         extra_glyphs_needed += n_copies * n_repeating;
 571         DEBUG_MSG (ARABIC, nullptr, "will add extra %d copies of repeating tiles", n_copies);
 572       }
 573       else
 574       {
 575         buffer->unsafe_to_break (context, end);
 576         hb_position_t x_offset = 0;
 577         for (unsigned int k = end; k > start; k--)
 578         {
 579           hb_position_t width = font->get_glyph_h_advance (info[k - 1].codepoint);
 580
 581           unsigned int repeat = 1;
 582           if (info[k - 1].arabic_shaping_action() == STCH_REPEATING)
 583             repeat += n_copies;
 584
 585           DEBUG_MSG (ARABIC, nullptr, "appending %d copies of glyph %d; j=%d",
 586                      repeat, info[k - 1].codepoint, j);
 587           for (unsigned int n = 0; n < repeat; n++)
 588           {
 589             x_offset -= width;
 590             if (n > 0)
 591               x_offset += extra_repeat_overlap;
 592             pos[k - 1].x_offset = x_offset;
 593             /* Append copy. */
 594             --j;
 595             info[j] = info[k - 1];
 596             pos[j] = pos[k - 1];
 597           }
 598         }
 599       }
 600     }
 601
 602     if (step == MEASURE)
 603     {
 604       if (unlikely (!buffer->ensure (count + extra_glyphs_needed)))
 605         break;
 606     }
 607     else
 608     {
 609       assert (j == 0);
 610       buffer->len = new_len;
 611     }
 612   }
 613 }
 614
 615
 616 static void
 617 postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
 618                            hb_buffer_t              *buffer,
 619                            hb_font_t                *font)
 620 {
 621   apply_stch (plan, buffer, font);
 622
 623   HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
 624 }
 625
 626 /* https://www.unicode.org/reports/tr53/ */
 627
 628 static hb_codepoint_t
 629 modifier_combining_marks[] =
 630 {
 631   0x0654u, /* ARABIC HAMZA ABOVE */
 632   0x0655u, /* ARABIC HAMZA BELOW */
 633   0x0658u, /* ARABIC MARK NOON GHUNNA */
 634   0x06DCu, /* ARABIC SMALL HIGH SEEN */
 635   0x06E3u, /* ARABIC SMALL LOW SEEN */
 636   0x06E7u, /* ARABIC SMALL HIGH YEH */
 637   0x06E8u, /* ARABIC SMALL HIGH NOON */
 638   0x08CAu, /* ARABIC SMALL HIGH FARSI YEH */
 639   0x08CBu, /* ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW */
 640   0x08CDu, /* ARABIC SMALL HIGH ZAH */
 641   0x08CEu, /* ARABIC LARGE ROUND DOT ABOVE */
 642   0x08CFu, /* ARABIC LARGE ROUND DOT BELOW */
 643   0x08D3u, /* ARABIC SMALL LOW WAW */
 644   0x08F3u, /* ARABIC SMALL HIGH WAW */
 645 };
 646
 647 static inline bool
 648 info_is_mcm (const hb_glyph_info_t &info)
 649 {
 650   hb_codepoint_t u = info.codepoint;
 651   for (unsigned int i = 0; i < ARRAY_LENGTH (modifier_combining_marks); i++)
 652     if (u == modifier_combining_marks[i])
 653       return true;
 654   return false;
 655 }
 656
 657 static void
 658 reorder_marks_arabic (const hb_ot_shape_plan_t *plan HB_UNUSED,
 659                       hb_buffer_t              *buffer,
 660                       unsigned int              start,
 661                       unsigned int              end)
 662 {
 663   hb_glyph_info_t *info = buffer->info;
 664
 665   DEBUG_MSG (ARABIC, buffer, "Reordering marks from %d to %d", start, end);
 666
 667   unsigned int i = start;
 668   for (unsigned int cc = 220; cc <= 230; cc += 10)
 669   {
 670     DEBUG_MSG (ARABIC, buffer, "Looking for %d's starting at %d", cc, i);
 671     while (i < end && info_cc(info[i]) < cc)
 672       i++;
 673     DEBUG_MSG (ARABIC, buffer, "Looking for %d's stopped at %d", cc, i);
 674
 675     if (i == end)
 676       break;
 677
 678     if (info_cc(info[i]) > cc)
 679       continue;
 680
 681     unsigned int j = i;
 682     while (j < end && info_cc(info[j]) == cc && info_is_mcm (info[j]))
 683       j++;
 684
 685     if (i == j)
 686       continue;
 687
 688     DEBUG_MSG (ARABIC, buffer, "Found %d's from %d to %d", cc, i, j);
 689
 690     /* Shift it! */
 691     DEBUG_MSG (ARABIC, buffer, "Shifting %d's: %d %d", cc, i, j);
 692     hb_glyph_info_t temp[HB_OT_SHAPE_COMPLEX_MAX_COMBINING_MARKS];
 693     assert (j - i <= ARRAY_LENGTH (temp));
 694     buffer->merge_clusters (start, j);
 695     memmove (temp, &info[i], (j - i) * sizeof (hb_glyph_info_t));
 696     memmove (&info[start + j - i], &info[start], (i - start) * sizeof (hb_glyph_info_t));
 697     memmove (&info[start], temp, (j - i) * sizeof (hb_glyph_info_t));
 698
 699     /* Renumber CC such that the reordered sequence is still sorted.
 700      * 22 and 26 are chosen because they are smaller than all Arabic categories,
 701      * and are folded back to 220/230 respectively during fallback mark positioning.
 702      *
 703      * We do this because the CGJ-handling logic in the normalizer relies on
 704      * mark sequences having an increasing order even after this reordering.
 705      * https://github.com/harfbuzz/harfbuzz/issues/554
 706      * This, however, does break some obscure sequences, where the normalizer
 707      * might compose a sequence that it should not.  For example, in the seequence
 708      * ALEF, HAMZAH, MADDAH, we should NOT try to compose ALEF+MADDAH, but with this
 709      * renumbering, we will.
 710      */
 711     unsigned int new_start = start + j - i;
 712     unsigned int new_cc = cc == 220 ? HB_MODIFIED_COMBINING_CLASS_CCC22 : HB_MODIFIED_COMBINING_CLASS_CCC26;
 713     while (start < new_start)
 714     {
 715       _hb_glyph_info_set_modified_combining_class (&info[start], new_cc);
 716       start++;
 717     }
 718
 719     i = j;
 720   }
 721 }
 722
 723 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
 724 {
 725   collect_features_arabic,
 726   nullptr, /* override_features */
 727   data_create_arabic,
 728   data_destroy_arabic,
 729   nullptr, /* preprocess_text */
 730   postprocess_glyphs_arabic,
 731   HB_OT_SHAPE_NORMALIZATION_MODE_DEFAULT,
 732   nullptr, /* decompose */
 733   nullptr, /* compose */
 734   setup_masks_arabic,
 735   HB_TAG_NONE, /* gpos_tag */
 736   reorder_marks_arabic,
 737   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
 738   true, /* fallback_position */
 739 };
 740
 741
 742 #endif